warnings: introduce -Wprecedence

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index cb594715480d32941f1090fd96ea2c5df0e2bb7a..be3669a91869f7de7b206e39fc2f40a5719ac623 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -2,16 +2,61 @@ 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:
+
+    int yylex (YYSTYPE *yylval);
+
+  This is has been fixed: yylval, yynerrs, yychar, and yylloc are now valid
+  identifiers for user-provided variables.

 
 

-** Warnings
+*** 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
 
 
 *** Enhancements of the -Werror option
 


@@ -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


@@ -211,15 +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).
 

-** 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
-

 ** 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


@@ -228,6 +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


@@ -240,28 +290,148 @@ 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
+
+  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.
+
+** Useless precedence and associativity
+
+  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
+    ;

 
 

-** Changes in the format of error messages
+  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

 
 

-** Exception safety (lalr1.cc)
+*** New format for error reports: carets

 
 

-  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.
+  Caret errors have been added to Bison:

 
 

-  This feature is somewhat experimental.  User feedback would be
-  appreciated.
+    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)
 
 
 ** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
 


@@ -282,7 +452,18 @@ GNU Bison NEWS
   position_type are deprecated in favor of api.location.type and
   api.position.type.
 
   position_type are deprecated in favor of api.location.type and
   api.position.type.
 

-** Graphviz improvements
+** 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
 
   The graphical presentation of the states is more readable: their shape is
   now rectangular, the state number is clearly displayed, and the items are


@@ -291,6 +472,24 @@ GNU Bison NEWS
   The reductions are now explicitly represented as transitions to other
   diamond shaped nodes.
 
   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.
 * Noteworthy changes in release 2.6.5 (2012-11-07) [stable]
 
   We consider compiler warnings about Bison generated parsers to be bugs.


@@ -676,6 +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):
 


@@ -706,7 +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


@@ -1192,6 +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
 


@@ -1205,6 +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:


@@ -2181,7 +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.