X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/29103e06b5c28c6f545c9f0f0aee57ff4c2ceef1..27622431dcbe1369cebac305a6d76ccd94ef8317:/NEWS diff --git a/NEWS b/NEWS index 5c5e8c41..e982759c 100644 --- a/NEWS +++ b/NEWS @@ -1,28 +1,172 @@ Bison News ---------- -Changes in version 1.875c: +Changes in version 2.1a: -Changes in version 1.875b, 2003-06-17: +* Bison now allows multiple %union declarations, and concatenates + their contents together. -* GLR grammars now support locations. +* New warning: unused values + Typed right-hand side symbols whose value are not used are reported. + For instance: -* 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. + 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 should be rewritten as: + + exp: exp "?" exp ":" exp { $$ = $1 ? $3 : $5; } + | exp "+" exp { $$ = $1 + $3; } + ; + + However, if the original actions were really intended, 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 (); }; + + Mid-rule actions that use $$ cause the corresponding value to be + set, therefore the following action must use it. The following rule + triggers a warning about $2. + + exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; }; + + The warning is intended to help catching lost values and memory leaks. + If a value is ignored, its associated memory typically is not reclaimed. + +* %destructor vs. YYABORT, YYACCEPT, and YYERROR. + Destructors are now called when user code invokes YYABORT, YYACCEPT, + and YYERROR, for all objects on the stack, other than objects + corresponding to the right-hand side of the current rule. + +* %expect, %expect-rr + Incorrect numbers of expected conflicts are now actual errors, + instead of warnings. + +* GLR, YACC parsers. + The %parse-params are available in the %destructor's (and the + experimental %printer's) as per the documentation. + +* Bison now warns if it finds a stray `$' or `@' in an action. + +* %require "VERSION" + To specify 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 "2.1a"'. + +* DJGPP support added. + +Changes in version 2.1, 2005-09-16: + +* The C++ lalr1.cc skeleton supports %lex-param. -Changes in version 1.875a, 2003-02-01: +* 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. -* 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. +* 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. -* New configure option --disable-yacc, to disable installation of the - yacc command and -ly library introduced in 1.875 for POSIX conformance. +* 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'. + The old spelling still works, but is not documented and will be + removed. + + - 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: @@ -194,7 +338,8 @@ 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. @@ -269,8 +414,8 @@ Changes in version 1.50, 2002-10-04: 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 and later] + explicitly associate look-ahead tokens to items - solved describe shift/reduce conflicts solving. Bison used to systematically output this information on top of @@ -357,6 +502,8 @@ 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. @@ -551,8 +698,8 @@ End: ----- -Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003 -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. @@ -568,5 +715,5 @@ 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.