Add support for spaces and newlines in runfiles paths (#4136)

**What type of PR is this?**

Feature

**What does this PR do? Why is it needed?**

In Bazel 8.0.0 since
bazelbuild/bazel@7407cef.

**Which issues(s) does this PR fix?**

Fixes #

**Other notes for review**

go/runfiles/manifest.go

@@ -79,11 +79,25 @@ func (f ManifestFile) parse() (manifest, error) {
 	s := bufio.NewScanner(r)
 	m := manifest{make(map[string]string),  nil}
 	for s.Scan() {
-		fields := strings.SplitN(s.Text(), " ", 2)
-		if len(fields) != 2 || fields[0] == "" {
-			return manifest{}, fmt.Errorf("runfiles: bad manifest line %q in file %s", s.Text(), f)
+		line := s.Text()
+		var link, target string
+		if strings.HasPrefix(line, " ") {
+			// In lines that start with a space, spaces, newlines, and backslashes are escaped as \s, \n, and \b in
+			// link and newlines and backslashes are escaped in target.
+			fields := strings.SplitN(s.Text()[1:], " ", 2)
+			link = fields[0]
+			target = fields[1]
+			link = strings.ReplaceAll(link, `\s`, " ")
+			link = strings.ReplaceAll(link, `\n`, "\n")
+			link = strings.ReplaceAll(link, `\b`, `\`)
+			target = strings.ReplaceAll(target, `\n`, "\n")
+			target = strings.ReplaceAll(target, `\b`, `\`)
+		} else {
+			fields := strings.SplitN(line, " ", 2)
+			link = fields[0]
+			target = fields[1]
 		}
-		m.index[fields[0]] = filepath.FromSlash(fields[1])
+		m.index[link] = filepath.FromSlash(target)
 	}
 
 	if err := s.Err(); err != nil {

tests/runfiles/runfiles_test.go

@@ -124,7 +124,9 @@ func TestRunfiles_empty(t *testing.T) {
 func TestRunfiles_manifestWithDir(t *testing.T) {
 	dir := t.TempDir()
 	manifest := filepath.Join(dir, "manifest")
-	if err := os.WriteFile(manifest, []byte("foo/dir path/to/foo/dir\n"), 0o600); err != nil {
+	if err := os.WriteFile(manifest, []byte(`foo/dir path/to/foo/dir
+ dir\swith\sspac\be\ns F:\bj k\bdir with spa\nces
+`), 0o600); err != nil {
 		t.Fatal(err)
 	}
 	r, err := runfiles.New(runfiles.ManifestFile(manifest))
@@ -136,6 +138,12 @@ func TestRunfiles_manifestWithDir(t *testing.T) {
 		"foo/dir":                    filepath.FromSlash("path/to/foo/dir"),
 		"foo/dir/file":               filepath.FromSlash("path/to/foo/dir/file"),
 		"foo/dir/deeply/nested/file": filepath.FromSlash("path/to/foo/dir/deeply/nested/file"),
+		`dir with spac\e
+s`:            filepath.FromSlash(`F:\j k\dir with spa
+ces`),
+		`dir with spac\e
+s/file`:            filepath.FromSlash(`F:\j k\dir with spa
+ces/file`),
 	} {
 		t.Run(rlocation, func(t *testing.T) {
 			got, err := r.Rlocation(rlocation)