Destructor cleanups and regularization among the three skeletons.

* NEWS: Document the behavior changes.
* data/glr.c (yyrecoverSyntaxError): Don't bother to pop the
stack before failing, as the cleanup code will do it for us now.
* data/lalr1.cc (yyerrlab): Likewise.
* data/glr.c (yyparse): Pop everything off the stack before
freeing it, so that destructors get called properly.
* data/lalr1.cc (yyreturn): Likewise.
* data/yacc.c (yyreturn): Pop and destroy the start symbol, too.
This is more consistent.
* doc/bison.texinfo (Destructor Decl): Mention more reasons
why destructors might be called.  1.875 -> 2.1.
(Destructor Decl, Decl Summary, Table of Symbols):
Some English-language cleanups for %destructor.
* tests/actions.at (_AT_CHECK_PRINTER_AND_DESTRUCTOR):
Add output line for destructor of start symbol.
* tests/calc.at (AT_CHECK_CALC): Add one to line counts,
because of that same extra output line.

ChangeLog

@@ -1,5 +1,24 @@
 2005-07-18  Paul Eggert  <eggert@cs.ucla.edu>
 
+	Destructor cleanups and regularization among the three skeletons.
+	* NEWS: Document the behavior changes.
+	* data/glr.c (yyrecoverSyntaxError): Don't bother to pop the
+	stack before failing, as the cleanup code will do it for us now.
+	* data/lalr1.cc (yyerrlab): Likewise.
+	* data/glr.c (yyparse): Pop everything off the stack before
+	freeing it, so that destructors get called properly.
+	* data/lalr1.cc (yyreturn): Likewise.
+	* data/yacc.c (yyreturn): Pop and destroy the start symbol, too.
+	This is more consistent.
+	* doc/bison.texinfo (Destructor Decl): Mention more reasons
+	why destructors might be called.  1.875 -> 2.1.
+	(Destructor Decl, Decl Summary, Table of Symbols):
+	Some English-language cleanups for %destructor.
+	* tests/actions.at (_AT_CHECK_PRINTER_AND_DESTRUCTOR):
+	Add output line for destructor of start symbol.
+	* tests/calc.at (AT_CHECK_CALC): Add one to line counts,
+	because of that same extra output line.
+
 	* NEWS: Document minor wording changes in diagnostics of
 	Bison-generated parsers.
 	* data/glr.c (yyMemoryExhausted): Renamed from yyStackOverflow.

NEWS

@@ -15,6 +15,10 @@ Changes in the next version (not yet released):
   has replaced "parser stack overflow", as the old message was not
   always accurate for modern Bison-generated parsers.
 
+* Destructors are now called when the parser aborts, for all symbols left
+  behind on the stack.  Also, the start symbol is now destroyed after a
+  successful parse.  In both cases, the behavior was formerly inconsistent.
+
 The following change was also in version 2.0a, 2005-05-22:
 
 * When generating verbose diagnostics, Bison-generated parsers no longer

data/glr.c

@@ -1846,21 +1846,7 @@ yyrecoverSyntaxError (yyGLRStack* yystack,
     while (yytrue)
       {
 	if (*yytokenp == YYEOF)
-	  {
-	    /* Now pop stack until empty and fail. */
-	    while (yystack->yytops.yystates[0] != NULL)
-	      {
-		yyGLRState *yys = yystack->yytops.yystates[0];
-]b4_location_if([[		yystack->yyerror_range[1].yystate.yyloc = yys->yyloc;]])[
-		yydestruct ("Error: popping",
-                            yystos[yys->yylrState],
-			    &yys->yysemantics.yysval]b4_location_if([, &yys->yyloc])[);
-		yystack->yytops.yystates[0] = yys->yypred;
-		yystack->yynextFree -= 1;
-		yystack->yyspaceLeft += 1;
-	      }
-	    yyFail (yystack][]b4_lpure_args[, NULL);
-	  }
+	  yyFail (yystack][]b4_lpure_args[, NULL);
 	if (*yytokenp != YYEMPTY)
 	  {]b4_location_if([[
 	    /* We throw away the lookahead, but the error range
@@ -2122,6 +2108,19 @@ b4_syncline([@oline@], [@ofile@])])dnl
     yydestruct ("Error: discarding lookahead",
                 yytoken, yylvalp]b4_location_if([, yyllocp])[);
 
+  /* Now pop stack until empty, destroying its entries as we go.  */
+  while (yystack.yytops.yystates[0] != NULL)
+    {
+      yyGLRState *yys = yystack.yytops.yystates[0];
+]b4_location_if([[      yystack.yyerror_range[1].yystate.yyloc = yys->yyloc;]])[
+      yydestruct ("Error: popping",
+		  yystos[yys->yylrState],
+		  &yys->yysemantics.yysval]b4_location_if([, &yys->yyloc])[);
+      yystack.yytops.yystates[0] = yys->yypred;
+      yystack.yynextFree -= 1;
+      yystack.yyspaceLeft += 1;
+    }
+
   yyfreeGLRStack (&yystack);
   return yyresult;
 }

data/lalr1.cc

@@ -729,23 +729,11 @@ yyerrlab:
       /* If just tried and failed to reuse look-ahead token after an
 	 error, discard it.  */
 
-      /* Return failure if at end of input.  */
       if (yylooka_ <= yyeof_)
         {
-          /* If at end of input, pop the error token,
-	     then the rest of the stack, then return failure.  */
+	  /* Return failure if at end of input.  */
 	  if (yylooka_ == yyeof_)
-	     for (;;)
-	       {
-                 yyerror_range_[0] = yylocation_stack_[0];
-                 yypop_ ();
-		 if (yystate_stack_.height () == 1)
-		   YYABORT;
-                 yydestruct_ ("Error: popping",
-                              yystos_[yystate_stack_[0]],
-                              &yysemantic_stack_[0],
-                              &yylocation_stack_[0]);
-	       }
+	    YYABORT;
         }
       else
         {
@@ -768,7 +756,7 @@ yyerrorlab:
      YYERROR and the label yyerrorlab therefore never appears in user
      code.  */
   if (false)
-     goto yyerrorlab;
+    goto yyerrorlab;
 
   yyerror_range_[0] = yylocation_stack_[yylen_ - 1];
   yypop_ (yylen_);
@@ -838,6 +826,16 @@ yyabortlab:
 yyreturn:
   if (yylooka_ != yyeof_ && yylooka_ != yyempty_)
     yydestruct_ ("Error: discarding lookahead", yyilooka_, &yylval, &yylloc);
+
+  while (yystate_stack_.height () != 1)
+    {
+      yydestruct_ ("Error: popping",
+		   yystos_[yystate_stack_[0]],
+		   &yysemantic_stack_[0],
+		   &yylocation_stack_[0]);
+      yypop_ ();
+    }
+
   return yyresult_;
 }
 

data/yacc.c

@@ -1220,8 +1220,7 @@ yyerrlab:
 
       if (yychar <= YYEOF)
         {
-          /* If at end of input, pop the error token,
-	     then the rest of the stack, then return failure.  */
+	  /* Return failure if at end of input.  */
 	  if (yychar == YYEOF)
 	    YYABORT;
         }
@@ -1333,16 +1332,12 @@ yyreturn:
   if (yychar != YYEOF && yychar != YYEMPTY)
      yydestruct ("Error: discarding lookahead",
 		 yytoken, &yylval]b4_location_if([, &yylloc])[);
-  if (yyssp != yyss)
-    for (;;)
-      {
-]b4_location_if([[	yyerror_range[0] = *yylsp;]])[
-	YYPOPSTACK;
-	if (yyssp == yyss)
-	  break;
-	yydestruct ("Error: popping",
-		    yystos[*yyssp], yyvsp]b4_location_if([, yylsp])[);
-      }
+  while (yyssp != yyss)
+    {
+      yydestruct ("Error: popping",
+		  yystos[*yyssp], yyvsp]b4_location_if([, yylsp])[);
+      YYPOPSTACK;
+    }
 #ifndef yyoverflow
   if (yyss != yyssa)
     YYSTACK_FREE (yyss);

doc/bison.texinfo

@@ -3792,28 +3792,31 @@ For instance, if your locations use a file name, you may use
 @cindex freeing discarded symbols
 @findex %destructor
 
-Some symbols can be discarded by the parser.  For instance, during error
-recovery (@pxref{Error Recovery}), embarrassing symbols already pushed
-on the stack, and embarrassing tokens coming from the rest of the file
-are thrown away until the parser falls on its feet.  If these symbols
-convey heap based information, this memory is lost.  While this behavior
-can be tolerable for batch parsers, such as in compilers, it is not for
-possibly ``never ending'' parsers such as shells, or implementations of
-communication protocols.
+Some symbols can be discarded by the parser.  During error
+recovery (@pxref{Error Recovery}), symbols already pushed
+on the stack and tokens coming from the rest of the file
+are discarded until the parser falls on its feet.  If the parser
+runs out of memory, all the symbols on the stack must be discarded.
+Even if the parser succeeds, it must discard the start symbol.
 
-The @code{%destructor} directive allows for the definition of code that
-is called when a symbol is thrown away.
+When discarded symbols convey heap based information, this memory is
+lost.  While this behavior can be tolerable for batch parsers, such as
+in traditional compilers, it is unacceptable for programs like shells
+or protocol implementations that may parse and execute indefinitely.
+
+The @code{%destructor} directive defines code that
+is called when a symbol is discarded.
 
 @deffn {Directive} %destructor @{ @var{code} @} @var{symbols}
 @findex %destructor
-Declare that the @var{code} must be invoked for each of the
-@var{symbols} that will be discarded by the parser.  The @var{code}
-should use @code{$$} to designate the semantic value associated to the
-@var{symbols}.  The additional parser parameters are also available
+Invoke @var{code} whenever the parser discards one of the
+@var{symbols}.  Within @var{code}, @code{$$} designates the semantic
+value associated with the discarded symbol.  The additional
+parser parameters are also available
 (@pxref{Parser Function, , The Parser Function @code{yyparse}}).
 
-@strong{Warning:} as of Bison 1.875, this feature is still considered as
-experimental, as there was not enough user feedback.  In particular,
+@strong{Warning:} as of Bison 2.1, this feature is still
+experimental, as there has not been enough user feedback.  In particular,
 the syntax might still change.
 @end deffn
 
@@ -3830,7 +3833,7 @@ For instance:
 @end smallexample
 
 @noindent
-guarantees that when a @code{STRING} or a @code{string} will be discarded,
+guarantees that when a @code{STRING} or a @code{string} is discarded,
 its associated memory will be freed.
 
 Note that in the future, Bison might also consider that right hand side
@@ -3862,8 +3865,11 @@ stacked symbols popped during the first phase of error recovery,
 @item
 incoming terminals during the second phase of error recovery,
 @item
-the current look-ahead when the parser aborts (either via an explicit
-call to @code{YYABORT}, or as a consequence of a failed error recovery).
+the current look-ahead and the entire stack when the parser aborts
+(either via an explicit call to @code{YYABORT}, or as a consequence of
+a failed error recovery or of memory exhaustion), and
+@item
+the start symbol, when the parser succeeds.
 @end itemize
 
 
@@ -4085,7 +4091,7 @@ above-mentioned declarations and to the token type codes.
 @end deffn
 
 @deffn {Directive} %destructor
-Specifying how the parser should reclaim the memory associated to
+Specify how the parser should reclaim the memory associated to
 discarded symbols.  @xref{Destructor Decl, , Freeing Discarded Symbols}.
 @end deffn
 
@@ -7821,7 +7827,7 @@ Bison declaration to create a header file meant for the scanner.
 @end deffn
 
 @deffn {Directive} %destructor
-Specifying how the parser should reclaim the memory associated to
+Specify how the parser should reclaim the memory associated to
 discarded symbols.  @xref{Destructor Decl, , Freeing Discarded Symbols}.
 @end deffn
 

tests/actions.at

@@ -373,6 +373,7 @@ line (0@0-29): '(' (0@0-9) thing (1@10-19) ')' (2@20-29)
 sending: EOF (3@30-39)
 input (0@29-29): /* Nothing */
 input (2@0-29): line (0@0-29) input (0@29-29)
+Freeing nterm input (2@0-29)
 Successful parse.
 ]])
 
@@ -391,6 +392,7 @@ line (-1@0-29): '(' (0@0-9) error (@10-19) ')' (2@20-29)
 sending: EOF (3@30-39)
 input (0@29-29): /* Nothing */
 input (2@0-29): line (-1@0-29) input (0@29-29)
+Freeing nterm input (2@0-29)
 Successful parse.
 ]])
 

tests/calc.at

@@ -463,7 +463,7 @@ _AT_CHECK_CALC([$1],
 
 2^2^3 = 256
 (2^2)^3 = 64],
-               [570])
+               [571])
 
 # Some syntax errors.
 _AT_CHECK_CALC_ERROR([$1], [1], [0 0], [13],
@@ -501,7 +501,7 @@ _AT_CHECK_CALC_ERROR([$1], [1], [/dev/null], [4],
 #
 _AT_CHECK_CALC_ERROR([$1], [0],
                      [() + (1 + 1 + 1 +) + (* * *) + (1 * 2 * *) = 1],
-                     [188],
+                     [189],
 [1.1: syntax error, unexpected ')', expecting number or '-' or '(' or '!'
 1.17: syntax error, unexpected ')', expecting number or '-' or '(' or '!'
 1.22: syntax error, unexpected '*', expecting number or '-' or '(' or '!'
@@ -510,10 +510,10 @@ calc: error: 4444 != 1])
 
 # The same, but this time exercising explicitly triggered syntax errors.
 # POSIX says the look-ahead causing the error should not be discarded.
-_AT_CHECK_CALC_ERROR([$1], [0], [(!) + (0 0) = 1], [75],
+_AT_CHECK_CALC_ERROR([$1], [0], [(!) + (0 0) = 1], [76],
 [1.9: syntax error, unexpected number
 calc: error: 2222 != 1])
-_AT_CHECK_CALC_ERROR([$1], [0], [(- *) + (0 0) = 1], [85],
+_AT_CHECK_CALC_ERROR([$1], [0], [(- *) + (0 0) = 1], [86],
 [1.3: syntax error, unexpected '*', expecting number or '-' or '(' or '!'
 1.11: syntax error, unexpected number
 calc: error: 2222 != 1])