X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/9d9b8b70061b84abff1222350bc94f033cee6d62..27622431dcbe1369cebac305a6d76ccd94ef8317:/NEWS

diff --git a/NEWS b/NEWS
index ae7c5c94..e982759c 100644
--- a/NEWS
+++ b/NEWS
@@ -3,17 +3,51 @@ Bison News
 
 Changes in version 2.1a:
 
+* Bison now allows multiple %union declarations, and concatenates
+  their contents together.
+
+* New warning: unused values
+  Typed right-hand side symbols whose value are not used are reported.
+  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 should be rewritten as:
+
+     exp: exp "?" exp ":" exp { $$ = $1 ? $3 : $5; }
+	| exp "+" exp         { $$ = $1 + $3; }
+	;
+
+  However, if the original actions were really intended, 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 (); };
+
+  Mid-rule actions that use $$ cause the corresponding value to be
+  set, therefore the following action must use it.  The following rule
+  triggers a warning about $2.
+
+     exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };
+
+  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.
@@ -664,8 +698,8 @@ 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.