template: move the empty check into parse, which needs it when constructing

tree sets.

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5449062

src/pkg/text/template/multi_test.go

@@ -13,35 +13,6 @@ import (
 	"text/template/parse"
 )
 
-type isEmptyTest struct {
-	name  string
-	input string
-	empty bool
-}
-
-var isEmptyTests = []isEmptyTest{
-	{"empty", ``, true},
-	{"nonempty", `hello`, false},
-	{"spaces only", " \t\n \t\n", true},
-	{"definition", `{{define "x"}}something{{end}}`, true},
-	{"definitions and space", "{{define `x`}}something{{end}}\n\n{{define `y`}}something{{end}}\n\n", true},
-	{"definitions and text", "{{define `x`}}something{{end}}\nx\n{{define `y`}}something{{end}}\ny\n}}", false},
-	{"definition and action", "{{define `x`}}something{{end}}{{if 3}}foo{{end}}", false},
-}
-
-func TestIsEmpty(t *testing.T) {
-	for _, test := range isEmptyTests {
-		template, err := New("root").Parse(test.input)
-		if err != nil {
-			t.Errorf("%q: unexpected error: %v", test.name, err)
-			continue
-		}
-		if empty := isEmpty(template.Root); empty != test.empty {
-			t.Errorf("%q: expected %t got %t", test.name, test.empty, empty)
-		}
-	}
-}
-
 const (
 	noError  = true
 	hasError = false

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

@@ -7,6 +7,7 @@
 package parse
 
 import (
+	"bytes"
 	"fmt"
 	"runtime"
 	"strconv"
@@ -177,10 +178,37 @@ func (t *Tree) Parse(s, leftDelim, rightDelim string, treeSet map[string]*Tree,
 
 // add adds tree to the treeSet.
 func (t *Tree) add(treeSet map[string]*Tree) {
-	if _, present := treeSet[t.Name]; present {
+	tree := treeSet[t.Name]
+	if tree == nil || IsEmptyTree(tree.Root) {
+		treeSet[t.Name] = t
+		return
+	}
+	if !IsEmptyTree(t.Root) {
 		t.errorf("template: multiple definition of template %q", t.Name)
 	}
-	treeSet[t.Name] = t
+}
+
+// IsEmptyTree reports whether this tree (node) is empty of everything but space.
+func IsEmptyTree(n Node) bool {
+	switch n := n.(type) {
+	case *ActionNode:
+	case *IfNode:
+	case *ListNode:
+		for _, node := range n.Nodes {
+			if !IsEmptyTree(node) {
+				return false
+			}
+		}
+		return true
+	case *RangeNode:
+	case *TemplateNode:
+	case *TextNode:
+		return len(bytes.TrimSpace(n.Text)) == 0
+	case *WithNode:
+	default:
+		panic("unknown node: " + n.String())
+	}
+	return false
 }
 
 // parse is the top-level parser for a template, essentially the same

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

@@ -257,3 +257,32 @@ func TestParse(t *testing.T) {
 		}
 	}
 }
+
+type isEmptyTest struct {
+	name  string
+	input string
+	empty bool
+}
+
+var isEmptyTests = []isEmptyTest{
+	{"empty", ``, true},
+	{"nonempty", `hello`, false},
+	{"spaces only", " \t\n \t\n", true},
+	{"definition", `{{define "x"}}something{{end}}`, true},
+	{"definitions and space", "{{define `x`}}something{{end}}\n\n{{define `y`}}something{{end}}\n\n", true},
+	{"definitions and text", "{{define `x`}}something{{end}}\nx\n{{define `y`}}something{{end}}\ny\n}}", false},
+	{"definition and action", "{{define `x`}}something{{end}}{{if 3}}foo{{end}}", false},
+}
+
+func TestIsEmpty(t *testing.T) {
+	for _, test := range isEmptyTests {
+		tree, err := New("root").Parse(test.input, "", "", make(map[string]*Tree), nil)
+		if err != nil {
+			t.Errorf("%q: unexpected error: %v", test.name, err)
+			continue
+		}
+		if empty := IsEmptyTree(tree.Root); empty != test.empty {
+			t.Errorf("%q: expected %t got %t", test.name, test.empty, empty)
+		}
+	}
+}

src/pkg/text/template/template.go

@@ -5,7 +5,6 @@
 package template
 
 import (
-	"bytes"
 	"fmt"
 	"reflect"
 	"text/template/parse"
@@ -198,8 +197,8 @@ func (t *Template) associate(new *Template) error {
 	}
 	name := new.name
 	if old := t.tmpl[name]; old != nil {
-		oldIsEmpty := isEmpty(old.Root)
-		newIsEmpty := isEmpty(new.Root)
+		oldIsEmpty := parse.IsEmptyTree(old.Root)
+		newIsEmpty := parse.IsEmptyTree(new.Root)
 		if !oldIsEmpty && !newIsEmpty {
 			return fmt.Errorf("template: redefinition of template %q", name)
 		}
@@ -211,26 +210,3 @@ func (t *Template) associate(new *Template) error {
 	t.tmpl[name] = new
 	return nil
 }
-
-// isEmpty reports whether this tree (node) is empty of everything but space.
-func isEmpty(n parse.Node) bool {
-	switch n := n.(type) {
-	case *parse.ActionNode:
-	case *parse.IfNode:
-	case *parse.ListNode:
-		for _, node := range n.Nodes {
-			if !isEmpty(node) {
-				return false
-			}
-		}
-		return true
-	case *parse.RangeNode:
-	case *parse.TemplateNode:
-	case *parse.TextNode:
-		return len(bytes.TrimSpace(n.Text)) == 0
-	case *parse.WithNode:
-	default:
-		panic("unknown node: " + n.String())
-	}
-	return false
-}