1 files changed, 33 insertions, 26 deletions

diff --git a/src/text/template/parse/parse.go b/src/text/template/parse/parse.go
index 496d8bfa1d..5e6e512eb4 100644
--- a/src/text/template/parse/parse.go
+++ b/src/text/template/parse/parse.go
@@ -24,13 +24,14 @@ type Tree struct {
 	Mode      Mode      // parsing mode.
 	text      string    // text parsed to create the template (or its parent)
 	// Parsing only; cleared after parse.
-	funcs     []map[string]interface{}
-	lex       *lexer
-	token     [3]item // three-token lookahead for parser.
-	peekCount int
-	vars      []string // variables defined at the moment.
-	treeSet   map[string]*Tree
-	mode      Mode
+	funcs      []map[string]interface{}
+	lex        *lexer
+	token      [3]item // three-token lookahead for parser.
+	peekCount  int
+	vars       []string // variables defined at the moment.
+	treeSet    map[string]*Tree
+	actionLine int // line of left delim starting action
+	mode       Mode
 }
 
 // A mode value is a set of flags (or 0). Modes control parser behavior.
@@ -187,6 +188,16 @@ func (t *Tree) expectOneOf(expected1, expected2 itemType, context string) item {
 
 // unexpected complains about the token and terminates processing.
 func (t *Tree) unexpected(token item, context string) {
+	if token.typ == itemError {
+		extra := ""
+		if t.actionLine != 0 && t.actionLine != token.line {
+			extra = fmt.Sprintf(" in action started at %s:%d", t.ParseName, t.actionLine)
+			if strings.HasSuffix(token.val, " action") {
+				extra = extra[len(" in action"):] // avoid "action in action"
+			}
+		}
+		t.errorf("%s%s", token, extra)
+	}
 	t.errorf("unexpected %s in %s", token, context)
 }
 
@@ -350,6 +361,8 @@ func (t *Tree) textOrAction() Node {
 	case itemText:
 		return t.newText(token.pos, token.val)
 	case itemLeftDelim:
+		t.actionLine = token.line
+		defer t.clearActionLine()
 		return t.action()
 	case itemComment:
 		return t.newComment(token.pos, token.val)
@@ -359,6 +372,10 @@ func (t *Tree) textOrAction() Node {
 	return nil
 }
 
+func (t *Tree) clearActionLine() {
+	t.actionLine = 0
+}
+
 // Action:
 //	control
 //	command ("|" command)*
@@ -384,12 +401,12 @@ func (t *Tree) action() (n Node) {
 	t.backup()
 	token := t.peek()
 	// Do not pop variables; they persist until "end".
-	return t.newAction(token.pos, token.line, t.pipeline("command"))
+	return t.newAction(token.pos, token.line, t.pipeline("command", itemRightDelim))
 }
 
 // Pipeline:
 //	declarations? command ('|' command)*
-func (t *Tree) pipeline(context string) (pipe *PipeNode) {
+func (t *Tree) pipeline(context string, end itemType) (pipe *PipeNode) {
 	token := t.peekNonSpace()
 	pipe = t.newPipeline(token.pos, token.line, nil)
 	// Are there declarations or assignments?
@@ -430,12 +447,9 @@ decls:
 	}
 	for {
 		switch token := t.nextNonSpace(); token.typ {
-		case itemRightDelim, itemRightParen:
+		case end:
 			// At this point, the pipeline is complete
 			t.checkPipeline(pipe, context)
-			if token.typ == itemRightParen {
-				t.backup()
-			}
 			return
 		case itemBool, itemCharConstant, itemComplex, itemDot, itemField, itemIdentifier,
 			itemNumber, itemNil, itemRawString, itemString, itemVariable, itemLeftParen:
@@ -464,7 +478,7 @@ func (t *Tree) checkPipeline(pipe *PipeNode, context string) {
 
 func (t *Tree) parseControl(allowElseIf bool, context string) (pos Pos, line int, pipe *PipeNode, list, elseList *ListNode) {
 	defer t.popVars(len(t.vars))
-	pipe = t.pipeline(context)
+	pipe = t.pipeline(context, itemRightDelim)
 	var next Node
 	list, next = t.itemList()
 	switch next.Type() {
@@ -550,7 +564,7 @@ func (t *Tree) blockControl() Node {
 
 	token := t.nextNonSpace()
 	name := t.parseTemplateName(token, context)
-	pipe := t.pipeline(context)
+	pipe := t.pipeline(context, itemRightDelim)
 
 	block := New(name) // name will be updated once we know it.
 	block.text = t.text
@@ -580,7 +594,7 @@ func (t *Tree) templateControl() Node {
 	if t.nextNonSpace().typ != itemRightDelim {
 		t.backup()
 		// Do not pop variables; they persist until "end".
-		pipe = t.pipeline(context)
+		pipe = t.pipeline(context, itemRightDelim)
 	}
 	return t.newTemplate(token.pos, token.line, name, pipe)
 }
@@ -614,13 +628,12 @@ func (t *Tree) command() *CommandNode {
 		switch token := t.next(); token.typ {
 		case itemSpace:
 			continue
-		case itemError:
-			t.errorf("%s", token.val)
 		case itemRightDelim, itemRightParen:
 			t.backup()
 		case itemPipe:
+			// nothing here; break loop below
 		default:
-			t.errorf("unexpected %s in operand", token)
+			t.unexpected(token, "operand")
 		}
 		break
 	}
@@ -675,8 +688,6 @@ func (t *Tree) operand() Node {
 // A nil return means the next item is not a term.
 func (t *Tree) term() Node {
 	switch token := t.nextNonSpace(); token.typ {
-	case itemError:
-		t.errorf("%s", token.val)
 	case itemIdentifier:
 		if !t.hasFunction(token.val) {
 			t.errorf("function %q not defined", token.val)
@@ -699,11 +710,7 @@ func (t *Tree) term() Node {
 		}
 		return number
 	case itemLeftParen:
-		pipe := t.pipeline("parenthesized pipeline")
-		if token := t.next(); token.typ != itemRightParen {
-			t.errorf("unclosed right paren: unexpected %s", token)
-		}
-		return pipe
+		return t.pipeline("parenthesized pipeline", itemRightParen)
 	case itemString, itemRawString:
 		s, err := strconv.Unquote(token.val)
 		if err != nil {