x/tools/go/analysis/passes/shadow/cmd/shadow: Failure/success of the linter depends also on filename, not just the content

[graywolf-at-work]

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

$ go version
1.14.6

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/wolf/.cache/go-build"
GOENV="/home/wolf/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY="go.showmax.cc,go.platfoo.cc"
GONOSUMDB="go.showmax.cc,go.platfoo.cc"
GOOS="linux"
GOPATH="/home/wolf/go"
GOPRIVATE="go.showmax.cc,go.platfoo.cc"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/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-build056422182=/tmp/go-build -gno-record-gcc-switches"

What did you do?

1. Install shadow vet:

   $ go install golang.org/x/tools/go/analysis/passes/shadow/cmd/shadow

2. Create following files:

   +$ tree .
   .
   ├── b.go
   ├── c.go
   └── go.mod

   0 directories, 3 files
   +$ cat b.go
   package foo

   func newX() int {
   x := 1
   return x
   }

   var x = newX()
   +$ cat c.go
   package foo

   func f() {
   x = 1
   }
   +$ cat go.mod
   module foo

   go 1.14

3. Run the shadow vet:

   $ go vet -vettool=/home/wolf/go/bin/shadow ./...

What did you expect to see?

# foo
./b.go:4:2: declaration of "x" shadows declaration at line 8

What did you see instead?

Nothing.

Some research notes

It looks like shadow vet depends on the filenames, because all one needs to do
to get the expected output is to rename c.go to a.go, so when sorted by
alphabet is is before b.go. My understanding is that the package is the
scope, so alphabetic ordering of the files should not matter.

[andybons]

@matloob

[matloob]

Yes it's like a bug that the names of the files affects the results. Shadow is an experimental analysis so we're not actively working on it, but if you want to work on this and fix it, feel free!