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>

3 files changed, 29 insertions, 3 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)
 		}
diff --git a/src/cmd/api/goapi_test.go b/src/cmd/api/goapi_test.go
index 0d00f6a297..3c4e50a21a 100644
--- a/src/cmd/api/goapi_test.go
+++ b/src/cmd/api/goapi_test.go
@@ -9,6 +9,7 @@ import (
 	"flag"
 	"fmt"
 	"go/build"
+	"internal/testenv"
 	"io/ioutil"
 	"os"
 	"os/exec"
@@ -163,7 +164,7 @@ func TestSkipInternal(t *testing.T) {
 }
 
 func BenchmarkAll(b *testing.B) {
-	stds, err := exec.Command("go", "list", "std").Output()
+	stds, err := exec.Command(testenv.GoToolPath(b), "list", "std").Output()
 	if err != nil {
 		b.Fatal(err)
 	}
diff --git a/src/cmd/api/run.go b/src/cmd/api/run.go
index 20cddb704b..219776cae4 100644
--- a/src/cmd/api/run.go
+++ b/src/cmd/api/run.go
@@ -14,8 +14,21 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
 )
 
+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"
+}
+
 var goroot string
 
 func main() {
@@ -25,7 +38,7 @@ func main() {
 		log.Fatal("No $GOROOT set.")
 	}
 
-	out, err := exec.Command("go", "tool", "api",
+	out, err := exec.Command(goCmd(), "tool", "api",
 		"-c", file("go1", "go1.1", "go1.2", "go1.3", "go1.4", "go1.5", "go1.6", "go1.7", "go1.8", "go1.9"),
 		"-next", file("next"),
 		"-except", file("except")).CombinedOutput()