X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/f74b6f91f65436df4ddf87a810cfd9e5672c5fcd..381ecb068724f3ae161d7de6bdc8b3ebd402cdb4:/NEWS diff --git a/NEWS b/NEWS index 9be90dd8..dd36e633 100644 --- a/NEWS +++ b/NEWS @@ -1,65 +1,260 @@ Bison News ---------- -Changes in version 1.875e: +Changes in version 2.3+: + +* 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. + +* 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. -* New directive: %initial-action. - This directive allows the user to run arbitrary code (including - initializing @$) from yyparse before parsing starts. +* 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. -* The option `--report=lookahead' was changed to `--report=look-ahead'. - The old spelling still works, but is not documented and will be - removed. + 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. -* 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. + If you wish to update, then make sure older version of Bison will + fail using `%require "2.2"'. -* Goto numbers are no longer arbitrarily limited to 16-bit counts. +* 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: -Changes in version 1.875d, 2004-05-21: +* Possibly-incompatible changes -* 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. + - 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. -* NUL bytes are no longer allowed in Bison string literals, unfortunately. + - 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. -* %token numbers can now be hexadecimal integers, e.g., `%token FOO 0x12d'. - This is a GNU extension. + - Semicolon changes: + . Stray semicolons are no longer allowed at the start of a grammar. + . Semicolons are now required after in-grammar declarations. -* A new directive "%expect-rr N" specifies the expected number of - reduce/reduce conflicts in GLR parsers. + - 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. -* Experimental %destructor support has been added to lalr1.cc. + - NUL bytes are no longer allowed in Bison string literals, unfortunately. -Changes in version 1.875c, 2003-08-25: +* New features - (Just bug fixes.) + - GLR grammars now support locations. -Changes in version 1.875b, 2003-06-17: + - New directive: %initial-action. + This directive allows the user to run arbitrary code (including + initializing @$) from yyparse before parsing starts. -* GLR grammars now support locations. + - A new directive "%expect-rr N" specifies the expected number of + reduce/reduce conflicts in GLR parsers. -* Semicolon changes: - - Semicolons are now allowed before "|" in grammar rules, as POSIX requires. - - Stray semicolons are no longer allowed at the start of a grammar. - - Semicolons are now required after in-grammar declarations. + - %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.] -Changes in version 1.875a, 2003-02-01: + - Experimental %destructor support has been added to lalr1.cc. -* 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. + - New configure option --disable-yacc, to disable installation of the + yacc command and -ly library introduced in 1.875 for POSIX conformance. -* 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: @@ -231,7 +426,8 @@ Changes in version 1.50, 2002-10-04: 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. @@ -306,8 +502,8 @@ Changes in version 1.50, 2002-10-04: produces additional information: - itemset complete the core item sets with their closure - - lookahead [changed to `look-ahead' in 1.875e and later] - explicitly associate look-ahead tokens 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 @@ -394,6 +590,8 @@ 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. @@ -588,8 +786,8 @@ End: ----- -Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004 -Free Software Foundation, Inc. +Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, +2004, 2005, 2006 Free Software Foundation, Inc. This file is part of Bison, the GNU Compiler Compiler. @@ -605,5 +803,5 @@ 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. +the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, +Boston, MA 02110-1301, USA.