errcheck
errcheck is a program for checking for unchecked errors in go programs.
Install
go get -u github.com/kisielk/errcheck
errcheck requires Go 1.12 or newer, and depends on the package go/packages from the golang.org/x/tools repository.
Use
For basic usage, just give the package path of interest as the first argument:
errcheck github.com/kisielk/errcheck/testdata
To check all packages beneath the current directory:
errcheck ./...
Or check all packages in your $GOPATH and $GOROOT:
errcheck all
errcheck also recognizes the following command-line options:
The -tags flag takes a space-separated list of build tags, just like go build. If you are using any custom build tags in your code base, you may need to specify the relevant tags here.
The -asserts flag enables checking for ignored type assertion results. It takes no arguments.
The -blank flag enables checking for assignments of errors to the blank identifier. It takes no arguments.
Excluding functions
Use the -exclude flag to specify a path to a file containing a list of functions to be excluded.
errcheck -exclude errcheck_excludes.txt path/to/package
The file should contain one function signature per line. The format for function signatures is package.FunctionName while for methods it's (package.Receiver).MethodName for value receivers and (*package.Receiver).MethodName for pointer receivers. If the function name is followed by string of form (TYPE), then the the function call is excluded only if the type of the first argument is TYPE. It also accepts a special suffix (os.Stdout) and (os.Stderr), which excludes the function only when the first argument is a literal os.Stdout or os.Stderr.
An example of an exclude file is:
io/ioutil.ReadFile
io.Copy(*bytes.Buffer)
io.Copy(os.Stdout)
// Sometimes we don't care if a HTTP request fails.
(*net/http.Client).Do
By default, the exclude list is combined with an internal list for functions in the Go standard library that have an error return type but are documented to never return an error. To disable the built-in exclude list, pass the -excludeonly flag.
Run errcheck in -verbose mode to see the resulting list of added excludes.
When using vendored dependencies, specify the full import path. For example:
- Your project's import path is
example.com/yourpkg - You've vendored
example.net/fmt2asvendor/example.net/fmt2 - You want to exclude
fmt2.Printlnfrom error checking
In this case, add this line to your exclude file:
example.com/yourpkg/vendor/example.net/fmt2.Println
Empty lines and lines starting with // are ignored.
The deprecated method
The -ignore flag takes a comma-separated list of pairs of the form package:regex. For each package, the regex describes which functions to ignore within that package. The package may be omitted to have the regex apply to all packages.
For example, you may wish to ignore common operations like Read and Write:
errcheck -ignore '[rR]ead|[wW]rite' path/to/package
or you may wish to ignore common functions like the print variants in fmt:
errcheck -ignore 'fmt:[FS]?[Pp]rint*' path/to/package
The -ignorepkg flag takes a comma-separated list of package import paths to ignore:
errcheck -ignorepkg 'fmt,encoding/binary' path/to/package
Note that this is equivalent to:
errcheck -ignore 'fmt:.*,encoding/binary:.*' path/to/package
If a regex is provided for a package pkg via -ignore, and pkg also appears in the list of packages passed to -ignorepkg, the latter takes precedence; that is, all functions within pkg will be ignored.
Note that by default the fmt package is ignored entirely, unless a regex is specified for it. To disable this, specify a regex that matches nothing:
errcheck -ignore 'fmt:a^' path/to/package
The -ignoretests flag disables checking of _test.go files. It takes no arguments.
Exit Codes
errcheck returns 1 if any problems were found in the checked files. It returns 2 if there were any other failures.
Editor Integration
Emacs
go-errcheck.el integrates errcheck with Emacs by providing a go-errcheck command and customizable variables to automatically pass flags to errcheck.
Vim
vim-go can run errcheck via both its :GoErrCheck and :GoMetaLinter commands.
