* Noteworthy changes in release ?.? (????-??-??) [?]
-** Incompatible changes
+** WARNING: Future backward-incompatibilities!
+
+ 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 YYFAIL is removed (deprecated in Bison 2.4.2).
- Support for yystype and yyltype (instead of YYSTYPE and YYLTYPE)
- is removed (deprecated in Bison 1.875).
- Support for YYPARSE_PARAM is removed (deprecated in Bison 1.875).
+ Support for YYFAIL is removed (deprecated in Bison 2.4.2): use YYERROR.
+
+ Support for yystype and yyltype is removed (deprecated in Bison 1.875):
+ use YYSTYPE and YYLTYPE.
+
+ Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison
+ 1.875): use %lex-param, %parse-param, or %param.
+
+ Missing semicolons at the end of actions are no longer added (as announced
+ in the release 2.5).
+
+** Bug fixes
+
+*** The epilogue is no longer affected by internal #defines (glr.c)
+
+ 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 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).
+
+ Some error messages that reproduced excerpts of the grammar are now using
+ the caret information only. For instance on:
+
+ %%
+ exp: 'a' | 'a';
+
+ Bison 2.7 reports:
+
+ in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
+ in.y:2.12-14: warning: rule useless in parser due to conflicts: exp: 'a' [-Wother]
+
+ Now bison reports:
-** Warnings
+ in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
+ in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
+ exp: 'a' | 'a';
+ ^^^
+
+ and "bison -fno-caret" reports:
+
+ in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
+ in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
*** Enhancements of the -Werror option
The -Werror=CATEGORY option is now recognized, and will treat specified
- warnings as errors. The warnings need not have been explictly activated
- using the -W option, this is similar to what gcc 4.7 does.
+ warnings as errors. The warnings need not have been explicitly activated
+ using the -W option, this is similar to what GCC 4.7 does.
For example, given the following command line, Bison will treat both
- warnings related to POSIX Yacc incompatiblities and S/R conflicts as
+ warnings related to POSIX Yacc incompatibilities and S/R conflicts as
errors (and only those):
$ bison -Werror=yacc,error=conflicts-sr input.y
In the case of warnings treated as errors, the prefix is changed from
"warning: " to "error: ", and the suffix is displayed, in a manner similar
- to gcc, as [-Werror=CATEGORY].
+ to GCC, as [-Werror=CATEGORY].
For instance, where the previous version of Bison would report (and exit
with failure):
bar.y: error: shift/reduce conflicts: 1 found, 0 expected
bar.y: error: reduce/reduce conflicts: 2 found, 0 expected
+** Incompatibilities with POSIX Yacc
+
+ The 'yacc' category is no longer part of '-Wall', enable it explicitly
+ with '-Wyacc'.
+
** Additional yylex/yyparse arguments
The new directive %param declares additional arguments to both yylex and
%param {arg1_type *arg1} {arg2_type *arg2}
+** Variable api.token.prefix
+
+ The variable api.token.prefix changes the way tokens are identified in
+ the generated files. This is especially useful to avoid collisions
+ with identifiers in the target language. For instance
+
+ %token FILE for ERROR
+ %define api.token.prefix "TOK_"
+ %%
+ start: FILE for ERROR;
+
+ will generate the definition of the symbols TOK_FILE, TOK_for, and
+ TOK_ERROR in the generated sources. In particular, the scanner must
+ 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
+ %error-verbose directive is deprecated in favor of "%define parse.error
+ verbose".
+
+** Renamed %define variables
+
+ The following variables have been renamed for consistency. Backward
+ compatibility is ensured, but upgrading is recommended.
+
+ lr.default-reductions -> lr.default-reduction
+ lr.keep-unreachable-states -> lr.keep-unreachable-state
+ namespace -> api.namespace
+ stype -> api.value.type
+
+** 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
+ in GLR parsers, rather than being deferred. The result is that they allow
+ the programmer to prune possible parses based on the values of run-time
+ expressions.
+
+** The directive %expect-rr is now an error in non GLR mode
+
+ It used to be an error only if used in non GLR mode, _and_ if there are
+ reduce/reduce conflicts.
+
+** Tokens are numbered in their order of appearance
+
+ Contributed by Valentin Tolmer.
+
+ With '%token A B', A had a number less than the one of B. However,
+ precedence declarations used to generate a reversed order. This is now
+ fixed, and introducing tokens with any of %token, %left, %right,
+ %precedence, or %nonassoc yields the same result.
+
+ When mixing declarations of tokens with a litteral character (e.g., 'a')
+ or with an identifier (e.g., B) in a precedence declaration, Bison
+ numbered the litteral characters first. For example
+
+ %right A B 'c' 'd'
+
+ would lead to the tokens declared in this order: 'c' 'd' A B. Again, the
+ input order is now preserved.
+
+ These changes were made so that one can remove useless precedence and
+ associativity declarations (i.e., map %nonassoc, %left or %right to
+ %precedence, or to %token) and get exactly the same output.
+
+** Useless precedence and associativity
+
+ Contributed by Valentin Tolmer.
+
+ When developing 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:
+ "number"
+ | exp '+' "number"
+ | 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" '=' "number";
+
+ 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" '=' "number";
+
+ The warning is:
+
+ warning: useless precedence and associativity for '=' [-Wprecedence]
+ %nonassoc '='
+ ^^^
+
+** Empty rules
+
+ With help from Joel E. Denny and Gabriel Rassoul.
+
+ Empty rules (i.e., with an empty right-hand side) can now be explicitly
+ marked by the new %empty directive. Using %empty on a non-empty rule is
+ an error. The new -Wempty-rule warning reports empty rules without
+ %empty. On the following grammar:
+
+ %%
+ s: a b c;
+ a: ;
+ b: %empty;
+ c: 'a' %empty;
+
+ bison reports:
+
+ 3.4-5: warning: empty rule without %empty [-Wempty-rule]
+ a: {}
+ ^^
+ 5.8-13: error: %empty on non-empty rule
+ c: 'a' %empty {};
+ ^^^^^^
+
** 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".
used by the scanner, or rejecting invalid combinations from a
factory invoked by the user actions).
-** Variable api.tokens.prefix
+*** %define api.value.type variant
- The variable api.tokens.prefix changes the way tokens are identified in
- the generated files. This is especially useful to avoid collisions
- with identifiers in the target language. For instance
+ This is based on a submission from Michiel De Wilde. With help
+ from Théophile Ranquet.
- %token FILE for ERROR
- %define api.tokens.prefix "TOK_"
+ In this mode, complex C++ objects can be used as semantic values. For
+ instance:
+
+ %token <::std::string> TEXT;
+ %token <int> NUMBER;
+ %token SEMICOLON ";"
+ %type <::std::string> item;
+ %type <::std::list<std::string>> list;
%%
- start: FILE for ERROR;
+ result:
+ list { std::cout << $1 << std::endl; }
+ ;
+
+ list:
+ %empty { /* Generates an empty string list. */ }
+ | list item ";" { std::swap ($$, $1); $$.push_back ($2); }
+ ;
+
+ item:
+ TEXT { std::swap ($$, $1); }
+ | NUMBER { $$ = string_cast ($1); }
+ ;
+
+*** %define api.token.constructor
+
+ When variants are enabled, Bison can generate functions to build the
+ tokens. This guarantees that the token type (e.g., NUMBER) is consistent
+ with the semantic value (e.g., int):
+
+ parser::symbol_type yylex ()
+ {
+ parser::location_type loc = ...;
+ ...
+ return parser::make_TEXT ("Hello, world!", loc);
+ ...
+ return parser::make_NUMBER (42, loc);
+ ...
+ return parser::make_SEMICOLON (loc);
+ ...
+ }
- will generate the definition of the symbols TOK_FILE, TOK_for, and
- TOK_ERROR in the generated sources. In particular, the scanner must
- use these prefixed token names, although the grammar itself still
- uses the short names (as in the sample rule given above).
+* Noteworthy changes in release 2.7 (2012-12-12) [stable]
+
+** Bug fixes
-** Variable api.namespace
+ Warnings about uninitialized yylloc in yyparse have been fixed.
- The 'namespace' variable is renamed 'api.namespace'. Backward
- compatibility is ensured, but upgrading is recommended.
+ Restored C90 compliance (yet no report was ever made).
-** Variable parse.error
+** Diagnostics are improved
- This variable controls the verbosity of error messages. The use of the
- %error-verbose directive is deprecated in favor of "%define parse.error
- verbose".
+ Contributed by Théophile Ranquet.
-** Semantic predicates
+*** Changes in the format of error messages
- 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
- in GLR parsers, rather than being deferred. The result is that they allow
- the programmer to prune possible parses based on the values of run-time
- expressions.
+ This used to be the format of many error reports:
-** The directive %expect-rr is now an error in non GLR mode
+ input.y:2.7-12: %type redeclaration for exp
+ input.y:1.7-12: previous declaration
- It used to be an error only if used in non GLR mode, _and_ if there are
- reduce/reduce conflicts.
+ It is now:
-* Noteworthy changes in release ?.? (????-??-??) [?]
+ input.y:2.7-12: error: %type redeclaration for exp
+ input.y:1.7-12: previous declaration
+
+*** New format for error reports: carets
+
+ Caret errors have been added to Bison:
+
+ input.y:2.7-12: error: %type redeclaration for exp
+ %type <sval> exp
+ ^^^^^^
+ input.y:1.7-12: previous declaration
+ %type <ival> exp
+ ^^^^^^
+
+ or
+
+ input.y:3.20-23: error: ambiguous reference: '$exp'
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^^
+ input.y:3.1-3: refers to: $exp at $$
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^
+ input.y:3.6-8: refers to: $exp at $1
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^
+ input.y:3.14-16: refers to: $exp at $3
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^
+
+ The default behavior for now is still not to display these unless
+ explicitly asked with -fcaret (or -fall). However, in a later release, it
+ will be made the default behavior (but may still be deactivated with
+ -fno-caret).
+
+** New value for %define variable: api.pure full
+
+ The %define variable api.pure requests a pure (reentrant) parser. However,
+ for historical reasons, using it in a location-tracking Yacc parser
+ resulted in a yyerror function that did not take a location as a
+ parameter. With this new value, the user may request a better pure parser,
+ where yyerror does take a location as a parameter (in location-tracking
+ parsers).
+
+ The use of "%define api.pure true" is deprecated in favor of this new
+ "%define api.pure full".
+
+** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
+
+ The %define variable api.location.type defines the name of the type to use
+ for locations. When defined, Bison no longer generates the position.hh
+ and location.hh files, nor does the parser will include them: the user is
+ then responsible to define her type.
+
+ This can be used in programs with several parsers to factor their location
+ and position files: let one of them generate them, and the others just use
+ them.
+
+ This feature was actually introduced, but not documented, in Bison 2.5,
+ under the name "location_type" (which is maintained for backward
+ compatibility).
+
+ For consistency, lalr1.java's %define variables location_type and
+ position_type are deprecated in favor of api.location.type and
+ api.position.type.
+
+** Exception safety (lalr1.cc)
+
+ The parse function now catches exceptions, uses the %destructors to
+ release memory (the lookahead symbol and the symbols pushed on the stack)
+ before re-throwing the exception.
+
+ This feature is somewhat experimental. User feedback would be
+ appreciated.
+
+** 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.
+
+ The reductions are now explicitly represented as transitions to other
+ diamond shaped nodes.
+
+ These changes are present in both --graph output and xml2dot.xsl XSLT
+ processing, with minor (documented) differences.
+
+** %language is no longer an experimental feature.
+
+ The introduction of this feature, in 2.4, was four years ago. The
+ --language option and the %language directive are no longer experimental.
+
+** Documentation
+
+ The sections about shift/reduce and reduce/reduce conflicts resolution
+ have been fixed and extended.
+
+ Although introduced more than four years ago, XML and Graphviz reports
+ were not properly documented.
+
+ The translation of mid-rule actions is now described.
+
+* Noteworthy changes in release 2.6.5 (2012-11-07) [stable]
+
+ We consider compiler warnings about Bison generated parsers to be bugs.
+ Rather than working around them in your own project, please consider
+ reporting them to us.
+
+** Bug fixes
+
+ Warnings about uninitialized yylval and/or yylloc for push parsers with a
+ pure interface have been fixed for GCC 4.0 up to 4.8, and Clang 2.9 to
+ 3.2.
+
+ Other issues in the test suite have been addressed.
+
+ Null characters are correctly displayed in error messages.
+
+ When possible, yylloc is correctly initialized before calling yylex. It
+ is no longer necessary to initialize it in the %initial-action.
+
+* Noteworthy changes in release 2.6.4 (2012-10-23) [stable]
+
+ Bison 2.6.3's --version was incorrect. This release fixes this issue.
+
+* Noteworthy changes in release 2.6.3 (2012-10-22) [stable]
** Bug fixes
- Bugs in the test suite have been fixed.
+ Bugs and portability issues in the test suite have been fixed.
Some errors in translations have been addressed, and --help now directs
users to the appropriate place to report them.
Incorrect definitions of YY_, issued by yacc.c when no parser header is
generated, are removed.
-** Changes in the format of errors and exceptions output
+ All the generated headers are self-contained.
- This used to be the format of many error reports:
+** Header guards (yacc.c, glr.c, glr.cc)
- foo.y:5.10-24: result type clash on merge function 'merge': <t3> != <t2>
- foo.y:4.13-27: previous declaration
+ In order to avoid collisions, the header guards are now
+ YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>.
+ For instance the header generated from
- It is now:
+ %define api.prefix "calc"
+ %defines "lib/parse.h"
+
+ will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
+
+** Fix compiler warnings in the generated parser (yacc.c, glr.c)
- foo.y:5.10-25: result type clash on merge function 'merge': <t3> != <t2>
- foo.y:4.13-27: previous declaration
+ The compilation of pure parsers (%define api.pure) can trigger GCC
+ warnings such as:
+
+ input.c: In function 'yyparse':
+ input.c:1503:12: warning: 'yylval' may be used uninitialized in this
+ function [-Wmaybe-uninitialized]
+ *++yyvsp = yylval;
+ ^
+
+ This is now fixed; pragmas to avoid these warnings are no longer needed.
+
+ Warnings from clang ("equality comparison with extraneous parentheses" and
+ "function declared 'noreturn' should not return") have also been
+ addressed.
* Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
* Noteworthy changes in release 2.6 (2012-07-19) [stable]
-** Future changes:
+** Future changes
The next major release of Bison will drop support for the following
deprecated features. Please report disagreements to bug-bison@gnu.org.
These features are experimental in this version. More user feedback
will help to stabilize them.
+ Contributed by Alex Rozenman.
** IELR(1) and canonical LR(1):
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
The current Java interface is experimental and may evolve. More user
feedback will help to stabilize it.
+ Contributed by Paolo Bonzini.
** %language
Bison can now generate an XML report of the LALR(1) automaton using the new
"--xml" option. The current XML schema is experimental and may evolve. More
user feedback will help to stabilize it.
+ Contributed by Wojciech Polak.
** The grammar file may now specify the name of the parser header file using
%defines. For example:
-----
-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.
LocalWords: Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
LocalWords: extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
LocalWords: lang yyoutput dvi html ps POSIX lvalp llocp Wother nterm arg init
- LocalWords: TOK
+ LocalWords: TOK calc yyo fval Wconflicts parsers yystackp yyval yynerrs
+ LocalWords: Théophile Ranquet Santet fno fnone stype associativity Tolmer
+ LocalWords: Wprecedence Rassoul Wempty Paolo Bonzini parser's Michiel loc
+ LocalWords: redeclaration sval fcaret reentrant XSLT xsl Wmaybe yyvsp Tedi
+ LocalWords: pragmas noreturn untyped Rozenman unexpanded Wojciech Polak
+ LocalWords: Alexandre MERCHANTABILITY
Local Variables:
mode: outline
projects / bison.git / blobdiff