Warn about unused values.

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 2ab95345109392bae414f129aa9bea4e2d371f3f..94e9cc17cfe181f07df0734bb9e78a64b3f87273 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,37 @@ Bison News
 
 Changes in version 2.1a:
 
+* 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; $3; }
+
+  This helps catching lost values and memory leaks: if a value is
+  ignored, its associated memory will never be reclaimed.
+
+* %destructor vs. YYABORT, YYACCEPT, and YYERROR.
+  Destructors are now called when user code invokes YYABORT, YYACCEPT,
+  and YYERROR, for all objects on the stack, other than objects
+  corresponding to the right-hand side of the current rule.
+
+* %expect, %expect-rr
+  Incorrect numbers of expected conflicts are now actual errors,
+  instead of warnings.
+
+* GLR, YACC parsers.
+  The %parse-params are available in the %destructor's (and the
+  experimental %printer's) as per the documentation.
+
 * Bison now warns if it finds a stray `$' or `@' in an action.
 
 * %require "VERSION"
@@ -10,8 +41,8 @@ Changes in version 2.1a:
   Bison version VERSION or higher.
 
 * lalr1.cc: The token and value types are now class members.
-  The tokens where defined as free form enums and cpp macros.  YYSTYPE
-  was defined as a free form union.  Both are now class members:
+  The tokens were defined as free form enums and cpp macros.  YYSTYPE
+  was defined as a free form union.  They are now class members:
   tokens are enumerations of the `yy::parser::token' struct, and the
   semantic values have the `yy::parser::semantic_type' type.
 
@@ -27,6 +58,8 @@ Changes in version 2.1a:
 
 Changes in version 2.1, 2005-09-16:
 
+* The C++ lalr1.cc skeleton supports %lex-param.
+
 * Bison-generated parsers now support the translation of diagnostics like
   "syntax error" into languages other than English.  The default
   language is still English.  For details, please see the new