fix(cli): fix case where linkLocalBazel fails when os.UserCacheDir returns path starting with ~ (#1182)

Also run `help flags-as-proto` command in a UserCacheDir() location
instead of the tmp dir and fix order of error handling for the result of
that call. UserCacheDir() is more robust since tmpdir is not guaranteed
to exist or to be writable (as per [golang
docs](https://pkg.go.dev/os#TempDir)). We already depend on
UserCacheDir() in the CLI code.

GitOrigin-RevId: df084e1effce5ba4a813f56b33260e9749c5526d

Author: gregmagolan

pkg/bazel/bazel.go

@@ -23,6 +23,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path"
 	"path/filepath"
 	"strings"
 
@@ -162,6 +163,23 @@ func (b *bazel) Flags() (map[string]*flags.FlagInfo, error) {
 	if allFlags != nil {
 		return allFlags, nil
 	}
+
+	// create a directory in the user cache dir with an empty WORKSPACE file to run
+	// `bazel help flags-as-proto` in so it doesn't affect the bazel server in the user's WORKSPACE
+	userCacheDir, err := UserCacheDir()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get user cache dir: %w", err)
+	}
+	tmpdir := path.Join(userCacheDir, ".aspect/cli-flags-as-proto")
+	err = os.MkdirAll(tmpdir, os.ModePerm)
+	if err != nil {
+		return nil, fmt.Errorf("failed write create directory %s: %w", tmpdir, err)
+	}
+	err = os.WriteFile(path.Join(tmpdir, "WORKSPACE"), []byte{}, 0644)
+	if err != nil {
+		return nil, fmt.Errorf("failed write WORKSPACE file in %s: %w", tmpdir, err)
+	}
+
 	var stdout bytes.Buffer
 	var stderr bytes.Buffer
 	streams := ioutils.Streams{
@@ -174,23 +192,23 @@ func (b *bazel) Flags() (map[string]*flags.FlagInfo, error) {
 	bazelExitCode := make(chan int, 1)
 	defer close(bazelErrs)
 	defer close(bazelExitCode)
-	go func() {
+
+	go func(wd string) {
 		// Running in batch mode will prevent bazel from spawning a daemon. Spawning a bazel daemon takes time which is something we don't want here.
 		// Also, instructing bazel to ignore all rc files will protect it from failing if any of the rc files is broken.
-		tmpdir := os.TempDir()
-		exitCode, err := b.RunCommand(streams, &tmpdir, "--nobatch", "--ignore_all_rc_files", "help", "flags-as-proto")
+		exitCode, err := b.RunCommand(streams, &wd, "--nobatch", "--ignore_all_rc_files", "help", "flags-as-proto")
 		bazelErrs <- err
 		bazelExitCode <- exitCode
-	}()
-
-	if exitCode := <-bazelExitCode; exitCode != 0 {
-		return nil, fmt.Errorf("failed to get bazel flags: %w", fmt.Errorf("bazel has quit with code %d\nstderr:\n%s", exitCode, stderr.String()))
-	}
+	}(tmpdir)
 
 	if err := <-bazelErrs; err != nil {
 		return nil, fmt.Errorf("failed to get bazel flags: %w", err)
 	}
 
+	if exitCode := <-bazelExitCode; exitCode != 0 {
+		return nil, fmt.Errorf("failed to get bazel flags running in %s: %w", tmpdir, fmt.Errorf("bazel has quit with code %d\nstderr:\n%s", exitCode, stderr.String()))
+	}
+
 	helpProtoBytes, err := io.ReadAll(stdoutDecoder)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get bazel flags: %w", err)

pkg/bazel/bazelisk.go

@@ -67,15 +67,31 @@ func NewBazelisk(workspaceRoot string) *Bazelisk {
 	return &Bazelisk{workspaceRoot: workspaceRoot}
 }
 
+func UserCacheDir() (string, error) {
+	userCacheDir, err := os.UserCacheDir()
+	if err != nil {
+		return "", fmt.Errorf("could not get the user's cache directory: %v", err)
+	}
+
+	// We hit a case in a bazel-in-bazel test where os.UserCacheDir() return a path starting with '~'.
+	// Run it through homedir.Expand to turn it into an absolute path incase that happens.
+	userCacheDir, err = homedir.Expand(userCacheDir)
+	if err != nil {
+		return "", fmt.Errorf("could not expand home directory in path: %v", err)
+	}
+
+	return userCacheDir, err
+}
+
 // Run runs the main Bazelisk logic for the given arguments and Bazel repositories.
 func (bazelisk *Bazelisk) Run(args []string, repos *core.Repositories, streams ioutils.Streams, env []string, wd *string) (int, error) {
 	httputil.UserAgent = bazelisk.getUserAgent()
 
 	bazeliskHome := bazelisk.GetEnvOrConfig("BAZELISK_HOME")
 	if len(bazeliskHome) == 0 {
-		userCacheDir, err := os.UserCacheDir()
+		userCacheDir, err := UserCacheDir()
 		if err != nil {
-			return -1, fmt.Errorf("could not get the user's cache directory: %v", err)
+			return -1, err
 		}
 
 		bazeliskHome = filepath.Join(userCacheDir, "bazelisk")
@@ -128,7 +144,7 @@ func (bazelisk *Bazelisk) Run(args []string, repos *core.Repositories, streams i
 		baseDirectory := filepath.Join(bazeliskHome, "local")
 		bazelPath, err = linkLocalBazel(baseDirectory, bazelPath)
 		if err != nil {
-			return -1, fmt.Errorf("cound not link local Bazel: %v", err)
+			return -1, fmt.Errorf("could not link local Bazel: %v", err)
 		}
 	}