X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/064e42b0aca1db0ca84b06b01cac5a40f3016591..fec5f3c0cc2c50a779dafb928fda105c1782446b:/NEWS diff --git a/NEWS b/NEWS index a1bb0f91..9489c51f 100644 --- a/NEWS +++ b/NEWS @@ -2,16 +2,84 @@ GNU Bison NEWS * 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 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. + +** 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 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). + + 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: -** Warnings + 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 @@ -168,33 +236,6 @@ GNU Bison NEWS %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 - -*** 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). - ** Variable api.token.prefix The variable api.token.prefix changes the way tokens are identified in @@ -211,6 +252,12 @@ GNU Bison NEWS 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 @@ -219,15 +266,12 @@ GNU Bison NEWS lr.default-reductions -> lr.default-reduction lr.keep-unreachable-states -> lr.keep-unreachable-state namespace -> api.namespace - -** 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". + 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 @@ -240,39 +284,225 @@ GNU Bison NEWS It used to be an error only if used in non GLR mode, _and_ if there are reduce/reduce conflicts. -* Noteworthy changes in release ?.? (????-??-??) [?] +** Token numbering has changed to preserve the user-defined order -** New value for %define variable: api.pure full + 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. - The %define variable api.pure requests a pure (reentrant) parser. However, - for historical reasons, using it in a location-tracking Yacc parser resulted - in an 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). +** Useless precedence and associativity - The use of "%define api.pure true" is deprecated in favor of this new - "%define api.pure full". + 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"; -** Changes in the format of error messages + 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 '=' + ^^^ + +** 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 NUMBER; + %token SEMICOLON ";" + %type <::std::string> item; + %type <::std::list> list; + %% + result: + list { std::cout << $1 << std::endl; } + ; + + list: + /* nothing */ { /* Generates an empty string list */ } + | list item ";" { std::swap ($$, $1); $$.push_back ($2); } + ; + + item: + TEXT { std::swap ($$, $1); } + | NUMBER { $$ = string_cast ($1); } + ; + +*** %define api.token.constructor + + When variants are enabled, Bison can generate functions to build the + tokens. This guarantees that the token type (e.g., NUMBER) is consistent + with the semantic value (e.g., int): + + parser::symbol_type yylex () + { + parser::location_type loc = ...; + ... + return parser::make_TEXT ("Hello, world!", loc); + ... + return parser::make_NUMBER (42, loc); + ... + return parser::make_SEMICOLON (loc); + ... + } + +* Noteworthy changes in release 2.7 (2012-12-12) [stable] + +** Bug fixes + + Warnings about uninitialized yylloc in yyparse have been fixed. + + Restored C90 compliance (yet no report was ever made). + +** Diagnostics are improved + + Contributed by Théophile Ranquet. + +*** Changes in the format of error messages This used to be the format of many error reports: - foo.y:5.10-24: result type clash on merge function 'merge': != - foo.y:4.13-27: previous declaration + input.y:2.7-12: %type redeclaration for exp + input.y:1.7-12: previous declaration It is now: - foo.y:5.10-25: result type clash on merge function 'merge': != - foo.y:4.13-27: previous declaration + input.y:2.7-12: error: %type redeclaration for exp + input.y:1.7-12: previous declaration -** Exception safety (lalr1.cc) +*** New format for error reports: carets - The parse function now catches exceptions, uses the %destructors to - release memory (the lookahead symbol and the symbols pushed on the stack) - before re-throwing the exception. + Caret errors have been added to Bison: - This feature is somewhat experimental. User feedback would be - appreciated. + input.y:2.7-12: error: %type redeclaration for exp + %type exp + ^^^^^^ + input.y:1.7-12: previous declaration + %type exp + ^^^^^^ + + or + + input.y:3.20-23: error: ambiguous reference: '$exp' + exp: exp '+' exp { $exp = $1 + $3; }; + ^^^^ + input.y:3.1-3: refers to: $exp at $$ + 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 behaviour for now is still not to display these unless + explictly 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) @@ -293,8 +523,19 @@ GNU Bison NEWS 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. @@ -305,19 +546,21 @@ GNU Bison NEWS These changes are present in both --graph output and xml2dot.xsl XSLT processing, with minor (documented) differences. - Two nodes were added to the documentation: Xml and Graphviz. - -* Noteworthy changes in release ?.? (????-??-??) [?] - -** Bug fixes +** %language is no longer an experimental feature. - Warnings about uninitialized yylloc in yyparse have been fixed. + 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. @@ -703,6 +946,7 @@ GNU Bison NEWS 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): @@ -733,7 +977,9 @@ GNU Bison NEWS 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 @@ -1219,6 +1465,7 @@ GNU Bison NEWS The current Java interface is experimental and may evolve. More user feedback will help to stabilize it. + Contributed by Paolo Bonzini. ** %language @@ -1232,6 +1479,7 @@ GNU Bison NEWS 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: @@ -2208,7 +2456,7 @@ Output file does not redefine const for C++. ----- -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.