X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/0f11eec272453d5646e5aeda135650b4fb8ac33d..ea9a35c605c075c79da41bfeaaaa07b076bafc01:/NEWS diff --git a/NEWS b/NEWS index fd51b61b..28654769 100644 --- a/NEWS +++ b/NEWS @@ -2,20 +2,158 @@ GNU Bison NEWS * Noteworthy changes in release ?.? (????-??-??) [?] +** Warnings about useless semantic types + + Bison now warns about useless (uninhabited) semantic types. Since + semantic types are not declared to Bison (they are defined in the opaque + %union structure), it is %printer/%destructor directives about useless + types that trigger the warning: + + %token term + %type nterm + %printer {} + %destructor {} + %% + nterm: term { $$ = $1; }; + + 3.28-34: warning: type is used, but is not associated to any symbol + 4.28-34: warning: type is used, but is not associated to any symbol + +** Warnings about undeclared symbols + + Bison used to raise an error for %printer and %destructor directives for + undefined symbols. + + %printer {} symbol1 + %destructor {} symbol2 + %% + exp: "a"; + + This is now only a warning. + +** Warnings about useless destructors or printers + + Bison now warns about useless destructors or printers. In the following + example, the printer for , and the destructor for are + useless: all symbols of (token1) already have a printer, and all + symbols of type (token2) already have a destructor. + + %token token1 + token2 + token3 + token4 + %printer {} token1 + %destructor {} token2 + +** Additional yylex/yyparse arguments + + The new directive %param declares additional arguments to both yylex and + yyparse. The %lex-param, %parse-param, and %param directives support one + or more arguments. Instead of + + %lex-param {arg1_type *arg1} + %lex-param {arg2_type *arg2} + %parse-param {arg1_type *arg1} + %parse-param {arg2_type *arg2} + + one may now declare + + %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++ skeleton improvements + + 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.tokens.prefix + + 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 + + %token FILE for ERROR + %define api.tokens.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 api.namespace + + The "namespace" variable is renamed "api.namespace". Backward + compatibility is ensured, but upgrading is recommended. + +** Variable parse.error + + The variable error controls the verbosity of error messages. The + use of the %error-verbose directive is deprecated in favor of + %define parse.error "verbose". + +** Semantic predicates + + 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 + runtime expressions. + +* Noteworthy changes in release ?.? (????-??-??) [?] + ** Future changes: The next major release will drop support for generating parsers in K&R C, - and remove the definition of yystype (removal announced since Bison - 1.875). - -** Changes in regular C parsers (yacc.c): + and remove the definitions of yystype and yyltype (removal announced since + Bison 1.875). YYPARSE_PARAM and YYLEX_PARAM, which were deprecated in + favor of %parse-param and %lex-param (introduced in Bison 1.875 too), will + no longer be supported. -*** The generated header is included +** The generated header is included (yacc.c) Instead of duplicating the content of the generated header (definition of YYSTYPE, yyltype etc.), the generated parser now includes it, as was already the case for GLR or C++ parsers. +** Headers (yacc.c, glr.c, glr.cc) + +*** Guards + + The generated headers are now guarded, as is already the case for C++ + parsers (lalr1.cc). For intance, with --defines=foo.h: + + #ifndef YY_FOO_H + # define YY_FOO_H + ... + #endif /* !YY_FOO_H */ + +*** New declarations + + The generated header now declares yydebug and yyparse. Both honor + --name-prefix=bar_, and yield + + int bar_parse (void); + + rather than + + #define yyparse bar_parse + int yyparse (void); + + in order to facilitate the inclusion of several parser headers inside a + single compilation unit. + * Noteworthy changes in release 2.5.1 (2012-06-05) [stable] ** Future changes: @@ -943,26 +1081,26 @@ GNU Bison NEWS if the symbols have destructors. For instance: exp: exp "?" exp ":" exp { $1 ? $1 : $3; } - | exp "+" exp - ; + | exp "+" exp + ; will trigger a warning about $$ and $5 in the first rule, and $3 in the second ($1 is copied to $$ by the default rule). This example most likely contains three errors, and could be rewritten as: exp: exp "?" exp ":" exp - { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); } - | exp "+" exp - { $$ = $1 ? $1 : $3; if ($1) free ($3); } - ; + { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); } + | exp "+" exp + { $$ = $1 ? $1 : $3; if ($1) free ($3); } + ; However, if the original actions were really intended, memory leaks and all, the warnings can be suppressed by letting Bison believe the values are used, e.g.: exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); } - | exp "+" exp { $$ = $1; (void) $3; } - ; + | exp "+" exp { $$ = $1; (void) $3; } + ; If there are mid-rule actions, the warning is issued if no action uses it. The following triggers no warning: $1 and $3 are used. @@ -1177,6 +1315,33 @@ GNU Bison NEWS - "parsing stack overflow..." -> "parser stack overflow" GLR parsers now report "parser stack overflow" as per the Bison manual. +** %parse-param and %lex-param + The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass + additional context to yyparse and yylex. They suffer from several + shortcomings: + + - a single argument only can be added, + - their types are weak (void *), + - this context is not passed to anciliary functions such as yyerror, + - only yacc.c parsers support them. + + The new %parse-param/%lex-param directives provide a more precise control. + For instance: + + %parse-param {int *nastiness} + %lex-param {int *nastiness} + %parse-param {int *randomness} + + results in the following signatures: + + int yylex (int *nastiness); + int yyparse (int *nastiness, int *randomness); + + or, if both %pure-parser and %locations are used: + + int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness); + int yyparse (int *nastiness, int *randomness); + ** Bison now warns if it detects conflicting outputs to the same file, e.g., it generates a warning for "bison -d -o foo.h foo.y" since that command outputs both code and header to foo.h. @@ -1206,16 +1371,16 @@ GNU Bison NEWS In agreement with POSIX and with other Yaccs, leaving a default action is valid when $$ is untyped, and $1 typed: - untyped: ... typed; + untyped: ... typed; but the converse remains an error: - typed: ... untyped; + typed: ... untyped; ** Values of mid-rule actions The following code: - foo: { ... } { $$ = $1; } ... + foo: { ... } { $$ = $1; } ... was incorrectly rejected: $1 is defined in the second mid-rule action, and is equal to the $$ of the first mid-rule action.