yacc.c: always initialize yylloc

The initial location might be used if the parser starts by an empty
reduction, so really ensure proper initialization of the initial
location.  The previous approach fails for PostgreSQL, which uses
Reported by Peter Eisentraut.
http://lists.gnu.org/archive/html/bug-bison/2012-11/msg00023.html
With help from Théophile Ranquet.

* data/yacc.c (b4_declare_scanner_communication_variables): Be sure
to initialize yylloc, even when its structure is unknown.
(yyparse): Simplify the call to b4_dollar_pushdef.
* tests/actions.at (Initial location): Check of similar pattern
as in the case of PostgreSQL.

NEWS

@@ -2,6 +2,10 @@ GNU Bison NEWS
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
+** Bug fixes
+
+  Warnings about uninitialized yylloc in yyparse have been fixed.
+
 ** Documentation
 
   The sections about shift/reduce and reduce/reduce conflicts resolution

THANKS

@@ -88,6 +88,7 @@ Pascal Bart               pascal.bart@epita.fr
 Paul Eggert               eggert@cs.ucla.edu
 Paul Hilfinger            Hilfinger@CS.Berkeley.EDU
 Per Allansson             per@appgate.com
+Peter Eisentraut          peter_e@gmx.net
 Peter Fales               psfales@lucent.com
 Peter Hamorsky            hamo@upjs.sk
 Peter Simons              simons@cryp.to

data/yacc.c

@@ -184,7 +184,8 @@ int yychar;
    or non-GCC compilers.  */
 static YYSTYPE yyval_default;
 # define YY_INITIAL_VALUE(Value) = Value
-#endif]])[
+#endif]b4_locations_if([[
+static YYLTYPE yyloc_default][]b4_yyloc_default[;]])])[
 #ifndef YY_IGNORE_MAYBE_UNINITIALIZED_BEGIN
 # define YY_IGNORE_MAYBE_UNINITIALIZED_BEGIN
 # define YY_IGNORE_MAYBE_UNINITIALIZED_END
@@ -197,7 +198,7 @@ static YYSTYPE yyval_default;
 YYSTYPE yylval YY_INITIAL_VALUE(yyval_default);]b4_locations_if([[
 
 /* Location data for the lookahead symbol.  */
-YYLTYPE yylloc][]b4_yyloc_default[;
+YYLTYPE yylloc]b4_pure_if([ = yyloc_default], [b4_yyloc_default])[;
 ]])b4_pure_if([], [[
 
 /* Number of syntax errors so far.  */
@@ -1410,7 +1411,8 @@ b4_c_function_def([[yyparse]], [[int]], b4_parse_param)[
   yypstate *yyps_local;]b4_pure_if([[
   int yychar;
   YYSTYPE yylval;]b4_locations_if([[
-  YYLTYPE yylloc][]b4_yyloc_default[;]])])[
+  static YYLTYPE yyloc_default][]b4_yyloc_default[;
+  YYLTYPE yylloc = yyloc_default;]])])[
   if (yyps)
     yyps_local = yyps;
   else
@@ -1559,8 +1561,7 @@ b4_c_function_def([[yyparse]], [[int]], b4_parse_param)[
   yychar = YYEMPTY; /* Cause a token to be read.  */
 ]m4_ifdef([b4_initial_action], [
 b4_dollar_pushdef([m4_define([b4_dollar_dollar_used])yylval], [],
-               [m4_define([b4_at_dollar_used])dnl
-b4_push_if([b4_pure_if([*])yypushed_loc], [yylloc])])dnl
+                  [b4_push_if([b4_pure_if([*])yypushed_loc], [yylloc])])dnl
 /* User initialization code.  */
 b4_user_initial_action
 b4_dollar_popdef[]dnl

tests/actions.at

@@ -73,8 +73,8 @@ AT_CLEANUP
 ## Initial location.  ##
 ## ------------------ ##
 
-# AT_TEST(SKELETON-NAME, DIRECTIVES)
-# ----------------------------------
+# AT_TEST(SKELETON-NAME, DIRECTIVES, [MORE-DIRECTIVES], [LOCATION = 1.1])
+# -----------------------------------------------------------------------
 # Check that the initial location is correct.
 m4_pushdef([AT_TEST],
 [AT_SETUP([Initial location: $1 $2])
@@ -85,7 +85,8 @@ AT_DATA_GRAMMAR([[input.y]],
 %locations
 %debug
 %skeleton "$1"
-$2
+]$2[
+]$3[
 %parse-param { int x } // Useless, but used to force yyerror purity.
 %code
 {
@@ -122,8 +123,8 @@ main (void)
 
 AT_FULL_COMPILE([input])
 AT_PARSER_CHECK([./input], 1, [],
-[[1.1
-1.1: syntax error
+[m4_default([$4], [1.1])
+m4_default([$4], [1.1])[: syntax error
 ]])
 AT_BISON_OPTION_POPDEFS
 AT_CLEANUP
@@ -138,6 +139,36 @@ AT_TEST([glr.c])
 AT_TEST([lalr1.cc])
 AT_TEST([glr.cc])
 
+## A very different test, based on PostgreSQL's implementation of the
+## locations.  See
+## http://lists.gnu.org/archive/html/bug-bison/2012-11/msg00023.html
+##
+## Weirdly enough, to trigger the warning with GCC 4.7, we must not
+## use fprintf, so run the test twice: once to check the warning
+## (absence thereof), and another time to check the value.
+AT_TEST([yacc.c], [%define api.pure],
+[[%{
+# define YYLTYPE int
+# define YY_LOCATION_PRINT(Stream, Loc)      \
+   (void) (Loc)
+# define YYLLOC_DEFAULT(Current, Rhs, N)    \
+  (Current) = ((Rhs)[N ? 1 : 0])
+%}
+]],
+[@&t@])
+
+AT_TEST([yacc.c], [%define api.pure],
+[[%{
+# define YYLTYPE int
+# define YY_LOCATION_PRINT(Stream, Loc)      \
+    fprintf ((Stream), "%d", (Loc))
+# define YYLLOC_DEFAULT(Current, Rhs, N)    \
+  (Current) = ((Rhs)[N ? 1 : 0])
+%}
+]],
+[0])
+
+
 m4_popdef([AT_TEST])