all: correct location of go tool

In general, there are no guarantee that `go` command exist on $PATH.
This CL tries to get `go` command from $GOROOT/bin instead.

There are three kinds of code we should handle:
    For normal code, the CL implements goCmd() or goCmdName().
    For unit tests, the CL uses testenv.GoTool() or testenv.GoToolPath().
    For integration tests, the CL sets PATH=$GOROOT/bin:$PATH in cmd/dist.

Note that make.bash sets PATH=$GOROOT/bin:$PATH in the build process.
So this change is only useful when we use toolchain manually.

Updates #21875

Change-Id: I963b9f22ea732dd735363ececde4cf94a5db5ca2
Reviewed-on: https://go-review.googlesource.com/64650
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 13 insertions, 1 deletions

diff --git a/src/cmd/api/goapi.go b/src/cmd/api/goapi.go
index 936f9e5511..8cc78c01ed 100644
--- a/src/cmd/api/goapi.go
+++ b/src/cmd/api/goapi.go
@@ -27,6 +27,18 @@ import (
 	"strings"
 )
 
+func goCmd() string {
+	var exeSuffix string
+	if runtime.GOOS == "windows" {
+		exeSuffix = ".exe"
+	}
+	path := filepath.Join(runtime.GOROOT(), "bin", "go"+exeSuffix)
+	if _, err := os.Stat(path); err == nil {
+		return path
+	}
+	return "go"
+}
+
 // Flags
 var (
 	checkFile  = flag.String("c", "", "optional comma-separated filename(s) to check API against")
@@ -127,7 +139,7 @@ func main() {
 	if flag.NArg() > 0 {
 		pkgNames = flag.Args()
 	} else {
-		stds, err := exec.Command("go", "list", "std").Output()
+		stds, err := exec.Command(goCmd(), "list", "std").Output()
 		if err != nil {
 			log.Fatal(err)
 		}