cmd/go/internal/base: in AppendPWD, check that PWD is absolute

The POSIX standard requires the PWD variable to be an absolute path.

Fixes #46832

Change-Id: I1938592538633e1a0a0958276f1fefc3c4808399
Reviewed-on: https://go-review.googlesource.com/c/go/+/378396
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

6 files changed, 42 insertions, 18 deletions

diff --git a/src/cmd/go/internal/base/env.go b/src/cmd/go/internal/base/env.go
index 5f2665d236..2f47300f2e 100644
--- a/src/cmd/go/internal/base/env.go
+++ b/src/cmd/go/internal/base/env.go
@@ -4,12 +4,20 @@
 
 package base
 
+import (
+	"fmt"
+	"path/filepath"
+)
+
 // 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.
+	// POSIX requires PWD to be absolute.
+	// Internally we only use absolute paths, so dir should already be absolute.
+	if !filepath.IsAbs(dir) {
+		panic(fmt.Sprintf("AppendPWD with relative path %q", dir))
+	}
 	return append(base, "PWD="+dir)
 }
diff --git a/src/cmd/go/internal/generate/generate_test.go b/src/cmd/go/internal/generate/generate_test.go
index 15b1279f36..d61ecf104a 100644
--- a/src/cmd/go/internal/generate/generate_test.go
+++ b/src/cmd/go/internal/generate/generate_test.go
@@ -5,7 +5,9 @@
 package generate
 
 import (
+	"internal/testenv"
 	"os"
+	"path/filepath"
 	"reflect"
 	"runtime"
 	"testing"
@@ -41,10 +43,11 @@ var splitTests = []splitTest{
 }
 
 func TestGenerateCommandParse(t *testing.T) {
+	dir := filepath.Join(testenv.GOROOT(t), "src", "sys")
 	g := &Generator{
 		r:        nil, // Unused here.
-		path:     "/usr/ken/sys/proc.go",
-		dir:      "/usr/ken/sys",
+		path:     filepath.Join(dir, "proc.go"),
+		dir:      dir,
 		file:     "proc.go",
 		pkg:      "sys",
 		commands: make(map[string][]string),
@@ -84,10 +87,11 @@ var defEnvMap = map[string]string{
 //     before executing the test.  i.e., execute the split as if it
 //     processing that source line.
 func TestGenerateCommandShorthand(t *testing.T) {
+	dir := filepath.Join(testenv.GOROOT(t), "src", "sys")
 	g := &Generator{
 		r:        nil, // Unused here.
-		path:     "/usr/ken/sys/proc.go",
-		dir:      "/usr/ken/sys",
+		path:     filepath.Join(dir, "proc.go"),
+		dir:      dir,
 		file:     "proc.go",
 		pkg:      "sys",
 		commands: make(map[string][]string),
@@ -222,10 +226,11 @@ var splitTestsLines = []splitTestWithLine{
 //     before executing the test.  i.e., execute the split as if it
 //     processing that source line.
 func TestGenerateCommandShortHand2(t *testing.T) {
+	dir := filepath.Join(testenv.GOROOT(t), "src", "sys")
 	g := &Generator{
 		r:        nil, // Unused here.
-		path:     "/usr/ken/sys/proc.go",
-		dir:      "/usr/ken/sys",
+		path:     filepath.Join(dir, "proc.go"),
+		dir:      dir,
 		file:     "proc.go",
 		pkg:      "sys",
 		commands: make(map[string][]string),
diff --git a/src/cmd/go/internal/vcs/vcs.go b/src/cmd/go/internal/vcs/vcs.go
index 2acabf7aaf..77208ab762 100644
--- a/src/cmd/go/internal/vcs/vcs.go
+++ b/src/cmd/go/internal/vcs/vcs.go
@@ -669,7 +669,7 @@ func (v *Cmd) run1(dir string, cmdline string, keyval []string, verbose bool) ([
 			if ee, ok := err.(*exec.ExitError); ok && len(ee.Stderr) > 0 {
 				os.Stderr.Write(ee.Stderr)
 			} else {
-				fmt.Fprintf(os.Stderr, err.Error())
+				fmt.Fprintln(os.Stderr, err.Error())
 			}
 		}
 	}
@@ -678,14 +678,24 @@ func (v *Cmd) run1(dir string, cmdline string, keyval []string, verbose bool) ([
 
 // Ping pings to determine scheme to use.
 func (v *Cmd) Ping(scheme, repo string) error {
-	return v.runVerboseOnly(".", v.PingCmd, "scheme", scheme, "repo", repo)
+	// Run the ping command in an arbitrary working directory,
+	// but don't let the current working directory pollute the results.
+	// In module mode, we expect GOMODCACHE to exist and be a safe place for
+	// commands; in GOPATH mode, we expect that to be true of GOPATH/src.
+	dir := cfg.GOMODCACHE
+	if !cfg.ModulesEnabled {
+		dir = filepath.Join(cfg.BuildContext.GOPATH, "src")
+	}
+	os.MkdirAll(dir, 0777) // Ignore errors — if unsuccessful, the command will likely fail.
+
+	return v.runVerboseOnly(dir, v.PingCmd, "scheme", scheme, "repo", repo)
 }
 
 // Create creates a new copy of repo in dir.
 // The parent of dir must exist; dir must not.
 func (v *Cmd) Create(dir, repo string) error {
 	for _, cmd := range v.CreateCmd {
-		if err := v.run(".", cmd, "dir", dir, "repo", repo); err != nil {
+		if err := v.run(filepath.Dir(dir), cmd, "dir", dir, "repo", repo); err != nil {
 			return err
 		}
 	}
diff --git a/src/cmd/go/internal/work/buildid.go b/src/cmd/go/internal/work/buildid.go
index 76335e9bb1..ac98aa344c 100644
--- a/src/cmd/go/internal/work/buildid.go
+++ b/src/cmd/go/internal/work/buildid.go
@@ -160,7 +160,6 @@ 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.AppendPWD(os.Environ(), cmd.Dir)
 	var stdout, stderr bytes.Buffer
 	cmd.Stdout = &stdout
 	cmd.Stderr = &stderr
@@ -219,9 +218,8 @@ func (b *Builder) gccToolID(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.AppendPWD(os.Environ(), cmd.Dir)
 	// Force untranslated output so that we see the string "version".
-	cmd.Env = append(cmd.Env, "LC_ALL=C")
+	cmd.Env = append(os.Environ(), "LC_ALL=C")
 	out, err := cmd.CombinedOutput()
 	if err != nil {
 		return "", fmt.Errorf("%s: %v; output: %q", name, err, out)
diff --git a/src/cmd/go/internal/work/exec.go b/src/cmd/go/internal/work/exec.go
index 9c9d58b2a1..f0e6c80029 100644
--- a/src/cmd/go/internal/work/exec.go
+++ b/src/cmd/go/internal/work/exec.go
@@ -2116,8 +2116,11 @@ func (b *Builder) runOut(a *Action, dir string, env []string, cmdargs ...any) ([
 	cmd.Stderr = &buf
 	cleanup := passLongArgsInResponseFiles(cmd)
 	defer cleanup()
-	cmd.Dir = dir
-	cmd.Env = base.AppendPWD(os.Environ(), cmd.Dir)
+	cmd.Env = os.Environ()
+	if dir != "." {
+		cmd.Dir = dir
+		cmd.Env = base.AppendPWD(cmd.Env, dir)
+	}
 
 	// Add the TOOLEXEC_IMPORTPATH environment variable for -toolexec tools.
 	// It doesn't really matter if -toolexec isn't being used.
@@ -3071,7 +3074,7 @@ var (
 )
 
 func (b *Builder) swigDoVersionCheck() error {
-	out, err := b.runOut(nil, "", nil, "swig", "-version")
+	out, err := b.runOut(nil, ".", nil, "swig", "-version")
 	if err != nil {
 		return err
 	}
diff --git a/src/cmd/go/testdata/script/mod_list_direct.txt b/src/cmd/go/testdata/script/mod_list_direct.txt
index 9b7a04c504..3aa1881554 100644
--- a/src/cmd/go/testdata/script/mod_list_direct.txt
+++ b/src/cmd/go/testdata/script/mod_list_direct.txt
@@ -10,7 +10,7 @@ env GOSUMDB=off
 # For a while, (*modfetch.codeRepo).Stat was not checking for a go.mod file,
 # which would produce a hard error at the subsequent call to GoMod.
 
-go get
+go get -v
 
 -- go.mod --
 module example.com