x/tools/analysis: printf pass should only allow %w in fmt.Errorf

[GiedriusS]

Seems like currently all functions which are called Errorf are created in the same way: https://github.com/golang/tools/blob/aafaee8bce8c38f7ce09907ff7430abcb6f58132/go/analysis/passes/printf/printf.go#L493-L495. However, only fmt.Errorf accepts %w in the standard library.

The way it is causes problems with exceptions to this rule. One notable one is github.com/pkg/errors. There %w doesn't make sense in the call to errors.Errorf: https://godoc.org/github.com/pkg/errors#Errorf.

Consider making that check more specific and treat fmt.Errorf differently from regular functions called Errorf.

I guess golang/tools@1d17272 should be extended.

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

$ go version
go version go1.13.7 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="on"              
GOARCH="amd64"                                       
GOBIN=""                                                                                                  
GOCACHE="/home/gstatkevicius/.cache/go-build"                                                             
GOENV="/home/gstatkevicius/.config/go/env"                                                                                                                                                                           
GOEXE=""                                                                                                  
GOFLAGS=""                         
GOHOSTARCH="amd64"
GOHOSTOS="linux"                              
GONOPROXY=""                                
GONOSUMDB=""                   
GOOS="linux"                   
GOPATH="/home/gstatkevicius/go"
GOPRIVATE=""  
GOPROXY="https://goproxy.io"
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="/dev/null"              
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-build587596761=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Wrote a program that uses github.com/pkg/errors.Errorf and used the %w verb in there. Ran go vet on it and expected the printf analysis to report errors but there were none.

What did you expect to see?

Errors that %w verb is unsupported with that function.

What did you see instead?

Success of go vet.

[smasher164]

I do not see this behavior with my version of vet. Are you sure you are running the latest version of vet?

main.go

package main

import "github.com/pkg/errors"

func main() {
	_ = errors.Errorf("%w", nil)
}

I see

./main.go:6:6: Errorf call has error-wrapping directive %w

[GiedriusS]

I do not see this behavior with my version of vet. Are you sure you are running the latest version of vet?

main.go

package main

import "github.com/pkg/errors"

func main() {
	_ = errors.Errorf("%w", nil)
}

I see

./main.go:6:6: Errorf call has error-wrapping directive %w

Yes, you are correct - I should've made a minimal test case and have tested it on the newest version before creating this. I created this issue because I couldn't remember anything from the change-log of Go about this and only quickly glanced at the source code. As it is evident now, I have missed some crucial things about it. As reported in the original issue, I have tried this on 1.13.x and got no such error. Updated now myself and got the same error that you've pasted. Thanks for the quick response and sorry for the noise. I guess it's one more reason to update to 1.14.