X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/fbca394ee1416fcfa41f839abc313a037732e84d..026816664ff8283a55f91915843a8ff0ac5cf86c:/NEWS diff --git a/NEWS b/NEWS index cb594715..5df8b81a 100644 --- a/NEWS +++ b/NEWS @@ -2,16 +2,132 @@ GNU Bison NEWS * Noteworthy changes in release ?.? (????-??-??) [?] -** Incompatible changes +** Bug fixes + +*** Errors in caret diagnostics + + On some platforms, some errors could result in endless diagnostics. + +*** Fixes of the -Werror option + + Options such as "-Werror -Wno-error=foo" were still turning "foo" + diagnostics into errors instead of warnings. This is fixed. + + Actually, for consistency with GCC, "-Wno-error=foo -Werror" now also + leaves "foo" diagnostics as warnings. Similarly, with "-Werror=foo + -Wno-error", "foo" diagnostics are now errors. + +*** GLR Predicates + + As demonstrated in the documentation, one can now leave spaces between + "%?" and its "{". + +*** Installation + + The yacc.1 man page is no longer installed if --disable-yacc was + specified. + +*** Fixes in the test suite + + Bugs and portability issues. + +* Noteworthy changes in release 3.0 (2013-07-25) [stable] + +** 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 -** Warnings +*** 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 + + 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 @@ -153,6 +269,11 @@ GNU Bison NEWS 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 @@ -168,32 +289,22 @@ GNU Bison NEWS %param {arg1_type *arg1} {arg2_type *arg2} -** Java skeleton improvements +** Types of values for %define variables - 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". + 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}'. -** C++ skeletons improvements + Keyword variables are used for fixed value sets, e.g., -*** The parser header is no longer mandatory (lalr1.cc, glr.cc) + %define lr.type lalr - 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). + Code variables are used for value in the target language, e.g., -*** Locations are no longer mandatory (lalr1.cc, glr.cc) + %define api.value.type {struct semantic_type} - 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). + String variables are used remaining cases, e.g. file names. ** Variable api.token.prefix @@ -202,7 +313,7 @@ GNU Bison NEWS 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; @@ -211,14 +322,78 @@ GNU Bison NEWS 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 INT "integer" + %token STRING "string" + %printer { fprintf (yyo, "%d", $$); } + %destructor { free ($$); } + + /* 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 "integer" + %token STRING "string" + %printer { fprintf (yyo, "%d", $$); } + %destructor { free ($$); } + + /* 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 "integer" + %token 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 INT "integer" + %token STRING "string" + %printer { fprintf (yyo, "%d", $$); } + %destructor { free ($$); } + + /* In yylex(). */ + yylval.u.ival = 42; return INT; + yylval.u.sval = "42"; return STRING; ** Variable parse.error @@ -226,8 +401,20 @@ GNU Bison NEWS %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 @@ -240,28 +427,282 @@ 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 ?.? (????-??-??) [?] +** 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 -** Changes in the format of error messages + 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 + + 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". + Contributed by Paolo Bonzini. + + The Java skeleton now supports push parsing. + Contributed by Dennis Heimbigner. + +** 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: + %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': != - 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 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) @@ -282,7 +723,18 @@ GNU Bison NEWS 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 @@ -291,6 +743,24 @@ GNU Bison NEWS 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. @@ -305,7 +775,7 @@ GNU Bison NEWS 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. @@ -676,6 +1146,7 @@ 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): @@ -706,7 +1177,9 @@ 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 @@ -1192,6 +1665,7 @@ 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 @@ -1205,6 +1679,7 @@ 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: @@ -2181,7 +2656,7 @@ 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. @@ -2216,7 +2691,12 @@ along with this program. If not, see . 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