Don't emit line tags when source code is printed as part of

package documentation using templates. The line tag interferes
with the anchor tag introduces by the template.

This fixes an an issue where some headers lost their ability
to link to the respective source code.

R=rsc
https://golang.org/cl/154166

src/cmd/godoc/godoc.go

@@ -470,16 +470,23 @@ func parse(path string, mode uint) (*ast.File, *parseErrors) {
 
 // Styler implements a printer.Styler.
 type Styler struct {
-	highlight string;
+	linetags	bool;
+	highlight	string;
 }
 
 
 // Use the defaultStyler when there is no specific styler.
+// The defaultStyler does not emit line tags since they may
+// interfere with tags emitted by templates.
+// TODO(gri): Should emit line tags at the beginning of a line;
+//            never in the middle of code.
 var defaultStyler Styler
 
 
 func (s *Styler) LineTag(line int) (text []byte, tag printer.HTMLTag) {
-	tag = printer.HTMLTag{fmt.Sprintf(`<a id="L%d">`, line), "</a>"};
+	if s.linetags {
+		tag = printer.HTMLTag{fmt.Sprintf(`<a id="L%d">`, line), "</a>"}
+	}
 	return;
 }
 
@@ -932,7 +939,7 @@ func serveFile(c *http.Conn, r *http.Request) {
 		return;
 
 	case ext == ".go":
-		serveGoSource(c, r, path, &Styler{highlight: r.FormValue("h")});
+		serveGoSource(c, r, path, &Styler{linetags: true, highlight: r.FormValue("h")});
 		return;
 	}