text/template/parse: print TextNodes using %s not %q

This means that printing a Node will produce output that can be used as valid input.
It won't be exactly the same - some spacing may be different - but it will mean the same.

Fixes #4593.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/12006047

src/pkg/text/template/multi_test.go

@@ -33,10 +33,10 @@ var multiParseTests = []multiParseTest{
 		nil},
 	{"one", `{{define "foo"}} FOO {{end}}`, noError,
 		[]string{"foo"},
-		[]string{`" FOO "`}},
+		[]string{" FOO "}},
 	{"two", `{{define "foo"}} FOO {{end}}{{define "bar"}} BAR {{end}}`, noError,
 		[]string{"foo", "bar"},
-		[]string{`" FOO "`, `" BAR "`}},
+		[]string{" FOO ", " BAR "}},
 	// errors
 	{"missing end", `{{define "foo"}} FOO `, hasError,
 		nil,

src/pkg/text/template/parse/node.go

@@ -13,6 +13,8 @@ import (
 	"strings"
 )
 
+var textFormat = "%s" // Changed to "%q" in tests for better error messages.
+
 // A Node is an element in the parse tree. The interface is trivial.
 // The interface contains an unexported method so that only
 // types local to this package can satisfy it.
@@ -125,7 +127,7 @@ func newText(pos Pos, text string) *TextNode {
 }
 
 func (t *TextNode) String() string {
-	return fmt.Sprintf("%q", t.Text)
+	return fmt.Sprintf(textFormat, t.Text)
 }
 
 func (t *TextNode) Copy() Node {

src/pkg/text/template/parse/parse_test.go

@@ -256,6 +256,8 @@ var builtins = map[string]interface{}{
 }
 
 func testParse(doCopy bool, t *testing.T) {
+	textFormat = "%q"
+	defer func() { textFormat = "%s" }()
 	for _, test := range parseTests {
 		tmpl, err := New(test.name).Parse(test.input, "", "", make(map[string]*Tree), builtins)
 		switch {