Clean up handling of %destructor for the end token (token 0).

Discussed starting at
<http://lists.gnu.org/archive/html/bison-patches/2006-07/msg00019.html>
and
<http://lists.gnu.org/archive/html/help-bison/2006-07/msg00013.html>.

Make the skeletons consistent in how they pop the end token and invoke
its %destructor.
* data/glr.c (yyrecoverSyntaxError, yyparse): Don't pop the start
state, which has token number 0, since this would invoke the
%destructor for the end token.
* data/lalr1.cc (yy::parser::parse): Don't check for the final state
until after shifting the end token, or else it won't be popped.
* data/yacc.c (yyparse): Likewise.

* data/glr.c (yyparse): Clear the lookahead after shifting it even when
it's the end token.  Upon termination, destroy an unshifted lookahead
even when it's the end token.
* data/lalr1.cc (yy::parser::parse): Likewise.
* data/yacc.c (yyparse): Likewise.

* src/reader.c (packgram): Don't check rule 0.  This suppresses unused
value warnings for the end token when the user gives the end token a
%destructor.

* tests/actions.at (Printers and Destructors): Test all the above.

data/glr.c

@@ -2261,7 +2261,8 @@ yyrecoverSyntaxError (yyGLRStack* yystackp]b4_user_formals[)
 	    }
 	}
 ]b4_locations_if([[      yystackp->yyerror_range[1].yystate.yyloc = yys->yyloc;]])[
-      yydestroyGLRState ("Error: popping", yys]b4_user_args[);
+      if (yys->yypred != NULL)
+	yydestroyGLRState ("Error: popping", yys]b4_user_args[);
       yystackp->yytops.yystates[0] = yys->yypred;
       yystackp->yynextFree -= 1;
       yystackp->yyspaceLeft += 1;
@@ -2373,8 +2374,7 @@ m4_popdef([b4_at_dollar])])dnl
 	      if (yyisShiftAction (yyaction))
 		{
 		  YY_SYMBOL_PRINT ("Shifting", yytoken, &yylval, &yylloc);
-		  if (yychar != YYEOF)
-		    yychar = YYEMPTY;
+		  yychar = YYEMPTY;
 		  yyposn += 1;
 		  yyglrShift (&yystack, 0, yyaction, yyposn, &yylval, &yylloc);
 		  if (0 < yystack.yyerrState)
@@ -2490,7 +2490,7 @@ m4_popdef([b4_at_dollar])])dnl
   goto yyreturn;
 
  yyreturn:
-  if (yychar != YYEOF && yychar != YYEMPTY)
+  if (yychar != YYEMPTY)
     yydestruct ("Cleanup: discarding lookahead",
 		YYTRANSLATE (yychar),
 		&yylval]b4_locations_if([, &yylloc])[]b4_user_args[);
@@ -2512,7 +2512,8 @@ m4_popdef([b4_at_dollar])])dnl
 		  {
 		    yyGLRState *yys = yystates[yyk];
 ]b4_locations_if([[		    yystack.yyerror_range[1].yystate.yyloc = yys->yyloc;]]
-)[		    yydestroyGLRState ("Cleanup: popping", yys]b4_user_args[);
+)[		    if (yys->yypred != NULL)
+		      yydestroyGLRState ("Cleanup: popping", yys]b4_user_args[);
 		    yystates[yyk] = yys->yypred;
 		    yystack.yynextFree -= 1;
 		    yystack.yyspaceLeft += 1;

data/lalr1.cc

@@ -567,6 +567,11 @@ m4_popdef([b4_at_dollar])])dnl
   yynewstate:
     yystate_stack_.push (yystate);
     YYCDEBUG << "Entering state " << yystate << std::endl;
+
+    /* Accept?  */
+    if (yystate == yyfinal_)
+      goto yyacceptlab;
+
     goto yybackup;
 
     /* Backup.  */
@@ -616,16 +621,11 @@ m4_ifdef([b4_lex_param], [, ]b4_lex_param))[;
 	goto yyreduce;
       }
 
-    /* Accept?  */
-    if (yyn == yyfinal_)
-      goto yyacceptlab;
-
     /* Shift the lookahead token.  */
     YY_SYMBOL_PRINT ("Shifting", yytoken, &yylval, &yylloc);
 
-    /* Discard the token being shifted unless it is eof.  */
-    if (yychar != yyeof_)
-      yychar = yyempty_;
+    /* Discard the token being shifted.  */
+    yychar = yyempty_;
 
     yysemantic_stack_.push (yylval);
     yylocation_stack_.push (yylloc);
@@ -780,9 +780,6 @@ b4_error_verbose_if([, yytoken])[));
 	YY_STACK_PRINT ();
       }
 
-    if (yyn == yyfinal_)
-      goto yyacceptlab;
-
     yyerror_range[1] = yylloc;
     // Using YYLLOC is tempting, but would change the location of
     // the lookahead.  YYLOC is available though.
@@ -808,7 +805,7 @@ b4_error_verbose_if([, yytoken])[));
     goto yyreturn;
 
   yyreturn:
-    if (yychar != yyeof_ && yychar != yyempty_)
+    if (yychar != yyempty_)
       yydestruct_ ("Cleanup: discarding lookahead", yytoken, &yylval, &yylloc);
 
     /* Do not reclaim the symbols of the rule which action triggered

data/yacc.c

@@ -1164,6 +1164,9 @@ m4_ifdef([b4_at_dollar_used], [[  yylsp[0] = yylloc;
 
   YYDPRINTF ((stderr, "Entering state %d\n", yystate));
 
+  if (yystate == YYFINAL)
+    YYACCEPT;
+
   goto yybackup;
 
 /*-----------.
@@ -1213,9 +1216,6 @@ yybackup:
       goto yyreduce;
     }
 
-  if (yyn == YYFINAL)
-    YYACCEPT;
-
   /* Count tokens shifted since error; after three, turn off error
      status.  */
   if (yyerrstatus)
@@ -1224,9 +1224,8 @@ yybackup:
   /* Shift the lookahead token.  */
   YY_SYMBOL_PRINT ("Shifting", yytoken, &yylval, &yylloc);
 
-  /* Discard the shifted token unless it is eof.  */
-  if (yychar != YYEOF)
-    yychar = YYEMPTY;
+  /* Discard the shifted token.  */
+  yychar = YYEMPTY;
 
   yystate = yyn;
   *++yyvsp = yylval;
@@ -1418,9 +1417,6 @@ yyerrlab1:
       YY_STACK_PRINT (yyss, yyssp);
     }
 
-  if (yyn == YYFINAL)
-    YYACCEPT;
-
   *++yyvsp = yylval;
 ]b4_locations_if([[
   yyerror_range[1] = yylloc;
@@ -1461,7 +1457,7 @@ yyexhaustedlab:
 #endif
 
 yyreturn:
-  if (yychar != YYEOF && yychar != YYEMPTY)
+  if (yychar != YYEMPTY)
      yydestruct ("Cleanup: discarding lookahead",
 		 yytoken, &yylval]b4_locations_if([, &yylloc])[]b4_user_args[);
   /* Do not reclaim the symbols of the rule which action triggered