filepath: fix Glob to return no error on nonmatching patterns

filepath.Glob is documented to return nil if no files match
and an error only if the pattern is invalid.  This change
fixes it to work as documented and adds a regression test.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5040045

src/pkg/path/filepath/match.go

@@ -215,7 +215,7 @@ func getEsc(chunk string) (r int, nchunk string, err os.Error) {
 func Glob(pattern string) (matches []string, err os.Error) {
 	if !hasMeta(pattern) {
 		if _, err = os.Stat(pattern); err != nil {
-			return
+			return nil, nil
 		}
 		return []string{pattern}, nil
 	}

src/pkg/path/filepath/match_test.go

@@ -124,6 +124,16 @@ func TestGlob(t *testing.T) {
 			t.Errorf("Glob(%#q) = %#v want %v", tt.pattern, matches, tt.result)
 		}
 	}
+	for _, pattern := range []string{"no_match", "../*/no_match"} {
+		matches, err := Glob(pattern)
+		if err != nil {
+			t.Errorf("Glob error for %q: %s", pattern, err)
+			continue
+		}
+		if len(matches) != 0 {
+			t.Errorf("Glob(%#q) = %#v want []", pattern, matches)
+		}
+	}
 }
 
 func TestGlobError(t *testing.T) {

src/pkg/template/helper.go

@@ -210,7 +210,8 @@ func ParseTemplateFiles(filenames ...string) (*Set, os.Error) {
 }
 
 // ParseTemplateGlob creates a set by parsing the files matched
-// by the pattern, each of which defines a single template. Each
+// by the pattern, each of which defines a single template. The pattern
+// is processed by filepath.Glob and must match at least one file. Each
 // template will be named the base name of its file.
 // Unlike with ParseGlob, each file should be a stand-alone template
 // definition suitable for Template.Parse (not Set.Parse); that is, the
@@ -225,6 +226,9 @@ func ParseTemplateGlob(pattern string) (*Set, os.Error) {
 	if err != nil {
 		return nil, err
 	}
+	if len(filenames) == 0 {
+		return nil, fmt.Errorf("pattern matches no files: %#q", pattern)
+	}
 	for _, filename := range filenames {
 		t, err := ParseFile(filename)
 		if err != nil {