+ 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 '='
+ ^^^
+
+* Noteworthy changes in release 2.7 (2012-12-12) [stable]
+
+** Bug fixes
+
+ Warnings about uninitialized yylloc in yyparse have been fixed.
+
+ Restored C90 compliance (yet no report was ever made).
+
+** Diagnostics are improved
+
+ Contributed by Théophile Ranquet.
+
+*** Changes in the format of error messages
+
+ This used to be the format of many error reports:
+
+ input.y:2.7-12: %type redeclaration for exp
+ input.y:1.7-12: previous declaration
+
+ It is now:
+
+ input.y:2.7-12: error: %type redeclaration for exp
+ input.y:1.7-12: previous declaration
+
+*** New format for error reports: carets
+
+ Caret errors have been added to Bison:
+
+ input.y:2.7-12: error: %type redeclaration for exp
+ %type <sval> exp
+ ^^^^^^
+ input.y:1.7-12: previous declaration
+ %type <ival> exp
+ ^^^^^^
+
+ or
+
+ input.y:3.20-23: error: ambiguous reference: '$exp'
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^^
+ input.y:3.1-3: refers to: $exp at $$
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^
+ input.y:3.6-8: refers to: $exp at $1
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^
+ input.y:3.14-16: refers to: $exp at $3
+ exp: exp '+' exp { $exp = $1 + $3; };
+ ^^^
+
+ The default behaviour for now is still not to display these unless
+ explictly asked with -fcaret (or -fall). However, in a later release, it
+ will be made the default behavior (but may still be deactivated with
+ -fno-caret).
+
+** New value for %define variable: api.pure full
+
+ The %define variable api.pure requests a pure (reentrant) parser. However,
+ for historical reasons, using it in a location-tracking Yacc parser
+ resulted in a yyerror function that did not take a location as a
+ parameter. With this new value, the user may request a better pure parser,
+ where yyerror does take a location as a parameter (in location-tracking
+ parsers).
+
+ The use of "%define api.pure true" is deprecated in favor of this new
+ "%define api.pure full".
+
+** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
+
+ The %define variable api.location.type defines the name of the type to use
+ for locations. When defined, Bison no longer generates the position.hh
+ and location.hh files, nor does the parser will include them: the user is
+ then responsible to define her type.
+
+ This can be used in programs with several parsers to factor their location
+ and position files: let one of them generate them, and the others just use
+ them.
+
+ This feature was actually introduced, but not documented, in Bison 2.5,
+ under the name "location_type" (which is maintained for backward
+ compatibility).
+
+ For consistency, lalr1.java's %define variables location_type and
+ position_type are deprecated in favor of api.location.type and
+ api.position.type.
+
+** Exception safety (lalr1.cc)
+
+ The parse function now catches exceptions, uses the %destructors to
+ release memory (the lookahead symbol and the symbols pushed on the stack)
+ before re-throwing the exception.
+
+ This feature is somewhat experimental. User feedback would be
+ appreciated.
+
+** Graph improvements in DOT and XSLT
+
+ Contributed by Théophile Ranquet.
+
+ The graphical presentation of the states is more readable: their shape is
+ now rectangular, the state number is clearly displayed, and the items are
+ numbered and left-justified.
+
+ The reductions are now explicitly represented as transitions to other
+ diamond shaped nodes.
+
+ These changes are present in both --graph output and xml2dot.xsl XSLT
+ processing, with minor (documented) differences.
+
+** %language is no longer an experimental feature.
+
+ The introduction of this feature, in 2.4, was four years ago. The
+ --language option and the %language directive are no longer experimental.
+
+** Documentation
+
+ The sections about shift/reduce and reduce/reduce conflicts resolution
+ have been fixed and extended.
+
+ Although introduced more than four years ago, XML and Graphviz reports
+ were not properly documented.
+
+ The translation of mid-rule actions is now described.
+
+* Noteworthy changes in release 2.6.5 (2012-11-07) [stable]
+
+ We consider compiler warnings about Bison generated parsers to be bugs.
+ Rather than working around them in your own project, please consider
+ reporting them to us.
+
+** Bug fixes
+
+ Warnings about uninitialized yylval and/or yylloc for push parsers with a
+ pure interface have been fixed for GCC 4.0 up to 4.8, and Clang 2.9 to
+ 3.2.
+
+ Other issues in the test suite have been addressed.
+
+ Nul characters are correctly displayed in error messages.
+
+ When possible, yylloc is correctly initialized before calling yylex. It
+ is no longer necessary to initialize it in the %initial-action.
+
+* Noteworthy changes in release 2.6.4 (2012-10-23) [stable]
+
+ Bison 2.6.3's --version was incorrect. This release fixes this issue.
+
+* Noteworthy changes in release 2.6.3 (2012-10-22) [stable]
+
+** Bug fixes
+
+ Bugs and portability issues in the test suite have been fixed.
+
+ Some errors in translations have been addressed, and --help now directs
+ users to the appropriate place to report them.
+
+ Stray Info files shipped by accident are removed.
+
+ Incorrect definitions of YY_, issued by yacc.c when no parser header is
+ generated, are removed.
+
+ All the generated headers are self-contained.
+
+** Header guards (yacc.c, glr.c, glr.cc)
+
+ In order to avoid collisions, the header guards are now
+ YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>.
+ For instance the header generated from
+
+ %define api.prefix "calc"
+ %defines "lib/parse.h"
+
+ will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
+
+** Fix compiler warnings in the generated parser (yacc.c, glr.c)
+
+ The compilation of pure parsers (%define api.pure) can trigger GCC
+ warnings such as:
+
+ input.c: In function 'yyparse':
+ input.c:1503:12: warning: 'yylval' may be used uninitialized in this
+ function [-Wmaybe-uninitialized]
+ *++yyvsp = yylval;
+ ^
+
+ This is now fixed; pragmas to avoid these warnings are no longer needed.
+
+ Warnings from clang ("equality comparison with extraneous parentheses" and
+ "function declared 'noreturn' should not return") have also been
+ addressed.
+
+* Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
+
+** Bug fixes
+
+ Buffer overruns, complaints from Flex, and portability issues in the test
+ suite have been fixed.
+
+** Spaces in %lex- and %parse-param (lalr1.cc, glr.cc)
+
+ Trailing end-of-lines in %parse-param or %lex-param would result in
+ invalid C++. This is fixed.
+
+** Spurious spaces and end-of-lines
+
+ The generated files no longer end (nor start) with empty lines.
+
+* Noteworthy changes in release 2.6.1 (2012-07-30) [stable]
+
+ Bison no longer executes user-specified M4 code when processing a grammar.
+
+** Future Changes
+
+ In addition to the removal of the features announced in Bison 2.6, the
+ next major release will remove the "Temporary hack for adding a semicolon
+ to the user action", as announced in the release 2.5. Instead of:
+
+ exp: exp "+" exp { $$ = $1 + $3 };
+
+ write:
+
+ exp: exp "+" exp { $$ = $1 + $3; };
+
+** Bug fixes
+
+*** Type names are now properly escaped.
+
+*** glr.cc: set_debug_level and debug_level work as expected.
+
+*** Stray @ or $ in actions
+
+ While Bison used to warn about stray $ or @ in action rules, it did not
+ for other actions such as printers, destructors, or initial actions. It
+ now does.
+
+** Type names in actions
+
+ For consistency with rule actions, it is now possible to qualify $$ by a
+ type-name in destructors, printers, and initial actions. For instance:
+
+ %printer { fprintf (yyo, "(%d, %f)", $<ival>$, $<fval>$); } <*> <>;
+
+ will display two values for each typed and untyped symbol (provided
+ that YYSTYPE has both "ival" and "fval" fields).
+
+* Noteworthy changes in release 2.6 (2012-07-19) [stable]
+
+** Future changes
projects / bison.git / blobdiff