cmd/gc: put 'not used' message on correct line

Fixes #4663.

R=ken2
CC=golang-dev
https://golang.org/cl/7235081

src/cmd/gc/go.y

@@ -405,6 +405,20 @@ simple_stmt:
 	expr
 	{
 		$$ = $1;
+
+		// These nodes do not carry line numbers.
+		// Since a bare name used as an expression is an error,
+		// introduce a wrapper node to give the correct line.
+		switch($$->op) {
+		case ONAME:
+		case ONONAME:
+		case OTYPE:
+		case OPACK:
+		case OLITERAL:
+			$$ = nod(OPAREN, $$, N);
+			$$->implicit = 1;
+			break;
+		}
 	}
 |	expr LASOP expr
 	{
@@ -989,6 +1003,7 @@ bare_complitexpr:
 		case OPACK:
 		case OLITERAL:
 			$$ = nod(OPAREN, $$, N);
+			$$->implicit = 1;
 		}
 	}
 |	'{' start_complit braced_keyval_list '}'

src/cmd/gc/y.tab.h

-/* A Bison parser, made by GNU Bison 2.5.  */
+/* A Bison parser, made by GNU Bison 2.3.  */
 
-/* Bison interface for Yacc-like parsers in C
+/* Skeleton interface for Bison's Yacc-like parsers in C
 
-      Copyright (C) 1984, 1989-1990, 2000-2011 Free Software Foundation, Inc.
+   Copyright (C) 1984, 1989, 1990, 2000, 2001, 2002, 2003, 2004, 2005, 2006
+   Free Software Foundation, Inc.
 
-   This program is free software: you can redistribute it and/or modify
+   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
-   the Free Software Foundation, either version 3 of the License, or
-   (at your option) any later version.
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
 
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ -15,7 +16,9 @@
    GNU General Public License for more details.
 
    You should have received a copy of the GNU General Public License
-   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor,
+   Boston, MA 02110-1301, USA.  */
 
 /* As a special exception, you may create a larger work that contains
    part or all of the Bison parser skeleton and distribute that work
@@ -30,7 +33,6 @@
    This special exception was added by the Free Software Foundation in
    version 2.2 of Bison.  */
 
-
 /* Tokens.  */
 #ifndef YYTOKENTYPE
 # define YYTOKENTYPE
@@ -144,28 +146,22 @@
 
 #if ! defined YYSTYPE && ! defined YYSTYPE_IS_DECLARED
 typedef union YYSTYPE
-{
-
-/* Line 2068 of yacc.c  */
 #line 28 "go.y"
-
+{
 	Node*		node;
 	NodeList*		list;
 	Type*		type;
 	Sym*		sym;
 	struct	Val	val;
 	int		i;
-
-
-
-/* Line 2068 of yacc.c  */
-#line 163 "y.tab.h"
-} YYSTYPE;
-# define YYSTYPE_IS_TRIVIAL 1
+}
+/* Line 1529 of yacc.c.  */
+#line 160 "y.tab.h"
+	YYSTYPE;
 # define yystype YYSTYPE /* obsolescent; will be withdrawn */
 # define YYSTYPE_IS_DECLARED 1
+# define YYSTYPE_IS_TRIVIAL 1
 #endif
 
 extern YYSTYPE yylval;
 
-

test/fixedbugs/bug357.go

@@ -15,7 +15,7 @@ func bla1() bool {
 
 func bla5() bool {
 	_ = 1
-	false  // ERROR "false not used|value computed is not used"
+	false  // ERROR "false evaluated but not used|value computed is not used"
 	_ = 2
 	return false
 }

test/fixedbugs/bug379.go

@@ -14,5 +14,5 @@
 package main
 
 func main() {
-	1 + 2 // ERROR "1 \+ 2 not used|value computed is not used"
+	1 + 2 // ERROR "1 \+ 2 evaluated but not used|value computed is not used"
 }

test/fixedbugs/issue4654.go

@@ -47,8 +47,8 @@ func f() {
 	defer println(1) // ok
 	defer recover() // ok
 
-	int(0) // ERROR "int\(0\) not used"
-	string([]byte("abc")) // ERROR "string\(\[\]byte literal\) not used"
+	int(0) // ERROR "int\(0\) evaluated but not used"
+	string([]byte("abc")) // ERROR "string\(\[\]byte literal\) evaluated but not used"
 
 	append(x, 1) // ERROR "not used"
 	cap(x) // ERROR "not used"

test/fixedbugs/issue4663.go

+// errorcheck
+
+// Copyright 2013 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 4663.
+// Make sure 'not used' message is placed correctly.
+
+package main
+
+func a(b int) int64 {
+  b // ERROR "not used"
+}