* Noteworthy changes in release ?.? (????-??-??) [?]
-** Incompatible changes
+
+* Noteworthy changes in release 2.7.90 (2013-05-30) [beta]
+
+** 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).
+
+*** Use of YACC='bison -y'
+
+ TL;DR: With Autoconf <= 2.69, pass -Wno-yacc to (AM_)YFLAGS if you use
+ Bison extensions.
+
+ Traditional Yacc generates 'y.tab.c' whatever the name of the input file.
+ Therefore Makefiles written for Yacc expect 'y.tab.c' (and possibly
+ 'y.tab.h' and 'y.outout') to be generated from 'foo.y'.
+
+ To this end, for ages, AC_PROG_YACC, Autoconf's macro to look for an
+ implementation of Yacc, was using Bison as 'bison -y'. While it does
+ ensure compatible output file names, it also enables warnings for
+ incompatibilities with POSIX Yacc. In other words, 'bison -y' triggers
+ warnings for Bison extensions.
+
+ Autoconf 2.70+ fixes this incompatibility by using YACC='bison -o y.tab.c'
+ (which also generates 'y.tab.h' and 'y.output' when needed).
+ Alternatively, disable Yacc warnings by passing '-Wno-yacc' to your Yacc
+ flags (YFLAGS, or AM_YFLAGS with Automake).
+
+** 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.
+
+*** Warnings about useless %pure-parser/%define api.pure are restored
+
+** Diagnostics reported by Bison
+
+ Most of these features were contributed by Théophile Ranquet and Victor
+ Santet.
+
+*** Carets
-** Warnings
+ 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:
+
+ 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
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}
-** Java skeleton improvements
-
- 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".
-
-** C++ skeletons improvements
+** Types of values for %define variables
-*** The parser header is no longer mandatory (lalr1.cc, glr.cc)
+ Bison used to make no difference between '%define foo bar' and '%define
+ foo "bar"'. The former is now called a 'keyword value', and the latter a
+ 'string value'. A third kind was added: 'code values', such as '%define
+ foo {bar}'.
- Using %defines is now optional. Without it, the needed support classes
- are defined in the generated parser, instead of additional files (such as
- location.hh, position.hh and stack.hh).
+ Keyword variables are used for fixed value sets, e.g.,
-*** Locations are no longer mandatory (lalr1.cc, glr.cc)
+ %define lr.type lalr
- Both lalr1.cc and glr.cc no longer require %location.
+ Code variables are used for value in the target language, e.g.,
-*** syntax_error exception (lalr1.cc)
+ %define api.value.type {struct semantic_type}
- The C++ parser features a syntax_error exception, which can be
- thrown from the scanner or from user rules to raise syntax errors.
- This facilitates reporting errors caught in sub-functions (e.g.,
- rejecting too large integral literals from a conversion function
- used by the scanner, or rejecting invalid combinations from a
- factory invoked by the user actions).
+ String variables are used remaining cases, e.g. file names.
** Variable api.token.prefix
with identifiers in the target language. For instance
%token FILE for ERROR
- %define api.token.prefix "TOK_"
+ %define api.token.prefix {TOK_}
%%
start: FILE for ERROR;
use these prefixed token names, although the grammar itself still
uses the short names (as in the sample rule given above).
-** Renamed %define variables
+** Variable api.value.type
- The following variables have been renamed for consistency. Backward
- compatibility is ensured, but upgrading is recommended.
+ This new %define variable supersedes the #define macro YYSTYPE. The use
+ of YYSTYPE is discouraged. In particular, #defining YYSTYPE *and* either
+ using %union or %defining api.value.type results in undefined behavior.
- lr.default-reductions -> lr.default-reduction
- lr.keep-unreachable-states -> lr.keep-unreachable-state
- namespace -> api.namespace
+ Either define api.value.type, or use "%union":
+
+ %union
+ {
+ int ival;
+ char *sval;
+ }
+ %token <ival> INT "integer"
+ %token <sval> STRING "string"
+ %printer { fprintf (yyo, "%d", $$); } <ival>
+ %destructor { free ($$); } <sval>
+
+ /* In yylex(). */
+ yylval.ival = 42; return INT;
+ yylval.sval = "42"; return STRING;
+
+ The %define variable api.value.type supports both keyword and code values.
+
+ The keyword value 'union' means that the user provides genuine types, not
+ union member names such as "ival" and "sval" above (WARNING: will fail if
+ -y/--yacc/%yacc is enabled).
+
+ %define api.value.type union
+ %token <int> INT "integer"
+ %token <char *> STRING "string"
+ %printer { fprintf (yyo, "%d", $$); } <int>
+ %destructor { free ($$); } <char *>
+
+ /* In yylex(). */
+ yylval.INT = 42; return INT;
+ yylval.STRING = "42"; return STRING;
+
+ The keyword value variant is somewhat equivalent, but for C++ special
+ provision is made to allow classes to be used (more about this below).
+
+ %define api.value.type variant
+ %token <int> INT "integer"
+ %token <std::string> STRING "string"
+
+ Code values (in braces) denote user defined types. This is where YYSTYPE
+ used to be used.
+
+ %code requires
+ {
+ struct my_value
+ {
+ enum
+ {
+ is_int, is_string
+ } kind;
+ union
+ {
+ int ival;
+ char *sval;
+ } u;
+ };
+ }
+ %define api.value.type {struct my_value}
+ %token <u.ival> INT "integer"
+ %token <u.sval> STRING "string"
+ %printer { fprintf (yyo, "%d", $$); } <u.ival>
+ %destructor { free ($$); } <u.sval>
+
+ /* In yylex(). */
+ yylval.u.ival = 42; return INT;
+ yylval.u.sval = "42"; return STRING;
** Variable parse.error
%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
It used to be an error only if used in non GLR mode, _and_ if there are
reduce/reduce conflicts.
-* Noteworthy changes in release ?.? (????-??-??) [?]
+** 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
-** Changes in the format of error messages
+ 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".
+
+** C++ skeletons improvements
+
+*** The parser header is no longer mandatory (lalr1.cc, glr.cc)
+
+ Using %defines is now optional. Without it, the needed support classes
+ are defined in the generated parser, instead of additional files (such as
+ location.hh, position.hh and stack.hh).
+
+*** Locations are no longer mandatory (lalr1.cc, glr.cc)
+
+ Both lalr1.cc and glr.cc no longer require %location.
+
+*** syntax_error exception (lalr1.cc)
+
+ The C++ parser features a syntax_error exception, which can be
+ thrown from the scanner or from user rules to raise syntax errors.
+ This facilitates reporting errors caught in sub-functions (e.g.,
+ rejecting too large integral literals from a conversion function
+ used by the scanner, or rejecting invalid combinations from a
+ factory invoked by the user actions).
+
+*** %define api.value.type variant
+
+ This is based on a submission from Michiel De Wilde. With help
+ from Théophile Ranquet.
+
+ 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;
+ %%
+ 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);
+ ...
+ }
+
+*** C++ locations
+
+ There are operator- and operator-= for 'location'. Negative line/column
+ increments can no longer underflow the resulting value.
+
+* Noteworthy changes in release 2.7.1 (2013-04-15) [stable]
+
+** Bug fixes
+
+*** Fix compiler attribute portability (yacc.c)
+
+ With locations enabled, __attribute__ was used unprotected.
+
+*** Fix some compiler warnings (lalr1.cc)
+
+* Noteworthy changes in release 2.7 (2012-12-12) [stable]
+
+** Bug fixes
+
+ Warnings about uninitialized yylloc in yyparse have been fixed.
+
+ Restored C90 compliance (yet no report was ever made).
+
+** Diagnostics are improved
+
+ Contributed by Théophile Ranquet.
+
+*** Changes in the format of error messages
This used to be the format of many error reports:
- foo.y:5.10-24: result type clash on merge function 'merge': <t3> != <t2>
- foo.y:4.13-27: previous declaration
+ input.y:2.7-12: %type redeclaration for exp
+ input.y:1.7-12: previous declaration
It is now:
- foo.y:5.10-25: result type clash on merge function 'merge': <t3> != <t2>
- foo.y:4.13-27: previous declaration
+ input.y:2.7-12: error: %type redeclaration for exp
+ input.y:1.7-12: previous declaration
-** Exception safety (lalr1.cc)
+*** New format for error reports: carets
- 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.
+ Caret errors have been added to Bison:
- This feature is somewhat experimental. User feedback would be
- appreciated.
+ 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)
position_type are deprecated in favor of api.location.type and
api.position.type.
-** Graphviz improvements
+** 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
The reductions are now explicitly represented as transitions to other
diamond shaped nodes.
-* Noteworthy changes in release ?.? (????-??-??) [?]
+ 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
Other issues in the test suite have been addressed.
- Nul characters are correctly displayed in error messages.
+ 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.
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 calc yyo fval Wconflicts
+ 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 yytype
Local Variables:
mode: outline
projects / bison.git / blobdiff