os: Stat does not follow relative symlinks prefixed with slash on windows

[hirochachacha]

Please answer these questions before submitting your issue. Thanks!

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

go version devel +4c9ac8c152 Tue Apr 11 10:21:18 2017 +0900 darwin/amd64

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/hiro/.go"
GORACE=""
GOROOT="/Users/hiro/go"
GOTOOLDIR="/Users/hiro/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/wq/dwn8hs0x7njbzty9f68y61700000gn/T/go-build355671010=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

What did you do?

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.
apply following patch

diff --git a/src/os/os_test.go b/src/os/os_test.go
index 410bfc8007..a7fbfa4cb3 100644
--- a/src/os/os_test.go
+++ b/src/os/os_test.go
@@ -1813,6 +1813,23 @@ func TestStatRelativeSymlink(t *testing.T) {
 	if !SameFile(st, st1) {
 		t.Error("Stat doesn't follow relative symlink")
 	}
+
+	if runtime.GOOS == "windows" {
+		Remove(link)
+		err = Symlink(target[len(filepath.VolumeName(target)):], link)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		st1, err := Stat(link)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !SameFile(st, st1) {
+			t.Error("Stat doesn't follow relative symlink")
+		}
+	}
 }

to os package. Then go test.

What did you expect to see?

no errors.

What did you see instead?

errors.

When I was fixing #19870, I couldn't recall this case. sorry.

[gopherbot]

CL https://golang.org/cl/40410 mentions this issue.