X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/284bc49c832ffe6280907cb6c7788fa06bc58c7c..4c9b8f1318c68238074ee19e7ab976a22924540e:/NEWS diff --git a/NEWS b/NEWS index 62f834b6..9a6a1e14 100644 --- a/NEWS +++ b/NEWS @@ -30,7 +30,7 @@ GNU Bison NEWS ** Bug fixes -*** The epilogue is no longer affected by internal #defines +*** 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 @@ -58,6 +58,29 @@ GNU Bison NEWS 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 The -Werror=CATEGORY option is now recognized, and will treat specified @@ -198,13 +221,6 @@ GNU Bison NEWS bar.y: error: shift/reduce conflicts: 1 found, 0 expected bar.y: error: reduce/reduce conflicts: 2 found, 0 expected -*** Useless precedence - - Bison now warns about symbols with a declared precedence but 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. - ** Additional yylex/yyparse arguments The new directive %param declares additional arguments to both yylex and @@ -220,45 +236,6 @@ GNU Bison NEWS %param {arg1_type *arg1} {arg2_type *arg2} -** 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). - -** 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 @@ -281,6 +258,16 @@ 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. @@ -303,6 +290,177 @@ GNU Bison NEWS 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 '=' + ^^^ + +** 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 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); + ... + } + * Noteworthy changes in release 2.7 (2012-12-12) [stable] ** Bug fixes