* Noteworthy changes in release ?.? (????-??-??) [?]
-** Incompatible changes
+** WARNING: Future backward-incompatibilities!
+
+ Bison will stop adding a semicolon at the end of the actions (as announced
+ in the release 2.5):
+
+ foo.y:2.22: warning: a ';' might be needed at the end of action code
+ exp: "num" { $$ = $1 }
+ ^
+ foo.y:2.22: future versions of Bison will not add the ';'
+
+ Like other GNU packages, Bison will start using some of the C99 features
+ for its own code, especially the definition of variables after statements.
+ The generated C parsers still aim at C90.
+
+** Backward incompatible changes
*** Obsolete features
Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison
1.875): use %lex-param, %parse-param, or %param.
-** Warnings
+** Bug fixes
+
+*** The epilogue is no longer affected by internal #defines
+
+ The glr.c skeleton uses defines such as #define yylval (yystackp->yyval) in
+ generated code. These weren't properly undefined before the inclusion of
+ the user epilogue, so functions such as the following were butchered by the
+ preprocessor expansion:
+
+ int yylex (YYSTYPE *yylval);
+
+ This is has been fixed: yylval, yynerrs, yychar, and yylloc are now valid
+ identifiers for user-provided variables.
+
+*** stdio.h is no longer needed when locations are enabled (yacc.c)
+
+ Changes in Bison 2.7 introduced a dependency on FILE and fprintf when
+ locations are enabled. This is fixed.
+
+** Diagnostics reported by Bison
+
+ Most of these features were contributed by Théophile Ranquet and Victor
+ Santet.
+
+*** Carets
+
+ Version 2.7 introduced caret errors, for a prettier output. These are now
+ activated by default. The old format can still be used by invoking Bison
+ with -fno-caret (or -fnone).
*** Enhancements of the -Werror option
** Java skeleton improvements
+ Contributed by Paolo Bonzini.
+
The constants for token names were moved to the Lexer interface. Also, it
is possible to add code to the parser's constructors using "%code init"
and "%define init_throws".
use these prefixed token names, although the grammar itself still
uses the short names (as in the sample rule given above).
-
-
** Variable parse.error
This variable controls the verbosity of error messages. The use of the
** Semantic predicates
+ Contributed by Paul Hilfinger.
+
The new, experimental, semantic-predicate feature allows actions of the
form "%?{ BOOLEAN-EXPRESSION }", which cause syntax errors (as for
YYERROR) if the expression evaluates to 0, and are evaluated immediately
It used to be an error only if used in non GLR mode, _and_ if there are
reduce/reduce conflicts.
+** Token numbering has changed to preserve the user-defined order
+
+ When declaring %token A B, the numbering for A is inferior to B. Up to now,
+ when declaring associativity at the same time, with %left (or %right,
+ %precedence, %nonassoc), B was inferior to A.
+
+** Useless precedence and associativity
+
+ Contributed by Valentin Tolmer.
+
+ When developping and maintaining a grammar, useless associativity and
+ precedence directives are common. They can be a nuisance: new ambiguities
+ arising are sometimes masked because their conflicts are resolved due to
+ the extra precedence or associativity information. Furthermore, it can
+ hinder the comprehension of a new grammar: one will wonder about the role
+ of a precedence, where in fact it is useless. The following changes aim
+ at detecting and reporting these extra directives.
+
+*** Precedence warning category
+
+ A new category of warning, -Wprecedence, was introduced. It flags the
+ useless precedence and associativity directives.
+
+*** Useless associativity
+
+ Bison now warns about symbols with a declared associativity that is never
+ used to resolve conflicts. In that case, using %precedence is sufficient;
+ the parsing tables will remain unchanged. Solving these warnings may raise
+ useless precedence warnings, as the symbols no longer have associativity.
+ For example:
+
+ %left '+'
+ %left '*'
+ %%
+ exp:
+ "num"
+ | exp '+' "num"
+ | exp '*' exp
+ ;
+
+ will produce a
+
+ warning: useless associativity for '+', use %precedence [-Wprecedence]
+ %left '+'
+ ^^^
+
+*** Useless precedence
+
+ Bison now warns about symbols with a declared precedence and no declared
+ associativity (i.e., declared with %precedence), and whose precedence is
+ never used. In that case, the symbol can be safely declared with %token
+ instead, without modifying the parsing tables. For example:
+
+ %precedence '='
+ %%
+ exp: "var" '=' "num";
+
+ will produce a
+
+ warning: useless precedence for '=' [-Wprecedence]
+ %precedence '='
+ ^^^
+
+*** Useless precedence and associativity
+
+ In case of both useless precedence and associativity, the issue is flagged
+ as follows:
+
+ %nonassoc '='
+ %%
+ exp: "var" '=' "num";
+
+ The warning is:
+
+ warning: useless precedence and associativity for '=' [-Wprecedence]
+ %nonassoc '='
+ ^^^
+
* Noteworthy changes in release 2.7 (2012-12-12) [stable]
** Bug fixes
** Diagnostics are improved
+ Contributed by Théophile Ranquet.
+
*** Changes in the format of error messages
This used to be the format of many error reports:
** Graph improvements in DOT and XSLT
+ Contributed by Théophile Ranquet.
+
The graphical presentation of the states is more readable: their shape is
now rectangular, the state number is clearly displayed, and the items are
numbered and left-justified.
These features are experimental. More user feedback will help to
stabilize them.
-** LAC (Lookahead Correction) for syntax error handling:
+** LAC (Lookahead Correction) for syntax error handling
+
+ Contributed by Joel E. Denny.
Canonical LR, IELR, and LALR can suffer from a couple of problems
upon encountering a syntax error. First, the parser might perform
-----
-Copyright (C) 1995-2012 Free Software Foundation, Inc.
+Copyright (C) 1995-2013 Free Software Foundation, Inc.
This file is part of Bison, the GNU Parser Generator.
projects / bison.git / blobdiff