Code Inspections in Go

'FailNow' in a non-test goroutine

Reports calls to testing.T.FailNow and similar methods located in goroutines in test files.

Methods like FailNow call runtime.Goexit and stop the calling goroutine, not the test. Therefore, they must only be called from the goroutine that runs the test or benchmark.

For more information about FailNow, refer to func (*T) FailNow at go.dev.

Example:

func TestFoo(t *testing.T) {
  go func() {
    t.Fatal("oops") //exits goroutine, not TestFoo
  }()
}

After the Replace with 'Error' and 'return' quick-fix is applied:

func TestFoo(t *testing.T) {
  go func() {
    t.Error("oops")
    return
  }()
}

Warning

'Unmarshal' is called with the incorrect argument

Reports calls to json.Unmarshal and similar functions if the argument that is passed to store the result is not a pointer or an interface.

These calls will fail and return an error.

For more information about Unmarshal, refer to func Unmarshal at go.dev.

Example:

var animals []Animal
err := json.Unmarshal(jsonData, animals) // always returns an error

After the Prepend '&' quick-fix is applied:

var animals []Animal
err := json.Unmarshal(jsonData, &animals)

Warning

'context.CancelFunc' is not called

Reports execution paths that do not call the cancel function returned by context.WithCancel and similar functions.

The WithCancel, WithDeadline, and WithTimeout functions take a Context (the parent) and return a derived Context (the child) and a CancelFunc. Calling the CancelFunc cancels the child and its children, removes the parent's reference to the child, and stops any associated timers. Failing to call the CancelFunc leaks the child and its children until the parent is canceled or the timer fires.

For more information about the context package, refer to Package context at go.dev.

Example:

func _(ctx context.Context, cancel func()) {
 var ctx2 context.Context
 ctx2, cancel = context.WithCancel(ctx)
 _ = ctx2
}

Warning

Defer/go statement calls 'recover' or 'panic' directly

Reports defer and go statements that call panic() or recover() directly.

Such statements are rarely useful and might indicate a misuse of the panic() and recover() mechanism. In particular:

• go panic(): a newly-started goroutine will panic immediately.

• defer panic(): a function with this statement will always panic on exit.

• go recover(): has no effect as newly-started goroutine cannot panic.

• defer recover(): function with this statement will silently stop panicking. This could be a valid usage, but an idiomatic way is to inspect the value returned by recover():

  defer func() {
    if r := recover(); r != nil {
      fmt.Println("Recovered from: ", r)
    }
  }()

For more information about go statements and panics handling, refer to Handling panics and Go statements in the Go Language Specification.

Weak warning

Division by zero

Reports division by zero.

Division by zero will lead to a runtime panic.

Example:

s := 3 / 0

Warning

Exceeded shift expression

Reports shift expressions that equal or exceed the width of the integer.

All the bits of the left operand are shifted in such expression resulting in a constant value. The constant value indicates that either the shift offset is incorrect or the shift expression is redundant.

Example:

func shift(i int8) {
  fmt.Println(i << 8) // always prints 0
}

Warning

Imported package name as a name identifier

Reports declarations of variables, arguments or functions that overlap with the used import.

While legal, such declarations will make using the package exported identifiers impossible after the declaration or create confusion when reading the code.

Example:

import "fmt"
import _ "fmt"
import iio "io"

func _() {
 fmt.Println("demo")
 demo := true
 _, _ = iio.EOF, demo
}

func demo() (int, int) {
 return 1, 2
}

func _() {
 _, _ = iio.EOF, demo
 fmt := "demo"
 iio := 1
 _, _ = iio, fmt
 a, _ := demo()
 _ = a
}

Variable names fmt and iio clash with names of import packages. Not to confuse them later in code, it is better to rename these variables.

Warning

Impossible interface type assertion

Reports impossible interface-to-interface type assertions.

Checks for type assertions v.(T) and corresponding type-switch cases in which the static type V of v is the 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.

This inspection only reports if the language version is 1.15 or higher.

Warning

Incorrect 'strings.Replace' count argument

Reports strings.Replace calls with the replace count 0 instead of -1.

The count argument for how many times a string should be replaced should not be 0 as it will not replace anything and make the function call redundant. Use -1 instead.

Example:

a := strings.Replace("SSS", "S", "H", 0) // replaces nothing
b := strings.Replace("SSS", "S", "H", -1) // replaces all S occurrences with H

Warning

Incorrect usage of 'fmt.Printf' and 'fmt.Println' functions

Reports incorrect usages of fmt.Printf, fmt.Println, and similar formatting and printing functions.

In their format strings, formatting functions use formatting verbs, like %s, %d, %v, and others. If formatting verbs are used incorrectly, the result of a formatting function will contain an error. For more information about formatting verbs, refer to Package fmt at go.dev.

Example:

fmt.Printf("id: %s", 42)

The output of this function is id: %!s(int=42). It might be not what you really want. The following function uses the %d formatting verb. The output with the %d formatting verb will be id: 42.

fmt.Printf("id: %d", 42)

Weak warning

Incorrect usage of the 'errors.As' function

Reports calls of the errors.As function when the second argument is not a pointer to an interface or to a type that implements an error.

Such calls panic at runtime.

For more information about the As function, refer to func As at go.dev.

Example:

_, err := os.Open("non-existing")
var pathError *fs.PathError
if errors.As(err, pathError) { // a pointer to *fs.PathError is required
}

After the Prepend '&' quick-fix is applied:

_, err := os.Open("non-existing")
var pathError *fs.PathError
if errors.As(err, &pathError) {
}

This inspection only reports if the language version is 1.13 or higher.

Warning

Incorrect usage of the 'sync/atomic' package

Reports assignment statements of the form x = atomic.AddUint64(&x, 1).

Such operations are not atomic, and is a common misuse of the sync/atomic API. To make them atomic, one need to remove the assignment to use a direct call: atomic.AddUint64(&x, 1). In that case, the value of x will be updated atomically by address.

Example:

import (
 "sync/atomic"
)

type Counter uint64

func AtomicTests() {
 x := uint64(1)
 x = atomic.AddUint64(&x, 1)         // ERROR "direct assignment to atomic value"
 _, x = 10, atomic.AddUint64(&x, 1)  // ERROR "direct assignment to atomic value"
 x, _ = atomic.AddUint64(&x, 1), 10  // ERROR "direct assignment to atomic value"
}

Warning

Integer to string type conversion

Reports conversions of string(x)-alike expressions where x is an integer but not byte or rune.

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.

Example:

func main() {
 a := 1
 _ = string(a)
}

After the Convert integer to rune quick-fix is applied:

func main() {
 a := 1
 _ = string(rune(a))
}

Warning

Invalid conversions of 'uintptr' to 'unsafe.Pointer'

Reports possibly incorrect conversions of uintptr to unsafe.Pointer.

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.

Example of invalid usage:

nums := []int8{42, 24}
ptr := unsafe.Pointer(&nums[0])
addr := uintptr(ptr) // address is stored to a local variable
ptr = unsafe.Pointer(addr + uintptr(1))

Example of valid usage:

nums := []int8{42, 24}
ptr := unsafe.Pointer(&nums[0])
ptr = unsafe.Pointer(uintptr(ptr) + uintptr(1))

Warning

Irregular usage of 'iota'

Reports irregular usage of iota within a constant declaration.

The iota identifier is reset for every constant declaration and automatically incremented for every constant specification. Within one constant specification, the identifier keeps its value. Explicitly referring to iota does not reset the counter.

For more information, refer to Iota in the Go specification.

This inspection is triggered if two constant specifications have a textually identical expression list containing at least one reference to iota and there are exclusively constant specifications without an expression list in between them.

Consider omitting the redundant expression list or writing out the expression list every time.

Example:

const (
  a = iota  // 0
  b         // 1
  c = iota  // 2
)

Triggers the inspection as the iota in the definition of c is redundant.

Example:

const (
  a, aa = iota, iota       // 0, 0
  b, bb                    // 1, 1
  c, cc = iota + 40, iota  // 42, 2
)

Does not trigger the inspection as none of the expression lists is redundant.

Weak warning

Leading whitespace in directive comment

Reports leading whitespaces before Go directives in comments.

Go directives are not recognized if there is whitespace between // and the Go directive.

The quick-fix removes the leading whitespace before the Go directive.

Example:

//  go:embed file.txt
var File string

After the quick fix is applied:

//go:embed file.txt
var File string

Warning

Locks mistakenly passed by value

Reports locks that are mistakenly passed by values.

Accidentally copying a value containing a lock may cause both copies to work incorrectly. Generally, such values should be referred to through a pointer. A lock here means a type implementing sync.Locker, such as sync.Mutex or sync.WaitGroup.

Example:

type SafeInt struct {
  m sync.Mutex
  i int
}

func (s SafeInt) Inc() { // mutex is copied
  s.m.Lock()
  s.i++
  s.m.Unlock()
}

After the Add pointer quick-fix is applied:

type SafeInt struct {
  m sync.Mutex
  i int
}

func (s *SafeInt) Inc() {
  s.m.Lock()
  s.i++
  s.m.Unlock()
}

Warning

Loop variables captured by the func literal

Reports references to loop variables from within func literals in defer and go statements. Such variables might have unexpected values because they are not copied to func literals, and the func literals in defer and go are not executed immediately.

For more information about closures and goroutines, refer to What happens with closures running as goroutines? at go.dev.

Example:

for _, v := range []string{"a", "b", "c"} {
  go func() {
    fmt.Println(v) // output will likely be `c c c`, not `a b c`
  }()
}

After the quick-fix is applied:

for _, v := range []string{"a", "b", "c"} {
  v := v // `v` is copied now
  go func() {
    fmt.Println(v)
  }()
}

Note the analyzer only checks defer and go statements when they are the last statement in the loop body. Otherwise, the analysis might produce false detections.

Warning

Malformed build tag

Reports malformed build tags and build tags in the incorrect location. The go tool expects build tags to be located in particular places and follow a special syntax. If these requirements are not followed, build tags could either be ignored or the files could be incorrectly excluded from the build.

See Build Constraints at go.dev.

Example:

package main

// +build ignore

func main() {}

The // +build ignore part should be before the package declaration. To fix that, you can apply the Place build tag before package quick-fix. After the quick-fix is applied:

// +build ignore

package main

import "fmt"

Weak warning

Malformed struct tag

Reports struct tags that do not conform to Go conventions for struct tags.

According to these conventions, tag strings are a concatenation of optionally space-separated key:"value" pairs. Each key is a non-empty string consisting of non-control characters other than space (U+0020 ' '), quote (U+0022 '"'), and colon (U+003A ':'). Each value is quoted using U+0022 '"' characters and Go string literal syntax.

Also, the inspection checks that fields with tags are exported.

Example of a valid tag:

type Example struct {
  Field int `json:"field" xml:"demo"`
}

Warning

Mixed value and pointer receivers

Reports structures with methods that use a mixture of types: value and pointer receivers. Such usage is not recommended by the Go Documentation.

For more information, refer to Should I define methods on values or pointers? in the Go FAQ.

Example:

type S struct{
}

func (s *S) fun() {}
func (s S) fun2() {}

Weak warning

Nilness analyzer

Reports problems caused by incorrect usage of the nil value.

The IDE analyzes data flow to determine if variables could have nil or not nil values. Based on this, the IDE reports potential issues in code. Consider the following list of situations that might lead to unintended consequences:

• Method calls with the nil receiver might lead to 'nil pointer dereference'.

• The nil slice indexing might cause panics.

• Comparisons like v == nil might be meaningless if v is known to be always nil or not nil.

• Variables with corresponding errors are not checked on not to be nil. An error corresponds to a variable when they are defined or assigned together in statements like v, err := foo().

Disabled

Non-standard signature for well-known function names

Reports methods with certain names in the following cases:

• the method's name matches the name of several well-known interface methods from the standard library

• the signature does not match the signature of the corresponding interface method

Such methods might indicate that the receiver type is intended to satisfy an interface from the standard library, but fails to do so because of the mistake in the method's signature.

Example:

type MyReader []byte

func (r MyReader) ReadByte(data []byte) (byte, error) {
}

The usage is suspicious because it looks like an attempt to implement io.ByteReader but the signature is wrong. More correct version will be as follows:

type MyReader []byte

func (r MyReader) ReadByte() (byte, error) {
}

Warning

Reserved word used as name

Reports declarations of variables, arguments or functions that overlap with the built-in or reserved keyword.

If you receive this error then your code might not be as explicit as possible and might confuse other users.

Example:

type byte struct{}
type string interface{}

Types byte and string collide with the built-in type aliases. Therefore, they will be highlighted. Consider renaming such declarations.

Warning

Shadowing variable

Reports declarations of variables that overlap with the declarations in the outer scope.

As the meaning of the variable depends on the scope in that case, it may create confusion and lead to unintended consequences.

Example:

for i := 0; i < len(nums); i++ {
    for i := 0; i < len(nums); i++ {
    }
  }

The i variable in the embedded loop is shadowed. To get rid of shadowing, consider renaming the variable in the embedded loop.

for i := 0; i < len(nums); i++ {
    for j := 0; j < len(nums); j++ {
    }
  }

Unhandled error

Reports calls to functions and methods that do not handle the call result of the error type.

An API of such functions imply that their execution might finish unsuccessfully and they would return an error. Calls that do not handle the error result could be an indication of the API misuse.

Example:

os.Remove("non-existing") // error is ignored

After the Handle error quick-fix is applied:

err := os.Remove("non-existing") // error is handled
if err != nil {
  return err
}

Warning

Unused function or method call result

Reports calls to certain functions and methods that do not handle a call result.

An API of such functions imply that users should call them mostly to get a return value and process it, not for side effects. Calls that do not handle the result could be an indication of a misuse of the API.

Example:

fmt.Errorf("error: %s", reason) // constructed error is ignored

After the Introduce local variable quick-fix is applied:

err := fmt.Errorf("error: %s", reason)

Warning

'defer' in the loop

Reports defer statements inside loops.

Using defer in loops can lead to resource leaks or unpredictable execution order of statements.

Example:

func main() {
 for {
  field, err := db.Query("SELECT 1")
  if err != nil {
   // ...
  }
  defer field.Close()
  // ...
 }
}

Calls of defer row.Close() inside the loop are not executed until the function completes its execution. Not at the end of each step of the for loop. Such implementation might lead to overflow of the function's stack and other issues.

Weak warning

Assignment to a receiver

Reports assignments to method receivers.

When you assign a value to the method receiver, the value will not be reflected outside of the method itself. Values will be reflected in subsequent calls from the same method.

Example:

package main

import "fmt"

type demo struct {
 Val int
}

func (d *demo) change() {
 d = nil // Assignment to the method receiver propagates only to callees but not to callers
 d.myVal()
}

func (d *demo) myVal() {
 fmt.Printf("my val: %#v\n", d)
}

func (d demo) change2() {
 d = demo{} // Assignment to the method receiver doesn't propagate to other calls
 d.myVal()
}

func (d *demo) change3() {
 d.Val = 3
 d.myVal()
}

func main() {
 d := &demo{}
 d.myVal()
 d.change()
 d.myVal()
 d.Val = 2
 d.change2()
 d.myVal()
 d.change3()
 d.myVal()
}

Weak warning

Infinite 'for' loop

Reports empty for loops.

Running this code will make the CPU usage stay at maximum and will make the machine nearly unusable.

Example:

func main() {
 for {
 }
}

Warning

Unreachable code

Reports code that can never be executed because there exists no control flow path to the code from the rest of the program.

Example:

func _() int {
 print(1)
 return 2
 println() // This code is unreachable
 return 0
}

Warning

Comment has no leading space

Reports comments without a leading space.

Note that the inspection works only if you select the Add a leading space to comments in Editor | Code Style | Go on the Other tab.

Comments with a leading space can be easier to read since the first word is separated from the comment by a space.

Example:

//Prints JSON received from the createJSON function
func printJSON(output []byte) {
	fmt.Println(string(output))
}

Weak warning

Comment of exported element starts with the incorrect name

Reports comments that do not start with the name of the exported element.

According to Comment Sentences at github.com/golang, this is a convention to begin a comment with the name of the exported element.

Example:

// represents a request to run a command.
type Request struct {}

The comment starts with the struct description, not with the struct name. To stick to the convention rules, you can apply the Add prefix to comment quick-fix. After the quick-fix is applied, the comment looks as follows:

// Request represents a request to run a command.
type Request struct {} // better

Weak warning

Convert string literals

Reports double-quoted string literals that can be converted into raw string literals and raw string literals that can be converted to double-quoted string literals.

Example:

var s = "Hello\n   \"World\""

After the quick fix is applied:

var s = `Hello
 "World"`

There are two notes that you should take into account while converting double-quoted strings to raw strings:

• According to the Go language specification, the carriage return character ('\r') is discarded from the raw string values. As there is no way to show carriage return in raw strings, we discard carriage return characters when converting a double-quoted string to a raw string.

• The backtick character ('`') cannot exist in raw string literals because there is no way to escape it. Therefore, converting double-quoted strings that contain the backtick character to raw strings is not possible and will result in a syntax error. The user can decide to undo the conversion or use some form of concatenation to preserve the backtick in a double-quoted string. For example, "`ab``" will result in `ab``, which is syntactically incorrect. The user can either undo the operation or change the resulting string to `ab` + "`".

No highlighting, only fix

Error string should not be capitalized or end with punctuation

Reports format issues in error strings.

Example:

err := fmt.Errorf("Cannot read the file!")
log.Printf("Reading %s: %v", file, err)

According to Error Strings at github.com/golang, error strings should not be capitalized or end with punctuation because they might appear among other context.

To fix the format, you can apply the Fix error string format quick-fix. After the quick-fix is applied, the error string will look like this:

err := fmt.Errorf("cannot read the file")
log.Printf("Reading %s: %v", file, err)

Weak warning

Exported element should have a comment

Reports exported declarations without a documentation comment. According to Doc Comments at github.com/golang, all top-level exported names should have doc comments.

Also, for more information about comment sentences, see Comment Sentences at github.com/golang.

To add a comment, you can apply the Add comment quick-fix.

No highlighting, only fix

Exported element should have its own declaration

Reports exported variables or constants in comma-separated lists of declarations.

Example:

const C1, C3, C2, C44, C9, C11, C6 = 1, 2, 3, 1, 3, 2, 1

This declaration makes it hard to understand what value each constant has. You can apply the Extract to own declaration quick-fix to make this declaration more readable. After the quick-fix is applied to each constant, the declaration looks as follows:

const (
 C3  = 2
 C2  = 3
 C44 = 1
 C9  = 3
 C11 = 2
 C6  = 1
 C1  = 1
)

Weak warning

Name starts with a package name

Reports exported names that start with a package name. This inspection does not report such names in the main package.

Example:

package myPackage

func MyPackageGetIP() {

}

The MyPackageGetIP name will be highlighted as it starts with the package name.

According to Package Names at github.com/golang, all references to names in a package will be done using the package name, so one can omit that name from the identifiers. For example, if you are in a package foo, you do not need a type FooFile, which clients will write as foo.FooFile. Instead, we name the type File, which clients will write as foo.File.

Weak warning

Receiver has a generic name

Reports receiver names like me, this, self, or names that differ from other receiver names for this type.

Example:

func (self *MeterSnapshot) Rate5() float64 { return math.Float64frombits(self.rate5) }

According to Receiver Names at github.com/golang, you should not use generic names such as "me", "this", or "self". These identifiers are typical for object-oriented languages and might give the method a special meaning.

Weak warning

Struct initialization without field names

Reports structures that are initialized without specifying their field names. By default, the inspection is available only when you use the type that is defined in a different package.

When initializing a structure, it is better to explicitly state field names in order to ensure that in case of changes in order of these fields or in names of the fields, they will correctly continue to be addressed.

Example:

_ = io.LimitedReader{nil, 10}

The LimitedReader initialization will be highlighted because explicit names for struct fields are missing. You can apply the Add keys and delete zero values quick-fix to the struct initialization. After the quick-fix is applied, the code looks as follows:

_ = io.LimitedReader{N: 10}

The inspection has the following options:

• Report types defined in current package: reports situations when you declare and initialize struct in the same package. Consider the following example.

  d := struct {
    c string
   }{ "dsd "}

• Report struct literals without types: reports fields without names when the type (struct or interface) is omitted. Consider the following example when the type is omitted.

  _ = []io.LimitedReader{
   {nil, 10},
   {nil, 20},
   }

  In the following example, the type is present but is redundant.

  _ = []io.LimitedReader{
   io.LimitedReader{nil, 10},
   io.LimitedReader{nil, 20},
  }

Weak warning

Type parameter is declared in lowercase

Reports type parameters that are declared in lowercase.

Examples in the official Go documentation use type parameters in uppercase. This inspection follows this uppercase rule for type parameters.

func PrintSlice[t any](s []t) {
    for _, v := range s{
        print(v)
    }
}

The type parameter t is declared in lowercase and thus will be reported.

No highlighting, only fix

Unit-specific suffix for 'time.Duration'

Reports unit-specific suffixes in constant and variable names of time.Duration type.

The inspection comes from go lint. A list of suffixes that imply a time unit is available in the golang repository at github.com.

time.Duration represents a value in nanoseconds, so adding a time unit suffix might make the meaning of the variable confusing, or even indicate a misuse of the time.Duration API.

Example:

var timeoutSeconds = 5 * time.Second

Weak warning

Unsorted imports

Reports unsorted imports.

All Go programs should be formatted in the same way, the formatting rules are fixed by the gofmt tool. Those rules require imports to be sorted.

Example of a wrong sorting:

import (
 "net"
 "errors"
 "fmt"
)

You can apply the Sort imports quick-fix to fix the sorting. After the quick-fix is applied, the sorting looks as follows:

import (
 "errors"
 "fmt"
 "net"
)

Weak warning

Usage of Snake_Case

Reports usage of snake case instead of camelcase for naming variables, constants and functions. According to MixedCaps at go.dev, camelcase is a convention in Go.

Example:

func get_external_IP() (string, error) {}

The get_external_IP is in snake case but should be in camelcase. You can apply a quick-fix to convert the function name to getExternalIp.

Weak warning

Deprecated element

Reports usages of deprecated elements.

Example:

// Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd.
const (
 SEEK_SET int = 0 // seek relative to the origin of the file
 SEEK_CUR int = 1 // seek relative to the current offset
 SEEK_END int = 2 // seek relative to the end
)

According to Constants at go.dev, SEEK_SET, SEEK_CUR, and SEEK_END are deprecated.

Warning

Disabled GOPATH indexing

Reports disabled GOPATH indexing that might prevent proper resolution of code references.

GOPATH stores your code base and all the files that are necessary for your development. Also, it includes packages that you download and install. If you disabled GOPATH indexing, only project and vendored packages are indexed. It might improve the overall performance but makes it impossible to use packages from GOPATH.

Weak warning

Fuzzing is supported starting with Go 1.18

Reports presence of fuzz tests when Go SDK version is less than 1.18

Fuzz testing is a method of automated testing that involves a directed search for input data that may cause a program crash or expose invalid behavior. Go supports fuzz testing starting from Go 1.18.

Example of a fuzz test:

func Div(a, b int) int {
	return a / b
}

func FuzzDiv(f *testing.F) {
	f.Fuzz(func(t *testing.T, a, b int) {
		Div(a, b) // reports runtime error: integer divide by zero
	})
}

See Go Fuzzing for more information.

Warning

Malformed test function name

Reports malformed names of tests, benchmarks, and examples.

According to Package testing at go.dev, names must follow a special convention in order to make the go tool process them correctly.

Example:

func Testfoo(*testing.T) {} // the 'go' tool will not run this test

After the Rename to quick-fix is applied:

func TestFoo(*testing.T) {}

Warning

Missing trailing comma before a newline in a composite literal

Reports a missing trailing comma before a newline in composite literals, function call arguments, and function parameter lists.

Example:

func f(f int) (
 int,
 bool   // missing a trailing comma
){
 println(1, 2  // missing a trailing comma
 )
}

Error

Redundant parentheses

Reports redundant parentheses in expressions and types.

Example:

func _(x (int), y ((string))) {
}
func _() {
 _ = (1 + 1)
 _ = (((1 + 1)))
 _ = (((1 + 1))) + (((2 + 2)))
}

After the Unwrap parentheses quick-fix is applied:

func _(x int, y string) {
}
func _() {
 _ = 1 + 1
 _ = 1 + 1
 _ = (1 + 1) + (2 + 2)
}

Weak warning

Unexported return type of the exported function

Reports exported functions with unexported return types.

Unexported types can be difficult to use when viewing documentation under go doc.

Example:

type hidden struct{}

func Exported() hidden { // Exported function with the `hidden` unexported return type
 return hidden{}
}

You can apply Export quick-fix to export the type. After the quick-fix is applied, type name will be capitalized:

type Hidden struct{}

func Exported() Hidden { // Fixed
 return Hidden{}
}

Warning

Unnecessarily exported identifier

Reports exported identifiers that are used only in the package where they are defined but are not used in other packages.

Making them exported is redundant and may clutter the API of the package.

Disabled

Usage of 'interface{}' as a type

Reports usages of the empty interface as a type or type constraint.

The empty interface denotes the set of all types. Go 1.18 introduced the more explicit alias any for interface{}, which is equivalent to interface{} in all ways.

The inspection is triggered for any usage of an empty interface as a type or type constraint. Aliases of the empty interface and interfaces that exclusively embed other empty interfaces do not trigger the inspection.

Consider using the more explicit alias any instead.

No highlighting, only fix

Usage of context.TODO()

Reports usages of context.TODO().

According to the documentation at pkg.go.dev, you need to use context.TODO when it is unclear what Context to use, or Context is not yet available. Context might not be available because of the surrounding function that has not yet been extended to accept the Context parameter.

Note that it is a temporary placeholder, and you must change it in the future to a more meaningful context (for example, context.Background()).

Disabled

Vulnerable API usage

Reports usages of Vulnerable APIs of imported dependencies.

Fixing the reported problems helps prevent your software from being compromised by an attacker.

To solve a problem, you can update to a version where the vulnerability is fixed (if available) or switch to a dependency that doesn't have the vulnerability.

Vulnerability data provided by Checkmarx (c).

Warning

Bool condition

Reports parts of boolean expressions that are either always true, always false, or redundant. Such boolean expressions can be simplified, which may improve a readability of the code. In some cases, this also indicates a presence of other issues.

Example:

func isNonZero(x, y int) bool {
  // the second comparison is either always true
  // or not executed at all
  return x > 0 && x > 0
}

You can apply the Simplify expression quick-fix for the x > 0 && x > 0 part. After the quick-fix is applied, the expression looks as follows: x > 0.

Warning

Empty declaration

Reports empty declarations.

Empty declarations have no effect. If you remove them, you might improve code readability.

Example:

func main() {
 const () // empty declaration
}

You can apply the Delete empty declaration quick-fix to remove this declaration.

Warning

Empty slice declared using a literal

Reports slice declarations with empty literal initializers used instead of nil.

An empty slice can be represented by nil or an empty slice literal. They are functionally equivalent — their len and cap are both zero — but the nil slice is the preferred style. For more information about empty slices, refer to Declaring Empty Slices at github.com/golang.

Example:

s := []string{}

To change the declaration, use the Replace with nil slice declaration (changes semantics) quick-fix. After the quick-fix is applied:

var s []string

Weak warning

Redundant blank argument in range

Reports optional blank variables in range loops.

When you use the range loop to iterate over a slice, two values are returned for each iteration. The first is the index number, and the second is a copy of the element at that index. If you do not need the second value, you can skip this element instead of using a blank identifier.

Example:

for a, _ = range v {} // `for a, _ =` is the same as `for a =`

To remove the blank identifier, you can use the Delete blank argument quick-fix. After the quick-fix is applied, the code will look as follows:

for a = range v {}

Warning

Redundant comma

Reports commas that may be omitted in the end of argument lists and composite literals.

The IDE suggests removing commas that are considered optional. Removing these commas might improve code readability.

Example:

s := []int{1, 2,} // the last comma may be omitted

Weak warning

Redundant import alias

Reports aliases of imported packages that may be omitted.

Usually, such aliases equal to the names of the imported packages, so aliases have no effect and one can use package names directly.

Example:

import fmt "fmt"

The fmt alias duplicates the package name that is also named "fmt". To delete the alias, use the Delete import alias quick-fix.

After the quick-fix is applied:

import "fmt"

Weak warning

Redundant second index in slices

Reports a redundant second index (a high bound) in slice expressions.

Usually, the second index is optional. If you remove it, you might improve code readability.

Example:

var a []int
a = a[0:len(a)] // `a[0:len(a)]` is the same as `a[0:]`

You can apply the Remove redundant index quick-fix to such cases. After the quick-fix is applied, this code looks as follows:

var a []int
a = a[0:]

Warning

Redundant semicolon

Reports redundant semicolons. Idiomatic Go programs have semicolons only in places such as for loop clauses, to separate the initializer, condition, and continuation elements. They are also necessary to separate multiple statements on a line. In other cases, you can omit them.

For more information about semicolons in Go, refer to Semicolons at go.dev.

Example:

i := 1;

Weak warning

Redundant type conversion

Reports type conversions that may be omitted.

Example:

var s = string("hello")

The "hello" value is the string type already, the additional conversion to string is redundant. To remove the conversion, consider using the Delete conversion quick-fix.

After the quick-fix is applied:

var s = "hello"

Sometimes conversion of a floating expression to a floating type can be intentional (see this issue as an example). In such cases, the IDE issues a warning about a possibly redundant conversion.

Weak warning

Redundant types in composite literals

Reports redundant type declarations in composite literals.

Example:

nums := [][]int{[]int{1}, []int{2}}

We have a slice of slices of the int type. In this case, you can use a shorter definition. You can fix this code manually or use the Delete redundant type quick-fix. After the quick-fix is applied, the code looks as follows:

nums := [][]int{{1},{2}}

For more information about composite literals, refer to Go Language Specification: Composite Literals at go.dev.

Warning

Self assignment

Reports expressions that are assigned to themselves.

Such assignments have no effect, removing them might improve code readability.

Example:

func importedVarSelfAssignment() {
 http.ErrNotSupported = http.ErrNotSupported
}

Weak warning

Type can be omitted

Reports types in variable and constant declarations that can be omitted since they can be inferred by the compiler. Such types are redundant, omitting them may improve readability of the code.

Example:

var s string = fmt.Sprintln("hi")

The string type in the variable declaration may be omitted. To remove the type, use the Delete type quick-fix. After the quick-fix is applied:

var s = fmt.Sprintln("hi")

Weak warning

Unused constant

Reports constants that are defined but are never used in code.

func main() {
 const i = 100
}

Unlike unused variables and imports, this code will compile. Unused constants might increase your code base and slow down program compilation. To delete the unused constant, consider using the Delete constant quick-fix.

Warning

Unused exported function

Reports unused exported functions.

In Go, a function is exported if it begins with a capital letter. Names of exported functions that were defined but never used are grayed out.

// Unused exported function
func ExportedUnusedFunc()  {

}

func main() {
 fmt.Println("Hello")
}

Warning

Unused exported type

Reports unused exported types in the main package and in tests. For more information about exported identifiers, refer to Exported identifiers at go.dev.

type User struct {}

func main() {}

The User struct type is declared but never used in the code. This type will be grayed out.

Warning

Unused function

Reports unused unexported functions.

In Go, a function is unexported if it begins with a small letter. Names of unexported functions that were defined but never used are grayed out.

// Unused unexported function
func unExportedUnusedFunc()  {

}

func main() {
 fmt.Println("Hello")
}

Warning

Unused global variable

Reports global variables that are defined but are never used in code.

If you have unused variables, the code will not compile. For more information about unused variables and imports, refer to Unused imports and variables at go.dev.

func main() {
 a := 422
}

Code in the example will not compile. Therefore, it is highlighted as an error. You can apply two quick-fixes for such cases: Delete variable and Rename to _. The first quick-fix deletes the variable, the second one will convert the variable to a blank identifier.

After the Rename to _ quick-fix is applied:

func main() {
 _ := 422
}

Warning

Unused parameter

Reports unused function parameters.

func main() {
 printAll(
  42,
  "bird",
 )
}

func printAll(
 i int,
 s string,
) {
 fmt.Println(i)
}

We call the printAll function passing 42 and bird as arguments. The printAll function accepts two parameters int and string but uses only the first of them. Therefore, the s string is grayed out.

Warning

Unused type

Reports unused types.

type user struct {
 FirstName string    `json:"firstname"`
 LastName  string    `json:"lastname"`
}

func main() {

}

The user type will be grayed out because it is not used anywhere in code.

Warning

Unused type parameter

Reports unused type parameters.

func main() {
 printAll(
  42,
  "bird",
 )
}

func printAll[I int, S string](
 i I,
 s string,
) {
 fmt.Println(i)
 fmt.Println(s)
}

The printAll function has two type parameters I and S but uses only the first of them. Therefore, the S string is grayed out.

Warning