Available since 2017.1
Default: `false` |
| `S1009` | Omit redundant nil check on slices, maps, and channels
The len function is defined for all slices, maps, and channels, even nil ones, which have a length of zero. It is not necessary to check for nil before checking that their length is not zero.
Before:
if x != nil && len(x) != 0 {}
After:
if len(x) != 0 {}
Available since 2017.1
Default: `true` |
| `S1010` | Omit default slice index
When slicing, the second index defaults to the length of the value, making s[n:len(s)] and s[n:] equivalent.
Available since 2017.1
Default: `true` |
| `S1011` | Use a single append to concatenate two slices
Before:
for _, e := range y { x = append(x, e) } for i := range y { x = append(x, y[i]) } for i := range y { v := y[i] x = append(x, v) }
After:
x = append(x, y...) x = append(x, y...) x = append(x, y...)
Available since 2017.1
Default: `false` |
| `S1012` | Replace time.Now().Sub(x) with time.Since(x)
The time.Since helper has the same effect as using time.Now().Sub(x) but is easier to read.
Before:
time.Now().Sub(x)
After:
time.Since(x)
Available since 2017.1
Default: `true` |
| `S1016` | Use a type conversion instead of manually copying struct fields
Two struct types with identical fields can be converted between each other. In older versions of Go, the fields had to have identical struct tags. Since Go 1.8, however, struct tags are ignored during conversions. It is thus not necessary to manually copy every field individually.
Before:
var x T1 y := T2{ Field1: x.Field1, Field2: x.Field2, }
After:
var x T1 y := T2(x)
Available since 2017.1
Default: `false` |
| `S1017` | Replace manual trimming with strings.TrimPrefix
Instead of using strings.HasPrefix and manual slicing, use the strings.TrimPrefix function. If the string doesn't start with the prefix, the original string will be returned. Using strings.TrimPrefix reduces complexity, and avoids common bugs, such as off-by-one mistakes.
Before:
if strings.HasPrefix(str, prefix) { str = str[len(prefix):] }
After:
str = strings.TrimPrefix(str, prefix)
Available since 2017.1
Default: `true` |
| `S1018` | Use 'copy' for sliding elements
copy() permits using the same source and destination slice, even with overlapping ranges. This makes it ideal for sliding elements in a slice.
Before:
for i := 0; i < n; i++ { bs[i] = bs[offset+i] }
After:
copy(bs[:n], bs[offset:])
Available since 2017.1
Default: `true` |
| `S1019` | Simplify 'make' call by omitting redundant arguments
The 'make' function has default values for the length and capacity arguments. For channels, the length defaults to zero, and for slices, the capacity defaults to the length.
Available since 2017.1
Default: `true` |
| `S1020` | Omit redundant nil check in type assertion
Before:
if _, ok := i.(T); ok && i != nil {}
After:
if _, ok := i.(T); ok {}
Available since 2017.1
Default: `true` |
| `S1021` | Merge variable declaration and assignment
Before:
var x uint x = 1
After:
var x uint = 1
Available since 2017.1
Default: `false` |
| `S1023` | Omit redundant control flow
Functions that have no return value do not need a return statement as the final statement of the function.
Switches in Go do not have automatic fallthrough, unlike languages like C. It is not necessary to have a break statement as the final statement in a case block.
Available since 2017.1
Default: `true` |
| `S1024` | Replace x.Sub(time.Now()) with time.Until(x)
The time.Until helper has the same effect as using x.Sub(time.Now()) but is easier to read.
Before:
x.Sub(time.Now())
After:
time.Until(x)
Available since 2017.1
Default: `true` |
| `S1025` | Don't use fmt.Sprintf("%s", x) unnecessarily
In many instances, there are easier and more efficient ways of getting a value's string representation. Whenever a value's underlying type is a string already, or the type has a String method, they should be used directly.
Given the following shared definitions
type T1 string type T2 int
func (T2) String() string { return "Hello, world" }
var x string var y T1 var z T2
we can simplify
fmt.Sprintf("%s", x) fmt.Sprintf("%s", y) fmt.Sprintf("%s", z)
to
x string(y) z.String()
Available since 2017.1
Default: `false` |
| `S1028` | Simplify error construction with fmt.Errorf
Before:
errors.New(fmt.Sprintf(...))
After:
fmt.Errorf(...)
Available since 2017.1
Default: `true` |
| `S1029` | Range over the string directly
Ranging over a string will yield byte offsets and runes. If the offset isn't used, this is functionally equivalent to converting the string to a slice of runes and ranging over that. Ranging directly over the string will be more performant, however, as it avoids allocating a new slice, the size of which depends on the length of the string.
Before:
for _, r := range []rune(s) {}
After:
for _, r := range s {}
Available since 2017.1
Default: `false` |
| `S1030` | Use bytes.Buffer.String or bytes.Buffer.Bytes
bytes.Buffer has both a String and a Bytes method. It is almost never necessary to use string(buf.Bytes()) or []byte(buf.String()) – simply use the other method.
The only exception to this are map lookups. Due to a compiler optimization, m[string(buf.Bytes())] is more efficient than m[buf.String()].
Available since 2017.1
Default: `true` |
| `S1031` | Omit redundant nil check around loop
You can use range on nil slices and maps, the loop will simply never execute. This makes an additional nil check around the loop unnecessary.
Before:
if s != nil { for _, x := range s { ... } }
After:
for _, x := range s { ... }
Available since 2017.1
Default: `true` |
| `S1032` | Use sort.Ints(x), sort.Float64s(x), and sort.Strings(x)
The sort.Ints, sort.Float64s and sort.Strings functions are easier to read than sort.Sort(sort.IntSlice(x)), sort.Sort(sort.Float64Slice(x)) and sort.Sort(sort.StringSlice(x)).
Before:
sort.Sort(sort.StringSlice(x))
After:
sort.Strings(x)
Available since 2019.1
Default: `true` |
| `S1033` | Unnecessary guard around call to 'delete'
Calling delete on a nil map is a no-op.
Available since 2019.2
Default: `true` |
| `S1034` | Use result of type assertion to simplify cases
Available since 2019.2
Default: `true` |
| `S1035` | Redundant call to net/http.CanonicalHeaderKey in method call on net/http.Header
The methods on net/http.Header, namely Add, Del, Get and Set, already canonicalize the given header name.
Available since 2020.1
Default: `true` |
| `S1036` | Unnecessary guard around map access
When accessing a map key that doesn't exist yet, one receives a zero value. Often, the zero value is a suitable value, for example when using append or doing integer math.
The following
if _, ok := m["foo"]; ok { m["foo"] = append(m["foo"], "bar") } else { m["foo"] = []string{"bar"} }
can be simplified to
m["foo"] = append(m["foo"], "bar")
and
if _, ok := m2["k"]; ok { m2["k"] += 4 } else { m2["k"] = 4 }
can be simplified to
m["k"] += 4
Available since 2020.1
Default: `true` |
| `S1037` | Elaborate way of sleeping
Using a select statement with a single case receiving from the result of time.After is a very elaborate way of sleeping that can much simpler be expressed with a simple call to time.Sleep.
Available since 2020.1
Default: `true` |
| `S1038` | Unnecessarily complex way of printing formatted string
Instead of using fmt.Print(fmt.Sprintf(...)), one can use fmt.Printf(...).
Available since 2020.1
Default: `true` |
| `S1039` | Unnecessary use of fmt.Sprint
Calling fmt.Sprint with a single string argument is unnecessary and identical to using the string directly.
Available since 2020.1
Default: `true` |
| `S1040` | Type assertion to current type
The type assertion x.(SomeInterface), when x already has type SomeInterface, can only fail if x is nil. Usually, this is left-over code from when x had a different type and you can safely delete the type assertion. If you want to check that x is not nil, consider being explicit and using an actual if x == nil comparison instead of relying on the type assertion panicking.
Available since 2021.1
Default: `true` |
| `SA1000` | Invalid regular expression
Available since 2017.1
Default: `false` |
| `SA1001` | Invalid template
Available since 2017.1
Default: `true` |
| `SA1002` | Invalid format in time.Parse
Available since 2017.1
Default: `false` |
| `SA1003` | Unsupported argument to functions in encoding/binary
The encoding/binary package can only serialize types with known sizes. This precludes the use of the int and uint types, as their sizes differ on different architectures. Furthermore, it doesn't support serializing maps, channels, strings, or functions.
Before Go 1.8, bool wasn't supported, either.
Available since 2017.1
Default: `false` |
| `SA1004` | Suspiciously small untyped constant in time.Sleep
The time.Sleep function takes a time.Duration as its only argument. Durations are expressed in nanoseconds. Thus, calling time.Sleep(1) will sleep for 1 nanosecond. This is a common source of bugs, as sleep functions in other languages often accept seconds or milliseconds.
The time package provides constants such as time.Second to express large durations. These can be combined with arithmetic to express arbitrary durations, for example 5 * time.Second for 5 seconds.
If you truly meant to sleep for a tiny amount of time, use n * time.Nanosecond to signal to Staticcheck that you did mean to sleep for some amount of nanoseconds.
Available since 2017.1
Default: `true` |
| `SA1005` | Invalid first argument to exec.Command
os/exec runs programs directly (using variants of the fork and exec system calls on Unix systems). This shouldn't be confused with running a command in a shell. The shell will allow for features such as input redirection, pipes, and general scripting. The shell is also responsible for splitting the user's input into a program name and its arguments. For example, the equivalent to
ls / /tmp
would be
exec.Command("ls", "/", "/tmp")
If you want to run a command in a shell, consider using something like the following – but be aware that not all systems, particularly Windows, will have a /bin/sh program:
exec.Command("/bin/sh", "-c", "ls | grep Awesome")
Available since 2017.1
Default: `true` |
| `SA1007` | Invalid URL in net/url.Parse
Available since 2017.1
Default: `false` |
| `SA1008` | Non-canonical key in http.Header map
Keys in http.Header maps are canonical, meaning they follow a specific combination of uppercase and lowercase letters. Methods such as http.Header.Add and http.Header.Del convert inputs into this canonical form before manipulating the map.
When manipulating http.Header maps directly, as opposed to using the provided methods, care should be taken to stick to canonical form in order to avoid inconsistencies. The following piece of code demonstrates one such inconsistency:
h := http.Header{} h["etag"] = []string{"1234"} h.Add("etag", "5678") fmt.Println(h)
// Output: // map[Etag:[5678] etag:[1234]]
The easiest way of obtaining the canonical form of a key is to use http.CanonicalHeaderKey.
Available since 2017.1
Default: `true` |
| `SA1010` | (*regexp.Regexp).FindAll called with n == 0, which will always return zero results
If n >= 0, the function returns at most n matches/submatches. To return all results, specify a negative number.
Available since 2017.1
Default: `false` |
| `SA1011` | Various methods in the 'strings' package expect valid UTF-8, but invalid input is provided
Available since 2017.1
Default: `false` |
| `SA1012` | A nil context.Context is being passed to a function, consider using context.TODO instead
Available since 2017.1
Default: `true` |
| `SA1013` | io.Seeker.Seek is being called with the whence constant as the first argument, but it should be the second
Available since 2017.1
Default: `true` |
| `SA1014` | Non-pointer value passed to Unmarshal or Decode
Available since 2017.1
Default: `false` |
| `SA1015` | Using time.Tick in a way that will leak. Consider using time.NewTicker, and only use time.Tick in tests, commands and endless functions
Before Go 1.23, time.Tickers had to be closed to be able to be garbage collected. Since time.Tick doesn't make it possible to close the underlying ticker, using it repeatedly would leak memory.
Go 1.23 fixes this by allowing tickers to be collected even if they weren't closed.
Available since 2017.1
Default: `false` |
| `SA1016` | Trapping a signal that cannot be trapped
Not all signals can be intercepted by a process. Specifically, on UNIX-like systems, the syscall.SIGKILL and syscall.SIGSTOP signals are never passed to the process, but instead handled directly by the kernel. It is therefore pointless to try and handle these signals.
Available since 2017.1
Default: `true` |
| `SA1017` | Channels used with os/signal.Notify should be buffered
The os/signal package uses non-blocking channel sends when delivering signals. If the receiving end of the channel isn't ready and the channel is either unbuffered or full, the signal will be dropped. To avoid missing signals, the channel should be buffered and of the appropriate size. For a channel used for notification of just one signal value, a buffer of size 1 is sufficient.
Available since 2017.1
Default: `false` |
| `SA1018` | strings.Replace called with n == 0, which does nothing
With n == 0, zero instances will be replaced. To replace all instances, use a negative number, or use strings.ReplaceAll.
Available since 2017.1
Default: `false` |
| `SA1020` | Using an invalid host:port pair with a net.Listen-related function
Available since 2017.1
Default: `false` |
| `SA1021` | Using bytes.Equal to compare two net.IP
A net.IP stores an IPv4 or IPv6 address as a slice of bytes. The length of the slice for an IPv4 address, however, can be either 4 or 16 bytes long, using different ways of representing IPv4 addresses. In order to correctly compare two net.IPs, the net.IP.Equal method should be used, as it takes both representations into account.
Available since 2017.1
Default: `false` |
| `SA1023` | Modifying the buffer in an io.Writer implementation
Write must not modify the slice data, even temporarily.
Available since 2017.1
Default: `false` |
| `SA1024` | A string cutset contains duplicate characters
The strings.TrimLeft and strings.TrimRight functions take cutsets, not prefixes. A cutset is treated as a set of characters to remove from a string. For example,
strings.TrimLeft("42133word", "1234")
will result in the string "word" – any characters that are 1, 2, 3 or 4 are cut from the left of the string.
In order to remove one string from another, use strings.TrimPrefix instead.
Available since 2017.1
Default: `false` |
| `SA1025` | It is not possible to use (*time.Timer).Reset's return value correctly
Available since 2019.1
Default: `false` |
| `SA1026` | Cannot marshal channels or functions
Available since 2019.2
Default: `false` |
| `SA1027` | Atomic access to 64-bit variable must be 64-bit aligned
On ARM, x86-32, and 32-bit MIPS, it is the caller's responsibility to arrange for 64-bit alignment of 64-bit words accessed atomically. The first word in a variable or in an allocated struct, array, or slice can be relied upon to be 64-bit aligned.
You can use the structlayout tool to inspect the alignment of fields in a struct.
Available since 2019.2
Default: `false` |
| `SA1028` | sort.Slice can only be used on slices
The first argument of sort.Slice must be a slice.
Available since 2020.1
Default: `false` |
| `SA1029` | Inappropriate key in call to context.WithValue
The provided key must be comparable and should not be of type string or any other built-in type to avoid collisions between packages using context. Users of WithValue should define their own types for keys.
To avoid allocating when assigning to an interface{}, context keys often have concrete type struct{}. Alternatively, exported context key variables' static type should be a pointer or interface.
Available since 2020.1
Default: `false` |
| `SA1030` | Invalid argument in call to a strconv function
This check validates the format, number base and bit size arguments of the various parsing and formatting functions in strconv.
Available since 2021.1
Default: `false` |
| `SA1031` | Overlapping byte slices passed to an encoder
In an encoding function of the form Encode(dst, src), dst and src were found to reference the same memory. This can result in src bytes being overwritten before they are read, when the encoder writes more than one byte per src byte.
Available since 2024.1
Default: `false` |
| `SA1032` | Wrong order of arguments to errors.Is
The first argument of the function errors.Is is the error that we have and the second argument is the error we're trying to match against. For example:
if errors.Is(err, io.EOF) { ... }
This check detects some cases where the two arguments have been swapped. It flags any calls where the first argument is referring to a package-level error variable, such as
if errors.Is(io.EOF, err) { /* this is wrong */ }
Available since 2024.1
Default: `false` |
| `SA2001` | Empty critical section, did you mean to defer the unlock?
Empty critical sections of the kind
mu.Lock() mu.Unlock()
are very often a typo, and the following was intended instead:
mu.Lock() defer mu.Unlock()
Do note that sometimes empty critical sections can be useful, as a form of signaling to wait on another goroutine. Many times, there are simpler ways of achieving the same effect. When that isn't the case, the code should be amply commented to avoid confusion. Combining such comments with a //lint:ignore directive can be used to suppress this rare false positive.
Available since 2017.1
Default: `true` |
| `SA2002` | Called testing.T.FailNow or SkipNow in a goroutine, which isn't allowed
Available since 2017.1
Default: `false` |
| `SA2003` | Deferred Lock right after locking, likely meant to defer Unlock instead
Available since 2017.1
Default: `false` |
| `SA3000` | TestMain doesn't call os.Exit, hiding test failures
Test executables (and in turn 'go test') exit with a non-zero status code if any tests failed. When specifying your own TestMain function, it is your responsibility to arrange for this, by calling os.Exit with the correct code. The correct code is returned by (*testing.M).Run, so the usual way of implementing TestMain is to end it with os.Exit(m.Run()).
Available since 2017.1
Default: `true` |
| `SA3001` | Assigning to b.N in benchmarks distorts the results
The testing package dynamically sets b.N to improve the reliability of benchmarks and uses it in computations to determine the duration of a single operation. Benchmark code must not alter b.N as this would falsify results.
Available since 2017.1
Default: `true` |
| `SA4000` | Binary operator has identical expressions on both sides
Available since 2017.1
Default: `true` |
| `SA4001` | &*x gets simplified to x, it does not copy x
Available since 2017.1
Default: `true` |
| `SA4003` | Comparing unsigned values against negative values is pointless
Available since 2017.1
Default: `true` |
| `SA4004` | The loop exits unconditionally after one iteration
Available since 2017.1
Default: `true` |
| `SA4005` | Field assignment that will never be observed. Did you mean to use a pointer receiver?
Available since 2021.1
Default: `false` |
| `SA4006` | A value assigned to a variable is never read before being overwritten. Forgotten error check or dead code?
Available since 2017.1
Default: `false` |
| `SA4008` | The variable in the loop condition never changes, are you incrementing the wrong variable?
For example:
for i := 0; i < 10; j++ { ... }
This may also occur when a loop can only execute once because of unconditional control flow that terminates the loop. For example, when a loop body contains an unconditional break, return, or panic:
func f() {
panic("oops")
}
func g() {
for i := 0; i < 10; i++ {
// f unconditionally calls panic, which means "i" is
// never incremented.
f()
}
}
Available since 2017.1
Default: `false` |
| `SA4009` | A function argument is overwritten before its first use
Available since 2017.1
Default: `false` |
| `SA4010` | The result of append will never be observed anywhere
Available since 2017.1
Default: `false` |
| `SA4011` | Break statement with no effect. Did you mean to break out of an outer loop?
Available since 2017.1
Default: `true` |
| `SA4012` | Comparing a value against NaN even though no value is equal to NaN
Available since 2017.1
Default: `false` |
| `SA4013` | Negating a boolean twice (!!b) is the same as writing b. This is either redundant, or a typo.
Available since 2017.1
Default: `true` |
| `SA4014` | An if/else if chain has repeated conditions and no side-effects; if the condition didn't match the first time, it won't match the second time, either
Available since 2017.1
Default: `true` |
| `SA4015` | Calling functions like math.Ceil on floats converted from integers doesn't do anything useful
Available since 2017.1
Default: `false` |
| `SA4016` | Certain bitwise operations, such as x ^ 0, do not do anything useful
Available since 2017.1
Default: `true` |
| `SA4017` | Discarding the return values of a function without side effects, making the call pointless
Available since 2017.1
Default: `false` |
| `SA4018` | Self-assignment of variables
Available since 2017.1
Default: `false` |
| `SA4019` | Multiple, identical build constraints in the same file
Available since 2017.1
Default: `true` |
| `SA4020` | Unreachable case clause in a type switch
In a type switch like the following
type T struct{} func (T) Read(b []byte) (int, error) { return 0, nil }
var v any = T{}
switch v.(type) { case io.Reader: // ... case T: // unreachable }
the second case clause can never be reached because T implements io.Reader and case clauses are evaluated in source order.
Another example:
type T struct{} func (T) Read(b []byte) (int, error) { return 0, nil } func (T) Close() error { return nil }
var v any = T{}
switch v.(type) { case io.Reader: // ... case io.ReadCloser: // unreachable }
Even though T has a Close method and thus implements io.ReadCloser, io.Reader will always match first. The method set of io.Reader is a subset of io.ReadCloser. Thus it is impossible to match the second case without matching the first case.
Structurally equivalent interfaces
A special case of the previous example are structurally identical interfaces. Given these declarations
type T error type V error
func doSomething() error { err, ok := doAnotherThing() if ok { return T(err) }
return U(err) }
the following type switch will have an unreachable case clause:
switch doSomething().(type) { case T: // ... case V: // unreachable }
T will always match before V because they are structurally equivalent and therefore doSomething()'s return value implements both.
Available since 2019.2
Default: `true` |
| `SA4022` | Comparing the address of a variable against nil
Code such as 'if &x == nil' is meaningless, because taking the address of a variable always yields a non-nil pointer.
Available since 2020.1
Default: `true` |
| `SA4023` | Impossible comparison of interface value with untyped nil
Under the covers, interfaces are implemented as two elements, a type T and a value V. V is a concrete value such as an int, struct or pointer, never an interface itself, and has type T. For instance, if we store the int value 3 in an interface, the resulting interface value has, schematically, (T=int, V=3). The value V is also known as the interface's dynamic value, since a given interface variable might hold different values V (and corresponding types T) during the execution of the program.
An interface value is nil only if the V and T are both unset, (T=nil, V is not set), In particular, a nil interface will always hold a nil type. If we store a nil pointer of type *int inside an interface value, the inner type will be *int regardless of the value of the pointer: (T=*int, V=nil). Such an interface value will therefore be non-nil even when the pointer value V inside is nil.
This situation can be confusing, and arises when a nil value is stored inside an interface value such as an error return:
func returnsError() error { var p *MyError = nil if bad() { p = ErrBad } return p // Will always return a non-nil error. }
If all goes well, the function returns a nil p, so the return value is an error interface value holding (T=*MyError, V=nil). This means that if the caller compares the returned error to nil, it will always look as if there was an error even if nothing bad happened. To return a proper nil error to the caller, the function must return an explicit nil:
func returnsError() error { if bad() { return ErrBad } return nil }
It's a good idea for functions that return errors always to use the error type in their signature (as we did above) rather than a concrete type such as *MyError, to help guarantee the error is created correctly. As an example, os.Open returns an error even though, if not nil, it's always of concrete type *os.PathError.
Similar situations to those described here can arise whenever interfaces are used. Just keep in mind that if any concrete value has been stored in the interface, the interface will not be nil. For more information, see The Laws of Reflection at https://golang.org/doc/articles/laws_of_reflection.html.
This text has been copied from https://golang.org/doc/faq#nil_error, licensed under the Creative Commons Attribution 3.0 License.
Available since 2020.2
Default: `false` |
| `SA4024` | Checking for impossible return value from a builtin function
Return values of the len and cap builtins cannot be negative.
See https://golang.org/pkg/builtin/#len and https://golang.org/pkg/builtin/#cap.
Example:
if len(slice) < 0 { fmt.Println("unreachable code") }
Available since 2021.1
Default: `true` |
| `SA4025` | Integer division of literals that results in zero
When dividing two integer constants, the result will also be an integer. Thus, a division such as 2 / 3 results in 0. This is true for all of the following examples:
_ = 2 / 3
const _ = 2 / 3
const _ float64 = 2 / 3
_ = float64(2 / 3)
Staticcheck will flag such divisions if both sides of the division are integer literals, as it is highly unlikely that the division was intended to truncate to zero. Staticcheck will not flag integer division involving named constants, to avoid noisy positives.
Available since 2021.1
Default: `true` |
| `SA4026` | Go constants cannot express negative zero
In IEEE 754 floating point math, zero has a sign and can be positive or negative. This can be useful in certain numerical code.
Go constants, however, cannot express negative zero. This means that the literals -0.0 and 0.0 have the same ideal value (zero) and will both represent positive zero at runtime.
To explicitly and reliably create a negative zero, you can use the math.Copysign function: math.Copysign(0, -1).
Available since 2021.1
Default: `true` |
| `SA4027` | (*net/url.URL).Query returns a copy, modifying it doesn't change the URL
(*net/url.URL).Query parses the current value of net/url.URL.RawQuery and returns it as a map of type net/url.Values. Subsequent changes to this map will not affect the URL unless the map gets encoded and assigned to the URL's RawQuery.
As a consequence, the following code pattern is an expensive no-op: u.Query().Add(key, value).
Available since 2021.1
Default: `true` |
| `SA4028` | x % 1 is always zero
Available since 2022.1
Default: `true` |
| `SA4029` | Ineffective attempt at sorting slice
sort.Float64Slice, sort.IntSlice, and sort.StringSlice are types, not functions. Doing x = sort.StringSlice(x) does nothing, especially not sort any values. The correct usage is sort.Sort(sort.StringSlice(x)) or sort.StringSlice(x).Sort(), but there are more convenient helpers, namely sort.Float64s, sort.Ints, and sort.Strings.
Available since 2022.1
Default: `true` |
| `SA4030` | Ineffective attempt at generating random number
Functions in the math/rand package that accept upper limits, such as Intn, generate random numbers in the half-open interval [0,n). In other words, the generated numbers will be >= 0 and < n – they don't include n. rand.Intn(1) therefore doesn't generate 0 or 1, it always generates 0.
Available since 2022.1
Default: `true` |
| `SA4031` | Checking never-nil value against nil
Available since 2022.1
Default: `false` |
| `SA4032` | Comparing runtime.GOOS or runtime.GOARCH against impossible value
Available since 2024.1
Default: `true` |
| `SA5000` | Assignment to nil map
Available since 2017.1
Default: `false` |
| `SA5001` | Deferring Close before checking for a possible error
Available since 2017.1
Default: `true` |
| `SA5002` | The empty for loop ('for {}') spins and can block the scheduler
Available since 2017.1
Default: `false` |
| `SA5003` | Defers in infinite loops will never execute
Defers are scoped to the surrounding function, not the surrounding block. In a function that never returns, i.e. one containing an infinite loop, defers will never execute.
Available since 2017.1
Default: `true` |
| `SA5004` | 'for { select { ...' with an empty default branch spins
Available since 2017.1
Default: `true` |
| `SA5005` | The finalizer references the finalized object, preventing garbage collection
A finalizer is a function associated with an object that runs when the garbage collector is ready to collect said object, that is when the object is no longer referenced by anything.
If the finalizer references the object, however, it will always remain as the final reference to that object, preventing the garbage collector from collecting the object. The finalizer will never run, and the object will never be collected, leading to a memory leak. That is why the finalizer should instead use its first argument to operate on the object. That way, the number of references can temporarily go to zero before the object is being passed to the finalizer.
Available since 2017.1
Default: `false` |
| `SA5007` | Infinite recursive call
A function that calls itself recursively needs to have an exit condition. Otherwise it will recurse forever, until the system runs out of memory.
This issue can be caused by simple bugs such as forgetting to add an exit condition. It can also happen "on purpose". Some languages have tail call optimization which makes certain infinite recursive calls safe to use. Go, however, does not implement TCO, and as such a loop should be used instead.
Available since 2017.1
Default: `false` |
| `SA5008` | Invalid struct tag
Available since 2019.2
Default: `true` |
| `SA5010` | Impossible type assertion
Some type assertions can be statically proven to be impossible. This is the case when the method sets of both arguments of the type assertion conflict with each other, for example by containing the same method with different signatures.
The Go compiler already applies this check when asserting from an interface value to a concrete type. If the concrete type misses methods from the interface, or if function signatures don't match, then the type assertion can never succeed.
This check applies the same logic when asserting from one interface to another. If both interface types contain the same method but with different signatures, then the type assertion can never succeed, either.
Available since 2020.1
Default: `false` |
| `SA5011` | Possible nil pointer dereference
A pointer is being dereferenced unconditionally, while also being checked against nil in another place. This suggests that the pointer may be nil and dereferencing it may panic. This is commonly a result of improperly ordered code or missing return statements. Consider the following examples:
func fn(x *int) { fmt.Println(*x)
// This nil check is equally important for the previous dereference if x != nil { foo(*x) } }
func TestFoo(t *testing.T) { x := compute() if x == nil { t.Errorf("nil pointer received") }
// t.Errorf does not abort the test, so if x is nil, the next line will panic. foo(*x) }
Staticcheck tries to deduce which functions abort control flow. For example, it is aware that a function will not continue execution after a call to panic or log.Fatal. However, sometimes this detection fails, in particular in the presence of conditionals. Consider the following example:
func Log(msg string, level int) { fmt.Println(msg) if level == levelFatal { os.Exit(1) } }
func Fatal(msg string) { Log(msg, levelFatal) }
func fn(x *int) { if x == nil { Fatal("unexpected nil pointer") } fmt.Println(*x) }
Staticcheck will flag the dereference of x, even though it is perfectly safe. Staticcheck is not able to deduce that a call to Fatal will exit the program. For the time being, the easiest workaround is to modify the definition of Fatal like so:
func Fatal(msg string) { Log(msg, levelFatal) panic("unreachable") }
We also hard-code functions from common logging packages such as logrus. Please file an issue if we're missing support for a popular package.
Available since 2020.1
Default: `false` |
| `SA5012` | Passing odd-sized slice to function expecting even size
Some functions that take slices as parameters expect the slices to have an even number of elements. Often, these functions treat elements in a slice as pairs. For example, strings.NewReplacer takes pairs of old and new strings, and calling it with an odd number of elements would be an error.
Available since 2020.2
Default: `false` |
| `SA6000` | Using regexp.Match or related in a loop, should use regexp.Compile
Available since 2017.1
Default: `false` |
| `SA6001` | Missing an optimization opportunity when indexing maps by byte slices
Map keys must be comparable, which precludes the use of byte slices. This usually leads to using string keys and converting byte slices to strings.
Normally, a conversion of a byte slice to a string needs to copy the data and causes allocations. The compiler, however, recognizes m[string(b)] and uses the data of b directly, without copying it, because it knows that the data can't change during the map lookup. This leads to the counter-intuitive situation that
k := string(b) println(m[k]) println(m[k])
will be less efficient than
println(m[string(b)]) println(m[string(b)])
because the first version needs to copy and allocate, while the second one does not.
For some history on this optimization, check out commit f5f5a8b6209f84961687d993b93ea0d397f5d5bf in the Go repository.
Available since 2017.1
Default: `false` |
| `SA6002` | Storing non-pointer values in sync.Pool allocates memory
A sync.Pool is used to avoid unnecessary allocations and reduce the amount of work the garbage collector has to do.
When passing a value that is not a pointer to a function that accepts an interface, the value needs to be placed on the heap, which means an additional allocation. Slices are a common thing to put in sync.Pools, and they're structs with 3 fields (length, capacity, and a pointer to an array). In order to avoid the extra allocation, one should store a pointer to the slice instead.
See the comments on https://go-review.googlesource.com/c/go/+/24371 that discuss this problem.
Available since 2017.1
Default: `false` |
| `SA6003` | Converting a string to a slice of runes before ranging over it
You may want to loop over the runes in a string. Instead of converting the string to a slice of runes and looping over that, you can loop over the string itself. That is,
for _, r := range s {}
and
for _, r := range []rune(s) {}
will yield the same values. The first version, however, will be faster and avoid unnecessary memory allocations.
Do note that if you are interested in the indices, ranging over a string and over a slice of runes will yield different indices. The first one yields byte offsets, while the second one yields indices in the slice of runes.
Available since 2017.1
Default: `false` |
| `SA6005` | Inefficient string comparison with strings.ToLower or strings.ToUpper
Converting two strings to the same case and comparing them like so
if strings.ToLower(s1) == strings.ToLower(s2) { ... }
is significantly more expensive than comparing them with strings.EqualFold(s1, s2). This is due to memory usage as well as computational complexity.
strings.ToLower will have to allocate memory for the new strings, as well as convert both strings fully, even if they differ on the very first byte. strings.EqualFold, on the other hand, compares the strings one character at a time. It doesn't need to create two intermediate strings and can return as soon as the first non-matching character has been found.
For a more in-depth explanation of this issue, see https://blog.digitalocean.com/how-to-efficiently-compare-strings-in-go/
Available since 2019.2
Default: `true` |
| `SA6006` | Using io.WriteString to write []byte
Using io.WriteString to write a slice of bytes, as in
io.WriteString(w, string(b))
is both unnecessary and inefficient. Converting from []byte to string has to allocate and copy the data, and we could simply use w.Write(b) instead.
Available since 2024.1
Default: `true` |
| `SA9001` | Defers in range loops may not run when you expect them to
Available since 2017.1
Default: `false` |
| `SA9002` | Using a non-octal os.FileMode that looks like it was meant to be in octal.
Available since 2017.1
Default: `true` |
| `SA9003` | Empty body in an if or else branch
Available since 2017.1, non-default
Default: `false` |
| `SA9004` | Only the first constant has an explicit type
In a constant declaration such as the following:
const ( First byte = 1 Second = 2 )
the constant Second does not have the same type as the constant First. This construct shouldn't be confused with
const ( First byte = iota Second )
where First and Second do indeed have the same type. The type is only passed on when no explicit value is assigned to the constant.
When declaring enumerations with explicit values it is therefore important not to write
const ( EnumFirst EnumType = 1 EnumSecond = 2 EnumThird = 3 )
This discrepancy in types can cause various confusing behaviors and bugs.
Wrong type in variable declarations
The most obvious issue with such incorrect enumerations expresses itself as a compile error:
package pkg
const ( EnumFirst uint8 = 1 EnumSecond = 2 )
func fn(useFirst bool) { x := EnumSecond if useFirst { x = EnumFirst } }
fails to compile with
./const.go:11:5: cannot use EnumFirst (type uint8) as type int in assignment
Losing method sets
A more subtle issue occurs with types that have methods and optional interfaces. Consider the following:
package main
import "fmt"
type Enum int
func (e Enum) String() string { return "an enum" }
const ( EnumFirst Enum = 1 EnumSecond = 2 )
func main() { fmt.Println(EnumFirst) fmt.Println(EnumSecond) }
This code will output
an enum 2
as EnumSecond has no explicit type, and thus defaults to int.
Available since 2019.1
Default: `true` |
| `SA9005` | Trying to marshal a struct with no public fields nor custom marshaling
The encoding/json and encoding/xml packages only operate on exported fields in structs, not unexported ones. It is usually an error to try to (un)marshal structs that only consist of unexported fields.
This check will not flag calls involving types that define custom marshaling behavior, e.g. via MarshalJSON methods. It will also not flag empty structs.
Available since 2019.2
Default: `false` |
| `SA9006` | Dubious bit shifting of a fixed size integer value
Bit shifting a value past its size will always clear the value.
For instance:
v := int8(42) v >>= 8
will always result in 0.
This check flags bit shifting operations on fixed size integer values only. That is, int, uint and uintptr are never flagged to avoid potential false positives in somewhat exotic but valid bit twiddling tricks:
// Clear any value above 32 bits if integers are more than 32 bits. func f(i int) int { v := i >> 32 v = v << 32 return i-v }
Available since 2020.2
Default: `true` |
| `SA9007` | Deleting a directory that shouldn't be deleted
It is virtually never correct to delete system directories such as /tmp or the user's home directory. However, it can be fairly easy to do by mistake, for example by mistakenly using os.TempDir instead of ioutil.TempDir, or by forgetting to add a suffix to the result of os.UserHomeDir.
Writing
d := os.TempDir() defer os.RemoveAll(d)
in your unit tests will have a devastating effect on the stability of your system.
This check flags attempts at deleting the following directories:
- os.TempDir - os.UserCacheDir - os.UserConfigDir - os.UserHomeDir
Available since 2022.1
Default: `false` |
| `SA9008` | else branch of a type assertion is probably not reading the right value
When declaring variables as part of an if statement (like in 'if foo := ...; foo {'), the same variables will also be in the scope of the else branch. This means that in the following example
if x, ok := x.(int); ok { // ... } else { fmt.Printf("unexpected type %T", x) }
x in the else branch will refer to the x from x, ok :=; it will not refer to the x that is being type-asserted. The result of a failed type assertion is the zero value of the type that is being asserted to, so x in the else branch will always have the value 0 and the type int.
Available since 2022.1
Default: `false` |
| `SA9009` | Ineffectual Go compiler directive
A potential Go compiler directive was found, but is ineffectual as it begins with whitespace.
Available since 2024.1
Default: `true` |
| `ST1000` | Incorrect or missing package comment
Packages must have a package comment that is formatted according to the guidelines laid out in https://go.dev/wiki/CodeReviewComments#package-comments.
Available since 2019.1, non-default
Default: `false` |
| `ST1001` | Dot imports are discouraged
Dot imports that aren't in external test packages are discouraged.
The dot_import_whitelist option can be used to whitelist certain imports.
Quoting Go Code Review Comments:
> The import . form can be useful in tests that, due to circular > dependencies, cannot be made part of the package being tested: > > package foo_test > > import ( > "bar/testutil" // also imports "foo" > . "foo" > ) > > In this case, the test file cannot be in package foo because it > uses bar/testutil, which imports foo. So we use the import . > form to let the file pretend to be part of package foo even though > it is not. Except for this one case, do not use import . in your > programs. It makes the programs much harder to read because it is > unclear whether a name like Quux is a top-level identifier in the > current package or in an imported package.
Available since 2019.1
Options dot_import_whitelist
Default: `false` |
| `ST1003` | Poorly chosen identifier
Identifiers, such as variable and package names, follow certain rules.
See the following links for details:
- https://go.dev/doc/effective_go#package-names - https://go.dev/doc/effective_go#mixed-caps - https://go.dev/wiki/CodeReviewComments#initialisms - https://go.dev/wiki/CodeReviewComments#variable-names
Available since 2019.1, non-default
Options initialisms
Default: `false` |
| `ST1005` | Incorrectly formatted error string
Error strings follow a set of guidelines to ensure uniformity and good composability.
Quoting Go Code Review Comments:
> Error strings should not be capitalized (unless beginning with > proper nouns or acronyms) or end with punctuation, since they are > usually printed following other context. That is, use > fmt.Errorf("something bad") not fmt.Errorf("Something bad"), so > that log.Printf("Reading %s: %v", filename, err) formats without a > spurious capital letter mid-message.
Available since 2019.1
Default: `false` |
| `ST1006` | Poorly chosen receiver name
Quoting Go Code Review Comments:
> The name of a method's receiver should be a reflection of its > identity; often a one or two letter abbreviation of its type > suffices (such as "c" or "cl" for "Client"). Don't use generic > names such as "me", "this" or "self", identifiers typical of > object-oriented languages that place more emphasis on methods as > opposed to functions. The name need not be as descriptive as that > of a method argument, as its role is obvious and serves no > documentary purpose. It can be very short as it will appear on > almost every line of every method of the type; familiarity admits > brevity. Be consistent, too: if you call the receiver "c" in one > method, don't call it "cl" in another.
Available since 2019.1
Default: `false` |
| `ST1008` | A function's error value should be its last return value
A function's error value should be its last return value.
Available since 2019.1
Default: `false` |
| `ST1011` | Poorly chosen name for variable of type time.Duration
time.Duration values represent an amount of time, which is represented as a count of nanoseconds. An expression like 5 * time.Microsecond yields the value 5000. It is therefore not appropriate to suffix a variable of type time.Duration with any time unit, such as Msec or Milli.
Available since 2019.1
Default: `false` |
| `ST1012` | Poorly chosen name for error variable
Error variables that are part of an API should be called errFoo or ErrFoo.
Available since 2019.1
Default: `false` |
| `ST1013` | Should use constants for HTTP error codes, not magic numbers
HTTP has a tremendous number of status codes. While some of those are well known (200, 400, 404, 500), most of them are not. The net/http package provides constants for all status codes that are part of the various specifications. It is recommended to use these constants instead of hard-coding magic numbers, to vastly improve the readability of your code.
Available since 2019.1
Options http_status_code_whitelist
Default: `false` |
| `ST1015` | A switch's default case should be the first or last case
Available since 2019.1
Default: `false` |
| `ST1016` | Use consistent method receiver names
Available since 2019.1, non-default
Default: `false` |
| `ST1017` | Don't use Yoda conditions
Yoda conditions are conditions of the kind 'if 42 == x', where the literal is on the left side of the comparison. These are a common idiom in languages in which assignment is an expression, to avoid bugs of the kind 'if (x = 42)'. In Go, which doesn't allow for this kind of bug, we prefer the more idiomatic 'if x == 42'.
Available since 2019.2
Default: `false` |
| `ST1018` | Avoid zero-width and control characters in string literals
Available since 2019.2
Default: `false` |
| `ST1019` | Importing the same package multiple times
Go allows importing the same package multiple times, as long as different import aliases are being used. That is, the following bit of code is valid:
import ( "fmt" fumpt "fmt" format "fmt" _ "fmt" )
However, this is very rarely done on purpose. Usually, it is a sign of code that got refactored, accidentally adding duplicate import statements. It is also a rarely known feature, which may contribute to confusion.
Do note that sometimes, this feature may be used intentionally (see for example https://github.com/golang/go/commit/3409ce39bfd7584523b7a8c150a310cea92d879d) – if you want to allow this pattern in your code base, you're advised to disable this check.
Available since 2020.1
Default: `false` |
| `ST1020` | The documentation of an exported function should start with the function's name
Doc comments work best as complete sentences, which allow a wide variety of automated presentations. The first sentence should be a one-sentence summary that starts with the name being declared.
If every doc comment begins with the name of the item it describes, you can use the doc subcommand of the go tool and run the output through grep.
See https://go.dev/doc/effective_go#commentary for more information on how to write good documentation.
Available since 2020.1, non-default
Default: `false` |
| `ST1021` | The documentation of an exported type should start with type's name
Doc comments work best as complete sentences, which allow a wide variety of automated presentations. The first sentence should be a one-sentence summary that starts with the name being declared.
If every doc comment begins with the name of the item it describes, you can use the doc subcommand of the go tool and run the output through grep.
See https://go.dev/doc/effective_go#commentary for more information on how to write good documentation.
Available since 2020.1, non-default
Default: `false` |
| `ST1022` | The documentation of an exported variable or constant should start with variable's name
Doc comments work best as complete sentences, which allow a wide variety of automated presentations. The first sentence should be a one-sentence summary that starts with the name being declared.
If every doc comment begins with the name of the item it describes, you can use the doc subcommand of the go tool and run the output through grep.
See https://go.dev/doc/effective_go#commentary for more information on how to write good documentation.
Available since 2020.1, non-default
Default: `false` |
| `ST1023` | Redundant type in variable declaration
Available since 2021.1, non-default
Default: `false` |
| `any` | replace interface{} with any
The any analyzer suggests replacing uses of the empty interface type, `interface{}`, with the `any` alias, which was introduced in Go 1.18. This is a purely stylistic change that makes code more readable.
Default: `true` |
| `appendclipped` | simplify append chains using slices.Concat
The appendclipped analyzer suggests replacing chains of append calls with a single call to slices.Concat, which was added in Go 1.21. For example, append(append(s, s1...), s2...) would be simplified to slices.Concat(s, s1, s2).
In the simple case of appending to a newly allocated slice, such as append([]T(nil), s...), the analyzer suggests the more concise slices.Clone(s). For byte slices, it will prefer bytes.Clone if the "bytes" package is already imported.
This fix is only applied when the base of the append tower is a "clipped" slice, meaning its length and capacity are equal (e.g. x[:0:0] or []T{}). This is to avoid changing program behavior by eliminating intended side effects on the base slice's underlying array.
This analyzer is currently disabled by default as the transformation does not preserve the nilness of the base slice in all cases; see https://go.dev/issue/73557.
Default: `false` |
| `appends` | check for missing values after append
This checker reports calls to append that pass no values to be appended to the slice.
s := []string{"a", "b", "c"}
_ = append(s)
Such calls are always no-ops and often indicate an underlying mistake.
Default: `true` |
| `asmdecl` | report mismatches between assembly files and Go declarations
Default: `true` |
| `assign` | check for useless assignments
This checker reports assignments of the form x = x or a[i] = a[i]. These are almost always useless, and even when they aren't they are usually a mistake.
Default: `true` |
| `atomic` | check for common mistakes using the sync/atomic package
The atomic checker looks for assignment statements of the form:
x = atomic.AddUint64(&x, 1)
which are not atomic.
Default: `true` |
| `atomicalign` | check for non-64-bits-aligned arguments to sync/atomic functions
Default: `true` |
| `bloop` | replace for-range over b.N with b.Loop
The bloop analyzer suggests replacing benchmark loops of the form `for i := 0; i < b.N; i++` or `for range b.N` with the more modern `for b.Loop()`, which was added in Go 1.24.
This change makes benchmark code more readable and also removes the need for manual timer control, so any preceding calls to b.StartTimer, b.StopTimer, or b.ResetTimer within the same function will also be removed.
Caveats: The b.Loop() method is designed to prevent the compiler from optimizing away the benchmark loop, which can occasionally result in slower execution due to increased allocations in some specific cases.
Default: `true` |
| `bools` | check for common mistakes involving boolean operators
Default: `true` |
| `buildtag` | check //go:build and // +build directives
Default: `true` |
| `cgocall` | detect some violations of the cgo pointer passing rules
Check for invalid cgo pointer passing. This looks for code that uses cgo to call C code passing values whose types are almost always invalid according to the cgo pointer sharing rules. Specifically, it warns about attempts to pass a Go chan, map, func, or slice to C, either directly, or via a pointer, array, or struct.
Default: `true` |
| `composites` | check for unkeyed composite literals
This analyzer reports a diagnostic for composite literals of struct types imported from another package that do not use the field-keyed syntax. Such literals are fragile because the addition of a new field (even if unexported) to the struct will cause compilation to fail.
As an example,
err = &net.DNSConfigError{err}
should be replaced by:
err = &net.DNSConfigError{Err: err}
Default: `true` |
| `copylocks` | check for locks erroneously passed by value
Inadvertently copying a value containing a lock, such as sync.Mutex or sync.WaitGroup, may cause both copies to malfunction. Generally such values should be referred to through a pointer.
Default: `true` |
| `deepequalerrors` | check for calls of reflect.DeepEqual on error values
The deepequalerrors checker looks for calls of the form:
reflect.DeepEqual(err1, err2)
where err1 and err2 are errors. Using reflect.DeepEqual to compare errors is discouraged.
Default: `true` |
| `defers` | report common mistakes in defer statements
The defers analyzer reports a diagnostic when a defer statement would result in a non-deferred call to time.Since, as experience has shown that this is nearly always a mistake.
For example:
start := time.Now()
...
defer recordLatency(time.Since(start)) // error: call to time.Since is not deferred
The correct code is:
defer func() { recordLatency(time.Since(start)) }()
Default: `true` |
| `deprecated` | check for use of deprecated identifiers
The deprecated analyzer looks for deprecated symbols and package imports.
See https://go.dev/wiki/Deprecated to learn about Go's convention for documenting and signaling deprecated identifiers.
Default: `true` |
| `directive` | check Go toolchain directives such as //go:debug
This analyzer checks for problems with known Go toolchain directives in all Go source files in a package directory, even those excluded by //go:build constraints, and all non-Go source files too.
For //go:debug (see https://go.dev/doc/godebug), the analyzer checks that the directives are placed only in Go source files, only above the package comment, and only in package main or *_test.go files.
Support for other known directives may be added in the future.
This analyzer does not check //go:build, which is handled by the buildtag analyzer.
Default: `true` |
| `embed` | check //go:embed directive usage
This analyzer checks that the embed package is imported if //go:embed directives are present, providing a suggested fix to add the import if it is missing.
This analyzer also checks that //go:embed directives precede the declaration of a single variable.
Default: `true` |
| `errorsas` | report passing non-pointer or non-error values to errors.As
The errorsas analyzer reports calls to errors.As where the type of the second argument is not a pointer to a type implementing error.
Default: `true` |
| `errorsastype` | replace errors.As with errors.AsType[T]
This analyzer suggests fixes to simplify uses of [errors.As] of this form:
var myerr *MyErr
if errors.As(err, &myerr) {
handle(myerr)
}
by using the less error-prone generic [errors.AsType] function, introduced in Go 1.26:
if myerr, ok := errors.AsType[*MyErr](err); ok {
handle(myerr)
}
The fix is only offered if the var declaration has the form shown and there are no uses of myerr outside the if statement.
Default: `true` |
| `fillreturns` | suggest fixes for errors due to an incorrect number of return values
This checker provides suggested fixes for type errors of the type "wrong number of return values (want %d, got %d)". For example:
func m() (int, string, *bool, error) {
return
}
will turn into
func m() (int, string, *bool, error) {
return 0, "", nil, nil
}
This functionality is similar to https://github.com/sqs/goreturns.
Default: `true` |
| `fmtappendf` | replace []byte(fmt.Sprintf) with fmt.Appendf
The fmtappendf analyzer suggests replacing `[]byte(fmt.Sprintf(...))` with `fmt.Appendf(nil, ...)`. This avoids the intermediate allocation of a string by Sprintf, making the code more efficient. The suggestion also applies to fmt.Sprint and fmt.Sprintln.
Default: `true` |
| `forvar` | remove redundant re-declaration of loop variables
The forvar analyzer removes unnecessary shadowing of loop variables. Before Go 1.22, it was common to write `for _, x := range s { x := x ... }` to create a fresh variable for each iteration. Go 1.22 changed the semantics of `for` loops, making this pattern redundant. This analyzer removes the unnecessary `x := x` statement.
This fix only applies to `range` loops.
Default: `true` |
| `framepointer` | report assembly that clobbers the frame pointer before saving it
Default: `true` |
| `hostport` | check format of addresses passed to net.Dial
This analyzer flags code that produce network address strings using fmt.Sprintf, as in this example:
addr := fmt.Sprintf("%s:%d", host, 12345) // "will not work with IPv6" ... conn, err := net.Dial("tcp", addr) // "when passed to dial here"
The analyzer suggests a fix to use the correct approach, a call to net.JoinHostPort:
addr := net.JoinHostPort(host, "12345") ... conn, err := net.Dial("tcp", addr)
A similar diagnostic and fix are produced for a format string of "%s:%s".
Default: `true` |
| `httpresponse` | check for mistakes using HTTP responses
A common mistake when using the net/http package is to defer a function call to close the http.Response Body before checking the error that determines whether the response is valid:
resp, err := http.Head(url)
defer resp.Body.Close()
if err != nil {
log.Fatal(err)
}
// (defer statement belongs here)
This checker helps uncover latent nil dereference bugs by reporting a diagnostic for such mistakes.
Default: `true` |
| `ifaceassert` | detect impossible interface-to-interface type assertions
This checker flags type assertions v.(T) and corresponding type-switch cases in which the static type V of v is an interface that cannot possibly implement the target interface T. This occurs when V and T contain methods with the same name but different signatures. Example:
var v interface {
Read()
}
_ = v.(io.Reader)
The Read method in v has a different signature than the Read method in io.Reader, so this assertion cannot succeed.
Default: `true` |
| `infertypeargs` | check for unnecessary type arguments in call expressions
Explicit type arguments may be omitted from call expressions if they can be inferred from function arguments, or from other type arguments:
func f[T any](T) {}
func _() {
f[string]("foo") // string could be inferred
}
Default: `true` |
| `inline` | apply fixes based on 'go:fix inline' comment directives
The inline analyzer inlines functions and constants that are marked for inlining.
## Functions
Given a function that is marked for inlining, like this one:
//go:fix inline
func Square(x int) int { return Pow(x, 2) }
this analyzer will recommend that calls to the function elsewhere, in the same or other packages, should be inlined.
Inlining can be used to move off of a deprecated function:
// Deprecated: prefer Pow(x, 2).
//go:fix inline
func Square(x int) int { return Pow(x, 2) }
It can also be used to move off of an obsolete package, as when the import path has changed or a higher major version is available:
package pkg
import pkg2 "pkg/v2"
//go:fix inline
func F() { pkg2.F(nil) }
Replacing a call pkg.F() by pkg2.F(nil) can have no effect on the program, so this mechanism provides a low-risk way to update large numbers of calls. We recommend, where possible, expressing the old API in terms of the new one to enable automatic migration.
The inliner takes care to avoid behavior changes, even subtle ones, such as changes to the order in which argument expressions are evaluated. When it cannot safely eliminate all parameter variables, it may introduce a "binding declaration" of the form
var params = args
to evaluate argument expressions in the correct order and bind them to parameter variables. Since the resulting code transformation may be stylistically suboptimal, such inlinings may be disabled by specifying the -inline.allow_binding_decl=false flag to the analyzer driver.
(In cases where it is not safe to "reduce" a call—that is, to replace a call f(x) by the body of function f, suitably substituted—the inliner machinery is capable of replacing f by a function literal, func(){...}(). However, the inline analyzer discards all such "literalizations" unconditionally, again on grounds of style.)
## Constants
Given a constant that is marked for inlining, like this one:
//go:fix inline
const Ptr = Pointer
this analyzer will recommend that uses of Ptr should be replaced with Pointer.
As with functions, inlining can be used to replace deprecated constants and constants in obsolete packages.
A constant definition can be marked for inlining only if it refers to another named constant.
The "//go:fix inline" comment must appear before a single const declaration on its own, as above; before a const declaration that is part of a group, as in this case:
const (
C = 1
//go:fix inline
Ptr = Pointer
)
or before a group, applying to every constant in the group:
//go:fix inline
const (
Ptr = Pointer
Val = Value
)
The proposal https://go.dev/issue/32816 introduces the "//go:fix inline" directives.
You can use this command to apply inline fixes en masse:
$ go run golang.org/x/tools/go/analysis/passes/inline/cmd/inline@latest -fix ./...
Default: `true` |
| `loopclosure` | check references to loop variables from within nested functions
This analyzer reports places where a function literal references the iteration variable of an enclosing loop, and the loop calls the function in such a way (e.g. with go or defer) that it may outlive the loop iteration and possibly observe the wrong value of the variable.
Note: An iteration variable can only outlive a loop iteration in Go versions <=1.21. In Go 1.22 and later, the loop variable lifetimes changed to create a new iteration variable per loop iteration. (See go.dev/issue/60078.)
In this example, all the deferred functions run after the loop has completed, so all observe the final value of v [ for _, v := range list {
defer func() {
use(v) // incorrect
}()
}
One fix is to create a new variable for each iteration of the loop:
for _, v := range list {
v := v // new var per iteration
defer func() {
use(v) // ok
}()
}
After Go version 1.22, the previous two for loops are equivalent and both are correct.
The next example uses a go statement and has a similar problem [ for _, v := range elem {
go func() {
use(v) // incorrect, and a data race
}()
}
A fix is the same as before. The checker also reports problems in goroutines started by golang.org/x/sync/errgroup.Group. A hard-to-spot variant of this form is common in parallel tests:
func Test(t *testing.T) {
for _, test := range tests {
t.Run(test.name, func(t *testing.T) {
t.Parallel()
use(test) // incorrect, and a data race
})
}
}
The t.Parallel() call causes the rest of the function to execute concurrent with the loop [ The analyzer reports references only in the last statement, as it is not deep enough to understand the effects of subsequent statements that might render the reference benign. ("Last statement" is defined recursively in compound statements such as if, switch, and select.)
See: https://golang.org/doc/go_faq.html#closures_and_goroutines
Default: `true` |
| `lostcancel` | check cancel func returned by context.WithCancel is called
The cancellation function returned by context.WithCancel, WithTimeout, WithDeadline and variants such as WithCancelCause must be called, or the new context will remain live until its parent context is cancelled. (The background context is never cancelled.)
Default: `true` |
| `maprange` | checks for unnecessary calls to maps.Keys and maps.Values in range statements
Consider a loop written like this:
for val := range maps.Values(m) {
fmt.Println(val)
}
This should instead be written without the call to maps.Values:
for _, val := range m {
fmt.Println(val)
}
golang.org/x/exp/maps returns slices for Keys/Values instead of iterators, but unnecessary calls should similarly be removed:
for _, key := range maps.Keys(m) {
fmt.Println(key)
}
should be rewritten as:
for key := range m {
fmt.Println(key)
}
Default: `true` |
| `mapsloop` | replace explicit loops over maps with calls to maps package
The mapsloop analyzer replaces loops of the form
for k, v := range x { m[k] = v }
with a single call to a function from the `maps` package, added in Go 1.23. Depending on the context, this could be `maps.Copy`, `maps.Insert`, `maps.Clone`, or `maps.Collect`.
The transformation to `maps.Clone` is applied conservatively, as it preserves the nilness of the source map, which may be a subtle change in behavior if the original code did not handle a nil map in the same way.
Default: `true` |
| `minmax` | replace if/else statements with calls to min or max
The minmax analyzer simplifies conditional assignments by suggesting the use of the built-in `min` and `max` functions, introduced in Go 1.21. For example,
if a < b { x = a } else { x = b }
is replaced by
x = min(a, b).
This analyzer avoids making suggestions for floating-point types, as the behavior of `min` and `max` with NaN values can differ from the original if/else statement.
Default: `true` |
| `newexpr` | simplify code by using go1.26's new(expr)
This analyzer finds declarations of functions of this form:
func varOf(x int) *int { return &x }
and suggests a fix to turn them into inlinable wrappers around go1.26's built-in new(expr) function:
//go:fix inline
func varOf(x int) *int { return new(x) }
(The directive comment causes the 'inline' analyzer to suggest that calls to such functions are inlined.)
In addition, this analyzer suggests a fix for each call to one of the functions before it is transformed, so that
use(varOf(123))
is replaced by:
use(new(123))
Wrapper functions such as varOf are common when working with Go serialization packages such as for JSON or protobuf, where pointers are often used to express optionality.
Default: `true` |
| `nilfunc` | check for useless comparisons between functions and nil
A useless comparison is one like f == nil as opposed to f() == nil.
Default: `true` |
| `nilness` | check for redundant or impossible nil comparisons
The nilness checker inspects the control-flow graph of each function in a package and reports nil pointer dereferences, degenerate nil pointers, and panics with nil values. A degenerate comparison is of the form x==nil or x!=nil where x is statically known to be nil or non-nil. These are often a mistake, especially in control flow related to errors. Panics with nil values are checked because they are not detectable by
if r := recover(); r != nil {
This check reports conditions such as:
if f == nil { // impossible condition (f is a function)
}
and:
p := &v
...
if p != nil { // tautological condition
}
and:
if p == nil {
print(*p) // nil dereference
}
and:
if p == nil {
panic(p)
}
Sometimes the control flow may be quite complex, making bugs hard to spot. In the example below, the err.Error expression is guaranteed to panic because, after the first return, err must be nil. The intervening loop is just a distraction.
...
err := g.Wait()
if err != nil {
return err
}
partialSuccess := false
for _, err := range errs {
if err == nil {
partialSuccess = true
break
}
}
if partialSuccess {
reportStatus(StatusMessage{
Code: code.ERROR,
Detail: err.Error(), // "nil dereference in dynamic method call"
})
return nil
}
...
Default: `true` |
| `nonewvars` | suggested fixes for "no new vars on left side of :="
This checker provides suggested fixes for type errors of the type "no new vars on left side of :=". For example:
z := 1
z := 2
will turn into
z := 1
z = 2
Default: `true` |
| `noresultvalues` | suggested fixes for unexpected return values
This checker provides suggested fixes for type errors of the type "no result values expected" or "too many return values". For example:
func z() { return nil }
will turn into
func z() { return }
Default: `true` |
| `omitzero` | suggest replacing omitempty with omitzero for struct fields
The omitzero analyzer identifies uses of the `omitempty` JSON struct tag on fields that are themselves structs. For struct-typed fields, the `omitempty` tag has no effect on the behavior of json.Marshal and json.Unmarshal. The analyzer offers two suggestions: either remove the tag, or replace it with `omitzero` (added in Go 1.24), which correctly omits the field if the struct value is zero.
However, some other serialization packages (notably kubebuilder, see https://book.kubebuilder.io/reference/markers.html) may have their own interpretation of the `json:",omitzero"` tag, so removing it may affect program behavior. For this reason, the omitzero modernizer will not make changes in any package that contains +kubebuilder annotations.
Replacing `omitempty` with `omitzero` is a change in behavior. The original code would always encode the struct field, whereas the modified code will omit it if it is a zero-value.
Default: `true` |
| `plusbuild` | remove obsolete //+build comments
The plusbuild analyzer suggests a fix to remove obsolete build tags of the form:
//+build linux,amd64
in files that also contain a Go 1.18-style tag such as:
//go:build linux && amd64
(It does not check that the old and new tags are consistent; that is the job of the 'buildtag' analyzer in the vet suite.)
Default: `true` |
| `printf` | check consistency of Printf format strings and arguments
The check applies to calls of the formatting functions such as [fmt.Printf] and [fmt.Sprintf], as well as any detected wrappers of those functions such as [log.Printf]. It reports a variety of mistakes such as syntax errors in the format string and mismatches (of number and type) between the verbs and their arguments.
See the documentation of the fmt package for the complete set of format operators and their operand types.
Default: `true` |
| `rangeint` | replace 3-clause for loops with for-range over integers
The rangeint analyzer suggests replacing traditional for loops such as
for i := 0; i < n; i++ { ... }
with the more idiomatic Go 1.22 style:
for i := range n { ... }
This transformation is applied only if (a) the loop variable is not modified within the loop body and (b) the loop's limit expression is not modified within the loop, as `for range` evaluates its operand only once.
Default: `true` |
| `recursiveiter` | check for inefficient recursive iterators
This analyzer reports when a function that returns an iterator (iter.Seq or iter.Seq2) calls itself as the operand of a range statement, as this is inefficient.
When implementing an iterator (e.g. iter.Seq[T]) for a recursive data type such as a tree or linked list, it is tempting to recursively range over the iterator for each child element.
Here's an example of a naive iterator over a binary tree:
type tree struct {
value int
left, right *tree
}
func (t *tree) All() iter.Seq[int] {
return func(yield func(int) bool) {
if t != nil {
for elem := range t.left.All() { // "inefficient recursive iterator"
if !yield(elem) {
return
}
}
if !yield(t.value) {
return
}
for elem := range t.right.All() { // "inefficient recursive iterator"
if !yield(elem) {
return
}
}
}
}
}
Though it correctly enumerates the elements of the tree, it hides a significant performance problem--two, in fact. Consider a balanced tree of N nodes. Iterating the root node will cause All to be called once on every node of the tree. This results in a chain of nested active range-over-func statements when yield(t.value) is called on a leaf node.
The first performance problem is that each range-over-func statement must typically heap-allocate a variable, so iteration of the tree allocates as many variables as there are elements in the tree, for a total of O(N) allocations, all unnecessary.
The second problem is that each call to yield for a leaf of the tree causes each of the enclosing range loops to receive a value, which they then immediately pass on to their respective yield function. This results in a chain of log(N) dynamic yield calls per element, a total of O(N*log N) dynamic calls overall, when only O(N) are necessary.
A better implementation strategy for recursive iterators is to first define the "every" operator for your recursive data type, where every(f) reports whether an arbitrary predicate f(x) is true for every element x in the data type. For our tree, the every function would be:
func (t *tree) every(f func(int) bool) bool {
return t == nil ||
t.left.every(f) && f(t.value) && t.right.every(f)
}
For example, this use of the every operator prints whether every element in the tree is an even number:
even := func(x int) bool { return x&1 == 0 }
println(t.every(even))
Then the iterator can be simply expressed as a trivial wrapper around the every operator:
func (t *tree) All() iter.Seq[int] {
return func(yield func(int) bool) {
_ = t.every(yield)
}
}
In effect, tree.All computes whether yield returns true for each element, short-circuiting if it ever returns false, then discards the final boolean result.
This has much better performance characteristics: it makes one dynamic call per element of the tree, and it doesn't heap-allocate anything. It is also clearer.
Default: `true` |
| `reflecttypefor` | replace reflect.TypeOf(x) with TypeFor[T]()
This analyzer suggests fixes to replace uses of reflect.TypeOf(x) with reflect.TypeFor, introduced in go1.22, when the desired runtime type is known at compile time, for example:
reflect.TypeOf(uint32(0)) -> reflect.TypeFor[uint32]()
reflect.TypeOf((*ast.File)(nil)) -> reflect.TypeFor[*ast.File]()
It also offers a fix to simplify the construction below, which uses reflect.TypeOf to return the runtime type for an interface type,
reflect.TypeOf((*io.Reader)(nil)).Elem()
to:
reflect.TypeFor[io.Reader]()
No fix is offered in cases when the runtime type is dynamic, such as:
var r io.Reader = ...
reflect.TypeOf(r)
or when the operand has potential side effects.
Default: `true` |
| `shadow` | check for possible unintended shadowing of variables
This analyzer check for shadowed variables. A shadowed variable is a variable declared in an inner scope with the same name and type as a variable in an outer scope, and where the outer variable is mentioned after the inner one is declared.
(This definition can be refined; the module generates too many false positives and is not yet enabled by default.)
For example:
func BadRead(f *os.File, buf []byte) error {
var err error
for {
n, err := f.Read(buf) // shadows the function variable 'err'
if err != nil {
break // causes return of wrong value
}
foo(buf)
}
return err
}
Default: `false` |
| `shift` | check for shifts that equal or exceed the width of the integer
Default: `true` |
| `sigchanyzer` | check for unbuffered channel of os.Signal
This checker reports call expression of the form
signal.Notify(c <-chan os.Signal, sig ...os.Signal),
where c is an unbuffered channel, which can be at risk of missing the signal.
Default: `true` |
| `simplifycompositelit` | check for composite literal simplifications
An array, slice, or map composite literal of the form:
[]T{T{}, T{}}
will be simplified to:
[]T{{}, {}}
This is one of the simplifications that "gofmt -s" applies.
This analyzer ignores generated code.
Default: `true` |
| `simplifyrange` | check for range statement simplifications
A range of the form:
for x, _ = range v {...}
will be simplified to:
for x = range v {...}
A range of the form:
for _ = range v {...}
will be simplified to:
for range v {...}
This is one of the simplifications that "gofmt -s" applies.
This analyzer ignores generated code.
Default: `true` |
| `simplifyslice` | check for slice simplifications
A slice expression of the form:
s[a:len(s)]
will be simplified to:
s[a:]
This is one of the simplifications that "gofmt -s" applies.
This analyzer ignores generated code.
Default: `true` |
| `slicescontains` | replace loops with slices.Contains or slices.ContainsFunc
The slicescontains analyzer simplifies loops that check for the existence of an element in a slice. It replaces them with calls to `slices.Contains` or `slices.ContainsFunc`, which were added in Go 1.21.
If the expression for the target element has side effects, this transformation will cause those effects to occur only once, not once per tested slice element.
Default: `true` |
| `slicesdelete` | replace append-based slice deletion with slices.Delete
The slicesdelete analyzer suggests replacing the idiom
s = append(s[:i], s[j:]...)
with the more explicit
s = slices.Delete(s, i, j)
introduced in Go 1.21.
This analyzer is disabled by default. The `slices.Delete` function zeros the elements between the new length and the old length of the slice to prevent memory leaks, which is a subtle difference in behavior compared to the append-based idiom; see https://go.dev/issue/73686.
Default: `false` |
| `slicessort` | replace sort.Slice with slices.Sort for basic types
The slicessort analyzer simplifies sorting slices of basic ordered types. It replaces
sort.Slice(s, func(i, j int) bool { return s[i] < s[j] })
with the simpler `slices.Sort(s)`, which was added in Go 1.21.
Default: `true` |
| `slog` | check for invalid structured logging calls
The slog checker looks for calls to functions from the log/slog package that take alternating key-value pairs. It reports calls where an argument in a key position is neither a string nor a slog.Attr, and where a final key is missing its value. For example,it would report
slog.Warn("message", 11, "k") // slog.Warn arg "11" should be a string or a slog.Attr
and
slog.Info("message", "k1", v1, "k2") // call to slog.Info missing a final value
Default: `true` |
| `sortslice` | check the argument type of sort.Slice
sort.Slice requires an argument of a slice type. Check that the interface{} value passed to sort.Slice is actually a slice.
Default: `true` |
| `stditerators` | use iterators instead of Len/At-style APIs
This analyzer suggests a fix to replace each loop of the form:
for i := 0; i < x.Len(); i++ {
use(x.At(i))
}
or its "for elem := range x.Len()" equivalent by a range loop over an iterator offered by the same data type:
for elem := range x.All() {
use(x.At(i)
}
where x is one of various well-known types in the standard library.
Default: `true` |
| `stdmethods` | check signature of methods of well-known interfaces
Sometimes a type may be intended to satisfy an interface but may fail to do so because of a mistake in its method signature. For example, the result of this WriteTo method should be (int64, error), not error, to satisfy io.WriterTo:
type myWriterTo struct{...}
func (myWriterTo) WriteTo(w io.Writer) error { ... }
This check ensures that each method whose name matches one of several well-known interface methods from the standard library has the correct signature for that interface.
Checked method names include:
Format GobEncode GobDecode MarshalJSON MarshalXML
Peek ReadByte ReadFrom ReadRune Scan Seek
UnmarshalJSON UnreadByte UnreadRune WriteByte
WriteTo
Default: `true` |
| `stdversion` | report uses of too-new standard library symbols
The stdversion analyzer reports references to symbols in the standard library that were introduced by a Go release higher than the one in force in the referring file. (Recall that the file's Go version is defined by the 'go' directive its module's go.mod file, or by a "//go:build go1.X" build tag at the top of the file.)
The analyzer does not report a diagnostic for a reference to a "too new" field or method of a type that is itself "too new", as this may have false positives, for example if fields or methods are accessed through a type alias that is guarded by a Go version constraint.
Default: `true` |
| `stringintconv` | check for string(int) conversions
This checker flags conversions of the form string(x) where x is an integer (but not byte or rune) type. Such conversions are discouraged because they return the UTF-8 representation of the Unicode code point x, and not a decimal string representation of x as one might expect. Furthermore, if x denotes an invalid code point, the conversion cannot be statically rejected.
For conversions that intend on using the code point, consider replacing them with string(rune(x)). Otherwise, strconv.Itoa and its equivalents return the string representation of the value in the desired base.
Default: `true` |
| `stringsbuilder` | replace += with strings.Builder
This analyzer replaces repeated string += string concatenation operations with calls to Go 1.10's strings.Builder.
For example:
var s = "["
for x := range seq {
s += x
s += "."
}
s += "]"
use(s)
is replaced by:
var s strings.Builder
s.WriteString("[")
for x := range seq {
s.WriteString(x)
s.WriteString(".")
}
s.WriteString("]")
use(s.String())
This avoids quadratic memory allocation and improves performance.
The analyzer requires that all references to s except the final one are += operations. To avoid warning about trivial cases, at least one must appear within a loop. The variable s must be a local variable, not a global or parameter.
The sole use of the finished string must be the last reference to the variable s. (It may appear within an intervening loop or function literal, since even s.String() is called repeatedly, it does not allocate memory.)
Default: `true` |
| `stringscut` | replace strings.Index etc. with strings.Cut
This analyzer replaces certain patterns of use of [strings.Index] and string slicing by [strings.Cut], added in go1.18.
For example:
idx := strings.Index(s, substr)
if idx >= 0 {
return s[:idx]
}
is replaced by:
before, _, ok := strings.Cut(s, substr)
if ok {
return before
}
And:
idx := strings.Index(s, substr)
if idx >= 0 {
return
}
is replaced by:
found := strings.Contains(s, substr)
if found {
return
}
It also handles variants using [strings.IndexByte] instead of Index, or the bytes package instead of strings.
Fixes are offered only in cases in which there are no potential modifications of the idx, s, or substr expressions between their definition and use.
Default: `true` |
| `stringscutprefix` | replace HasPrefix/TrimPrefix with CutPrefix
The stringscutprefix analyzer simplifies a common pattern where code first checks for a prefix with `strings.HasPrefix` and then removes it with `strings.TrimPrefix`. It replaces this two-step process with a single call to `strings.CutPrefix`, introduced in Go 1.20. The analyzer also handles the equivalent functions in the `bytes` package.
For example, this input:
if strings.HasPrefix(s, prefix) {
use(strings.TrimPrefix(s, prefix))
}
is fixed to:
if after, ok := strings.CutPrefix(s, prefix); ok {
use(after)
}
The analyzer also offers fixes to use CutSuffix in a similar way. This input:
if strings.HasSuffix(s, suffix) {
use(strings.TrimSuffix(s, suffix))
}
is fixed to:
if before, ok := strings.CutSuffix(s, suffix); ok {
use(before)
}
Default: `true` |
| `stringsseq` | replace ranging over Split/Fields with SplitSeq/FieldsSeq
The stringsseq analyzer improves the efficiency of iterating over substrings. It replaces
for range strings.Split(...)
with the more efficient
for range strings.SplitSeq(...)
which was added in Go 1.24 and avoids allocating a slice for the substrings. The analyzer also handles strings.Fields and the equivalent functions in the bytes package.
Default: `true` |
| `structtag` | check that struct field tags conform to reflect.StructTag.Get
Also report certain struct tags (json, xml) used with unexported fields.
Default: `true` |
| `testingcontext` | replace context.WithCancel with t.Context in tests
The testingcontext analyzer simplifies context management in tests. It replaces the manual creation of a cancellable context,
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
with a single call to t.Context(), which was added in Go 1.24.
This change is only suggested if the `cancel` function is not used for any other purpose.
Default: `true` |
| `testinggoroutine` | report calls to (*testing.T).Fatal from goroutines started by a test
Functions that abruptly terminate a test, such as the Fatal, Fatalf, FailNow, and Skip{,f,Now} methods of *testing.T, must be called from the test goroutine itself. This checker detects calls to these functions that occur within a goroutine started by the test. For example:
func TestFoo(t *testing.T) {
go func() {
t.Fatal("oops") // error: (*T).Fatal called from non-test goroutine
}()
}
Default: `true` |
| `tests` | check for common mistaken usages of tests and examples
The tests checker walks Test, Benchmark, Fuzzing and Example functions checking malformed names, wrong signatures and examples documenting non-existent identifiers.
Please see the documentation for package testing in golang.org/pkg/testing for the conventions that are enforced for Tests, Benchmarks, and Examples.
Default: `true` |
| `timeformat` | check for calls of (time.Time).Format or time.Parse with 2006-02-01
The timeformat checker looks for time formats with the 2006-02-01 (yyyy-dd-mm) format. Internationally, "yyyy-dd-mm" does not occur in common calendar date standards, and so it is more likely that 2006-01-02 (yyyy-mm-dd) was intended.
Default: `true` |
| `unmarshal` | report passing non-pointer or non-interface values to unmarshal
The unmarshal analysis reports calls to functions such as json.Unmarshal in which the argument type is not a pointer or an interface.
Default: `true` |
| `unreachable` | check for unreachable code
The unreachable analyzer finds statements that execution can never reach because they are preceded by a return statement, a call to panic, an infinite loop, or similar constructs.
Default: `true` |
| `unsafefuncs` | replace unsafe pointer arithmetic with function calls
The unsafefuncs analyzer simplifies pointer arithmetic expressions by replacing them with calls to helper functions such as unsafe.Add, added in Go 1.17.
Example:
unsafe.Pointer(uintptr(ptr) + uintptr(n))
where ptr is an unsafe.Pointer, is replaced by:
unsafe.Add(ptr, n)
Default: `true` |
| `unsafeptr` | check for invalid conversions of uintptr to unsafe.Pointer
The unsafeptr analyzer reports likely incorrect uses of unsafe.Pointer to convert integers to pointers. A conversion from uintptr to unsafe.Pointer is invalid if it implies that there is a uintptr-typed word in memory that holds a pointer value, because that word will be invisible to stack copying and to the garbage collector.
Default: `true` |
| `unusedfunc` | check for unused functions, methods, etc
The unusedfunc analyzer reports functions and methods that are never referenced outside of their own declaration.
A function is considered unused if it is unexported and not referenced (except within its own declaration).
A method is considered unused if it is unexported, not referenced (except within its own declaration), and its name does not match that of any method of an interface type declared within the same package.
The tool may report false positives in some situations, for example:
- for a declaration of an unexported function that is referenced from another package using the go:linkname mechanism, if the declaration's doc comment does not also have a go:linkname comment.
(Such code is in any case strongly discouraged: linkname annotations, if they must be used at all, should be used on both the declaration and the alias.)
- for compiler intrinsics in the "runtime" package that, though never referenced, are known to the compiler and are called indirectly by compiled object code.
- for functions called only from assembly.
- for functions called only from files whose build tags are not selected in the current build configuration.
Since these situations are relatively common in the low-level parts of the runtime, this analyzer ignores the standard library. See https://go.dev/issue/71686 and https://go.dev/issue/74130 for further discussion of these limitations.
The unusedfunc algorithm is not as precise as the golang.org/x/tools/cmd/deadcode tool, but it has the advantage that it runs within the modular analysis framework, enabling near real-time feedback within gopls.
The unusedfunc analyzer also reports unused types, vars, and constants. Enums--constants defined with iota--are ignored since even the unused values must remain present to preserve the logical ordering.
Default: `true` |
| `unusedparams` | check for unused parameters of functions
The unusedparams analyzer checks functions to see if there are any parameters that are not being used.
To ensure soundness, it ignores: - "address-taken" functions, that is, functions that are used as a value rather than being called directly; their signatures may be required to conform to a func type. - exported functions or methods, since they may be address-taken in another package. - unexported methods whose name matches an interface method declared in the same package, since the method's signature may be required to conform to the interface type. - functions with empty bodies, or containing just a call to panic. - parameters that are unnamed, or named "_", the blank identifier.
The analyzer suggests a fix of replacing the parameter name by "_", but in such cases a deeper fix can be obtained by invoking the "Refactor: remove unused parameter" code action, which will eliminate the parameter entirely, along with all corresponding arguments at call sites, while taking care to preserve any side effects in the argument expressions; see https://github.com/golang/tools/releases/tag/gopls%2Fv0.14.
This analyzer ignores generated code.
Default: `true` |
| `unusedresult` | check for unused results of calls to some functions
Some functions like fmt.Errorf return a result and have no side effects, so it is always a mistake to discard the result. Other functions may return an error that must not be ignored, or a cleanup operation that must be called. This analyzer reports calls to functions like these when the result of the call is ignored.
The set of functions may be controlled using flags.
Default: `true` |
| `unusedvariable` | check for unused variables and suggest fixes
Default: `true` |
| `unusedwrite` | checks for unused writes
The analyzer reports instances of writes to struct fields and arrays that are never read. Specifically, when a struct object or an array is copied, its elements are copied implicitly by the compiler, and any element write to this copy does nothing with the original object.
For example:
type T struct { x int }
func f(input []T) {
for i, v := range input { // v is a copy
v.x = i // unused write to field x
}
}
Another example is about non-pointer receiver:
type T struct { x int }
func (t T) f() { // t is a copy
t.x = i // unused write to field x
}
Default: `true` |
| `waitgroup` | replace wg.Add(1)/go/wg.Done() with wg.Go
The waitgroup analyzer simplifies goroutine management with `sync.WaitGroup`. It replaces the common pattern
wg.Add(1)
go func() {
defer wg.Done()
...
}()
with a single call to
wg.Go(func(){ ... })
which was added in Go 1.25.
Default: `true` |
| `yield` | report calls to yield where the result is ignored
After a yield function returns false, the caller should not call the yield function again; generally the iterator should return promptly.
This example fails to check the result of the call to yield, causing this analyzer to report a diagnostic:
yield(1) // yield may be called again (on L2) after returning false
yield(2)
The corrected code is either this:
if yield(1) { yield(2) }
or simply:
_ = yield(1) && yield(2)
It is not always a mistake to ignore the result of yield. For example, this is a valid single-element iterator:
yield(1) // ok to ignore result
return
It is only a mistake when the yield call that returned false may be followed by another call.
Default: `true` |
### `ui.diagnostic.analysisProgressReporting`
analysisProgressReporting controls whether gopls sends progress
notifications when construction of its index of analysis facts is taking a
long time. Cancelling these notifications will cancel the indexing task,
though it will restart after the next change in the workspace.
When a package is opened for the first time and heavyweight analyses such as
staticcheck are enabled, it can take a while to construct the index of
analysis facts for all its dependencies. The index is cached in the
filesystem, so subsequent analysis should be faster.
Default: `true`
### `ui.diagnostic.annotations`
annotations specifies the various kinds of compiler
optimization details that should be reported as diagnostics
when enabled for a package by the "Toggle compiler
optimization details" (`gopls.gc_details`) command.
(Some users care only about one kind of annotation in their
profiling efforts. More importantly, in large packages, the
number of annotations can sometimes overwhelm the user
interface and exceed the per-file diagnostic limit.)
TODO(adonovan): rename this field to CompilerOptDetail.
| Properties | Description |
| --- | --- |
| `bounds` | `"bounds"` controls bounds checking diagnostics.
Default: `true` |
| `escape` | `"escape"` controls diagnostics about escape choices.
Default: `true` |
| `inline` | `"inline"` controls diagnostics about inlining choices.
Default: `true` |
| `nil` | `"nil"` controls nil checks.
Default: `true` |
### `ui.diagnostic.diagnosticsDelay`
(Advanced) diagnosticsDelay controls the amount of time that gopls waits
after the most recent file modification before computing deep diagnostics.
Simple diagnostics (parsing and type-checking) are always run immediately
on recently modified packages.
This option must be set to a valid duration string, for example `"250ms"`.
Default: `"1s"`
### `ui.diagnostic.diagnosticsTrigger`
(Experimental) diagnosticsTrigger controls when to run diagnostics.
Allowed Options:
* `Edit`: `"Edit"`: Trigger diagnostics on file edit and save. (default)
* `Save`: `"Save"`: Trigger diagnostics only on file save. Events like initial workspace load
or configuration change will still trigger diagnostics.
Default: `"Edit"`
### `ui.diagnostic.staticcheck`
(Experimental) staticcheck configures the default set of analyses staticcheck.io.
These analyses are documented on
[Staticcheck's website](https://staticcheck.io/docs/checks/).
The "staticcheck" option has three values:
- false: disable all staticcheck analyzers
- true: enable all staticcheck analyzers
- unset: enable a subset of staticcheck analyzers
selected by gopls maintainers for runtime efficiency
and analytic precision.
Regardless of this setting, individual analyzers can be
selectively enabled or disabled using the `analyses` setting.
Default: `false`
### `ui.diagnostic.staticcheckProvided`
(Experimental)
Default: `false`
### `ui.documentation.hoverKind`
hoverKind controls the information that appears in the hover text.
SingleLine is intended for use only by authors of editor plugins.
Allowed Options:
* `FullDocumentation`
* `NoDocumentation`
* `SingleLine`
* `Structured`: `"Structured"` is a misguided experimental setting that returns a JSON
hover format. This setting should not be used, as it will be removed in a
future release of gopls.
* `SynopsisDocumentation`
Default: `"FullDocumentation"`
### `ui.documentation.linkTarget`
linkTarget is the base URL for links to Go package
documentation returned by LSP operations such as Hover and
DocumentLinks and in the CodeDescription field of each
Diagnostic.
It might be one of:
* `"godoc.org"`
* `"pkg.go.dev"`
If company chooses to use its own `godoc.org`, its address can be used as well.
Modules matching the GOPRIVATE environment variable will not have
documentation links in hover.
Default: `"pkg.go.dev"`
### `ui.documentation.linksInHover`
linksInHover controls the presence of documentation links in hover markdown.
Allowed Options:
* `false`: false: do not show links
* `true`: true: show links to the `linkTarget` domain
* `gopls`: `"gopls"`: show links to gopls' internal documentation viewer
Default: `true`
### `ui.navigation.importShortcut`
importShortcut specifies whether import statements should link to
documentation or go to definitions.
Allowed Options: `Both`, `Definition`, `Link`
Default: `"Both"`
### `ui.navigation.symbolMatcher`
(Advanced) symbolMatcher sets the algorithm that is used when finding workspace symbols.
Allowed Options: `CaseInsensitive`, `CaseSensitive`, `FastFuzzy`, `Fuzzy`
Default: `"FastFuzzy"`
### `ui.navigation.symbolScope`
symbolScope controls which packages are searched for workspace/symbol
requests. When the scope is "workspace", gopls searches only workspace
packages. When the scope is "all", gopls searches all loaded packages,
including dependencies and the standard library.
Allowed Options:
* `all`: `"all"` matches symbols in any loaded package, including
dependencies.
* `workspace`: `"workspace"` matches symbols in workspace packages only.
Default: `"all"`
### `ui.navigation.symbolStyle`
(Advanced) symbolStyle controls how symbols are qualified in symbol responses.
Example Usage:
```json5
"gopls": {
...
"symbolStyle": "Dynamic",
...
}
```
Allowed Options:
* `Dynamic`: `"Dynamic"` uses whichever qualifier results in the highest scoring
match for the given symbol query. Here a "qualifier" is any "/" or "."
delimited suffix of the fully qualified symbol. i.e. "to/pkg.Foo.Field" or
just "Foo.Field".
* `Full`: `"Full"` is fully qualified symbols, i.e.
"path/to/pkg.Foo.Field".
* `Package`: `"Package"` is package qualified symbols i.e.
"pkg.Foo.Field".
Default: `"Dynamic"`
### `ui.newGoFileHeader`
newGoFileHeader enables automatic insertion of the copyright comment
and package declaration in a newly created Go file.
Default: `true`
### `ui.noSemanticNumber (deprecated)`
use SemanticTokenTypes["number"] = false instead. See
golang/vscode-go#3632.
(Experimental) noSemanticNumber turns off the sending of the semantic token 'number'
Deprecated: Use SemanticTokenTypes["number"] = false instead. See
golang/vscode-go#3632.
Default: `false`
### `ui.noSemanticString (deprecated)`
use SemanticTokenTypes["string"] = false instead. See
golang/vscode-go#3632
(Experimental) noSemanticString turns off the sending of the semantic token 'string'
Deprecated: Use SemanticTokenTypes["string"] = false instead. See
golang/vscode-go#3632
Default: `false`
### `ui.renameMovesSubpackages`
(Experimental) renameMovesSubpackages enables Rename operations on packages to
move subdirectories of the target package.
Default: `false`
### `ui.semanticTokenModifiers`
(Experimental) semanticTokenModifiers configures the semantic token modifiers. It allows
disabling modifiers by setting each value to false.
By default, all modifiers are enabled.
### `ui.semanticTokenTypes`
(Experimental) semanticTokenTypes configures the semantic token types. It allows
disabling types by setting each value to false.
By default, all types are enabled.
### `ui.semanticTokens`
(Experimental) semanticTokens controls whether the LSP server will send
semantic tokens to the client.
Default: `false`
### `verboseOutput`
(For Debugging) verboseOutput enables additional debug logging.
Default: `false`
---
# Source: https://github.com/golang/vscode-go/blob/master/docs/smoke-test.md
# Smoke Test
Before releasing a new version of the extension, please run the following smoke test to make sure that all features are working.
## Set up
First, clone [golang.org/x/example](https://github.com/golang/example). At the time of writing (June 2020), this repository has not changed since 2017. If it has changed since, these steps may not be exactly reproducible and should be adjusted.
For now, we smoke test the extension only in [`GOPATH`](gopath.md) mode.
If it does not already exist:
```bash
mkdir $GOPATH/src/github.com/golang
```
Then,
```bash
cd $GOPATH/src/github.com/golang
git clone https://github.com/golang/example
cd example
```
Next, [build and sideload the modified Go extension](contributing.md#sideload) and open the `example/hello` directory. Open `hello.go`.
## Test code navigation
1. Go to definition on `fmt.Println`.
2. Go to definition on `stringutil.Reverse`.
3. Find all references of `fmt.Println`.
4. Find all references of `stringutil.Reverse`.
5. Hover over `fmt.Println`.
6. Hover over `stringutil.Reverse`.
## Test autocompletion
1. Trigger autocompletion (Ctrl+Space) after `fmt.`.
2. Trigger autocompletion (Ctrl+Space) after `stringutil.`.
3. Enter a newline in the `main` function and type `fmt.`.
4. Enter a newline in the `main` function and type `parser.`. Expect suggestions from the unimported standard library `go/parser` package.
5. Enter a newline in the `main` function and type `fmt.`. Select the `fmt.Println` completion and observe the outcome. Toggle the `go.useCodeSnippetsOnFunctionSuggest` setting to ensure that placeholders are provided.
6. Test signature help by manually triggering it (Ctrl+Shift+Space) while completing `fmt.Println`.
7. Test signature help by manually triggering it (Ctrl+Shift+Space) while completing `stringutil.Reverse`.
## Test diagnostics
Enable `go.buildOnSave`, `go.vetOnSave`, and `go.lintOnSave`.
1. Add `var x int` to the `main` function and expect a build diagnostic.
2. Add `fmt.Printf("hi", 1)` and expect a vet diagnostic.
3. Add the following function to the bottom of the file and expect a lint diagnostic.
```go
// Hello is hi.
func Hi() {}
```
You can also try toggling the `"package"` and `"workspace"` configurations for these settings.
## Test formatting and import organization
1. Hit enter 3 times in the `main` function and save. Expect formatting to remove all but one line.
2. Remove the `"fmt"` import. Save and expect it to return.
3. Remove the `"github.com/golang/example/stringutil"` import. Save and expect it to return.
4. Confirm that the `Go: Add Import` command works (add `"archive/tar"`).
## Test renaming
1. Add the following to the `main` function, then rename `x` to `y`.
```go
var x int
fmt.Println(x)
```
2. Rename `stringutil.Reverse`. `reverse.go` and `reverse_test.go` should be dirtied.
---
# Source: https://github.com/golang/vscode-go/blob/master/docs/tasks.md
# Using [VS Code Tasks] with Go
From the [VS Code Tasks] documentation:
> Tasks in VS Code can be configured to run scripts and start processes so that . . . existing tools can be used from within VS Code without having to enter a command line or write new code. Workspace or folder specific tasks are configured from the tasks.json file in the .vscode folder for a workspace.
To begin configuring tasks, run the `Tasks: Configure Task` command from the Command Palette (Ctrl+Shift+P).
This will create a `tasks.json` file in your workspace's `.vscode` folder.
Replace the contents of this file with the following and adjust the tasks as needed.
```json5
{
"version": "2.0.0",
"type": "shell",
"command": "go",
"cwd": "${workspaceFolder}",
"tasks": [
{
"label": "install",
"args": ["install", "-v", "./..."],
"group": "build",
},
{
"label": "run",
"args": ["run", "${file}"],
"group": "build",
},
{
"label": "test",
"args": ["test", "-v", "./..."],
"group": "test",
},
],
}
```
You can run these tasks via the `Tasks: Run Task` command or by using the Ctrl+Shift+B shortcut.
You can also define additional tasks to run other commands, like `go generate`. Here's an example of a task to run only a specific test (`MyTestFunction`, in this case):
```json5
{
"label": "MyTestFunction",
"args": [ "test", "./...", "-test.run", "MyTestFunction"]
}
```
If you want to invoke tools other than `go`, you will have to move the `"command": "go"` setting into the task objects. For example:
```json5
{
"version": "2.0.0",
"cwd": "${workspaceFolder}",
"tasks": [
{
"label": "install",
"command": "go",
"args": ["install", "-v", "./..."],
"group": "build",
"type": "shell",
},
{
"label": "run",
"command": "go",
"args": ["run", "${file}"],
"group": "build",
"type": "shell",
},
{
"label": "test",
"command": "go",
"args": ["test", "-v", "./..."],
"group": "test",
"type": "shell",
},
],
}
```
Learn more by reading the [VS Code Tasks] documentation.
[VS Code Tasks]: https://code.visualstudio.com/docs/editor/tasks
---
# Source: https://github.com/golang/vscode-go/blob/master/docs/tools.md
# Tools
This document describes the tools that power the VS Code Go extension.
Tools will be installed by default when you install the extension. You can also manually install or update all of these tools by running the [`Go: Install/Update Tools`](commands.md#go-installupdate-tools) command. The extension uses pinned versions of command-line tools. See the pinned versions in tools information [here](https://github.com/golang/vscode-go/blob/master/extension/src/goToolsInformation.ts). If any tools are missing, you will see an `Analysis Tools Missing` warning in the bottom-right corner of the editor, which will prompt you to install these tools.
VS Code Go will install the tools to your `$GOPATH/bin` by default.
### [`go`]
This extension requires you to install the Go toolchain, meaning that you have the `go` command on your [`PATH`](https://en.wikipedia.org/wiki/PATH_(variable)). To do this, follow [the Go installation guide](https://golang.org/doc/install).
The extension runs the [`go`] command to debug and test your go program. By default, this extension assumes that Go is already installed in your system and the `go` command can be found from the `PATH` (or `Path` in some Windows) environment variable.
This extension works best with the [latest versions of Go](https://golang.org/doc/devel/release.html#policy) but some of the features may continue to work with older versions of Go. The Go release policy states that the two newer major releases are officially supported.
The extension checks for the availability of the new Go release by periodically checking the [official Go distribution site](https://golang.org/dl) and notifies you of the new version.
### [`gopls`]
[`gopls`] is the official Go [language server](https://langserver.org/) developed by the Go team. It is the default backend for most of this extension's IntelliSense, code navigation, code editing, and diagnostics features. When the extension starts, it spawns a `gopls` instance in server mode for each VS Code project.
`gopls` uses the `go` command to analyze your code. The extension automatically propagates necessary settings such as `"go.buildFlags"`, `"go.buildTags"`, `"go.toolsEnvVars"` and the path to the right `go` command to `gopls`. No extra settings should be necessary, but when you need to adjust `gopls`'s behavior further (e.g., enable more advanced analysis features), please see [all the settings for `gopls`](settings.md#settings-for-gopls).
If you encounter issues with `gopls`, please read the [troubleshooting guide](troubleshooting.md#collect-gopls-information). If you want to run the extension without the language server, you can disable it by setting `"go.useLanguageServer": false`.
`gopls` officially supports the four newer major versions of Go. If you are using a very old version of Go, or you explicitly disable the language server, the extension will automatically fall back to the legacy mode. The legacy mode uses old tools instead of `gopls`. Unfortunately many of them are no longer actively maintained and many features the extension provides will not be available.
You can tell whether the extension is using `gopls`, by checking whether the high voltage icon (⚡) is present in the [Go status bar](./ui.md).
`gopls` is under active development, and updating it is important to get new features. The extension periodically checks the [module proxy](https://golang.org/cmd/go/#hdr-Module_proxy_protocol) to detect a new version has been released. When a newer version is available, a pop-up will appear, prompting you to update. If you would like to opt out of this automated update check, set `"go.toolsManagement.checkForUpdates"` to `false`.
For more information about `gopls`, please visit its [documentation](https://golang.org/s/gopls).
### [`dlv`](https://github.com/go-delve/delve)
This extension uses Delve for its debug/test functionalities. The extension currently ships with a thin Debug Adapter that implements the [Debug Adapter protocol](https://microsoft.github.io/debug-adapter-protocol/) and connects VS Code and `dlv`.
For a comprehensive overview of how to debug your Go programs, please see the [debugging guide](./debugging.md).
### [`vscgo`](https://pkg.go.dev/github.com/golang/vscode-go/vscgo)
This tool provides utilities needed by this extension but do not belong to the language server
or debug adapter server. Examples include dependency tools management, developer survey
configuration, and [Go telemetry collection](https://github.com/golang/vscode-go/issues/3121).
This tool is released with the extension and installed in the extension's directory.
### [`goplay`](https://pkg.go.dev/github.com/haya14busa/goplay?tab=overview)
This tool provides support for the [`Go: Run on Go Playground`](features.md#go-playground) command.
### [`gomodifytags`](https://pkg.go.dev/github.com/fatih/gomodifytags?tab=overview)
This tool provides support for the [`Go: Add Tags to Struct Fields`](features.md#add-or-remove-struct-tags) and [`Go: Remove Tags From Struct Fields`](features.md#add-or-remove-struct-tags) commands when using older versions of gopls. The latest
version of gopls has a gopls.modify_tags command which directly invokes the
gomodifytags library.
### [`impl`](https://github.com/josharian/impl)
This tool provides support for the [`Go: Generate Interface Stubs`](features.md#generate-interface-implementation) command.
### [`gotests`](https://github.com/cweill/gotests/)
This tool provides support for the [`Go: Generate Unit Tests`](features.md#generate-unit-tests) set of commands.
### [`staticcheck`]
This is the default lint tool. See the [full list of checks](https://staticcheck.io/docs/checks) that `staticcheck` provides. Other lint tools can be used by configuring the [`"go.lintTool"`](settings.md#go.lintTool) setting.
Other options include:
* [`golangci-lint`]: This meta-linter combines a number of existing lint tools, including [staticcheck](#staticcheck), into one interface.
* [`revive`]: This tool is an enhancement on top of [`golint`], and it provides additional checks.
* [`golint`]: This used to be the default linter used by this extension before it was officially deprecated.
You can use the [`"go.lintFlags"`](settings.md#go.lintFlags) setting to further configure your linter of choice. Most linters can be configured via special configuration files, but you may still need to pass these command-line flags. The configuration documentation for each supported linter is listed here:
* [`staticcheck`](https://staticcheck.io/docs/#configuration)
* [`golangci-lint`](https://golangci-lint.run/usage/configuration/)
* [`revive`](https://github.com/mgechev/revive#command-line-flags)
#### Examples
Enable all [`golangci-lint`] linters and only show errors in new code:
```json5
"go.lintFlags": ["--enable-all", "--new"]
```
Configure `revive` to exclude `vendor` directories and apply extra configuration with a `config.toml` file:
```json5
"go.lintFlags": [
"-exclude=vendor/...",
"-config=${workspaceFolder}/config.toml"
]
```
[`goimports`]: https://pkg.go.dev/golang.org/x/tools/cmd/goimports?tab=doc
[`gofmt`]: https://golang.org/cmd/gofmt/
[`golint`]: https://pkg.go.dev/golang.org/x/lint/golint?tab=overview
[`staticcheck`]: https://pkg.go.dev/honnef.co/go/tools/staticcheck?tab=overview
[`golangci-lint`]: https://golangci-lint.run/
[`revive`]: https://pkg.go.dev/github.com/mgechev/revive?tab=overview
[`gopls`]: https://golang.org/s/gopls
[`go`]: https://golang.org/cmd/go
---
# Source: https://github.com/golang/vscode-go/blob/master/docs/troubleshooting.md
# Troubleshooting
If you suspect that the Go extension is not working correctly, please follow the troubleshooting steps below.
**NOTE: [Debugging](debugging.md#troubleshooting) has its own troubleshooting documentation.**
## Make sure your project compiles
Verify that your project is in good shape by working with it at the command line. Running a command like `go build ./...` in the workspace directory will compile everything. For modules, `go mod tidy` is another good check, though it may modify your `go.mod`.
## Look for serious errors and diagnostics
Check that there aren't any diagnostics that indicate a problem with your workspace. First, check the bottom-center of the VS Code window for any errors. After that, check the package declaration of the any Go files you're working in, and your `go.mod` file. Problems in the workspace configuration can cause many different symptoms. See the [`gopls` workspace setup instructions](https://github.com/golang/tools/blob/master/gopls/doc/workspace.md) for help.
## Check your extension setup
Check the bottom of the VS Code window for any warnings and notifications. For example, address warnings such as "⚠️ Analysis Tools Missing".
Run the [`Go: Locate Configured Go Tools`](commands.md#go-locate-configured-go-tools) command. The output is split into sections.
In the first indented section, check that at least `go-outline`, `dlv`, and `gopls` are installed -- they're necessary for the extension's basic functionality. The other tools [provide optional features](tools.md) and are less important unless you need those features. You can install tools by running the [`Go: Install/Update Tools`](commands.md#go-installupdate-tools) command.
Then, look at the `Workspace Folder` section(s) for the environment in use. Verify that `GOROOT` is set to a valid Go installation; if not, follow the [getting started guide](../README.md#install-go). If `GOPATH` is unset, or surprising, read more about [setting up your `GOPATH`](gopath.md#setting-gopath). Also, `GOMOD` should usually point to your project's `go.mod` file if you're in module mode. (More complicated workspace setups may have a blank `GOMOD`. See the `gopls` [workspace documentation](https://github.com/golang/tools/blob/master/gopls/doc/workspace.md) for more on valid workspace setups.) To change the workspace environment, use settings such as [`go.gopath`](settings.md#go.gopath) and [`go.toolsEnvVars`](settings.md#go.toolsEnvVars).
Finally, take a look at your settings in the JSON form (`Preferences: Open Settings (JSON)`). This is an easier way to quickly see what non-default configurations you have. Consider [reading about](settings.md) any settings you don't understand, or just commenting them out.
## Update tools
It's possible that you are using an outdated version of a tool, so the bug you are encountering may have already been fixed. You can update all tools at once by running the [`Go: Install/Update Tools`](commands.md#go-installupdate-tools) command.
## Restart `gopls`
Many of the extension's features are provided by [`gopls`](https://golang.org/s/gopls), the official language server for Go. `gopls` has no persistent state, so restarting it will fix transient problems. This is good and bad: good, because you can keep working, and bad, because you won't be able to debug the issue until it recurs. You can restart `gopls` using the `Go: Restart Language Server` command.
## Ask for help
After you've done the basic steps above, it's a good time to ask for help. Gophers Slack has a channel for [#vscode](https://gophers.slack.com/archives/C2B4L99RS) that can help debug further. If you're confident the problem is with `gopls`, you can go to [#gopls](https://gophers.slack.com/archives/CJZH85XCZ). Invites are [available to everyone](https://invite.slack.golangbridge.org). Come prepared with a short description of the issue, and try to be available to answer questions for a while afterward.
## Collect extension logs
Start off by opening the `View` -> `Output` pane. On the right side, open the drop-down titled "Tasks". Any item that starts with "Go" is related to this extension. Browse through these output channels and make note of any error messages.
You can also look directly in the logs of the Extension Host by selecting `Log (Extension Host)`. These may contain a lot of unrelated information, but they may prove useful. If you are trying to get the logs for a specific operation, like go to definition, clear the logs (Clear Output button on the right side), and perform the operation.
Errors may also be logged to the Developer Tools console. These errors may be more difficult to parse, but you can take a look at them by running the `Developer: Toggle Developer Tools` command from the Command Palette (Ctrl+Shift+P).
## Collect `gopls` information
Enable `gopls` tracing by adding the following to your settings:
```json5
"go.languageServerFlags": [
"-rpc.trace"
]
```
The gopls log can be found by navigating to `View` -> `Output`. There will be a drop-down menu titled `Tasks` in the top-right corner. Select the `gopls (server)` item, which will contain the `gopls` logs.
In special cases, you may want to increase the verbosity further:
```json5
"gopls": {
"verboseOutput": true
}
```
## File an issue
We can't diagnose a problem from just a description. When filing an issue, please include as much as possible of the following information:
1. Your Go version: `go version`
1. Your `gopls` version: `gopls -v version`
1. Your vscode version: `code -v` (The minimum required VS Code version is in the ["engines"](https://github.com/golang/vscode-go/blob/master/package.json#L89) attribute in the package.json file.)
1. Your Go extension version: `Extensions: Show Installed Extensions`
1. Your Go environment: `go env` in the workspace folder
1. Relevant VS Code settings: run `Preferences: Open Settings (JSON)` and include anything in a `[go]` block, and anything that starts with `go.` or `gopls.`
1. Extension and `gopls` logs as seems appropriate for the bug. (Include from the beginning of the logs if possible.)
Once you've collected that information, [file your issue](https://github.com/golang/vscode-go/issues/new/choose).
---
# Source: https://github.com/golang/vscode-go/blob/master/docs/ui.md
# Extension UI
## Using The Go Status Bar
The Go status bar appears in the lower right of the extension window, next to the Editor Language status bar item. Clicking the Go status bar brings up a menu that provides easy access to see and update important information about your Go project. This includes information about the Go environment, the current Go version, the `gopls` trace, and about the current module.
Go: Toggle Vulncheck (vulncheck.mp4) 
