Re: Enum for token '0', EOF

[Joel E. Denny]

On Tue, 25 Jul 2006, Joel E. Denny wrote:

> On Wed, 12 Jul 2006, Joel E. Denny wrote:
> 
> > I went ahead.  As far as I can tell, all the skeletons now (after my 
> > uncommitted patch below) consistently pop EOF one time upon a successful 
> > parse.
> 
> I'd like to commit this patch.  I'll do so in a few days if there are no 
> objections.

> The full patch is here:
> 
>   http://lists.gnu.org/archive/html/help-bison/2006-07/msg00023.html

I committed the following.

Joel

Index: ChangeLog
===================================================================
RCS file: /sources/bison/bison/ChangeLog,v
retrieving revision 1.1538
diff -p -u -r1.1538 ChangeLog
--- ChangeLog   25 Jul 2006 06:45:05 -0000      1.1538
+++ ChangeLog   29 Jul 2006 04:10:32 -0000
@@ -1,3 +1,32 @@
+2006-07-29  Joel E. Denny  <address@hidden>
+
+       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.
+
 2006-07-24  Paul Eggert  <address@hidden>
 
        Update to latest gnulib and gettext versions.
Index: data/glr.c
===================================================================
RCS file: /sources/bison/bison/data/glr.c,v
retrieving revision 1.185
diff -p -u -r1.185 glr.c
--- data/glr.c  9 Jul 2006 20:36:33 -0000       1.185
+++ data/glr.c  29 Jul 2006 04:10:33 -0000
@@ -2261,7 +2261,8 @@ yyrecoverSyntaxError (yyGLRStack* yystac
            }
        }
 ]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;
Index: data/lalr1.cc
===================================================================
RCS file: /sources/bison/bison/data/lalr1.cc,v
retrieving revision 1.138
diff -p -u -r1.138 lalr1.cc
--- data/lalr1.cc       12 Jul 2006 18:01:19 -0000      1.138
+++ data/lalr1.cc       29 Jul 2006 04:10:33 -0000
@@ -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_para
        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
Index: data/yacc.c
===================================================================
RCS file: /sources/bison/bison/data/yacc.c,v
retrieving revision 1.150
diff -p -u -r1.150 yacc.c
--- data/yacc.c 9 Jul 2006 20:36:33 -0000       1.150
+++ data/yacc.c 29 Jul 2006 04:10:34 -0000
@@ -1164,6 +1164,9 @@ m4_ifdef([b4_at_dollar_used], [[  yylsp[
 
   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
Index: src/reader.c
===================================================================
RCS file: /sources/bison/bison/src/reader.c,v
retrieving revision 1.265
diff -p -u -r1.265 reader.c
--- src/reader.c        9 Jul 2006 20:36:33 -0000       1.265
+++ src/reader.c        29 Jul 2006 04:10:34 -0000
@@ -488,7 +488,11 @@ packgram (void)
         rule.  Thus, the midrule actions have already been scanned in order to
         set `used' flags for this rule's rhs, so grammar_rule_check will work
         properly.  */
-      grammar_rule_check (p);
+      /* Don't check the generated rule 0.  It has no action, so some rhs
+        symbols may appear unused, but the parsing algorithm ensures that
+        %destructor's are invoked appropriately.  */
+      if (p != grammar)
+       grammar_rule_check (p);
 
       for (p = p->next; p && p->sym; p = p->next)
        {
Index: tests/actions.at
===================================================================
RCS file: /sources/bison/bison/tests/actions.at,v
retrieving revision 1.60
diff -p -u -r1.60 actions.at
--- tests/actions.at    23 Jun 2006 20:17:28 -0000      1.60
+++ tests/actions.at    29 Jul 2006 04:10:34 -0000
@@ -197,8 +197,9 @@ AT_LALR1_CC_IF([typedef yy::location YYL
 ]AT_LALR1_CC_IF([], [static void yyerror (const char *msg);])
 [}
 
-]m4_ifval([$6], [%type <ival> '(' 'x' 'y' ')' ';' thing line input])[
+]m4_ifval([$6], [%type <ival> '(' 'x' 'y' ')' ';' thing line input END])[
 
+/* FIXME: This %printer isn't actually tested.  */
 %printer
   {
     ]AT_LALR1_CC_IF([debug_stream () << $$;],
@@ -226,6 +227,11 @@ AT_LALR1_CC_IF([typedef yy::location YYL
   { printf ("Freeing token 'y' (address@hidden)\n", $$, RANGE (@$)); }
   'y'
 
+%token END 0
+%destructor
+  { printf ("Freeing token END (address@hidden)\n", $$, RANGE (@$)); }
+  END
+
 %%
 /*
    This grammar is made to exercise error recovery.
@@ -241,7 +247,7 @@ input:
       printf ("input (address@hidden): /* Nothing */\n", $$, RANGE (@$));
     }
 | line input /* Right recursive to load the stack so that popping at
-               EOF can be exercised.  */
+               END can be exercised.  */
     {
       $$ = 2;
       printf ("input (address@hidden): line (address@hidden) input 
(address@hidden)\n",
@@ -308,7 +314,7 @@ yylex (]AT_LEX_FORMALS[)
   if (source[c])
     printf ("sending: '%c'", source[c]);
   else
-    printf ("sending: EOF");
+    printf ("sending: END");
   printf (" (address@hidden)\n", c, RANGE (]AT_LOC[));
   return source[c];
 }
@@ -372,9 +378,10 @@ sending: 'x' (address@hidden)
 thing (address@hidden): 'x' (address@hidden)
 sending: ')' (address@hidden)
 line (address@hidden): '(' (address@hidden) thing (address@hidden) ')' 
(address@hidden)
-sending: EOF (address@hidden)
+sending: END (address@hidden)
 input (address@hidden): /* Nothing */
 input (address@hidden): line (address@hidden) input (address@hidden)
+Freeing token END (address@hidden)
 Freeing nterm input (address@hidden)
 Successful parse.
 ]])
@@ -391,9 +398,10 @@ sending: 'y' (address@hidden)
 Freeing token 'y' (address@hidden)
 sending: ')' (address@hidden)
 line (address@hidden): '(' (address@hidden) error (@10-19) ')' (address@hidden)
-sending: EOF (address@hidden)
+sending: END (address@hidden)
 input (address@hidden): /* Nothing */
 input (address@hidden): line (address@hidden) input (address@hidden)
+Freeing token END (address@hidden)
 Freeing nterm input (address@hidden)
 Successful parse.
 ]])
@@ -445,12 +453,45 @@ input (address@hidden): /* Nothing */
 input (address@hidden): line (address@hidden) input (address@hidden)
 input (address@hidden): line (address@hidden) input (address@hidden)
 input (address@hidden): line (address@hidden) input (address@hidden)
-130-139: syntax error, unexpected 'y', expecting $end
+130-139: syntax error, unexpected 'y', expecting END
 Freeing nterm input (address@hidden)
 Freeing token 'y' (address@hidden)
 Parsing FAILED.
 ]])
 
+
+# Syntax error caught by the parser where lookahead = END
+# --------------------------------------------------------
+# Load the stack and provoke an error that cannot be caught by the
+# grammar, to check that the stack is cleared.  And make sure the
+# lookahead is freed.
+#
+#     '(', 'x', ')',
+#     '(', 'x', ')',
+#     'x'
+AT_PARSER_CHECK([./input '(x)(x)x'], 1,
+[[sending: '(' (address@hidden)
+sending: 'x' (address@hidden)
+thing (address@hidden): 'x' (address@hidden)
+sending: ')' (address@hidden)
+line (address@hidden): '(' (address@hidden) thing (address@hidden) ')' 
(address@hidden)
+sending: '(' (address@hidden)
+sending: 'x' (address@hidden)
+thing (address@hidden): 'x' (address@hidden)
+sending: ')' (address@hidden)
+line (address@hidden): '(' (address@hidden) thing (address@hidden) ')' 
(address@hidden)
+sending: 'x' (address@hidden)
+thing (address@hidden): 'x' (address@hidden)
+sending: END (address@hidden)
+70-79: syntax error, unexpected END, expecting 'x'
+Freeing nterm thing (address@hidden)
+Freeing nterm line (address@hidden)
+Freeing nterm line (address@hidden)
+Freeing token END (address@hidden)
+Parsing FAILED.
+]])
+
+
 # Check destruction upon stack overflow
 # -------------------------------------
 # Upon stack overflow, all symbols on the stack should be destroyed.