* data/lalr1.cc, data/yacc.c, data/glr.c, data/c.m4

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 293101698a24e69947ffbeb6ec257b6e67658e71..94e9cc17cfe181f07df0734bb9e78a64b3f87273 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -3,16 +3,28 @@ Bison News
 
 Changes in version 2.1a:
 
-* %destructor vs. YYACCEPT, YYERROR, and YYABORT.
-  When the parsing/action is cut by the user using one of these
-  special actions, the stack is freed except the right-hand side
-  symbols 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.
+* New warning: unused values
+  Typed right-hand side symbols whose value are not used are reported.
+  For instance
+
+       exp: exp "?" exp ":" exp { $$ = $1 + $3; }
+          | exp "+" exp
+         ;
+
+  will trigger a warning about $5 of the first rule, and $3 in the
+  second ($1 is copied to $$ by the default rule).  To avoid this
+  warning, let Bison believe the value is used, e.g.
+
+       exp: exp "?" exp ":" exp { $$ = $1 + $3; $5; }
+          | exp "+" exp         { $$ = $1; $3; }
+
+  This helps catching lost values and memory leaks: if a value is
+  ignored, its associated memory will never be 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.
 
 * %expect, %expect-rr
   Incorrect numbers of expected conflicts are now actual errors,