cmd/gc: Give better line numbers for errors in composite literals.

Credit to Russ for suggesting this fix.

Fixes #3925.

R=golang-dev, franciscossouza, rsc
CC=golang-dev
https://golang.org/cl/6920051

src/cmd/gc/go.y

@@ -54,7 +54,7 @@ static void fixlbrace(int);
 %type	<node>	stmt ntype
 %type	<node>	arg_type
 %type	<node>	case caseblock
-%type	<node>	compound_stmt dotname embed expr complitexpr
+%type	<node>	compound_stmt dotname embed expr complitexpr bare_complitexpr
 %type	<node>	expr_or_type
 %type	<node>	fndcl hidden_fndcl fnliteral
 %type	<node>	for_body for_header for_stmt if_header if_stmt non_dcl_stmt
@@ -974,6 +974,29 @@ keyval:
 		$$ = nod(OKEY, $1, $3);
 	}
 
+bare_complitexpr:
+	expr
+	{
+		// These nodes do not carry line numbers.
+		// Since a composite literal commonly spans several lines,
+		// the line number on errors may be misleading.
+		// Introduce a wrapper node to give the correct line.
+		$$ = $1;
+		switch($$->op) {
+		case ONAME:
+		case ONONAME:
+		case OTYPE:
+		case OPACK:
+		case OLITERAL:
+			$$ = nod(OPAREN, $$, N);
+		}
+	}
+|	'{' start_complit braced_keyval_list '}'
+	{
+		$$ = $2;
+		$$->list = $3;
+	}
+
 complitexpr:
 	expr
 |	'{' start_complit braced_keyval_list '}'
@@ -1761,7 +1784,7 @@ keyval_list:
 	{
 		$$ = list1($1);
 	}
-|	complitexpr
+|	bare_complitexpr
 	{
 		$$ = list1($1);
 	}
@@ -1769,7 +1792,7 @@ keyval_list:
 	{
 		$$ = list($1, $3);
 	}
-|	keyval_list ',' complitexpr
+|	keyval_list ',' bare_complitexpr
 	{
 		$$ = list($1, $3);
 	}

src/cmd/gc/y.tab.h

-/* A Bison parser, made by GNU Bison 2.6.5.  */
+/* A Bison parser, made by GNU Bison 2.5.  */
 
 /* Bison interface for Yacc-like parsers in C
    
-      Copyright (C) 1984, 1989-1990, 2000-2012 Free Software Foundation, Inc.
+      Copyright (C) 1984, 1989-1990, 2000-2011 Free Software Foundation, Inc.
    
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -30,15 +30,6 @@
    This special exception was added by the Free Software Foundation in
    version 2.2 of Bison.  */
 
-#ifndef YY_YY_Y_TAB_H_INCLUDED
-# define YY_YY_Y_TAB_H_INCLUDED
-/* Enabling traces.  */
-#ifndef YYDEBUG
-# define YYDEBUG 0
-#endif
-#if YYDEBUG
-extern int yydebug;
-#endif
 
 /* Tokens.  */
 #ifndef YYTOKENTYPE
@@ -150,10 +141,12 @@ extern int yydebug;
 
 
 
+
 #if ! defined YYSTYPE && ! defined YYSTYPE_IS_DECLARED
 typedef union YYSTYPE
 {
-/* Line 2042 of yacc.c  */
+
+/* Line 2068 of yacc.c  */
 #line 28 "go.y"
 
 	Node*		node;
@@ -164,8 +157,9 @@ typedef union YYSTYPE
 	int		i;
 
 
-/* Line 2042 of yacc.c  */
-#line 169 "y.tab.h"
+
+/* Line 2068 of yacc.c  */
+#line 163 "y.tab.h"
 } YYSTYPE;
 # define YYSTYPE_IS_TRIVIAL 1
 # define yystype YYSTYPE /* obsolescent; will be withdrawn */
@@ -174,18 +168,4 @@ typedef union YYSTYPE
 
 extern YYSTYPE yylval;
 
-#ifdef YYPARSE_PARAM
-#if defined __STDC__ || defined __cplusplus
-int yyparse (void *YYPARSE_PARAM);
-#else
-int yyparse ();
-#endif
-#else /* ! YYPARSE_PARAM */
-#if defined __STDC__ || defined __cplusplus
-int yyparse (void);
-#else
-int yyparse ();
-#endif
-#endif /* ! YYPARSE_PARAM */
 
-#endif /* !YY_YY_Y_TAB_H_INCLUDED  */

src/cmd/gc/yerr.h

@@ -71,6 +71,6 @@ static struct {
 	112, LNAME,
 	"nested func not allowed",
 
-	639, ';',
+	641, ';',
 	"else must be followed by if or statement block"
 };

test/fixedbugs/issue3925.go

+// errorcheck
+
+// Copyright 2012 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 3925: wrong line number for error message "missing key in map literal"
+
+// also a test for correct line number in other malformed composite literals.
+
+package foo
+
+var _ = map[string]string{
+	"1": "2",
+	"3", "4", // ERROR "missing key"
+}
+
+var _ = []string{
+	"foo",
+	"bar",
+	20, // ERROR "cannot use"
+}
+