template: change the signature of formatters for future development.

Make them more like Printf, with a ... final argument.  This breaks
code with existing formatters but not the templates that use them.

R=rsc, gri
CC=golang-dev
https://golang.org/cl/3378041

5 files changed, 54 insertions, 44 deletions

diff --git a/src/cmd/godoc/godoc.go b/src/cmd/godoc/godoc.go
index 919b41626e..293a7fb19e 100644
--- a/src/cmd/godoc/godoc.go
+++ b/src/cmd/godoc/godoc.go
@@ -563,7 +563,7 @@ func writeText(w io.Writer, text []byte, html bool) {
 
 
 // Write anything to w; optionally html-escaped.
-func writeAny(w io.Writer, x interface{}, html bool) {
+func writeAny(w io.Writer, html bool, x interface{}) {
 	switch v := x.(type) {
 	case []byte:
 		writeText(w, v, html)
@@ -584,23 +584,23 @@ func writeAny(w io.Writer, x interface{}, html bool) {
 
 
 // Template formatter for "html" format.
-func htmlFmt(w io.Writer, x interface{}, format string) {
-	writeAny(w, x, true)
+func htmlFmt(w io.Writer, format string, x ...interface{}) {
+	writeAny(w, true, x[0])
 }
 
 
 // Template formatter for "html-esc" format.
-func htmlEscFmt(w io.Writer, x interface{}, format string) {
+func htmlEscFmt(w io.Writer, format string, x ...interface{}) {
 	var buf bytes.Buffer
-	writeAny(&buf, x, false)
+	writeAny(&buf, false, x[0])
 	template.HTMLEscape(w, buf.Bytes())
 }
 
 
 // Template formatter for "html-comment" format.
-func htmlCommentFmt(w io.Writer, x interface{}, format string) {
+func htmlCommentFmt(w io.Writer, format string, x ...interface{}) {
 	var buf bytes.Buffer
-	writeAny(&buf, x, false)
+	writeAny(&buf, false, x[0])
 	// TODO(gri) Provide list of words (e.g. function parameters)
 	//           to be emphasized by ToHTML.
 	doc.ToHTML(w, buf.Bytes(), nil) // does html-escaping
@@ -608,13 +608,13 @@ func htmlCommentFmt(w io.Writer, x interface{}, format string) {
 
 
 // Template formatter for "" (default) format.
-func textFmt(w io.Writer, x interface{}, format string) {
-	writeAny(w, x, false)
+func textFmt(w io.Writer, format string, x ...interface{}) {
+	writeAny(w, false, x[0])
 }
 
 
 // Template formatter for the various "url-xxx" formats.
-func urlFmt(w io.Writer, x interface{}, format string) {
+func urlFmt(w io.Writer, format string, x ...interface{}) {
 	var path string
 	var line int
 
@@ -622,7 +622,7 @@ func urlFmt(w io.Writer, x interface{}, format string) {
 	type positioner interface {
 		Pos() token.Position
 	}
-	switch t := x.(type) {
+	switch t := x[0].(type) {
 	case string:
 		path = t
 	case positioner:
@@ -676,14 +676,14 @@ var infoKinds = [nKinds]string{
 
 
 // Template formatter for "infoKind" format.
-func infoKindFmt(w io.Writer, x interface{}, format string) {
-	fmt.Fprintf(w, infoKinds[x.(SpotKind)]) // infoKind entries are html-escaped
+func infoKindFmt(w io.Writer, format string, x ...interface{}) {
+	fmt.Fprintf(w, infoKinds[x[0].(SpotKind)]) // infoKind entries are html-escaped
 }
 
 
 // Template formatter for "infoLine" format.
-func infoLineFmt(w io.Writer, x interface{}, format string) {
-	info := x.(SpotInfo)
+func infoLineFmt(w io.Writer, format string, x ...interface{}) {
+	info := x[0].(SpotInfo)
 	line := info.Lori()
 	if info.IsIndex() {
 		index, _ := searchIndex.get()
@@ -702,8 +702,8 @@ func infoLineFmt(w io.Writer, x interface{}, format string) {
 
 
 // Template formatter for "infoSnippet" format.
-func infoSnippetFmt(w io.Writer, x interface{}, format string) {
-	info := x.(SpotInfo)
+func infoSnippetFmt(w io.Writer, format string, x ...interface{}) {
+	info := x[0].(SpotInfo)
 	text := `<span class="alert">no snippet text available</span>`
 	if info.IsIndex() {
 		index, _ := searchIndex.get()
@@ -716,30 +716,30 @@ func infoSnippetFmt(w io.Writer, x interface{}, format string) {
 
 
 // Template formatter for "padding" format.
-func paddingFmt(w io.Writer, x interface{}, format string) {
-	for i := x.(int); i > 0; i-- {
+func paddingFmt(w io.Writer, format string, x ...interface{}) {
+	for i := x[0].(int); i > 0; i-- {
 		fmt.Fprint(w, `<td width="25"></td>`)
 	}
 }
 
 
 // Template formatter for "time" format.
-func timeFmt(w io.Writer, x interface{}, format string) {
-	template.HTMLEscape(w, []byte(time.SecondsToLocalTime(x.(int64)/1e9).String()))
+func timeFmt(w io.Writer, format string, x ...interface{}) {
+	template.HTMLEscape(w, []byte(time.SecondsToLocalTime(x[0].(int64)/1e9).String()))
 }
 
 
 // Template formatter for "dir/" format.
-func dirslashFmt(w io.Writer, x interface{}, format string) {
-	if x.(*os.FileInfo).IsDirectory() {
+func dirslashFmt(w io.Writer, format string, x ...interface{}) {
+	if x[0].(*os.FileInfo).IsDirectory() {
 		w.Write([]byte{'/'})
 	}
 }
 
 
 // Template formatter for "localname" format.
-func localnameFmt(w io.Writer, x interface{}, format string) {
-	_, localname := pathutil.Split(x.(string))
+func localnameFmt(w io.Writer, format string, x ...interface{}) {
+	_, localname := pathutil.Split(x[0].(string))
 	template.HTMLEscape(w, []byte(localname))
 }
 
diff --git a/src/cmd/godoc/main.go b/src/cmd/godoc/main.go
index 6b94ff5612..0e8c0ed97f 100644
--- a/src/cmd/godoc/main.go
+++ b/src/cmd/godoc/main.go
@@ -367,7 +367,7 @@ func main() {
 				if i > 0 {
 					fmt.Println()
 				}
-				writeAny(os.Stdout, d, *html)
+				writeAny(os.Stdout, *html, d)
 				fmt.Println()
 			}
 			return
diff --git a/src/pkg/template/format.go b/src/pkg/template/format.go
index 8a31de970a..9156b08081 100644
--- a/src/pkg/template/format.go
+++ b/src/pkg/template/format.go
@@ -16,12 +16,14 @@ import (
 // It is stored under the name "str" and is the default formatter.
 // You can override the default formatter by storing your default
 // under the name "" in your custom formatter map.
-func StringFormatter(w io.Writer, value interface{}, format string) {
-	if b, ok := value.([]byte); ok {
-		w.Write(b)
-		return
+func StringFormatter(w io.Writer, format string, value ...interface{}) {
+	if len(value) == 1 {
+		if b, ok := value[0].([]byte); ok {
+			w.Write(b)
+			return
+		}
 	}
-	fmt.Fprint(w, value)
+	fmt.Fprint(w, value...)
 }
 
 var (
@@ -60,11 +62,15 @@ func HTMLEscape(w io.Writer, s []byte) {
 }
 
 // HTMLFormatter formats arbitrary values for HTML
-func HTMLFormatter(w io.Writer, value interface{}, format string) {
-	b, ok := value.([]byte)
+func HTMLFormatter(w io.Writer, format string, value ...interface{}) {
+	ok := false
+	var b []byte
+	if len(value) == 1 {
+		b, ok = value[0].([]byte)
+	}
 	if !ok {
 		var buf bytes.Buffer
-		fmt.Fprint(&buf, value)
+		fmt.Fprint(&buf, value...)
 		b = buf.Bytes()
 	}
 	HTMLEscape(w, b)
diff --git a/src/pkg/template/template.go b/src/pkg/template/template.go
index 082c06261b..b750fc60e8 100644
--- a/src/pkg/template/template.go
+++ b/src/pkg/template/template.go
@@ -55,9 +55,10 @@
 	map passed to the template set up routines or in the default
 	set ("html","str","") and is used to process the data for
 	output.  The formatter function has signature
-		func(wr io.Writer, data interface{}, formatter string)
-	where wr is the destination for output, data is the field
-	value, and formatter is its name at the invocation site.
+		func(wr io.Writer, formatter string, data ...interface{})
+	where wr is the destination for output, data holds the field
+	values at the instantiation, and formatter is its name at
+	the invocation site.
 */
 package template
 
@@ -101,7 +102,7 @@ const (
 
 // FormatterMap is the type describing the mapping from formatter
 // names to the functions that implement them.
-type FormatterMap map[string]func(io.Writer, interface{}, string)
+type FormatterMap map[string]func(io.Writer, string, ...interface{})
 
 // Built-in formatters.
 var builtins = FormatterMap{
@@ -690,13 +691,13 @@ func (t *Template) writeVariable(v *variableElement, st *state) {
 	// is it in user-supplied map?
 	if t.fmap != nil {
 		if fn, ok := t.fmap[formatter]; ok {
-			fn(st.wr, val, formatter)
+			fn(st.wr, formatter, val)
 			return
 		}
 	}
 	// is it in builtin map?
 	if fn, ok := builtins[formatter]; ok {
-		fn(st.wr, val, formatter)
+		fn(st.wr, formatter, val)
 		return
 	}
 	t.execError(st, v.linenum, "missing formatter %s for variable %s", formatter, v.name)
diff --git a/src/pkg/template/template_test.go b/src/pkg/template/template_test.go
index 00fd69a029..d66394bf78 100644
--- a/src/pkg/template/template_test.go
+++ b/src/pkg/template/template_test.go
@@ -76,9 +76,12 @@ func plus1(v interface{}) string {
 	return fmt.Sprint(i + 1)
 }
 
-func writer(f func(interface{}) string) func(io.Writer, interface{}, string) {
-	return func(w io.Writer, v interface{}, format string) {
-		io.WriteString(w, f(v))
+func writer(f func(interface{}) string) func(io.Writer, string, ...interface{}) {
+	return func(w io.Writer, format string, v ...interface{}) {
+		if len(v) != 1 {
+			panic("test writer expected one arg")
+		}
+		io.WriteString(w, f(v[0]))
 	}
 }
 
@@ -601,7 +604,7 @@ func TestHTMLFormatterWithByte(t *testing.T) {
 	s := "Test string."
 	b := []byte(s)
 	var buf bytes.Buffer
-	HTMLFormatter(&buf, b, "")
+	HTMLFormatter(&buf, "", b)
 	bs := buf.String()
 	if bs != s {
 		t.Errorf("munged []byte, expected: %s got: %s", s, bs)