c++: fix the use of destructors when variants are enabled

When using variants, destructors generate invalid code.
<http://lists.gnu.org/archive/html/bug-bison/2014-09/msg00005.html>
Reported by Michael Catanzaro.

* data/c++.m4 (~basic_symbol): b4_symbol_foreach works on yysym:
define it.
* tests/c++.at (Variants): Check it.

NEWS

@@ -4,19 +4,23 @@ GNU Bison NEWS
 
 ** Bug fixes
 
-*** Named %union support
+*** C++ with Variants (lalr1.cc)
+
+  Problems with %destructor and '%define parse.assert' have been fixed.
+
+*** Named %union support (yacc.c, glr.c)
 
   Bison 3.0 introduced a regression on named %union such as
 
     %union foo { int ival; };
 
-  The possibility to use a name was introduced ``for Yacc compatibility''.
+  The possibility to use a name was introduced "for Yacc compatibility".
   It is however not required by POSIX Yacc, and its usefulness is not clear.
 
-*** %define api.value.type union with %defines
+*** %define api.value.type union with %defines (yacc.c, glr.c)
 
-  The yacc.c and glr.c parsers were broken when %defines was used
+  The C parsers were broken when %defines was used together with "%define
-  together with "%define api.value.type union".
+  api.value.type union".
 
 *** Redeclarations are reported in proper order
 

THANKS

@@ -83,6 +83,7 @@ Martin Mokrejs            mmokrejs@natur.cuni.cz
 Martin Nylin              martin.nylin@linuxmail.org
 Matt Kraai                kraai@alumni.cmu.edu
 Matt Rosing               rosing@peakfive.com
+Michael Catanzaro         mcatanzaro@gnome.org
 Michael Felt              mamfelt@gmail.com
 Michael Hayes             m.hayes@elec.canterbury.ac.nz
 Michael Raskin            7c6f434c@mail.ru

data/c++.m4

@@ -346,6 +346,7 @@ m4_define([b4_public_types_define],
   {]b4_variant_if([[
     // User destructor.
     symbol_number_type yytype = this->type_get ();
+    basic_symbol<Base>& yysym = *this;
     switch (yytype)
     {
 ]b4_symbol_foreach([b4_symbol_destructor])dnl

tests/c++.at

@@ -252,10 +252,12 @@ typedef std::list<std::string> strings_type;
 // Using the template type to exercize its parsing.
 // Starting with :: to ensure we don't output "<::" which starts by the
 // digraph for the left square bracket.
-%type <::std::list<std::string>> list result;
+%type <::std::list<std::string>> list;
 
 %printer { yyo << $$; }
   <int> <::std::string> <::std::list<std::string>>;
+%destructor { std::cerr << "Destroy: " << $$ << '\n'; } <*>;
+%destructor { std::cerr << "Destroy: \"" << $$ << "\"\n"; } <::std::string>;
 %%
 
 result:
@@ -336,8 +338,31 @@ namespace yy
 
 AT_FULL_COMPILE([list])
 AT_PARSER_CHECK([./list], 0,
-[(0, 1, 2, 4, 6)
+[[(0, 1, 2, 4, 6)
-])
+]],
+[[Destroy: ""
+Destroy: "0"
+Destroy: (0)
+Destroy: 1
+Destroy: "1"
+Destroy: ()
+Destroy: ""
+Destroy: "2"
+Destroy: ()
+Destroy: ""
+Destroy: 3
+Destroy: ()
+Destroy: ""
+Destroy: "4"
+Destroy: ()
+Destroy: ()
+Destroy: 5
+Destroy: ()
+Destroy: ""
+Destroy: "6"
+Destroy: ()
+Destroy: (0, 1, 2, 4, 6)
+]])
 
 AT_BISON_OPTION_POPDEFS
 AT_CLEANUP
@@ -826,10 +851,10 @@ list:
 
 item:
   'a'     { $$ = $][1; }
-| 'e'     { YYUSE ($$); YYUSE($][1); error ("syntax error"); }
+| 'e'     { YYUSE ($$); YYUSE ($][1); error ("syntax error"); }
 // Not just 'E', otherwise we reduce when 'E' is the lookahead, and
 // then the stack is emptied, defeating the point of the test.
-| 'E' 'a' { YYUSE($][1); $$ = $][2; }
+| 'E' 'a' { YYUSE ($][1); $$ = $][2; }
 | 'R'     { ]AT_VARIANT_IF([], [$$ = YY_NULLPTR; delete $][1]; )[YYERROR; }
 | 'p'     { $$ = $][1; }
 | 's'     { $$ = $][1; throw std::runtime_error ("reduction"); }