warnings: introduce -Wprecedence

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 619d36cdc985f128cbe7514362eab41a52cc2484..be3669a91869f7de7b206e39fc2f40a5719ac623 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -2,7 +2,21 @@ 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
 


@@ -14,7 +28,29 @@ GNU Bison NEWS
   Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison
   1.875): use %lex-param, %parse-param, or %param.
 
   Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison
   1.875): use %lex-param, %parse-param, or %param.
 

-** Warnings
+** 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.
+
+*** 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
 
 
 *** Carets
 


@@ -179,6 +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".


@@ -204,18 +242,6 @@ 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).
 

-*** 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 (yy::parser::semantic_type *yylval);
-
-  This is has been fixed: yylval, ynerrs, yychar, and yylloc are now valid
-  identifiers for user-provided variables.
-

 ** Renamed %define variables
 
   The following variables have been renamed for consistency.  Backward
 ** Renamed %define variables
 
   The following variables have been renamed for consistency.  Backward


@@ -242,8 +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 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


@@ -252,6 +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


@@ -264,6 +290,82 @@ 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.
 

+** 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
+    ;
+
+  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
 * Noteworthy changes in release 2.7 (2012-12-12) [stable]
 
 ** Bug fixes


@@ -274,6 +376,8 @@ GNU Bison NEWS
 
 ** Diagnostics are improved
 
 
 ** Diagnostics are improved
 

+  Contributed by Théophile Ranquet.
+

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


@@ -359,6 +463,8 @@ GNU Bison NEWS
 
 ** Graph improvements in DOT and XSLT
 
 
 ** 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 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.


@@ -800,7 +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


@@ -2277,7 +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.