cmd/compile: omit file:pos for non-existent, permission errors

Omits printing the file:line:column when trying to open either
* non-existent files
* files without permission

Given:
    go tool compile x.go

For either of x.go not existing, or if no read permissions:

* Before:
    x.go:0: open x.go: no such file or directory
    x.go:0: open x.go: permission denied

* After:
    open x.go: no such file or directory
    open x.go: permission denied

While here, noticed an oddity with the Linux builders, that appear
to always be running under root, hence the test for permission errors
with 0222 -W-*-W-*-W- can't pass on linux-amd64 builders.
The filed bug is golang#38608.

Fixes golang#36437

Change-Id: I9645ef73177c286c99547e3a0f3719fa07b35cb5
Reviewed-on: https://go-review.googlesource.com/c/go/+/229357
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/gc/subr.go

@@ -60,9 +60,15 @@ func adderrorname(n *Node) {
 }
 
 func adderr(pos src.XPos, format string, args ...interface{}) {
+	msg := fmt.Sprintf(format, args...)
+	// Only add the position if we have a file.
+	// See issue golang.org/issue/11361.
+	if !strings.HasSuffix(msg, ": no such file or directory") && !strings.HasSuffix(msg, ": permission denied") {
+		msg = fmt.Sprintf("%v: %s", linestr(pos), msg)
+	}
 	errors = append(errors, Error{
 		pos: pos,
-		msg: fmt.Sprintf("%v: %s\n", linestr(pos), fmt.Sprintf(format, args...)),
+		msg: msg + "\n",
 	})
 }
 

test/fixedbugs/issue36437.go

@@ -0,0 +1,69 @@
+// run
+
+// +build !nacl,!js
+
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Tests that when non-existent files are passed to the
+// compiler, such as in:
+//    go tool compile foo
+// we don't print the beginning position:
+//    foo:0: open foo: no such file or directory
+// but instead omit it and print out:
+//    open foo: no such file or directory
+
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+)
+
+func main() {
+	tmpDir, err := ioutil.TempDir("", "issue36437")
+	if err != nil {
+		panic(err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	msgOrErr := func(msg []byte, err error) string {
+		if len(msg) == 0 && err != nil {
+			return err.Error()
+		}
+		return string(msg)
+	}
+
+	// 1. Pass in a non-existent file.
+	output, err := exec.Command("go", "tool", "compile", "x.go").CombinedOutput()
+	want := "open x.go: no such file or directory\n"
+	if got := msgOrErr(output, err); got != want {
+		fmt.Printf("Expected an error, but got:\n\t%q\nwant:\n\t%q", got, want)
+		return
+	}
+
+	if runtime.GOOS == "linux" && runtime.GOARCH == "amd64" {
+		// The Go Linux builders seem to be running under root, thus
+		// linux-amd64 doesn't seem to be respecting 0222 file permissions,
+		// and reads files with -W-*-W-*-W- permissions.
+		// Filed bug: https://golang.org/issues/38608
+		return
+	}
+
+	// 2. Invoke the compiler with a file that we don't have read permissions to.
+	path := filepath.Join(tmpDir, "p.go")
+	if err := ioutil.WriteFile(path, []byte("package p"), 0222); err != nil {
+		panic(err)
+	}
+	output, err = exec.Command("go", "tool", "compile", path).CombinedOutput()
+	want = fmt.Sprintf("open %s: permission denied\n", path)
+	if got := msgOrErr(output, err); got != want {
+		fmt.Printf("Expected an error, but got:\n\t%q\nwant:\n\t%q", got, want)
+		return
+	}
+}