X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/ad6a9b97e2faacc5bbdaead4072982e294b27f2f..378f4bd846c4312ddeb11f151382226e30050d3c:/NEWS

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@@ -3,21 +3,71 @@ Bison News
 
 Changes in version 2.1a:
 
-* DJGPP support added.
+* 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) $3; }
+	;
+
+  The warning is intended to help catching lost values and memory leaks.
+  If a value is ignored, its associated memory typically is not reclaimed.
+
+* %destructor vs. YYABORT, YYACCEPT, and YYERROR.
+  Destructors are now called when user code invokes YYABORT, YYACCEPT,
+  and YYERROR, for all objects on the stack, other than objects
+  corresponding to the right-hand side of the current rule.
+
+* %expect, %expect-rr
+  Incorrect numbers of expected conflicts are now actual errors,
+  instead of warnings.
+
+* GLR, YACC parsers.
+  The %parse-params are available in the %destructor's (and the
+  experimental %printer's) as per the documentation.
+
+* Bison now warns if it finds a stray `$' 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 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.
 
   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.
+  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
   language is still English.  For details, please see the new