cmd/vet: method Seek() should have signature Seek(int64, int)

[sabey]

What version of Go are you using (go version)?

$ go version
go version go1.13.6 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/jackson/.cache/go-build"
GOENV="/home/jackson/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/jackson/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build498302187=/tmp/go-build -gno-record-gcc-switches"

What did you do?

func (self *File) Seek(
	offset int64,
) (
	io.Reader,
	error,
) {
	return nil, nil
}

go vet

What did you expect to see?

no error

I do have the package "io" included, but I do also have a Read and Write method which go vet does not complain about

What did you see instead?

./file.go:286:19: method Seek(offset int64) (io.Reader, error) should have signature Seek(int64, int) (int64, error)

[robpike]

Do Read and Write have the correct signatures? Please include a full example, not a snippet.

The error as shown here is correct: the standard Seek method takes two arguments.

[sabey]

no, Read and Write are different, I only get an error for seek

https://play.golang.org/p/zbCVv7Y8TlE

I just tried it without any reference to io and got the same error:

https://play.golang.org/p/7NFpmLvsh7G

[fzipp]

no, Read and Write are different, I only get an error for seek

Seek is one of the canonical methods that go vet checks, while Read and Write are not: https://github.com/golang/tools/blob/master/go/analysis/passes/stdmethods/stdmethods.go#L74

If you add a "whence int" parameter to your Seek method and change the type of the first return value from io.Reader to int64 vet will be silent: https://play.golang.org/p/7Pbq67pGGl-

[robpike]

Or just change the name of the function.

[cagedmantis]

/cc @alandonovan @josharian @mvdan

[mvdan]

I agree that this seems like a correct vet diagnostic. The io.Seeker interface is defined by itself, so it doesn't matter what other methods your named type has defined.