cmd/go/internal/base: rename EnvForDir to AppendPWD

EnvForDir does not immediately evoke “append”, and thus may not prompt
the reader to consider the possibility of aliasing bugs (as in
issue #38077). To make this behavior more obvious at the call site, rename
cmd/go/internal/base.EnvForDir to AppendPWD and swap the order of
arguments to a conventional “append” function (similar to those in the
strconv package).

For #38077

Change-Id: I16f09aa0fa8a269d51f0511eb402a44e2759eb94
Reviewed-on: https://go-review.googlesource.com/c/go/+/225578
Reviewed-by: Jay Conrod <jayconrod@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

src/cmd/go/internal/base/env.go

@@ -4,12 +4,12 @@
 
 package base
 
-// EnvForDir returns a modified environment suitable for running in the given
-// directory.
-// The environment is the supplied base environment but with an updated $PWD, so
-// that an os.Getwd in the child will be faster.
-func EnvForDir(dir string, base []string) []string {
-	// Internally we only use rooted paths, so dir is rooted.
-	// Even if dir is not rooted, no harm done.
+// AppendPWD returns the result of appending PWD=dir to the environment base.
+//
+// The resulting environment makes os.Getwd more efficient for a subprocess
+// running in dir.
+func AppendPWD(base []string, dir string) []string {
+	// Internally we only use absolute paths, so dir is absolute.
+	// Even if dir is not absolute, no harm done.
 	return append(base, "PWD="+dir)
 }

src/cmd/go/internal/get/vcs.go

@@ -430,7 +430,7 @@ func (v *vcsCmd) run1(dir string, cmdline string, keyval []string, verbose bool)
 
 	cmd := exec.Command(v.cmd, args...)
 	cmd.Dir = dir
-	cmd.Env = base.EnvForDir(cmd.Dir, os.Environ())
+	cmd.Env = base.AppendPWD(os.Environ(), cmd.Dir)
 	if cfg.BuildX {
 		fmt.Fprintf(os.Stderr, "cd %s\n", dir)
 		fmt.Fprintf(os.Stderr, "%s %s\n", v.cmd, strings.Join(args, " "))

src/cmd/go/internal/test/test.go

@@ -1157,7 +1157,7 @@ func (c *runCache) builderRunTest(b *work.Builder, a *work.Action) error {
 
 	cmd := exec.Command(args[0], args[1:]...)
 	cmd.Dir = a.Package.Dir
-	cmd.Env = base.EnvForDir(cmd.Dir, cfg.OrigEnv[:len(cfg.OrigEnv):len(cfg.OrigEnv)])
+	cmd.Env = base.AppendPWD(cfg.OrigEnv[:len(cfg.OrigEnv):len(cfg.OrigEnv)], cmd.Dir)
 	cmd.Stdout = stdout
 	cmd.Stderr = stdout
 

src/cmd/go/internal/work/buildid.go

@@ -185,7 +185,7 @@ func (b *Builder) toolID(name string) string {
 
 	cmdline := str.StringList(cfg.BuildToolexec, path, "-V=full")
 	cmd := exec.Command(cmdline[0], cmdline[1:]...)
-	cmd.Env = base.EnvForDir(cmd.Dir, os.Environ())
+	cmd.Env = base.AppendPWD(os.Environ(), cmd.Dir)
 	var stdout, stderr bytes.Buffer
 	cmd.Stdout = &stdout
 	cmd.Stderr = &stderr
@@ -244,7 +244,7 @@ func (b *Builder) gccgoToolID(name, language string) (string, error) {
 	// compile an empty file on standard input.
 	cmdline := str.StringList(cfg.BuildToolexec, name, "-###", "-x", language, "-c", "-")
 	cmd := exec.Command(cmdline[0], cmdline[1:]...)
-	cmd.Env = base.EnvForDir(cmd.Dir, os.Environ())
+	cmd.Env = base.AppendPWD(os.Environ(), cmd.Dir)
 	// Force untranslated output so that we see the string "version".
 	cmd.Env = append(cmd.Env, "LC_ALL=C")
 	out, err := cmd.CombinedOutput()

src/cmd/go/internal/work/exec.go

@@ -1925,7 +1925,7 @@ func (b *Builder) runOut(a *Action, dir string, env []string, cmdargs ...interfa
 	cleanup := passLongArgsInResponseFiles(cmd)
 	defer cleanup()
 	cmd.Dir = dir
-	cmd.Env = base.EnvForDir(cmd.Dir, os.Environ())
+	cmd.Env = base.AppendPWD(os.Environ(), cmd.Dir)
 	cmd.Env = append(cmd.Env, env...)
 	start := time.Now()
 	err := cmd.Run()
@@ -2381,7 +2381,7 @@ func (b *Builder) gccSupportsFlag(compiler []string, flag string) bool {
 	}
 	cmd := exec.Command(cmdArgs[0], cmdArgs[1:]...)
 	cmd.Dir = b.WorkDir
-	cmd.Env = base.EnvForDir(cmd.Dir, os.Environ())
+	cmd.Env = base.AppendPWD(os.Environ(), cmd.Dir)
 	cmd.Env = append(cmd.Env, "LC_ALL=C")
 	out, _ := cmd.CombinedOutput()
 	// GCC says "unrecognized command line option".