X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/7d6bad195977b0204fc8406cac57cf5a4f1c769b..9a9130f26d8df2c1fe2051c5881e0da804ba8e9c:/NEWS?ds=sidebyside diff --git a/NEWS b/NEWS index 461959e0..5b9a6e80 100644 --- a/NEWS +++ b/NEWS @@ -2,7 +2,21 @@ 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 @@ -14,7 +28,29 @@ GNU Bison NEWS Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison 1.875): use %lex-param, %parse-param, or %param. -** Warnings +** 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 @@ -177,55 +213,6 @@ 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). - -*** The epilogue is no longer affected by internal #defines - - 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 (yy::parser::semantic_type *yylval); - - This is has been fixed: yylval, ynerrs, yychar, and yylloc are now valid - identifiers for user-provided variables. - -** 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 - ** Variable api.token.prefix The variable api.token.prefix changes the way tokens are identified in @@ -242,16 +229,26 @@ 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 + 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 @@ -264,6 +261,159 @@ GNU Bison NEWS 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 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"; + + 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 @@ -274,6 +424,8 @@ GNU Bison NEWS ** Diagnostics are improved + Contributed by Théophile Ranquet. + *** Changes in the format of error messages This used to be the format of many error reports: @@ -359,6 +511,8 @@ GNU Bison NEWS ** 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. @@ -800,7 +954,9 @@ 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