govet

Documentation

Overview

Vet examines Go source code and reports suspicious constructs, such as Printf calls whose arguments do not align with the format string. Vet uses heuristics that do not guarantee all reports are genuine problems, but it can find errors not caught by the compilers.

It can be invoked three ways:

By package, from the go tool:

go vet package/path/name

vets the package whose path is provided.

By files:

go tool vet source/directory/*.go

vets the files named, all of which must be in the same package.

By directory:

go tool vet source/directory

recursively descends the directory, vetting each package it finds.

Vet's exit code is 2 for erroneous invocation of the tool, 1 if a problem was reported, and 0 otherwise. Note that the tool does not check every possible problem and depends on unreliable heuristics so it should be used as guidance only, not as a firm indicator of program correctness.

By default the -all flag is set so all checks are performed. If any flags are explicitly set to true, only those tests are run. Conversely, if any flag is explicitly set to false, only those tests are disabled. Thus -printf=true runs the printf check, -printf=false runs all checks except the printf check.

Available checks:

Assembly declarations

Flag: -asmdecl

Mismatches between assembly files and Go function declarations.

Useless assignments

Flag: -assign

Check for useless assignments.

Atomic mistakes

Flag: -atomic

Common mistaken usages of the sync/atomic package.

Boolean conditions

Flag: -bool

Mistakes involving boolean operators.

Build tags

Flag: -buildtags

Badly formed or misplaced +build tags.

Invalid uses of cgo

Flag: -cgocall

Detect some violations of the cgo pointer passing rules.

Unkeyed composite literals

Flag: -composites

Composite struct literals that do not use the field-keyed syntax.

Copying locks

Flag: -copylocks

Locks that are erroneously passed by value.

Tests, benchmarks and documentation examples

Flag: -tests

Mistakes involving tests including functions with incorrect names or signatures and example tests that document identifiers not in the package.

Failure to call the cancelation function returned by context.WithCancel.

Flag: -lostcancel

The cancelation function returned by context.WithCancel, WithTimeout, and WithDeadline must be called or the new context will remain live until its parent context is cancelled. (The background context is never cancelled.)

Methods

Flag: -methods

Non-standard signatures for methods with familiar names, including:

Format GobEncode GobDecode MarshalJSON MarshalXML
Peek ReadByte ReadFrom ReadRune Scan Seek
UnmarshalJSON UnreadByte UnreadRune WriteByte
WriteTo

Nil function comparison

Flag: -nilfunc

Comparisons between functions and nil.

Printf family

Flag: -printf

Suspicious calls to functions in the Printf family, including any functions with these names, disregarding case:

Print Printf Println
Fprint Fprintf Fprintln
Sprint Sprintf Sprintln
Error Errorf
Fatal Fatalf
Log Logf
Panic Panicf Panicln

The -printfuncs flag can be used to redefine this list. If the function name ends with an 'f', the function is assumed to take a format descriptor string in the manner of fmt.Printf. If not, vet complains about arguments that look like format descriptor strings.

It also checks for errors such as using a Writer as the first argument of Printf.

Struct tags

Range loop variables

Flag: -rangeloops

Incorrect uses of range loop variables in closures.

Shadowed variables

Flag: -shadow=false (experimental; must be set explicitly)

Variables that may have been unintentionally shadowed.

Shifts

Flag: -shift

Shifts equal to or longer than the variable's length.

Flag: -structtags

Struct tags that do not follow the format understood by reflect.StructTag.Get. Well-known encoding struct tags (json, xml) used with unexported fields.

Unreachable code

Flag: -unreachable

Unreachable code.

Misuse of unsafe Pointers

Flag: -unsafeptr

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.

Unused result of certain function calls

Flag: -unusedresult

Calls to well-known functions and methods that return a value that is discarded. By default, this includes functions like fmt.Errorf and fmt.Sprintf and methods like String and Error. The flags -unusedfuncs and -unusedstringmethods control the set.

Other flags

These flags configure the behavior of vet:

-all (default true)
	Enable all non-experimental checks.
-v
	Verbose mode
-printfuncs
	A comma-separated list of print-like function names
	to supplement the standard list.
	For more information, see the discussion of the -printf flag.
-shadowstrict
	Whether to be strict about shadowing; can be noisy.

Vet is a simple checker for static errors in Go source code. See doc.go for more information.