Add "2.1b".

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index ae7c5c9499d3197ca41350ccdd41529195864ef2..702f45b715821be9ec5a4c23881d4bc3d0f641ea 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -1,32 +1,67 @@
 Bison News
 ----------
 
-Changes in version 2.1a:
+Changes in version 2.1b:
+
+* No user-visible changes.
+
+Changes in version 2.1a, 2006-02-13:
+
+* Bison now allows multiple %union declarations, and concatenates
+  their contents together.
+
+* New warning: unused values
+  Right-hand side symbols whose values are not used are reported,
+  if the symbols have destructors.  For instance:
+
+     exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
+       | exp "+" exp
+       ;
+
+  will trigger a warning about $$ and $5 in the first rule, and $3 in
+  the second ($1 is copied to $$ by the default rule).  This example
+  most likely contains three errors, and could be rewritten as:
+
+     exp: exp "?" exp ":" exp
+           { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
+       | exp "+" exp
+           { $$ = $1 ? $1 : $3; if ($1) free ($3); }
+       ;
+
+  However, if the original actions were really intended, memory leaks
+  and all, the warnings can be suppressed by letting Bison believe the
+  values are used, e.g.:
+
+     exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
+       | exp "+" exp         { $$ = $1; (void) $3; }
+       ;
+
+  If there are mid-rule actions, the warning is issued if no action
+  uses it.  The following triggers no warning: $1 and $3 are used.
+
+     exp: exp { push ($1); } '+' exp { push ($3); sum (); };
+
+  The warning is intended to help catching lost values and memory leaks.
+  If a value is ignored, its associated memory typically is not reclaimed.
 
 * %destructor vs. YYABORT, YYACCEPT, and YYERROR.
   Destructors are now called when user code invokes YYABORT, YYACCEPT,
   and YYERROR, for all objects on the stack, other than objects
   corresponding to the right-hand side of the current rule.
 
-* GLR, C++ LALR(1) parsers.
-  These parser skeletons are now distributed with the same special
-  license exception that the C LALR(1) parser skeleton has had since
-  Bison 1.24.  Hence the FSF imposes no copyright restriction on the
-  output of Bison when it is generating such parsers.
-
 * %expect, %expect-rr
   Incorrect numbers of expected conflicts are now actual errors,
   instead of warnings.
 
 * GLR, YACC parsers.
-  The %parse-params are available in the %destructor's (and the
-  experimental %printer's) as per the documentation.
+  The %parse-params are available in the destructors (and the
+  experimental printers) as per the documentation.
 
 * Bison now warns if it finds a stray `$' or `@' in an action.
 
 * %require "VERSION"
-  To specify that the grammar file depends on features implemented in
-  Bison version VERSION or higher.
+  This specifies that the grammar file depends on features implemented
+  in Bison version VERSION or higher.
 
 * lalr1.cc: The token and value types are now class members.
   The tokens were defined as free form enums and cpp macros.  YYSTYPE
@@ -664,8 +699,8 @@ End:
 
 -----
 
-Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
-Free Software Foundation, Inc.
+Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
+2004, 2005, 2006 Free Software Foundation, Inc.
 
 This file is part of Bison, the GNU Compiler Compiler.