* data/glr.c, data/lalr1.cc, data/yacc.c: When YYABORT was

invoked, yydestruct the lookahead.
* tests/calc.at (Calculator $1): Update the expected lengths of
traces: there is an added line for the discarded lookahead.
* doc/bison.texinfo (Destructor Decl): Some rewording.
Define "discarded" symbols.

ChangeLog

@@ -1,3 +1,12 @@
+2004-09-03  Akim Demaille  <akim@epita.fr>
+
+	* data/glr.c, data/lalr1.cc, data/yacc.c: When YYABORT was
+	invoked, yydestruct the lookahead.
+	* tests/calc.at (Calculator $1): Update the expected lengths of
+	traces: there is an added line for the discarded lookahead.
+	* doc/bison.texinfo (Destructor Decl): Some rewording.
+	Define "discarded" symbols.
+
 2004-09-02  Akim Demaille  <akim@epita.fr>
 
 	* data/lalr1.cc (translate_, destruct_): No reason to be static.

data/glr.c

@@ -1916,7 +1916,13 @@ yyrecoverSyntaxError (yyGLRStack* yystack,
       yyposn = yystack.yytops.yystates[0]->yyposn;
     }
  yyDone:
-  ;
+  /* On YYABORT, free the lookahead. */
+  if (yystack.yyerrflag == 1 && yytoken != YYEMPTY)
+    {
+      YY_SYMBOL_PRINT ("Error: discarding lookahead",
+                       yytoken, yylvalp, yyllocp);
+      yydestruct (yytoken, yylvalp]b4_location_if([, yyllocp])[);
+    }
 
   yyfreeGLRStack (&yystack);
   return yystack.yyerrflag;

data/lalr1.cc

@@ -714,6 +714,10 @@ yyacceptlab:
 
   /* Abort.  */
 yyabortlab:
+  /* Free the lookahead. */
+  YY_SYMBOL_PRINT ("Error: discarding lookahead", ilooka_, &value, &location);
+  destruct_ (ilooka_, &value, &location);
+  looka_ = empty_;
   return 1;
 }
 

data/yacc.c

@@ -1209,6 +1209,9 @@ yyacceptlab:
 | yyabortlab -- YYABORT comes here.  |
 `-----------------------------------*/
 yyabortlab:
+  YY_SYMBOL_PRINT ("Error: discarding lookahead", yytoken, &yylval, &yylloc);
+  yydestruct (yytoken, &yylval]b4_location_if([, &yylloc])[);
+  yychar = YYEMPTY;
   yyresult = 1;
   goto yyreturn;
 

doc/bison.texinfo

@@ -3734,14 +3734,13 @@ terminal symbol.  All kinds of token declarations allow
 @cindex freeing discarded symbols
 @findex %destructor
 
-Some symbols can be discarded by the parser, typically during error
+Some symbols can be discarded by the parser.  For instance, during error
-recovery (@pxref{Error Recovery}).  Basically, during error recovery,
+recovery (@pxref{Error Recovery}), embarrassing symbols already pushed
-embarrassing symbols already pushed on the stack, and embarrassing
+on the stack, and embarrassing tokens coming from the rest of the file
-tokens coming from the rest of the file are thrown away until the parser
+are thrown away until the parser falls on its feet.  If these symbols
-falls on its feet.  If these symbols convey heap based information, this
+convey heap based information, this memory is lost.  While this behavior
-memory is lost.  While this behavior is tolerable for batch parsers,
+can be tolerable for batch parsers, such as in compilers, it is not for
-such as in compilers, it is unacceptable for parsers that can
+possibly ``never ending'' parsers such as shells, or implementations of
-possibility ``never end'' such as shells, or implementations of
 communication protocols.
 
 The @code{%destructor} directive allows for the definition of code that
@@ -3794,6 +3793,22 @@ typeless: string;  // $$ = $1 does not apply; $1 is destroyed.
 typefull: string;  // $$ = $1 applies, $1 is not destroyed.
 @end smallexample
 
+@sp 1
+
+@cindex discarded symbols
+@dfn{Discarded symbols} are the following:
+
+@itemize
+@item
+stacked symbols popped during the first phase of error recovery,
+@item
+incoming terminals during the second phase of error recovery,
+@item
+the current lookahead when the parser aborts (either via an explicit
+call to @code{YYABORT}, or as a consequence of a failed error recovery).
+@end itemize
+
+
 @node Expect Decl
 @subsection Suppressing Conflict Warnings
 @cindex suppressing conflict warnings

tests/calc.at

@@ -466,21 +466,21 @@ _AT_CHECK_CALC([$1],
                [486])
 
 # Some syntax errors.
-_AT_CHECK_CALC_ERROR([$1], [1], [0 0], [11],
+_AT_CHECK_CALC_ERROR([$1], [1], [0 0], [12],
                      [1.2: syntax error, unexpected "number"])
-_AT_CHECK_CALC_ERROR([$1], [1], [1//2], [15],
+_AT_CHECK_CALC_ERROR([$1], [1], [1//2], [16],
                      [1.2: syntax error, unexpected '/', expecting "number" or '-' or '(' or '!'])
-_AT_CHECK_CALC_ERROR([$1], [1], [error], [4],
+_AT_CHECK_CALC_ERROR([$1], [1], [error], [5],
                      [1.0: syntax error, unexpected $undefined])
-_AT_CHECK_CALC_ERROR([$1], [1], [1 = 2 = 3], [22],
+_AT_CHECK_CALC_ERROR([$1], [1], [1 = 2 = 3], [23],
                      [1.6: syntax error, unexpected '='])
 _AT_CHECK_CALC_ERROR([$1], [1],
                      [
 +1],
-                     [14],
+                     [15],
                      [2.0: syntax error, unexpected '+'])
 # Exercise error messages with EOF: work on an empty file.
-_AT_CHECK_CALC_ERROR([$1], [1], [/dev/null], [4],
+_AT_CHECK_CALC_ERROR([$1], [1], [/dev/null], [5],
                      [1.0: syntax error, unexpected "end of input"])
 
 # Exercise the error token: without it, we die at the first error,