X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/805e703284f0f337311b98c1bf50cda85c68433c..32f19b6b47b41c46fdeb66b26cc67b609f8ae48c:/NEWS diff --git a/NEWS b/NEWS index 4ae7da6e..96cfa7a7 100644 --- a/NEWS +++ b/NEWS @@ -1,10 +1,542 @@ Bison News ---------- -Changes in version 1.49d: +Changes in version 2.3a+ (????-??-??): +* Previously, Bison sometimes generated parser tables containing unreachable + states. A state can become unreachable during conflict resolution if Bison + disables a shift action leading to it from a predecessor state. Bison now: -Changes in version 1.49b, 2002-08-12: + 1. Removes unreachable states. + + 2. Does not report any conflicts that appeared in unreachable states. + WARNING: As a result, you may need to update %expect and %expect-rr + directives in existing grammar files. + + 3. For any rule used only in such states, Bison now reports the rule as + "never reduced because of conflicts". + + This feature can be disabled with the following directive: + + %define lr.keep_unreachable_states + + See the %define entry in the `Bison Declaration Summary' in the Bison manual + for further discussion. + +* When instructed to generate a `.output' file including lookahead sets + (using `--report=lookahead', for example), Bison now prints each reduction's + lookahead set only next to the associated state's one item that (1) is + associated with the same rule as the reduction and (2) has its dot at the end + of its RHS. Previously, Bison also erroneously printed the lookahead set + next to all of the state's other items associated with the same rule. This + bug affected only the `.output' file and not the generated parser source + code. + +* The -g and --graph options now output graphs in Graphviz DOT format, + not VCG format. + +* An experimental directive %language specifies the language of the + generated parser, which can be C (the default) or C++. This + directive affects the skeleton used, and the names of the generated + files if the grammar file's name ends in ".y". + +* The grammar file may now specify the name of the parser header file using + %defines. For example: + + %defines "parser.h" + +* The `=' that used to be required in the following directives is now + deprecated: + + %file-prefix "parser" + %name-prefix "c_" + %output "parser.c" + +* The quotes around NAME that used to be required in the following directive + are now deprecated: + + %define NAME "VALUE" + +* Bison 2.3a provided a new set of directives as a more flexible alternative to + the traditional Yacc prologue blocks. Those have now been consolidated into + a single %code directive with an optional qualifier field, which identifies + the purpose of the code and thus the location(s) where Bison should generate + it: + + 1. `%code {CODE}' replaces `%after-header {CODE}' + 2. `%code requires {CODE}' replaces `%start-header {CODE}' + 3. `%code provides {CODE}' replaces `%end-header {CODE}' + 4. `%code top {CODE}' replaces `%before-header {CODE}' + + See the %code entries in section `Bison Declaration Summary' in the Bison + manual for a summary of the new functionality. See the new section `Prologue + Alternatives' for a detailed discussion including the advantages of %code + over the traditional Yacc prologues. + + The prologue alternatives are experimental. More user feedback will help to + determine whether they should become permanent features. + +* Revised warning: unset or unused mid-rule values + + Since Bison 2.2, Bison has warned about mid-rule values that are set but not + used within any of the actions of the parent rule. For example, Bison warns + about unused $2 in: + + exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; }; + + Now, Bison also warns about mid-rule values that are used but not set. For + example, Bison warns about unset $$ in the mid-rule action in: + + exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; }; + + However, Bison now disables both of these warnings by default since they + sometimes prove to be false alarms in existing grammars employing the Yacc + constructs $0 or $-N (where N is some positive integer). + + To enable these warnings, specify the flag `--warnings=midrule-values' or + `-W', which is a synonym for `--warnings=all'. + +* Bison now recognizes two separate kinds of default %destructor's and + %printer's: + + 1. Place `<*>' in a %destructor/%printer symbol list to define a default + %destructor/%printer for all grammar symbols for which you have formally + declared semantic type tags. + + 2. Place `<>' in a %destructor/%printer symbol list to define a default + %destructor/%printer for all grammar symbols without declared semantic + type tags. + + Bison no longer supports the `%symbol-default' notation from Bison 2.3a. + `<*>' and `<>' combined achieve the same effect with one exception: Bison no + longer applies any %destructor to a mid-rule value if that mid-rule value is + not actually ever referenced using either $$ or $n in a semantic action. + + The default %destructor's and %printer's are experimental. More user + feedback will help to determine whether they should become permanent + features. + + See the section `Freeing Discarded Symbols' in the Bison manual for further + details. + +Changes in version 2.3a, 2006-09-13: + +* Instead of %union, you can define and use your own union type + YYSTYPE if your grammar contains at least one tag. + Your YYSTYPE need not be a macro; it can be a typedef. + This change is for compatibility with other Yacc implementations, + and is required by POSIX. + +* Locations columns and lines start at 1. + In accordance with the GNU Coding Standards and Emacs. + +* You may now declare per-type and default %destructor's and %printer's: + + For example: + + %union { char *string; } + %token STRING1 + %token STRING2 + %type string1 + %type string2 + %union { char character; } + %token CHR + %type chr + %destructor { free ($$); } %symbol-default + %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1 + %destructor { } + + guarantees that, when the parser discards any user-defined symbol that has a + semantic type tag other than `', it passes its semantic value to + `free'. However, when the parser discards a `STRING1' or a `string1', it + also prints its line number to `stdout'. It performs only the second + `%destructor' in this case, so it invokes `free' only once. + + [Although we failed to mention this here in the 2.3a release, the default + %destructor's and %printer's were experimental, and they were rewritten in + future versions.] + +* Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y', + `--yacc', or `%yacc'), Bison no longer generates #define statements for + associating token numbers with token names. Removing the #define statements + helps to sanitize the global namespace during preprocessing, but POSIX Yacc + requires them. Bison still generates an enum for token names in all cases. + +* Handling of traditional Yacc prologue blocks is now more consistent but + potentially incompatible with previous releases of Bison. + + As before, you declare prologue blocks in your grammar file with the + `%{ ... %}' syntax. To generate the pre-prologue, Bison concatenates all + prologue blocks that you've declared before the first %union. To generate + the post-prologue, Bison concatenates all prologue blocks that you've + declared after the first %union. + + Previous releases of Bison inserted the pre-prologue into both the header + file and the code file in all cases except for LALR(1) parsers in C. In the + latter case, Bison inserted it only into the code file. For parsers in C++, + the point of insertion was before any token definitions (which associate + token numbers with names). For parsers in C, the point of insertion was + after the token definitions. + + Now, Bison never inserts the pre-prologue into the header file. In the code + file, it always inserts it before the token definitions. + +* Bison now provides a more flexible alternative to the traditional Yacc + prologue blocks: %before-header, %start-header, %end-header, and + %after-header. + + For example, the following declaration order in the grammar file reflects the + order in which Bison will output these code blocks. However, you are free to + declare these code blocks in your grammar file in whatever order is most + convenient for you: + + %before-header { + /* Bison treats this block like a pre-prologue block: it inserts it into + * the code file before the contents of the header file. It does *not* + * insert it into the header file. This is a good place to put + * #include's that you want at the top of your code file. A common + * example is `#include "system.h"'. */ + } + %start-header { + /* Bison inserts this block into both the header file and the code file. + * In both files, the point of insertion is before any Bison-generated + * token, semantic type, location type, and class definitions. This is a + * good place to define %union dependencies, for example. */ + } + %union { + /* Unlike the traditional Yacc prologue blocks, the output order for the + * new %*-header blocks is not affected by their declaration position + * relative to any %union in the grammar file. */ + } + %end-header { + /* Bison inserts this block into both the header file and the code file. + * In both files, the point of insertion is after the Bison-generated + * definitions. This is a good place to declare or define public + * functions or data structures that depend on the Bison-generated + * definitions. */ + } + %after-header { + /* Bison treats this block like a post-prologue block: it inserts it into + * the code file after the contents of the header file. It does *not* + * insert it into the header file. This is a good place to declare or + * define internal functions or data structures that depend on the + * Bison-generated definitions. */ + } + + If you have multiple occurrences of any one of the above declarations, Bison + will concatenate the contents in declaration order. + + [Although we failed to mention this here in the 2.3a release, the prologue + alternatives were experimental, and they were rewritten in future versions.] + +* The option `--report=look-ahead' has been changed to `--report=lookahead'. + The old spelling still works, but is not documented and may be removed + in a future release. + +Changes in version 2.3, 2006-06-05: + +* GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING', + for compatibility with LALR(1) grammars. + +* It is now documented that any definition of YYSTYPE or YYLTYPE should + be to a type name that does not contain parentheses or brackets. + +Changes in version 2.2, 2006-05-19: + +* The distribution terms for all Bison-generated parsers now permit + using the parsers in nonfree programs. Previously, this permission + was granted only for Bison-generated LALR(1) parsers in C. + +* %name-prefix changes the namespace name in C++ outputs. + +* The C++ parsers export their token_type. + +* Bison now allows multiple %union declarations, and concatenates + their contents together. + +* New warning: unused values + Right-hand side symbols whose values are not used are reported, + if the symbols have destructors. For instance: + + exp: exp "?" exp ":" exp { $1 ? $1 : $3; } + | 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 + { $$ = $1 ? $1 : $3; if ($1) free ($3); } + ; + + However, if the original actions were really intended, memory leaks + and all, the warnings can be suppressed by letting Bison believe the + values are used, e.g.: + + exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); } + | exp "+" exp { $$ = $1; (void) $3; } + ; + + 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. + + exp: exp { push ($1); } '+' exp { push ($3); sum (); }; + + The warning is intended to help catching lost values and memory leaks. + If a value is ignored, its associated memory typically is not reclaimed. + +* %destructor vs. YYABORT, YYACCEPT, and YYERROR. + Destructors are now called when user code invokes YYABORT, YYACCEPT, + and YYERROR, for all objects on the stack, other than objects + corresponding to the right-hand side of the current rule. + +* %expect, %expect-rr + Incorrect numbers of expected conflicts are now actual errors, + instead of warnings. + +* GLR, YACC parsers. + The %parse-params are available in the destructors (and the + experimental printers) as per the documentation. + +* Bison now warns if it finds a stray `$' or `@' in an action. + +* %require "VERSION" + This specifies that the grammar file depends on features implemented + in Bison version VERSION or higher. + +* lalr1.cc: The token and value types are now class members. + The tokens were defined as free form enums and cpp macros. YYSTYPE + was defined as a free form union. They are now class members: + tokens are enumerations of the `yy::parser::token' struct, and the + semantic values have the `yy::parser::semantic_type' type. + + If you do not want or can update to this scheme, the directive + `%define "global_tokens_and_yystype" "1"' triggers the global + definition of tokens and YYSTYPE. This change is suitable both + for previous releases of Bison, and this one. + + If you wish to update, then make sure older version of Bison will + fail using `%require "2.2"'. + +* DJGPP support added. + +Changes in version 2.1, 2005-09-16: + +* The C++ lalr1.cc skeleton supports %lex-param. + +* Bison-generated parsers now support the translation of diagnostics like + "syntax error" into languages other than English. The default + language is still English. For details, please see the new + Internationalization section of the Bison manual. Software + distributors should also see the new PACKAGING file. Thanks to + Bruno Haible for this new feature. + +* Wording in the Bison-generated parsers has been changed slightly to + simplify translation. In particular, the message "memory exhausted" + has replaced "parser stack overflow", as the old message was not + always accurate for modern Bison-generated parsers. + +* Destructors are now called when the parser aborts, for all symbols left + behind on the stack. Also, the start symbol is now destroyed after a + successful parse. In both cases, the behavior was formerly inconsistent. + +* When generating verbose diagnostics, Bison-generated parsers no longer + quote the literal strings associated with tokens. For example, for + a syntax error associated with '%token NUM "number"' they might + print 'syntax error, unexpected number' instead of 'syntax error, + unexpected "number"'. + +Changes in version 2.0, 2004-12-25: + +* Possibly-incompatible changes + + - Bison-generated parsers no longer default to using the alloca function + (when available) to extend the parser stack, due to widespread + problems in unchecked stack-overflow detection. You can "#define + YYSTACK_USE_ALLOCA 1" to require the use of alloca, but please read + the manual to determine safe values for YYMAXDEPTH in that case. + + - Error token location. + During error recovery, the location of the syntax error is updated + to cover the whole sequence covered by the error token: it includes + the shifted symbols thrown away during the first part of the error + recovery, and the lookahead rejected during the second part. + + - Semicolon changes: + . Stray semicolons are no longer allowed at the start of a grammar. + . Semicolons are now required after in-grammar declarations. + + - Unescaped newlines are no longer allowed in character constants or + string literals. They were never portable, and GCC 3.4.0 has + dropped support for them. Better diagnostics are now generated if + forget a closing quote. + + - NUL bytes are no longer allowed in Bison string literals, unfortunately. + +* New features + + - GLR grammars now support locations. + + - New directive: %initial-action. + This directive allows the user to run arbitrary code (including + initializing @$) from yyparse before parsing starts. + + - A new directive "%expect-rr N" specifies the expected number of + reduce/reduce conflicts in GLR parsers. + + - %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'. + This is a GNU extension. + + - The option `--report=lookahead' was changed to `--report=look-ahead'. + [However, this was changed back after 2.3.] + + - Experimental %destructor support has been added to lalr1.cc. + + - New configure option --disable-yacc, to disable installation of the + yacc command and -ly library introduced in 1.875 for POSIX conformance. + +* Bug fixes + + - For now, %expect-count violations are now just warnings, not errors. + This is for compatibility with Bison 1.75 and earlier (when there are + reduce/reduce conflicts) and with Bison 1.30 and earlier (when there + are too many or too few shift/reduce conflicts). However, in future + versions of Bison we plan to improve the %expect machinery so that + these violations will become errors again. + + - Within Bison itself, numbers (e.g., goto numbers) are no longer + arbitrarily limited to 16-bit counts. + + - Semicolons are now allowed before "|" in grammar rules, as POSIX requires. + +Changes in version 1.875, 2003-01-01: + +* The documentation license has been upgraded to version 1.2 + of the GNU Free Documentation License. + +* syntax error processing + + - In Yacc-style parsers YYLLOC_DEFAULT is now used to compute error + locations too. This fixes bugs in error-location computation. + + - %destructor + It is now possible to reclaim the memory associated to symbols + discarded during error recovery. This feature is still experimental. + + - %error-verbose + This new directive is preferred over YYERROR_VERBOSE. + + - #defining yyerror to steal internal variables is discouraged. + It is not guaranteed to work forever. + +* POSIX conformance + + - Semicolons are once again optional at the end of grammar rules. + This reverts to the behavior of Bison 1.33 and earlier, and improves + compatibility with Yacc. + + - `parse error' -> `syntax error' + Bison now uniformly uses the term `syntax error'; formerly, the code + and manual sometimes used the term `parse error' instead. POSIX + requires `syntax error' in diagnostics, and it was thought better to + be consistent. + + - The documentation now emphasizes that yylex and yyerror must be + declared before use. C99 requires this. + + - Bison now parses C99 lexical constructs like UCNs and + backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires. + + - File names are properly escaped in C output. E.g., foo\bar.y is + output as "foo\\bar.y". + + - Yacc command and library now available + The Bison distribution now installs a `yacc' command, as POSIX requires. + Also, Bison now installs a small library liby.a containing + implementations of Yacc-compatible yyerror and main functions. + This library is normally not useful, but POSIX requires it. + + - Type clashes now generate warnings, not errors. + + - If the user does not define YYSTYPE as a macro, Bison now declares it + using typedef instead of defining it as a macro. + For consistency, YYLTYPE is also declared instead of defined. + +* Other compatibility issues + + - %union directives can now have a tag before the `{', e.g., the + directive `%union foo {...}' now generates the C code + `typedef union foo { ... } YYSTYPE;'; this is for Yacc compatibility. + The default union tag is `YYSTYPE', for compatibility with Solaris 9 Yacc. + For consistency, YYLTYPE's struct tag is now `YYLTYPE' not `yyltype'. + This is for compatibility with both Yacc and Bison 1.35. + + - `;' is output before the terminating `}' of an action, for + compatibility with Bison 1.35. + + - Bison now uses a Yacc-style format for conflict reports, e.g., + `conflicts: 2 shift/reduce, 1 reduce/reduce'. + + - `yystype' and `yyltype' are now obsolescent macros instead of being + typedefs or tags; they are no longer documented and are planned to be + withdrawn in a future release. + +* GLR parser notes + + - GLR and inline + Users of Bison have to decide how they handle the portability of the + C keyword `inline'. + + - `parsing stack overflow...' -> `parser stack overflow' + GLR parsers now report `parser stack overflow' as per the Bison manual. + +* 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. + +* #line in output files + - --no-line works properly. + +* Bison can no longer be built by a K&R C compiler; it requires C89 or + later to be built. This change originally took place a few versions + ago, but nobody noticed until we recently asked someone to try + building Bison with a K&R C compiler. + +Changes in version 1.75, 2002-10-14: + +* Bison should now work on 64-bit hosts. + +* Indonesian translation thanks to Tedi Heriyanto. + +* GLR parsers + Fix spurious parse errors. + +* Pure parsers + Some people redefine yyerror to steal yyparse' private variables. + Reenable this trick until an official feature replaces it. + +* Type Clashes + In agreement with POSIX and with other Yaccs, leaving a default + action is valid when $$ is untyped, and $1 typed: + + untyped: ... typed; + + but the converse remains an error: + + typed: ... untyped; + +* Values of mid-rule actions + The following code: + + 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. + +Changes in version 1.50, 2002-10-04: * GLR parsing The declaration @@ -14,27 +546,30 @@ Changes in version 1.49b, 2002-08-12: %dprec and %merge on grammar rules allow parse-time resolution of ambiguities. Contributed by Paul Hilfinger. + Unfortunately Bison 1.50 does not work properly on 64-bit hosts + like the Alpha, so please stick to 32-bit hosts for now. + * Output Directory When not in Yacc compatibility mode, when the output file was not - specified, runnning `bison foo/bar.y' created `foo/bar.c'. It + specified, running `bison foo/bar.y' created `foo/bar.c'. It now creates `bar.c'. * Undefined token The undefined token was systematically mapped to 2 which prevented - the use of 2 from the user. This is no longer the case. + the use of 2 by the user. This is no longer the case. * Unknown token numbers - If yylex returned a code out of range, yyparse could die. This is + If yylex returned an out of range value, yyparse could die. This is no longer the case. * Error token - According to POSIX, the error token should be numbered as 256. + According to POSIX, the error token must be 256. Bison extends this requirement by making it a preference: *if* the user specified that one of her tokens is numbered 256, then error will be mapped onto another number. * Verbose error messages - They no longer report `..., expecting error or...' for state where + They no longer report `..., expecting error or...' for states where error recovery is possible. * End token @@ -47,7 +582,8 @@ Changes in version 1.49b, 2002-08-12: allowed some non-error action other than a default reduction on the error token. The new behavior has long been the documented behavior, and has long been required by POSIX. For more details, please see - . + Paul Eggert, "Reductions during Bison error handling" (2002-05-20) + . * Traces Popped tokens and nonterminals are now reported. @@ -98,9 +634,9 @@ Changes in version 1.49b, 2002-08-12: the user symbol is used in the reports, the graphs, and the verbose error messages instead of `$end', which remains being the default. For instance - %token YYEOF 0 + %token MYEOF 0 or - %token YYEOF 0 "end of file" + %token MYEOF 0 "end of file" * Semantic parser This old option, which has been broken for ages, is removed. @@ -110,20 +646,20 @@ Changes in version 1.49b, 2002-08-12: Croatian, thanks to Denis Lackovic. * Incorrect token definitions - When fed with `%token 'a' "A"', Bison used to output `#define 'a' 65'. + When given `%token 'a' "A"', Bison used to output `#define 'a' 65'. * Token definitions as enums Tokens are output both as the traditional #define's, and, provided the compiler supports ANSI C or is a C++ compiler, as enums. - This helps debuggers producing symbols instead of values. + This lets debuggers display names instead of integers. * Reports In addition to --verbose, bison supports --report=THINGS, which produces additional information: - itemset complete the core item sets with their closure - - lookahead - explicitly associate lookaheads to items + - lookahead [changed to `look-ahead' in 1.875e through 2.3, but changed back] + explicitly associate lookahead tokens to items - solved describe shift/reduce conflicts solving. Bison used to systematically output this information on top of @@ -155,7 +691,6 @@ Changes in version 1.35, 2002-03-25: This kludge also addresses some C++ problems when the stack was extended. - Changes in version 1.34, 2002-03-12: @@ -211,6 +746,8 @@ Changes in version 1.31, 2002-01-14: alloca is used only when compiled with GCC, to avoid portability problems as on AIX. +* yyparse now returns 2 if memory is exhausted; formerly it dumped core. + * When the generated parser lacks debugging code, YYDEBUG is now 0 (as POSIX requires) instead of being undefined. @@ -281,8 +818,8 @@ Changes in version 1.31, 2002-01-14: Changes in version 1.30, 2001-10-26: -* `--defines' and `--graph' have now an optionnal argument which is the - output file name. `-d' and `-g' do not change, they do not take any +* `--defines' and `--graph' have now an optional argument which is the + output file name. `-d' and `-g' do not change; they do not take any argument. * `%source_extension' and `%header_extension' are removed, failed @@ -405,21 +942,20 @@ End: ----- -Copyright (C) 2001, 2002 Free Software Foundation, Inc. +Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, +2004, 2005, 2006, 2007 Free Software Foundation, Inc. -This file is part of GNU Autoconf. +This file is part of Bison, the GNU Compiler Compiler. -GNU Autoconf is free software; you can redistribute it and/or modify +This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by -the Free Software Foundation; either version 2, or (at your option) -any later version. +the Free Software Foundation, either version 3 of the License, or +(at your option) any later version. -GNU Autoconf is distributed in the hope that it will be useful, +This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License -along with autoconf; see the file COPYING. If not, write to -the Free Software Foundation, Inc., 59 Temple Place - Suite 330, -Boston, MA 02111-1307, USA. +along with this program. If not, see .