libgo: Update to go1.6rc1.

    
    Reviewed-on: https://go-review.googlesource.com/19200

From-SVN: r233110

11 files changed, 553 insertions, 152 deletions

diff --git a/libgo/go/text/scanner/scanner.go b/libgo/go/text/scanner/scanner.go
index 3ab01ed..0155800 100644
--- a/libgo/go/text/scanner/scanner.go
+++ b/libgo/go/text/scanner/scanner.go
@@ -73,7 +73,7 @@ const (
 	GoTokens       = ScanIdents | ScanFloats | ScanChars | ScanStrings | ScanRawStrings | ScanComments | SkipComments
 )
 
-// The result of Scan is one of the following tokens or a Unicode character.
+// The result of Scan is one of these tokens or a Unicode character.
 const (
 	EOF = -(iota + 1)
 	Ident
diff --git a/libgo/go/text/template/doc.go b/libgo/go/text/template/doc.go
index 0ce63f6..df8c95f 100644
--- a/libgo/go/text/template/doc.go
+++ b/libgo/go/text/template/doc.go
@@ -36,10 +36,35 @@ Here is a trivial example that prints "17 items are made of wool".
 
 More intricate examples appear below.
 
+Text and spaces
+
+By default, all text between actions is copied verbatim when the template is
+executed. For example, the string " items are made of " in the example above appears
+on standard output when the program is run.
+
+However, to aid in formatting template source code, if an action's left delimiter
+(by default "{{") is followed immediately by a minus sign and ASCII space character
+("{{- "), all trailing white space is trimmed from the immediately preceding text.
+Similarly, if the right delimiter ("}}") is preceded by a space and minus sign
+(" -}}"), all leading white space is trimmed from the immediately following text.
+In these trim markers, the ASCII space must be present; "{{-3}}" parses as an
+action containing the number -3.
+
+For instance, when executing the template whose source is
+
+	"{{23 -}} < {{- 45}}"
+
+the generated output would be
+
+	"23<45"
+
+For this trimming, the definition of white space characters is the same as in Go:
+space, horizontal tab, carriage return, and newline.
+
 Actions
 
 Here is the list of actions. "Arguments" and "pipelines" are evaluations of
-data, defined in detail below.
+data, defined in detail in the corresponding sections that follow.
 
 */
 //	{{/* a comment */}}
@@ -90,6 +115,14 @@ data, defined in detail below.
 		The template with the specified name is executed with dot set
 		to the value of the pipeline.
 
+	{{block "name" pipeline}} T1 {{end}}
+		A block is shorthand for defining a template
+			{{define "name"}} T1 {{end}}
+		and then executing it in place
+			{{template "name" .}}
+		The typical use is to define a set of root templates that are
+		then customized by redefining the block templates within.
+
 	{{with pipeline}} T1 {{end}}
 		If the value of the pipeline is empty, no output is generated;
 		otherwise, dot is set to the value of the pipeline and T1 is
@@ -167,6 +200,8 @@ field of a struct, the function is not invoked automatically, but it
 can be used as a truth value for an if action and the like. To invoke
 it, use the call function, defined below.
 
+Pipelines
+
 A pipeline is a possibly chained sequence of "commands". A command is a simple
 value (argument) or a function or method call, possibly with multiple arguments:
 
@@ -184,8 +219,6 @@ value (argument) or a function or method call, possibly with multiple arguments:
 			function(Argument1, etc.)
 		Functions and function names are described below.
 
-Pipelines
-
 A pipeline may be "chained" by separating a sequence of commands with pipeline
 characters '|'. In a chained pipeline, the result of the each command is
 passed as the last argument of the following command. The output of the final
diff --git a/libgo/go/text/template/exec.go b/libgo/go/text/template/exec.go
index daba788..efe1817 100644
--- a/libgo/go/text/template/exec.go
+++ b/libgo/go/text/template/exec.go
@@ -78,7 +78,23 @@ func doublePercent(str string) string {
 	return str
 }
 
-// errorf formats the error and terminates processing.
+// TODO: It would be nice if ExecError was more broken down, but
+// the way ErrorContext embeds the template name makes the
+// processing too clumsy.
+
+// ExecError is the custom error type returned when Execute has an
+// error evaluating its template. (If a write error occurs, the actual
+// error is returned; it will not be of type ExecError.)
+type ExecError struct {
+	Name string // Name of template.
+	Err  error  // Pre-formatted error.
+}
+
+func (e ExecError) Error() string {
+	return e.Err.Error()
+}
+
+// errorf records an ExecError and terminates processing.
 func (s *state) errorf(format string, args ...interface{}) {
 	name := doublePercent(s.tmpl.Name())
 	if s.node == nil {
@@ -87,7 +103,24 @@ func (s *state) errorf(format string, args ...interface{}) {
 		location, context := s.tmpl.ErrorContext(s.node)
 		format = fmt.Sprintf("template: %s: executing %q at <%s>: %s", location, name, doublePercent(context), format)
 	}
-	panic(fmt.Errorf(format, args...))
+	panic(ExecError{
+		Name: s.tmpl.Name(),
+		Err:  fmt.Errorf(format, args...),
+	})
+}
+
+// writeError is the wrapper type used internally when Execute has an
+// error writing to its output. We strip the wrapper in errRecover.
+// Note that this is not an implementation of error, so it cannot escape
+// from the package as an error value.
+type writeError struct {
+	Err error // Original error.
+}
+
+func (s *state) writeError(err error) {
+	panic(writeError{
+		Err: err,
+	})
 }
 
 // errRecover is the handler that turns panics into returns from the top
@@ -98,8 +131,10 @@ func errRecover(errp *error) {
 		switch err := e.(type) {
 		case runtime.Error:
 			panic(e)
-		case error:
-			*errp = err
+		case writeError:
+			*errp = err.Err // Strip the wrapper.
+		case ExecError:
+			*errp = err // Keep the wrapper.
 		default:
 			panic(e)
 		}
@@ -145,7 +180,7 @@ func (t *Template) Execute(wr io.Writer, data interface{}) (err error) {
 }
 
 // DefinedTemplates returns a string listing the defined templates,
-// prefixed by the string "defined templates are: ". If there are none,
+// prefixed by the string "; defined templates are: ". If there are none,
 // it returns the empty string. For generating an error message here
 // and in html/template.
 func (t *Template) DefinedTemplates() string {
@@ -193,7 +228,7 @@ func (s *state) walk(dot reflect.Value, node parse.Node) {
 		s.walkTemplate(dot, node)
 	case *parse.TextNode:
 		if _, err := s.wr.Write(node.Text); err != nil {
-			s.errorf("%s", err)
+			s.writeError(err)
 		}
 	case *parse.WithNode:
 		s.walkIfOrWith(parse.NodeWith, dot, node.Pipe, node.List, node.ElseList)
@@ -222,8 +257,13 @@ func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.
 	}
 }
 
-// isTrue reports whether the value is 'true', in the sense of not the zero of its type,
-// and whether the value has a meaningful truth value.
+// IsTrue reports whether the value is 'true', in the sense of not the zero of its type,
+// and whether the value has a meaningful truth value. This is the definition of
+// truth used by if and other such actions.
+func IsTrue(val interface{}) (truth, ok bool) {
+	return isTrue(reflect.ValueOf(val))
+}
+
 func isTrue(val reflect.Value) (truth, ok bool) {
 	if !val.IsValid() {
 		// Something like var x interface{}, never set. It's a form of nil.
@@ -483,7 +523,7 @@ func (s *state) evalField(dot reflect.Value, fieldName string, node parse.Node,
 		return zero
 	}
 	typ := receiver.Type()
-	receiver, _ = indirect(receiver)
+	receiver, isNil := indirect(receiver)
 	// Unless it's an interface, need to get to a value of type *T to guarantee
 	// we see all methods of T and *T.
 	ptr := receiver
@@ -495,7 +535,6 @@ func (s *state) evalField(dot reflect.Value, fieldName string, node parse.Node,
 	}
 	hasArgs := len(args) > 1 || final.IsValid()
 	// It's not a method; must be a field of a struct or an element of a map. The receiver must not be nil.
-	receiver, isNil := indirect(receiver)
 	if isNil {
 		s.errorf("nil pointer evaluating %s.%s", typ, fieldName)
 	}
@@ -789,16 +828,11 @@ func (s *state) evalEmptyInterface(dot reflect.Value, n parse.Node) reflect.Valu
 }
 
 // indirect returns the item at the end of indirection, and a bool to indicate if it's nil.
-// We indirect through pointers and empty interfaces (only) because
-// non-empty interfaces have methods we might need.
 func indirect(v reflect.Value) (rv reflect.Value, isNil bool) {
 	for ; v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface; v = v.Elem() {
 		if v.IsNil() {
 			return v, true
 		}
-		if v.Kind() == reflect.Interface && v.NumMethod() > 0 {
-			break
-		}
 	}
 	return v, false
 }
@@ -811,7 +845,10 @@ func (s *state) printValue(n parse.Node, v reflect.Value) {
 	if !ok {
 		s.errorf("can't print %s of type %s", n, v.Type())
 	}
-	fmt.Fprint(s.wr, iface)
+	_, err := fmt.Fprint(s.wr, iface)
+	if err != nil {
+		s.writeError(err)
+	}
 }
 
 // printableValue returns the, possibly indirected, interface value inside v that
diff --git a/libgo/go/text/template/exec_test.go b/libgo/go/text/template/exec_test.go
index ba0e434..e507e91 100644
--- a/libgo/go/text/template/exec_test.go
+++ b/libgo/go/text/template/exec_test.go
@@ -9,6 +9,7 @@ import (
 	"errors"
 	"flag"
 	"fmt"
+	"io/ioutil"
 	"reflect"
 	"strings"
 	"testing"
@@ -50,8 +51,9 @@ type T struct {
 	Empty2 interface{}
 	Empty3 interface{}
 	Empty4 interface{}
-	// Non-empty interface.
-	NonEmptyInterface I
+	// Non-empty interfaces.
+	NonEmptyInterface    I
+	NonEmptyInterfacePtS *I
 	// Stringer.
 	Str fmt.Stringer
 	Err error
@@ -72,6 +74,12 @@ type T struct {
 	unexported int
 }
 
+type S []string
+
+func (S) Method0() string {
+	return "M0"
+}
+
 type U struct {
 	V string
 }
@@ -98,6 +106,8 @@ func (w *W) Error() string {
 	return fmt.Sprintf("[%d]", w.k)
 }
 
+var siVal = I(S{"a", "b"})
+
 var tVal = &T{
 	True:   true,
 	I:      17,
@@ -118,22 +128,23 @@ var tVal = &T{
 		{"one": 1, "two": 2},
 		{"eleven": 11, "twelve": 12},
 	},
-	Empty1:            3,
-	Empty2:            "empty2",
-	Empty3:            []int{7, 8},
-	Empty4:            &U{"UinEmpty"},
-	NonEmptyInterface: new(T),
-	Str:               bytes.NewBuffer([]byte("foozle")),
-	Err:               errors.New("erroozle"),
-	PI:                newInt(23),
-	PS:                newString("a string"),
-	PSI:               newIntSlice(21, 22, 23),
-	BinaryFunc:        func(a, b string) string { return fmt.Sprintf("[%s=%s]", a, b) },
-	VariadicFunc:      func(s ...string) string { return fmt.Sprint("<", strings.Join(s, "+"), ">") },
-	VariadicFuncInt:   func(a int, s ...string) string { return fmt.Sprint(a, "=<", strings.Join(s, "+"), ">") },
-	NilOKFunc:         func(s *int) bool { return s == nil },
-	ErrFunc:           func() (string, error) { return "bla", nil },
-	Tmpl:              Must(New("x").Parse("test template")), // "x" is the value of .X
+	Empty1:               3,
+	Empty2:               "empty2",
+	Empty3:               []int{7, 8},
+	Empty4:               &U{"UinEmpty"},
+	NonEmptyInterface:    &T{X: "x"},
+	NonEmptyInterfacePtS: &siVal,
+	Str:                  bytes.NewBuffer([]byte("foozle")),
+	Err:                  errors.New("erroozle"),
+	PI:                   newInt(23),
+	PS:                   newString("a string"),
+	PSI:                  newIntSlice(21, 22, 23),
+	BinaryFunc:           func(a, b string) string { return fmt.Sprintf("[%s=%s]", a, b) },
+	VariadicFunc:         func(s ...string) string { return fmt.Sprint("<", strings.Join(s, "+"), ">") },
+	VariadicFuncInt:      func(a int, s ...string) string { return fmt.Sprint(a, "=<", strings.Join(s, "+"), ">") },
+	NilOKFunc:            func(s *int) bool { return s == nil },
+	ErrFunc:              func() (string, error) { return "bla", nil },
+	Tmpl:                 Must(New("x").Parse("test template")), // "x" is the value of .X
 }
 
 // A non-empty interface.
@@ -336,6 +347,7 @@ var execTests = []execTest{
 	{"if not .BinaryFunc call", "{{ if not .BinaryFunc}}{{call .BinaryFunc `1` `2`}}{{else}}No{{end}}", "No", tVal, true},
 	{"Interface Call", `{{stringer .S}}`, "foozle", map[string]interface{}{"S": bytes.NewBufferString("foozle")}, true},
 	{".ErrFunc", "{{call .ErrFunc}}", "bla", tVal, true},
+	{"call nil", "{{call nil}}", "", tVal, false},
 
 	// Erroneous function calls (check args).
 	{".BinaryFuncTooFew", "{{call .BinaryFunc `1`}}", "", tVal, false},
@@ -424,12 +436,15 @@ var execTests = []execTest{
 	{"slice[1]", "{{index .SI 1}}", "4", tVal, true},
 	{"slice[HUGE]", "{{index .SI 10}}", "", tVal, false},
 	{"slice[WRONG]", "{{index .SI `hello`}}", "", tVal, false},
+	{"slice[nil]", "{{index .SI nil}}", "", tVal, false},
 	{"map[one]", "{{index .MSI `one`}}", "1", tVal, true},
 	{"map[two]", "{{index .MSI `two`}}", "2", tVal, true},
 	{"map[NO]", "{{index .MSI `XXX`}}", "0", tVal, true},
-	{"map[nil]", "{{index .MSI nil}}", "0", tVal, true},
+	{"map[nil]", "{{index .MSI nil}}", "", tVal, false},
+	{"map[``]", "{{index .MSI ``}}", "0", tVal, true},
 	{"map[WRONG]", "{{index .MSI 10}}", "", tVal, false},
 	{"double index", "{{index .SMSI 1 `eleven`}}", "11", tVal, true},
+	{"nil[1]", "{{index nil 1}}", "", tVal, false},
 
 	// Len.
 	{"slice", "{{len .SI}}", "3", tVal, true},
@@ -545,6 +560,11 @@ var execTests = []execTest{
 	{"bug16i", "{{\"aaa\"|oneArg}}", "oneArg=aaa", tVal, true},
 	{"bug16j", "{{1+2i|printf \"%v\"}}", "(1+2i)", tVal, true},
 	{"bug16k", "{{\"aaa\"|printf }}", "aaa", tVal, true},
+	{"bug17a", "{{.NonEmptyInterface.X}}", "x", tVal, true},
+	{"bug17b", "-{{.NonEmptyInterface.Method1 1234}}-", "-1234-", tVal, true},
+	{"bug17c", "{{len .NonEmptyInterfacePtS}}", "2", tVal, true},
+	{"bug17d", "{{index .NonEmptyInterfacePtS 0}}", "a", tVal, true},
+	{"bug17e", "{{range .NonEmptyInterfacePtS}}-{{.}}-{{end}}", "-a--b-", tVal, true},
 }
 
 func zeroArgs() string {
@@ -796,18 +816,19 @@ type Tree struct {
 }
 
 // Use different delimiters to test Set.Delims.
+// Also test the trimming of leading and trailing spaces.
 const treeTemplate = `
-	(define "tree")
+	(- define "tree" -)
 	[
-		(.Val)
-		(with .Left)
-			(template "tree" .)
-		(end)
-		(with .Right)
-			(template "tree" .)
-		(end)
+		(- .Val -)
+		(- with .Left -)
+			(template "tree" . -)
+		(- end -)
+		(- with .Right -)
+			(- template "tree" . -)
+		(- end -)
 	]
-	(end)
+	(- end -)
 `
 
 func TestTree(t *testing.T) {
@@ -852,19 +873,13 @@ func TestTree(t *testing.T) {
 		t.Fatal("parse error:", err)
 	}
 	var b bytes.Buffer
-	stripSpace := func(r rune) rune {
-		if r == '\t' || r == '\n' {
-			return -1
-		}
-		return r
-	}
 	const expect = "[1[2[3[4]][5[6]]][7[8[9]][10[11]]]]"
 	// First by looking up the template.
 	err = tmpl.Lookup("tree").Execute(&b, tree)
 	if err != nil {
 		t.Fatal("exec error:", err)
 	}
-	result := strings.Map(stripSpace, b.String())
+	result := b.String()
 	if result != expect {
 		t.Errorf("expected %q got %q", expect, result)
 	}
@@ -874,7 +889,7 @@ func TestTree(t *testing.T) {
 	if err != nil {
 		t.Fatal("exec error:", err)
 	}
-	result = strings.Map(stripSpace, b.String())
+	result = b.String()
 	if result != expect {
 		t.Errorf("expected %q got %q", expect, result)
 	}
@@ -1141,3 +1156,127 @@ func TestUnterminatedStringError(t *testing.T) {
 		t.Fatalf("unexpected error: %s", str)
 	}
 }
+
+const alwaysErrorText = "always be failing"
+
+var alwaysError = errors.New(alwaysErrorText)
+
+type ErrorWriter int
+
+func (e ErrorWriter) Write(p []byte) (int, error) {
+	return 0, alwaysError
+}
+
+func TestExecuteGivesExecError(t *testing.T) {
+	// First, a non-execution error shouldn't be an ExecError.
+	tmpl, err := New("X").Parse("hello")
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = tmpl.Execute(ErrorWriter(0), 0)
+	if err == nil {
+		t.Fatal("expected error; got none")
+	}
+	if err.Error() != alwaysErrorText {
+		t.Errorf("expected %q error; got %q", alwaysErrorText, err)
+	}
+	// This one should be an ExecError.
+	tmpl, err = New("X").Parse("hello, {{.X.Y}}")
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = tmpl.Execute(ioutil.Discard, 0)
+	if err == nil {
+		t.Fatal("expected error; got none")
+	}
+	eerr, ok := err.(ExecError)
+	if !ok {
+		t.Fatalf("did not expect ExecError %s", eerr)
+	}
+	expect := "field X in type int"
+	if !strings.Contains(err.Error(), expect) {
+		t.Errorf("expected %q; got %q", expect, err)
+	}
+}
+
+func funcNameTestFunc() int {
+	return 0
+}
+
+func TestGoodFuncNames(t *testing.T) {
+	names := []string{
+		"_",
+		"a",
+		"a1",
+		"a1",
+		"Ӵ",
+	}
+	for _, name := range names {
+		tmpl := New("X").Funcs(
+			FuncMap{
+				name: funcNameTestFunc,
+			},
+		)
+		if tmpl == nil {
+			t.Fatalf("nil result for %q", name)
+		}
+	}
+}
+
+func TestBadFuncNames(t *testing.T) {
+	names := []string{
+		"",
+		"2",
+		"a-b",
+	}
+	for _, name := range names {
+		testBadFuncName(name, t)
+	}
+}
+
+func testBadFuncName(name string, t *testing.T) {
+	defer func() {
+		recover()
+	}()
+	New("X").Funcs(
+		FuncMap{
+			name: funcNameTestFunc,
+		},
+	)
+	// If we get here, the name did not cause a panic, which is how Funcs
+	// reports an error.
+	t.Errorf("%q succeeded incorrectly as function name", name)
+}
+
+func TestBlock(t *testing.T) {
+	const (
+		input   = `a({{block "inner" .}}bar({{.}})baz{{end}})b`
+		want    = `a(bar(hello)baz)b`
+		overlay = `{{define "inner"}}foo({{.}})bar{{end}}`
+		want2   = `a(foo(goodbye)bar)b`
+	)
+	tmpl, err := New("outer").Parse(input)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tmpl2, err := Must(tmpl.Clone()).Parse(overlay)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var buf bytes.Buffer
+	if err := tmpl.Execute(&buf, "hello"); err != nil {
+		t.Fatal(err)
+	}
+	if got := buf.String(); got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+
+	buf.Reset()
+	if err := tmpl2.Execute(&buf, "goodbye"); err != nil {
+		t.Fatal(err)
+	}
+	if got := buf.String(); got != want2 {
+		t.Errorf("got %q, want %q", got, want2)
+	}
+}
diff --git a/libgo/go/text/template/funcs.go b/libgo/go/text/template/funcs.go
index ccd0dfc..49e9e74 100644
--- a/libgo/go/text/template/funcs.go
+++ b/libgo/go/text/template/funcs.go
@@ -58,6 +58,9 @@ func createValueFuncs(funcMap FuncMap) map[string]reflect.Value {
 // addValueFuncs adds to values the functions in funcs, converting them to reflect.Values.
 func addValueFuncs(out map[string]reflect.Value, in FuncMap) {
 	for name, fn := range in {
+		if !goodName(name) {
+			panic(fmt.Errorf("function name %s is not a valid identifier", name))
+		}
 		v := reflect.ValueOf(fn)
 		if v.Kind() != reflect.Func {
 			panic("value for " + name + " not a function")
@@ -77,7 +80,7 @@ func addFuncs(out, in FuncMap) {
 	}
 }
 
-// goodFunc checks that the function or method has the right result signature.
+// goodFunc reports whether the function or method has the right result signature.
 func goodFunc(typ reflect.Type) bool {
 	// We allow functions with 1 result or 2 results where the second is an error.
 	switch {
@@ -89,6 +92,23 @@ func goodFunc(typ reflect.Type) bool {
 	return false
 }
 
+// goodName reports whether the function name is a valid identifier.
+func goodName(name string) bool {
+	if name == "" {
+		return false
+	}
+	for i, r := range name {
+		switch {
+		case r == '_':
+		case i == 0 && !unicode.IsLetter(r):
+			return false
+		case !unicode.IsLetter(r) && !unicode.IsDigit(r):
+			return false
+		}
+	}
+	return true
+}
+
 // findFunction looks for a function in the template, and global map.
 func findFunction(name string, tmpl *Template) (reflect.Value, bool) {
 	if tmpl != nil && tmpl.common != nil {
@@ -104,6 +124,21 @@ func findFunction(name string, tmpl *Template) (reflect.Value, bool) {
 	return reflect.Value{}, false
 }
 
+// prepareArg checks if value can be used as an argument of type argType, and
+// converts an invalid value to appropriate zero if possible.
+func prepareArg(value reflect.Value, argType reflect.Type) (reflect.Value, error) {
+	if !value.IsValid() {
+		if !canBeNil(argType) {
+			return reflect.Value{}, fmt.Errorf("value is nil; should be of type %s", argType)
+		}
+		value = reflect.Zero(argType)
+	}
+	if !value.Type().AssignableTo(argType) {
+		return reflect.Value{}, fmt.Errorf("value has type %s; should be %s", value.Type(), argType)
+	}
+	return value, nil
+}
+
 // Indexing.
 
 // index returns the result of indexing its first argument by the following
@@ -111,6 +146,9 @@ func findFunction(name string, tmpl *Template) (reflect.Value, bool) {
 // indexed item must be a map, slice, or array.
 func index(item interface{}, indices ...interface{}) (interface{}, error) {
 	v := reflect.ValueOf(item)
+	if !v.IsValid() {
+		return nil, fmt.Errorf("index of untyped nil")
+	}
 	for _, i := range indices {
 		index := reflect.ValueOf(i)
 		var isNil bool
@@ -125,6 +163,8 @@ func index(item interface{}, indices ...interface{}) (interface{}, error) {
 				x = index.Int()
 			case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
 				x = int64(index.Uint())
+			case reflect.Invalid:
+				return nil, fmt.Errorf("cannot index slice/array with nil")
 			default:
 				return nil, fmt.Errorf("cannot index slice/array with type %s", index.Type())
 			}
@@ -133,17 +173,18 @@ func index(item interface{}, indices ...interface{}) (interface{}, error) {
 			}
 			v = v.Index(int(x))
 		case reflect.Map:
-			if !index.IsValid() {
-				index = reflect.Zero(v.Type().Key())
-			}
-			if !index.Type().AssignableTo(v.Type().Key()) {
-				return nil, fmt.Errorf("%s is not index type for %s", index.Type(), v.Type())
+			index, err := prepareArg(index, v.Type().Key())
+			if err != nil {
+				return nil, err
 			}
 			if x := v.MapIndex(index); x.IsValid() {
 				v = x
 			} else {
 				v = reflect.Zero(v.Type().Elem())
 			}
+		case reflect.Invalid:
+			// the loop holds invariant: v.IsValid()
+			panic("unreachable")
 		default:
 			return nil, fmt.Errorf("can't index item of type %s", v.Type())
 		}
@@ -155,7 +196,11 @@ func index(item interface{}, indices ...interface{}) (interface{}, error) {
 
 // length returns the length of the item, with an error if it has no defined length.
 func length(item interface{}) (int, error) {
-	v, isNil := indirect(reflect.ValueOf(item))
+	v := reflect.ValueOf(item)
+	if !v.IsValid() {
+		return 0, fmt.Errorf("len of untyped nil")
+	}
+	v, isNil := indirect(v)
 	if isNil {
 		return 0, fmt.Errorf("len of nil pointer")
 	}
@@ -172,6 +217,9 @@ func length(item interface{}) (int, error) {
 // The function must return 1 result, or 2 results, the second of which is an error.
 func call(fn interface{}, args ...interface{}) (interface{}, error) {
 	v := reflect.ValueOf(fn)
+	if !v.IsValid() {
+		return nil, fmt.Errorf("call of nil")
+	}
 	typ := v.Type()
 	if typ.Kind() != reflect.Func {
 		return nil, fmt.Errorf("non-function of type %s", typ)
@@ -201,13 +249,11 @@ func call(fn interface{}, args ...interface{}) (interface{}, error) {
 		} else {
 			argType = dddType
 		}
-		if !value.IsValid() && canBeNil(argType) {
-			value = reflect.Zero(argType)
-		}
-		if !value.Type().AssignableTo(argType) {
-			return nil, fmt.Errorf("arg %d has type %s; should be %s", i, value.Type(), argType)
+
+		var err error
+		if argv[i], err = prepareArg(value, argType); err != nil {
+			return nil, fmt.Errorf("arg %d: %s", i, err)
 		}
-		argv[i] = value
 	}
 	result := v.Call(argv)
 	if len(result) == 2 && !result[1].IsNil() {
@@ -219,7 +265,7 @@ func call(fn interface{}, args ...interface{}) (interface{}, error) {
 // Boolean logic.
 
 func truth(a interface{}) bool {
-	t, _ := isTrue(reflect.ValueOf(a))
+	t, _ := IsTrue(a)
 	return t
 }
 
@@ -254,9 +300,8 @@ func or(arg0 interface{}, args ...interface{}) interface{} {
 }
 
 // not returns the Boolean negation of its argument.
-func not(arg interface{}) (truth bool) {
-	truth, _ = isTrue(reflect.ValueOf(arg))
-	return !truth
+func not(arg interface{}) bool {
+	return !truth(arg)
 }
 
 // Comparison.
diff --git a/libgo/go/text/template/multi_test.go b/libgo/go/text/template/multi_test.go
index ea01875..a8342f5 100644
--- a/libgo/go/text/template/multi_test.go
+++ b/libgo/go/text/template/multi_test.go
@@ -9,7 +9,6 @@ package template
 import (
 	"bytes"
 	"fmt"
-	"strings"
 	"testing"
 	"text/template/parse"
 )
@@ -277,17 +276,11 @@ func TestRedefinition(t *testing.T) {
 	if tmpl, err = New("tmpl1").Parse(`{{define "test"}}foo{{end}}`); err != nil {
 		t.Fatalf("parse 1: %v", err)
 	}
-	if _, err = tmpl.Parse(`{{define "test"}}bar{{end}}`); err == nil {
-		t.Fatal("expected error")
+	if _, err = tmpl.Parse(`{{define "test"}}bar{{end}}`); err != nil {
+		t.Fatalf("got error %v, expected nil", err)
 	}
-	if !strings.Contains(err.Error(), "redefinition") {
-		t.Fatalf("expected redefinition error; got %v", err)
-	}
-	if _, err = tmpl.New("tmpl2").Parse(`{{define "test"}}bar{{end}}`); err == nil {
-		t.Fatal("expected error")
-	}
-	if !strings.Contains(err.Error(), "redefinition") {
-		t.Fatalf("expected redefinition error; got %v", err)
+	if _, err = tmpl.New("tmpl2").Parse(`{{define "test"}}bar{{end}}`); err != nil {
+		t.Fatalf("got error %v, expected nil", err)
 	}
 }
 
@@ -345,7 +338,6 @@ func TestNew(t *testing.T) {
 func TestParse(t *testing.T) {
 	// In multiple calls to Parse with the same receiver template, only one call
 	// can contain text other than space, comments, and template definitions
-	var err error
 	t1 := New("test")
 	if _, err := t1.Parse(`{{define "test"}}{{end}}`); err != nil {
 		t.Fatalf("parsing test: %s", err)
@@ -356,10 +348,4 @@ func TestParse(t *testing.T) {
 	if _, err := t1.Parse(`{{define "test"}}foo{{end}}`); err != nil {
 		t.Fatalf("parsing test: %s", err)
 	}
-	if _, err = t1.Parse(`{{define "test"}}foo{{end}}`); err == nil {
-		t.Fatal("no error from redefining a template")
-	}
-	if !strings.Contains(err.Error(), "redefinition") {
-		t.Fatalf("expected redefinition error; got %v", err)
-	}
 }
diff --git a/libgo/go/text/template/parse/lex.go b/libgo/go/text/template/parse/lex.go
index 8f9fe1d..ea93e05 100644
--- a/libgo/go/text/template/parse/lex.go
+++ b/libgo/go/text/template/parse/lex.go
@@ -58,6 +58,7 @@ const (
 	itemVariable   // variable starting with '$', such as '$' or  '$1' or '$hello'
 	// Keywords appear after all the rest.
 	itemKeyword  // used only to delimit the keywords
+	itemBlock    // block keyword
 	itemDot      // the cursor, spelled '.'
 	itemDefine   // define keyword
 	itemElse     // else keyword
@@ -71,6 +72,7 @@ const (
 
 var key = map[string]itemType{
 	".":        itemDot,
+	"block":    itemBlock,
 	"define":   itemDefine,
 	"else":     itemElse,
 	"end":      itemEnd,
@@ -83,6 +85,21 @@ var key = map[string]itemType{
 
 const eof = -1
 
+// Trimming spaces.
+// If the action begins "{{- " rather than "{{", then all space/tab/newlines
+// preceding the action are trimmed; conversely if it ends " -}}" the
+// leading spaces are trimmed. This is done entirely in the lexer; the
+// parser never sees it happen. We require an ASCII space to be
+// present to avoid ambiguity with things like "{{-3}}". It reads
+// better with the space present anyway. For simplicity, only ASCII
+// space does the job.
+const (
+	spaceChars      = " \t\r\n" // These are the space characters defined by Go itself.
+	leftTrimMarker  = "- "      // Attached to left delimiter, trims trailing spaces from preceding text.
+	rightTrimMarker = " -"      // Attached to right delimiter, trims leading spaces from following text.
+	trimMarkerLen   = Pos(len(leftTrimMarker))
+)
+
 // stateFn represents the state of the scanner as a function that returns the next state.
 type stateFn func(*lexer) stateFn
 
@@ -220,10 +237,18 @@ const (
 // lexText scans until an opening action delimiter, "{{".
 func lexText(l *lexer) stateFn {
 	for {
-		if strings.HasPrefix(l.input[l.pos:], l.leftDelim) {
+		delim, trimSpace := l.atLeftDelim()
+		if delim {
+			trimLength := Pos(0)
+			if trimSpace {
+				trimLength = rightTrimLength(l.input[l.start:l.pos])
+			}
+			l.pos -= trimLength
 			if l.pos > l.start {
 				l.emit(itemText)
 			}
+			l.pos += trimLength
+			l.ignore()
 			return lexLeftDelim
 		}
 		if l.next() == eof {
@@ -238,13 +263,56 @@ func lexText(l *lexer) stateFn {
 	return nil
 }
 
-// lexLeftDelim scans the left delimiter, which is known to be present.
+// atLeftDelim reports whether the lexer is at a left delimiter, possibly followed by a trim marker.
+func (l *lexer) atLeftDelim() (delim, trimSpaces bool) {
+	if !strings.HasPrefix(l.input[l.pos:], l.leftDelim) {
+		return false, false
+	}
+	// The left delim might have the marker afterwards.
+	trimSpaces = strings.HasPrefix(l.input[l.pos+Pos(len(l.leftDelim)):], leftTrimMarker)
+	return true, trimSpaces
+}
+
+// rightTrimLength returns the length of the spaces at the end of the string.
+func rightTrimLength(s string) Pos {
+	return Pos(len(s) - len(strings.TrimRight(s, spaceChars)))
+}
+
+// atRightDelim reports whether the lexer is at a right delimiter, possibly preceded by a trim marker.
+func (l *lexer) atRightDelim() (delim, trimSpaces bool) {
+	if strings.HasPrefix(l.input[l.pos:], l.rightDelim) {
+		return true, false
+	}
+	// The right delim might have the marker before.
+	if strings.HasPrefix(l.input[l.pos:], rightTrimMarker) {
+		if strings.HasPrefix(l.input[l.pos+trimMarkerLen:], l.rightDelim) {
+			return true, true
+		}
+	}
+	return false, false
+}
+
+// leftTrimLength returns the length of the spaces at the beginning of the string.
+func leftTrimLength(s string) Pos {
+	return Pos(len(s) - len(strings.TrimLeft(s, spaceChars)))
+}
+
+// lexLeftDelim scans the left delimiter, which is known to be present, possibly with a trim marker.
 func lexLeftDelim(l *lexer) stateFn {
 	l.pos += Pos(len(l.leftDelim))
-	if strings.HasPrefix(l.input[l.pos:], leftComment) {
+	trimSpace := strings.HasPrefix(l.input[l.pos:], leftTrimMarker)
+	afterMarker := Pos(0)
+	if trimSpace {
+		afterMarker = trimMarkerLen
+	}
+	if strings.HasPrefix(l.input[l.pos+afterMarker:], leftComment) {
+		l.pos += afterMarker
+		l.ignore()
 		return lexComment
 	}
 	l.emit(itemLeftDelim)
+	l.pos += afterMarker
+	l.ignore()
 	l.parenDepth = 0
 	return lexInsideAction
 }
@@ -257,19 +325,34 @@ func lexComment(l *lexer) stateFn {
 		return l.errorf("unclosed comment")
 	}
 	l.pos += Pos(i + len(rightComment))
-	if !strings.HasPrefix(l.input[l.pos:], l.rightDelim) {
+	delim, trimSpace := l.atRightDelim()
+	if !delim {
 		return l.errorf("comment ends before closing delimiter")
-
+	}
+	if trimSpace {
+		l.pos += trimMarkerLen
 	}
 	l.pos += Pos(len(l.rightDelim))
+	if trimSpace {
+		l.pos += leftTrimLength(l.input[l.pos:])
+	}
 	l.ignore()
 	return lexText
 }
 
-// lexRightDelim scans the right delimiter, which is known to be present.
+// lexRightDelim scans the right delimiter, which is known to be present, possibly with a trim marker.
 func lexRightDelim(l *lexer) stateFn {
+	trimSpace := strings.HasPrefix(l.input[l.pos:], rightTrimMarker)
+	if trimSpace {
+		l.pos += trimMarkerLen
+		l.ignore()
+	}
 	l.pos += Pos(len(l.rightDelim))
 	l.emit(itemRightDelim)
+	if trimSpace {
+		l.pos += leftTrimLength(l.input[l.pos:])
+		l.ignore()
+	}
 	return lexText
 }
 
@@ -278,7 +361,8 @@ func lexInsideAction(l *lexer) stateFn {
 	// Either number, quoted string, or identifier.
 	// Spaces separate arguments; runs of spaces turn into itemSpace.
 	// Pipe symbols separate and are emitted.
-	if strings.HasPrefix(l.input[l.pos:], l.rightDelim) {
+	delim, _ := l.atRightDelim()
+	if delim {
 		if l.parenDepth == 0 {
 			return lexRightDelim
 		}
diff --git a/libgo/go/text/template/parse/lex_test.go b/libgo/go/text/template/parse/lex_test.go
index be551d8..e35ebf1 100644
--- a/libgo/go/text/template/parse/lex_test.go
+++ b/libgo/go/text/template/parse/lex_test.go
@@ -33,6 +33,7 @@ var itemName = map[itemType]string{
 
 	// keywords
 	itemDot:      ".",
+	itemBlock:    "block",
 	itemDefine:   "define",
 	itemElse:     "else",
 	itemIf:       "if",
@@ -58,6 +59,8 @@ type lexTest struct {
 }
 
 var (
+	tDot        = item{itemDot, 0, "."}
+	tBlock      = item{itemBlock, 0, "block"}
 	tEOF        = item{itemEOF, 0, ""}
 	tFor        = item{itemIdentifier, 0, "for"}
 	tLeft       = item{itemLeftDelim, 0, "{{"}
@@ -104,6 +107,9 @@ var lexTests = []lexTest{
 	}},
 	{"empty action", `{{}}`, []item{tLeft, tRight, tEOF}},
 	{"for", `{{for}}`, []item{tLeft, tFor, tRight, tEOF}},
+	{"block", `{{block "foo" .}}`, []item{
+		tLeft, tBlock, tSpace, {itemString, 0, `"foo"`}, tSpace, tDot, tRight, tEOF,
+	}},
 	{"quote", `{{"abc \n\t\" "}}`, []item{tLeft, tQuote, tRight, tEOF}},
 	{"raw quote", "{{" + raw + "}}", []item{tLeft, tRawQuote, tRight, tEOF}},
 	{"raw quote with newline", "{{" + rawNL + "}}", []item{tLeft, tRawQuoteNL, tRight, tEOF}},
@@ -155,7 +161,7 @@ var lexTests = []lexTest{
 	}},
 	{"dot", "{{.}}", []item{
 		tLeft,
-		{itemDot, 0, "."},
+		tDot,
 		tRight,
 		tEOF,
 	}},
@@ -169,7 +175,7 @@ var lexTests = []lexTest{
 		tLeft,
 		{itemField, 0, ".x"},
 		tSpace,
-		{itemDot, 0, "."},
+		tDot,
 		tSpace,
 		{itemNumber, 0, ".2"},
 		tSpace,
@@ -278,6 +284,19 @@ var lexTests = []lexTest{
 		tRight,
 		tEOF,
 	}},
+	{"trimming spaces before and after", "hello- {{- 3 -}} -world", []item{
+		{itemText, 0, "hello-"},
+		tLeft,
+		{itemNumber, 0, "3"},
+		tRight,
+		{itemText, 0, "-world"},
+		tEOF,
+	}},
+	{"trimming spaces before and after comment", "hello- {{- /* hello */ -}} -world", []item{
+		{itemText, 0, "hello-"},
+		{itemText, 0, "-world"},
+		tEOF,
+	}},
 	// errors
 	{"badchar", "#{{\x01}}", []item{
 		{itemText, 0, "#"},
@@ -339,7 +358,7 @@ var lexTests = []lexTest{
 		{itemText, 0, "hello-"},
 		{itemError, 0, `unclosed comment`},
 	}},
-	{"text with comment close separted from delim", "hello-{{/* */ }}-world", []item{
+	{"text with comment close separated from delim", "hello-{{/* */ }}-world", []item{
 		{itemText, 0, "hello-"},
 		{itemError, 0, `comment ends before closing delimiter`},
 	}},
@@ -488,9 +507,9 @@ func TestShutdown(t *testing.T) {
 func (t *Tree) parseLexer(lex *lexer, text string) (tree *Tree, err error) {
 	defer t.recover(&err)
 	t.ParseName = t.Name
-	t.startParse(nil, lex)
-	t.parse(nil)
-	t.add(nil)
+	t.startParse(nil, lex, map[string]*Tree{})
+	t.parse()
+	t.add()
 	t.stopParse()
 	return t, nil
 }
diff --git a/libgo/go/text/template/parse/parse.go b/libgo/go/text/template/parse/parse.go
index 88aacd1..dc56cf7 100644
--- a/libgo/go/text/template/parse/parse.go
+++ b/libgo/go/text/template/parse/parse.go
@@ -28,6 +28,7 @@ type Tree struct {
 	token     [3]item // three-token lookahead for parser.
 	peekCount int
 	vars      []string // variables defined at the moment.
+	treeSet   map[string]*Tree
 }
 
 // Copy returns a copy of the Tree. Any parsing state is discarded.
@@ -205,11 +206,12 @@ func (t *Tree) recover(errp *error) {
 }
 
 // startParse initializes the parser, using the lexer.
-func (t *Tree) startParse(funcs []map[string]interface{}, lex *lexer) {
+func (t *Tree) startParse(funcs []map[string]interface{}, lex *lexer, treeSet map[string]*Tree) {
 	t.Root = nil
 	t.lex = lex
 	t.vars = []string{"$"}
 	t.funcs = funcs
+	t.treeSet = treeSet
 }
 
 // stopParse terminates parsing.
@@ -217,6 +219,7 @@ func (t *Tree) stopParse() {
 	t.lex = nil
 	t.vars = nil
 	t.funcs = nil
+	t.treeSet = nil
 }
 
 // Parse parses the template definition string to construct a representation of
@@ -226,19 +229,19 @@ func (t *Tree) stopParse() {
 func (t *Tree) Parse(text, leftDelim, rightDelim string, treeSet map[string]*Tree, funcs ...map[string]interface{}) (tree *Tree, err error) {
 	defer t.recover(&err)
 	t.ParseName = t.Name
-	t.startParse(funcs, lex(t.Name, text, leftDelim, rightDelim))
+	t.startParse(funcs, lex(t.Name, text, leftDelim, rightDelim), treeSet)
 	t.text = text
-	t.parse(treeSet)
-	t.add(treeSet)
+	t.parse()
+	t.add()
 	t.stopParse()
 	return t, nil
 }
 
-// add adds tree to the treeSet.
-func (t *Tree) add(treeSet map[string]*Tree) {
-	tree := treeSet[t.Name]
+// add adds tree to t.treeSet.
+func (t *Tree) add() {
+	tree := t.treeSet[t.Name]
 	if tree == nil || IsEmptyTree(tree.Root) {
-		treeSet[t.Name] = t
+		t.treeSet[t.Name] = t
 		return
 	}
 	if !IsEmptyTree(t.Root) {
@@ -274,7 +277,7 @@ func IsEmptyTree(n Node) bool {
 // parse is the top-level parser for a template, essentially the same
 // as itemList except it also parses {{define}} actions.
 // It runs to EOF.
-func (t *Tree) parse(treeSet map[string]*Tree) (next Node) {
+func (t *Tree) parse() (next Node) {
 	t.Root = t.newList(t.peek().pos)
 	for t.peek().typ != itemEOF {
 		if t.peek().typ == itemLeftDelim {
@@ -283,8 +286,8 @@ func (t *Tree) parse(treeSet map[string]*Tree) (next Node) {
 				newT := New("definition") // name will be updated once we know it.
 				newT.text = t.text
 				newT.ParseName = t.ParseName
-				newT.startParse(t.funcs, t.lex)
-				newT.parseDefinition(treeSet)
+				newT.startParse(t.funcs, t.lex, t.treeSet)
+				newT.parseDefinition()
 				continue
 			}
 			t.backup2(delim)
@@ -300,9 +303,9 @@ func (t *Tree) parse(treeSet map[string]*Tree) (next Node) {
 }
 
 // parseDefinition parses a {{define}} ...  {{end}} template definition and
-// installs the definition in the treeSet map.  The "define" keyword has already
+// installs the definition in t.treeSet. The "define" keyword has already
 // been scanned.
-func (t *Tree) parseDefinition(treeSet map[string]*Tree) {
+func (t *Tree) parseDefinition() {
 	const context = "define clause"
 	name := t.expectOneOf(itemString, itemRawString, context)
 	var err error
@@ -316,7 +319,7 @@ func (t *Tree) parseDefinition(treeSet map[string]*Tree) {
 	if end.Type() != nodeEnd {
 		t.errorf("unexpected %s in %s", end, context)
 	}
-	t.add(treeSet)
+	t.add()
 	t.stopParse()
 }
 
@@ -358,6 +361,8 @@ func (t *Tree) textOrAction() Node {
 // First word could be a keyword such as range.
 func (t *Tree) action() (n Node) {
 	switch token := t.nextNonSpace(); token.typ {
+	case itemBlock:
+		return t.blockControl()
 	case itemElse:
 		return t.elseControl()
 	case itemEnd:
@@ -522,13 +527,51 @@ func (t *Tree) elseControl() Node {
 	return t.newElse(t.expect(itemRightDelim, "else").pos, t.lex.lineNumber())
 }
 
+// Block:
+//	{{block stringValue pipeline}}
+// Block keyword is past.
+// The name must be something that can evaluate to a string.
+// The pipeline is mandatory.
+func (t *Tree) blockControl() Node {
+	const context = "block clause"
+
+	token := t.nextNonSpace()
+	name := t.parseTemplateName(token, context)
+	pipe := t.pipeline(context)
+
+	block := New(name) // name will be updated once we know it.
+	block.text = t.text
+	block.ParseName = t.ParseName
+	block.startParse(t.funcs, t.lex, t.treeSet)
+	var end Node
+	block.Root, end = block.itemList()
+	if end.Type() != nodeEnd {
+		t.errorf("unexpected %s in %s", end, context)
+	}
+	block.add()
+	block.stopParse()
+
+	return t.newTemplate(token.pos, t.lex.lineNumber(), name, pipe)
+}
+
 // Template:
 //	{{template stringValue pipeline}}
 // Template keyword is past.  The name must be something that can evaluate
 // to a string.
 func (t *Tree) templateControl() Node {
-	var name string
+	const context = "template clause"
 	token := t.nextNonSpace()
+	name := t.parseTemplateName(token, context)
+	var pipe *PipeNode
+	if t.nextNonSpace().typ != itemRightDelim {
+		t.backup()
+		// Do not pop variables; they persist until "end".
+		pipe = t.pipeline(context)
+	}
+	return t.newTemplate(token.pos, t.lex.lineNumber(), name, pipe)
+}
+
+func (t *Tree) parseTemplateName(token item, context string) (name string) {
 	switch token.typ {
 	case itemString, itemRawString:
 		s, err := strconv.Unquote(token.val)
@@ -537,15 +580,9 @@ func (t *Tree) templateControl() Node {
 		}
 		name = s
 	default:
-		t.unexpected(token, "template invocation")
-	}
-	var pipe *PipeNode
-	if t.nextNonSpace().typ != itemRightDelim {
-		t.backup()
-		// Do not pop variables; they persist until "end".
-		pipe = t.pipeline("template")
+		t.unexpected(token, context)
 	}
-	return t.newTemplate(token.pos, t.lex.lineNumber(), name, pipe)
+	return
 }
 
 // command:
diff --git a/libgo/go/text/template/parse/parse_test.go b/libgo/go/text/template/parse/parse_test.go
index 200d50c..b4512d3 100644
--- a/libgo/go/text/template/parse/parse_test.go
+++ b/libgo/go/text/template/parse/parse_test.go
@@ -228,6 +228,15 @@ var parseTests = []parseTest{
 		`{{with .X}}"hello"{{end}}`},
 	{"with with else", "{{with .X}}hello{{else}}goodbye{{end}}", noError,
 		`{{with .X}}"hello"{{else}}"goodbye"{{end}}`},
+	// Trimming spaces.
+	{"trim left", "x \r\n\t{{- 3}}", noError, `"x"{{3}}`},
+	{"trim right", "{{3 -}}\n\n\ty", noError, `{{3}}"y"`},
+	{"trim left and right", "x \r\n\t{{- 3 -}}\n\n\ty", noError, `"x"{{3}}"y"`},
+	{"comment trim left", "x \r\n\t{{- /* hi */}}", noError, `"x"`},
+	{"comment trim right", "{{/* hi */ -}}\n\n\ty", noError, `"y"`},
+	{"comment trim left and right", "x \r\n\t{{- /* */ -}}\n\n\ty", noError, `"x""y"`},
+	{"block definition", `{{block "foo" .}}hello{{end}}`, noError,
+		`{{template "foo" .}}`},
 	// Errors.
 	{"unclosed action", "hello{{range", hasError, ""},
 	{"unmatched end", "{{end}}", hasError, ""},
@@ -277,6 +286,8 @@ var parseTests = []parseTest{
 	{"wrong pipeline boolean", "{{.|true}}", hasError, ""},
 	{"wrong pipeline nil", "{{'c'|nil}}", hasError, ""},
 	{"empty pipeline", `{{printf "%d" ( ) }}`, hasError, ""},
+	// Missing pipeline in block
+	{"block definition", `{{block "foo"}}hello{{end}}`, hasError, ""},
 }
 
 var builtins = map[string]interface{}{
@@ -450,3 +461,26 @@ func TestErrors(t *testing.T) {
 		}
 	}
 }
+
+func TestBlock(t *testing.T) {
+	const (
+		input = `a{{block "inner" .}}bar{{.}}baz{{end}}b`
+		outer = `a{{template "inner" .}}b`
+		inner = `bar{{.}}baz`
+	)
+	treeSet := make(map[string]*Tree)
+	tmpl, err := New("outer").Parse(input, "", "", treeSet, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if g, w := tmpl.Root.String(), outer; g != w {
+		t.Errorf("outer template = %q, want %q", g, w)
+	}
+	inTmpl := treeSet["inner"]
+	if inTmpl == nil {
+		t.Fatal("block did not define template")
+	}
+	if g, w := inTmpl.Root.String(), inner; g != w {
+		t.Errorf("inner template = %q, want %q", g, w)
+	}
+}
diff --git a/libgo/go/text/template/template.go b/libgo/go/text/template/template.go
index 3e80982..7a7f42a 100644
--- a/libgo/go/text/template/template.go
+++ b/libgo/go/text/template/template.go
@@ -5,7 +5,6 @@
 package template
 
 import (
-	"fmt"
 	"reflect"
 	"sync"
 	"text/template/parse"
@@ -117,11 +116,10 @@ func (t *Template) copy(c *common) *Template {
 
 // AddParseTree adds parse tree for template with given name and associates it with t.
 // If the template does not already exist, it will create a new one.
-// It is an error to reuse a name except to overwrite an empty template.
+// If the template does exist, it will be replaced.
 func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error) {
 	t.init()
 	// If the name is the name of this template, overwrite this template.
-	// The associate method checks it's not a redefinition.
 	nt := t
 	if name != t.name {
 		nt = t.New(name)
@@ -162,8 +160,9 @@ func (t *Template) Delims(left, right string) *Template {
 
 // Funcs adds the elements of the argument map to the template's function map.
 // It panics if a value in the map is not a function with appropriate return
-// type. However, it is legal to overwrite elements of the map. The return
-// value is the template, so calls can be chained.
+// type or if the name cannot be used syntactically as a function in a template.
+// It is legal to overwrite elements of the map. The return value is the template,
+// so calls can be chained.
 func (t *Template) Funcs(funcMap FuncMap) *Template {
 	t.init()
 	t.muFuncs.Lock()
@@ -184,11 +183,7 @@ func (t *Template) Lookup(name string) *Template {
 
 // Parse defines the template by parsing the text. Nested template definitions will be
 // associated with the top-level template t. Parse may be called multiple times
-// to parse definitions of templates to associate with t. It is an error if a
-// resulting template is non-empty (contains content other than template
-// definitions) and would replace a non-empty template with the same name.
-// (In multiple calls to Parse with the same receiver template, only one call
-// can contain text other than space, comments, and template definitions.)
+// to parse definitions of templates to associate with t.
 func (t *Template) Parse(text string) (*Template, error) {
 	t.init()
 	t.muFuncs.RLock()
@@ -207,25 +202,17 @@ func (t *Template) Parse(text string) (*Template, error) {
 }
 
 // associate installs the new template into the group of templates associated
-// with t. It is an error to reuse a name except to overwrite an empty
-// template. The two are already known to share the common structure.
-// The boolean return value reports wither to store this tree as t.Tree.
+// with t. The two are already known to share the common structure.
+// The boolean return value reports whether to store this tree as t.Tree.
 func (t *Template) associate(new *Template, tree *parse.Tree) (bool, error) {
 	if new.common != t.common {
 		panic("internal error: associate not common")
 	}
-	name := new.name
-	if old := t.tmpl[name]; old != nil {
-		oldIsEmpty := parse.IsEmptyTree(old.Root)
-		newIsEmpty := parse.IsEmptyTree(tree.Root)
-		if newIsEmpty {
-			// Whether old is empty or not, new is empty; no reason to replace old.
-			return false, nil
-		}
-		if !oldIsEmpty {
-			return false, fmt.Errorf("template: redefinition of template %q", name)
-		}
+	if t.tmpl[new.name] != nil && parse.IsEmptyTree(tree.Root) {
+		// If a template by that name exists,
+		// don't replace it with an empty template.
+		return false, nil
 	}
-	t.tmpl[name] = new
+	t.tmpl[new.name] = new
 	return true, nil
 }