warnings: introduce -Wprecedence

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 29b6b3230ebac5ae128a77d43a9c16496ce6988b..be3669a91869f7de7b206e39fc2f40a5719ac623 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -2,25 +2,70 @@ GNU Bison NEWS
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 

-** Incompatible changes
+** WARNING: Future backward-incompatibilities!
+
+  Bison will stop adding a semicolon at the end of the actions (as announced
+  in the release 2.5):
+
+    foo.y:2.22: warning: a ';' might be needed at the end of action code
+     exp: "num" { $$ = $1 }
+                          ^
+    foo.y:2.22:     future versions of Bison will not add the ';'
+
+  Like other GNU packages, Bison will start using some of the C99 features
+  for its own code, especially the definition of variables after statements.
+  The generated C parsers still aim at C90.
+
+** Backward incompatible changes

 
 *** Obsolete features
 
 
 *** Obsolete features
 

-  Support for YYFAIL is removed (deprecated in Bison 2.4.2).
-  Support for yystype and yyltype (instead of YYSTYPE and YYLTYPE)
-  is removed (deprecated in Bison 1.875).
-  Support for YYPARSE_PARAM is removed (deprecated in Bison 1.875).
+  Support for YYFAIL is removed (deprecated in Bison 2.4.2): use YYERROR.
+
+  Support for yystype and yyltype is removed (deprecated in Bison 1.875):
+  use YYSTYPE and YYLTYPE.
+
+  Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison
+  1.875): use %lex-param, %parse-param, or %param.
+
+** Bug fixes
+
+*** The epilogue is no longer affected by internal #defines
+
+  The glr.c skeleton uses defines such as #define yylval (yystackp->yyval) in
+  generated code.  These weren't properly undefined before the inclusion of
+  the user epilogue, so functions such as the following were butchered by the
+  preprocessor expansion:

 
 

-** Warnings
+    int yylex (YYSTYPE *yylval);
+
+  This is has been fixed: yylval, yynerrs, yychar, and yylloc are now valid
+  identifiers for user-provided variables.
+
+*** stdio.h is no longer needed when locations are enabled (yacc.c)
+
+  Changes in Bison 2.7 introduced a dependency on FILE and fprintf when
+  locations are enabled.  This is fixed.
+
+** Diagnostics reported by Bison
+
+  Most of these features were contributed by Théophile Ranquet and Victor
+  Santet.
+
+*** Carets
+
+  Version 2.7 introduced caret errors, for a prettier output.  These are now
+  activated by default.  The old format can still be used by invoking Bison
+  with -fno-caret (or -fnone).

 
 *** Enhancements of the -Werror option
 
   The -Werror=CATEGORY option is now recognized, and will treat specified
 
 *** Enhancements of the -Werror option
 
   The -Werror=CATEGORY option is now recognized, and will treat specified

-  warnings as errors. The warnings need not have been explictly activated
-  using the -W option, this is similar to what gcc 4.7 does.
+  warnings as errors. The warnings need not have been explicitly activated
+  using the -W option, this is similar to what GCC 4.7 does.

 
   For example, given the following command line, Bison will treat both
 
   For example, given the following command line, Bison will treat both

-  warnings related to POSIX Yacc incompatiblities and S/R conflicts as
+  warnings related to POSIX Yacc incompatibilities and S/R conflicts as

   errors (and only those):
 
     $ bison -Werror=yacc,error=conflicts-sr input.y
   errors (and only those):
 
     $ bison -Werror=yacc,error=conflicts-sr input.y


@@ -47,7 +92,7 @@ GNU Bison NEWS
 
   In the case of warnings treated as errors, the prefix is changed from
   "warning: " to "error: ", and the suffix is displayed, in a manner similar
 
   In the case of warnings treated as errors, the prefix is changed from
   "warning: " to "error: ", and the suffix is displayed, in a manner similar

-  to gcc, as [-Werror=CATEGORY].
+  to GCC, as [-Werror=CATEGORY].

 
   For instance, where the previous version of Bison would report (and exit
   with failure):
 
   For instance, where the previous version of Bison would report (and exit
   with failure):


@@ -170,6 +215,8 @@ GNU Bison NEWS
 
 ** Java skeleton improvements
 
 
 ** Java skeleton improvements
 

+  Contributed by Paolo Bonzini.
+

   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".
   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".


@@ -195,6 +242,16 @@ GNU Bison NEWS
   used by the scanner, or rejecting invalid combinations from a
   factory invoked by the user actions).
 
   used by the scanner, or rejecting invalid combinations from a
   factory invoked by the user actions).
 

+** Renamed %define variables
+
+  The following variables have been renamed for consistency.  Backward
+  compatibility is ensured, but upgrading is recommended.
+
+    lr.default-reductions      -> lr.default-reduction
+    lr.keep-unreachable-states -> lr.keep-unreachable-state
+    namespace                  -> api.namespace
+    stype                      -> api.value.type
+

 ** Variable api.token.prefix
 
   The variable api.token.prefix changes the way tokens are identified in
 ** Variable api.token.prefix
 
   The variable api.token.prefix changes the way tokens are identified in


@@ -211,11 +268,6 @@ GNU Bison NEWS
   use these prefixed token names, although the grammar itself still
   uses the short names (as in the sample rule given above).
 
   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
 
   This variable controls the verbosity of error messages.  The use of the
 ** Variable parse.error
 
   This variable controls the verbosity of error messages.  The use of the


@@ -224,6 +276,8 @@ GNU Bison NEWS
 
 ** Semantic predicates
 
 
 ** Semantic predicates
 

+  Contributed by Paul Hilfinger.
+

   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
   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


@@ -236,54 +290,256 @@ GNU Bison NEWS
   It used to be an error only if used in non GLR mode, _and_ if there are
   reduce/reduce conflicts.
 
   It used to be an error only if used in non GLR mode, _and_ if there are
   reduce/reduce conflicts.
 

-* Noteworthy changes in release ?.? (????-??-??) [?]
+** Token numbering has changed to preserve the user-defined order

 
 

-** Bug fixes
+  When declaring %token A B, the numbering for A is inferior to B. Up to now,
+  when declaring associativity at the same time, with %left (or %right,
+  %precedence, %nonassoc), B was inferior to A.

 
 

-  Bugs and portability issues in the test suite have been fixed.
+** Useless precedence and associativity

 
 

-  Some errors in translations have been addressed, and --help now directs
-  users to the appropriate place to report them.
+  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.

 
 

-  Stray Info files shipped by accident are removed.
+*** Precedence warning category

 
 

-  Incorrect definitions of YY_, issued by yacc.c when no parser header is
-  generated, are removed.
+  A new category of warning, -Wprecedence, was introduced. It flags the
+  useless precedence and associativity directives.

 
 

-  All the generated headers are self-contained.
+*** Useless associativity

 
 

-** Changes in the format of error messages
+  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:
 
 
   This used to be the format of many error reports:
 

-    foo.y:5.10-24: result type clash on merge function 'merge': <t3> != <t2>
-    foo.y:4.13-27: previous declaration
+    input.y:2.7-12: %type redeclaration for exp
+    input.y:1.7-12: previous declaration

 
   It is now:
 
 
   It is now:
 

-    foo.y:5.10-25: result type clash on merge function 'merge': <t3> != <t2>
-    foo.y:4.13-27:     previous declaration
+    input.y:2.7-12: error: %type redeclaration for exp
+    input.y:1.7-12:     previous declaration

 
 

-** Header guards (yacc.c, glr.c, glr.cc)
+*** New format for error reports: carets

 
 

-  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
+  Caret errors have been added to Bison:

 
 

-    %define api.prefix "calc"
-    %defines "lib/parse.h"
+    input.y:2.7-12: error: %type redeclaration for exp
+     %type <sval> exp
+           ^^^^^^
+    input.y:1.7-12:     previous declaration
+     %type <ival> exp
+           ^^^^^^

 
 

-  will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
+  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)
 
 ** 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 rethrowing the exception.
+  before re-throwing the exception.

 
   This feature is somewhat experimental.  User feedback would be
   appreciated.
 
 
   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
 ** Fix compiler warnings in the generated parser (yacc.c, glr.c)
 
   The compilation of pure parsers (%define api.pure) can trigger GCC


@@ -301,21 +557,6 @@ GNU Bison NEWS
   "function declared 'noreturn' should not return") have also been
   addressed.
 
   "function declared 'noreturn' should not return") have also been
   addressed.
 

-** New %define variable: api.location.type (glr.cc, lalr1.cc)
-
-  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).
-

 * Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
 
 ** Bug fixes
 * Noteworthy changes in release 2.6.2 (2012-08-03) [stable]
 
 ** Bug fixes


@@ -372,7 +613,7 @@ GNU Bison NEWS
 
 * Noteworthy changes in release 2.6 (2012-07-19) [stable]
 
 
 * Noteworthy changes in release 2.6 (2012-07-19) [stable]
 

-** Future changes:
+** Future changes

 
   The next major release of Bison will drop support for the following
   deprecated features.  Please report disagreements to bug-bison@gnu.org.
 
   The next major release of Bison will drop support for the following
   deprecated features.  Please report disagreements to bug-bison@gnu.org.


@@ -634,6 +875,7 @@ GNU Bison NEWS
 
   These features are experimental in this version.  More user feedback
   will help to stabilize them.
 
   These features are experimental in this version.  More user feedback
   will help to stabilize them.

+  Contributed by Alex Rozenman.

 
 ** IELR(1) and canonical LR(1):
 
 
 ** IELR(1) and canonical LR(1):
 


@@ -664,7 +906,9 @@ GNU Bison NEWS
   These features are experimental.  More user feedback will help to
   stabilize them.
 
   These features are experimental.  More user feedback will help to
   stabilize them.
 

-** LAC (Lookahead Correction) for syntax error handling:
+** LAC (Lookahead Correction) for syntax error handling
+
+  Contributed by Joel E. Denny.

 
   Canonical LR, IELR, and LALR can suffer from a couple of problems
   upon encountering a syntax error.  First, the parser might perform
 
   Canonical LR, IELR, and LALR can suffer from a couple of problems
   upon encountering a syntax error.  First, the parser might perform


@@ -1150,6 +1394,7 @@ GNU Bison NEWS
 
   The current Java interface is experimental and may evolve.  More user
   feedback will help to stabilize it.
 
   The current Java interface is experimental and may evolve.  More user
   feedback will help to stabilize it.

+  Contributed by Paolo Bonzini.

 
 ** %language
 
 
 ** %language
 


@@ -1163,6 +1408,7 @@ GNU Bison NEWS
   Bison can now generate an XML report of the LALR(1) automaton using the new
   "--xml" option.  The current XML schema is experimental and may evolve.  More
   user feedback will help to stabilize it.
   Bison can now generate an XML report of the LALR(1) automaton using the new
   "--xml" option.  The current XML schema is experimental and may evolve.  More
   user feedback will help to stabilize it.

+  Contributed by Wojciech Polak.

 
 ** The grammar file may now specify the name of the parser header file using
   %defines.  For example:
 
 ** The grammar file may now specify the name of the parser header file using
   %defines.  For example:


@@ -2139,7 +2385,7 @@ Output file does not redefine const for C++.
 
 -----
 
 
 -----
 

-Copyright (C) 1995-2012 Free Software Foundation, Inc.
+Copyright (C) 1995-2013 Free Software Foundation, Inc.

 
 This file is part of Bison, the GNU Parser Generator.
 
 
 This file is part of Bison, the GNU Parser Generator.
 


@@ -2174,7 +2420,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
  LocalWords:  Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
  LocalWords:  extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
  LocalWords:  lang yyoutput dvi html ps POSIX lvalp llocp Wother nterm arg init
  LocalWords:  Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
  LocalWords:  extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
  LocalWords:  lang yyoutput dvi html ps POSIX lvalp llocp Wother nterm arg init

- LocalWords:  TOK calc yyo fval
+ LocalWords:  TOK calc yyo fval Wconflicts

 
 Local Variables:
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 Local Variables:
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