* NEWS: Improve wording for unused-value warnings.

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 52064e7f22c21b0dd56c36220b489e8674cb9a47..176ce6f27df09ec78e2954172852b64eeade8674 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -1,7 +1,72 @@
 Bison News
 ----------
 
-Changes in the next version (not yet released):
+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 { $$ = $1 ? $1 : $3; }
+       | exp "+" exp
+       ;
+
+  will trigger a warning about $5 of the first rule, and $3 in the
+  second ($1 is copied to $$ by the default rule).  This example
+  most likely contains two 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) $3; }
+       ;
+
+  The warning is intended to help catching lost values and memory leaks.
+  If a value is ignored, its associated memory typically is not reclaimed.
+
+* %destructor vs. YYABORT, YYACCEPT, and YYERROR.
+  Destructors are now called when user code invokes YYABORT, YYACCEPT,
+  and YYERROR, for all objects on the stack, other than objects
+  corresponding to the right-hand side of the current rule.
+
+* %expect, %expect-rr
+  Incorrect numbers of expected conflicts are now actual errors,
+  instead of warnings.
+
+* GLR, YACC parsers.
+  The %parse-params are available in the %destructor's (and the
+  experimental %printer's) as per the documentation.
+
+* Bison now warns if it finds a stray `$' or `@' in an action.
+
+* %require "VERSION"
+  To specify 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
+  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.
+
+  If you do not want or can update to this scheme, the directive
+  `%define "global_tokens_and_yystype" "1"' triggers the global
+  definition of tokens and YYSTYPE.  This change is suitable both
+  for previous releases of Bison, and this one.
+
+  If you wish to update, then make sure older version of Bison will
+  fail using `%require "2.1a"'.
+
+* DJGPP support added.
+
+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
@@ -15,7 +80,9 @@ Changes in the next version (not yet released):
   has replaced "parser stack overflow", as the old message was not
   always accurate for modern Bison-generated parsers.
 
-The following change was also in version 2.0a, 2005-05-22:
+* Destructors are now called when the parser aborts, for all symbols left
+  behind on the stack.  Also, the start symbol is now destroyed after a
+  successful parse.  In both cases, the behavior was formerly inconsistent.
 
 * When generating verbose diagnostics, Bison-generated parsers no longer
   quote the literal strings associated with tokens.  For example, for
@@ -421,6 +488,8 @@ Changes in version 1.31, 2002-01-14:
   alloca is used only when compiled with GCC, to avoid portability
   problems as on AIX.
 
+* yyparse now returns 2 if memory is exhausted; formerly it dumped core.
+
 * When the generated parser lacks debugging code, YYDEBUG is now 0
   (as POSIX requires) instead of being undefined.