README

Vet is a tool that checks correctness of Go programs. It runs a suite of tests,
each tailored to check for a particular class of errors. Examples include incorrect
Printf format verbs and malformed build tags.

Over time many checks have been added to vet's suite, but many more have been
rejected as not appropriate for the tool. The criteria applied when selecting which
checks to add are:

Correctness:

Vet's checks are about correctness, not style. A vet check must identify real or
potential bugs that could cause incorrect compilation or execution. A check that
only identifies stylistic points or alternative correct approaches to a situation
is not acceptable.

Frequency:

Vet is run every day by many programmers, often as part of every compilation or
submission. The cost in execution time is considerable, especially in aggregate,
so checks must be likely enough to find real problems that they are worth the
overhead of the added check. A new check that finds only a handful of problems
across all existing programs, even if the problem is significant, is not worth
adding to the suite everyone runs daily.

Precision:

Most of vet's checks are heuristic and can generate both false positives (flagging
correct programs) and false negatives (not flagging incorrect ones). The rate of
both these failures must be very small. A check that is too noisy will be ignored
by the programmer overwhelmed by the output; a check that misses too many of the
cases it's looking for will give a false sense of security. Neither is acceptable.
A vet check must be accurate enough that everything it reports is worth examining,
and complete enough to encourage real confidence.

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.

Vet is normally invoked through the go command. This command vets the package in the current directory:

go vet

whereas this one vets the packages whose path is provided:

go vet my/project/...

Use "go help packages" to see other ways of specifying which packages to vet.

Vet's exit code is non-zero for erroneous invocation of the tool or 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.

To list the available checks, run "go tool vet help":

asmdecl      report mismatches between assembly files and Go declarations
assign       check for useless assignments
atomic       check for common mistakes using the sync/atomic package
bools        check for common mistakes involving boolean operators
buildtag     check that +build tags are well-formed and correctly located
cgocall      detect some violations of the cgo pointer passing rules
composites   check for unkeyed composite literals
copylocks    check for locks erroneously passed by value
httpresponse check for mistakes using HTTP responses
loopclosure  check references to loop variables from within nested functions
lostcancel   check cancel func returned by context.WithCancel is called
nilfunc      check for useless comparisons between functions and nil
printf       check consistency of Printf format strings and arguments
shift        check for shifts that equal or exceed the width of the integer
stdmethods   check signature of methods of well-known interfaces
structtag    check that struct field tags conform to reflect.StructTag.Get
tests        check for common mistaken usages of tests and examples
unmarshal    report passing non-pointer or non-interface values to unmarshal
unreachable  check for unreachable code
unsafeptr    check for invalid conversions of uintptr to unsafe.Pointer
unusedresult check for unused results of calls to some functions

For details and flags of a particular check, such as printf, run "go tool vet help printf".

By default, 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, and -printf=false runs all checks except the printf check.

For information on writing a new check, see golang.org/x/tools/go/analysis.

Core flags:

-c=N
  	display offending line plus N lines of surrounding context
-json
  	emit analysis diagnostics (and errors) in JSON format