X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/9503b0a4a8928afa0fdab88672f6127ee7e87963..42fef012562597732cdf8044dbd4602bf1122170:/NEWS diff --git a/NEWS b/NEWS index 7e5bda2d..5046a9b4 100644 --- a/NEWS +++ b/NEWS @@ -2,16 +2,130 @@ 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:2.25: warning: a ';' might be needed at the end of action code + exp: "number" { $$ = $1 } + ^ + foo.y:2.25: 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: + + 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'; + ^^^ -** Warnings + 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 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 incompatibilities and S/R conflicts as + errors (and only those): + + $ bison -Werror=yacc,error=conflicts-sr input.y + + If no categories are specified, -Werror will make all active warnings into + errors. For example, the following line does the same the previous example: + + $ bison -Werror -Wnone -Wyacc -Wconflicts-sr input.y + + (By default -Wconflicts-sr,conflicts-rr,deprecated,other is enabled.) + + Note that the categories in this -Werror option may not be prefixed with + "no-". However, -Wno-error[=CATEGORY] is valid. + + Note that -y enables -Werror=yacc. Therefore it is now possible to require + Yacc-like behavior (e.g., always generate y.tab.c), but to report + incompatibilities as warnings: "-y -Wno-error=yacc". + +*** The display of warnings is now richer + + The option that controls a given warning is now displayed: + + foo.y:4.6: warning: type clash on default action: != [-Wother] + + 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]. + + For instance, where the previous version of Bison would report (and exit + with failure): + + bison: warnings being treated as errors + input.y:1.1: warning: stray ',' treated as white space + + it now reports: + + input.y:1.1: error: stray ',' treated as white space [-Werror=other] *** Deprecated constructs @@ -19,12 +133,6 @@ GNU Bison NEWS support will be discontinued. It is enabled by default. These warnings used to be reported as 'other' warnings. -*** Warning categories are now displayed - - For instance: - - foo.y:4.6: warning: type clash on default action: != [-Wother] - *** Useless semantic types Bison now warns about useless (uninhabited) semantic types. Since @@ -128,8 +236,160 @@ GNU Bison NEWS %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. + +** 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 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". @@ -155,52 +415,204 @@ GNU Bison NEWS 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 NUMBER; + %token SEMICOLON ";" + %type <::std::string> item; + %type <::std::list> 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] -** Variable api.namespace +** Bug fixes - The 'namespace' variable is renamed 'api.namespace'. Backward - compatibility is ensured, but upgrading is recommended. + Warnings about uninitialized yylloc in yyparse have been fixed. -** Variable parse.error + Restored C90 compliance (yet no report was ever made). - This variable controls the verbosity of error messages. The use of the - %error-verbose directive is deprecated in favor of "%define parse.error - verbose". +** Diagnostics are improved -** Semantic predicates + Contributed by Théophile Ranquet. - 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. +*** Changes in the format of error messages -** The directive %expect-rr is now an error in non GLR mode + This used to be the format of many error reports: - It used to be an error only if used in non GLR mode, _and_ if there are - reduce/reduce conflicts. + input.y:2.7-12: %type redeclaration for exp + input.y:1.7-12: previous declaration -* Noteworthy changes in release ?.? (????-??-??) [?] + It is now: + + 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 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) + + 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. @@ -210,17 +622,35 @@ GNU Bison NEWS 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': != - foo.y:4.13-27: previous declaration + In order to avoid collisions, the header guards are now + YY___INCLUDED, instead of merely _. + 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. - foo.y:5.10-25: result type clash on merge function 'merge': != - foo.y:4.13-27: previous declaration +** Fix compiler warnings in the generated parser (yacc.c, glr.c) + + 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] @@ -278,7 +708,7 @@ GNU Bison NEWS * 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. @@ -540,6 +970,7 @@ 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): @@ -570,7 +1001,9 @@ 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 @@ -1056,6 +1489,7 @@ 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 @@ -1069,6 +1503,7 @@ 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: @@ -2045,7 +2480,7 @@ 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. @@ -2080,7 +2515,12 @@ 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 + 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