build: use gnulib's new bootstrap_sync option.

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index cacdb7702cc0d9803504a5f33b82b317e2fb0a31..c8188395f01d6b227d8c5fe997ac697787491a8b 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -3,42 +3,6 @@ Bison News
 
 * Changes in version ?.? (????-??-??):
 
 
 * Changes in version ?.? (????-??-??):
 

-** C++ parsers use YYRHSLOC
-
-  Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
-  macro and use it in the default YYLLOC_DEFAULT.  You are encouraged
-  to use it.  If, for instance, your location structure has "first"
-  and "last" members, instead of
-
-      # define YYLLOC_DEFAULT(Current, Rhs, N)                             \
-        do                                                                 \
-          if (N)                                                           \
-            {                                                              \
-              (Current).first = (Rhs)[1].location.first;                   \
-              (Current).last  = (Rhs)[N].location.last;                    \
-            }                                                              \
-          else                                                             \
-            {                                                              \
-              (Current).first = (Current).last = (Rhs)[0].location.last;   \
-            }                                                              \
-        while (false)
-
-  use:
-
-      # define YYLLOC_DEFAULT(Current, Rhs, N)                             \
-        do                                                                 \
-          if (N)                                                           \
-            {                                                              \
-              (Current).first = YYRHSLOC (Rhs, 1).first;                   \
-              (Current).last  = YYRHSLOC (Rhs, N).last;                    \
-            }                                                              \
-          else                                                             \
-            {                                                              \
-              (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last;   \
-            }                                                              \
-        while (false)
-
-

 ** Additional yylex/yyparse arguments
 
   The new directive %param declare additional argument to both yylex
 ** Additional yylex/yyparse arguments
 
   The new directive %param declare additional argument to both yylex


@@ -87,6 +51,15 @@ Bison News
   use of the %error-verbose directive is deprecated in favor of
   %define parse.error "verbose".
 
   use of the %error-verbose directive is deprecated in favor of
   %define parse.error "verbose".
 

+** Semantic predicates
+
+  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
+  in GLR parsers, rather than being deferred.  The result is that they
+  allow the programmer to prune possible parses based on the values of
+  runtime expressions.
+

 * Changes in version 2.5 (????-??-??):
 
 ** Named References Support
 * Changes in version 2.5 (????-??-??):
 
 ** Named References Support


@@ -250,14 +223,41 @@ Bison News
   Bison now warns when a character literal is not of length one.  In
   some future release, Bison will report an error instead.
 
   Bison now warns when a character literal is not of length one.  In
   some future release, Bison will report an error instead.
 

-** Verbose error messages fixed for nonassociative tokens.
-
-  When %error-verbose is specified, syntax error messages produced by
-  the generated parser include the unexpected token as well as a list of
-  expected tokens.  Previously, this list erroneously included tokens
-  that would actually induce a syntax error because conflicts for them
-  were resolved with %nonassoc.  Such tokens are now properly omitted
-  from the list.
+** Verbose syntax error message fixes:
+
+  When %error-verbose or `#define YYERROR_VERBOSE' is specified, syntax
+  error messages produced by the generated parser include the unexpected
+  token as well as a list of expected tokens.  The effect of %nonassoc
+  on these verbose messages has been corrected in two ways, but
+  additional fixes are still being implemented:
+
+*** When %nonassoc is used, there can exist parser states that accept no
+    tokens, and so the parser does not always require a lookahead token
+    in order to detect a syntax error.  Because no unexpected token or
+    expected tokens can then be reported, the verbose syntax error
+    message described above is suppressed, and the parser instead
+    reports the simpler message, "syntax error".  Previously, this
+    suppression was sometimes erroneously triggered by %nonassoc when a
+    lookahead was actually required.  Now verbose messages are
+    suppressed only when all previous lookaheads have already been
+    shifted or discarded.
+
+*** Previously, the list of expected tokens erroneously included tokens
+    that would actually induce a syntax error because conflicts for them
+    were resolved with %nonassoc in the current parser state.  Such
+    tokens are now properly omitted from the list.
+
+*** Expected token lists are still often wrong due to state merging
+    (from LALR or IELR) and default reductions, which can both add and
+    subtract valid tokens.  Canonical LR almost completely fixes this
+    problem by eliminating state merging and default reductions.
+    However, there is one minor problem left even when using canonical
+    LR and even after the fixes above.  That is, if the resolution of a
+    conflict with %nonassoc appears in a later parser state than the one
+    at which some syntax error is discovered, the conflicted token is
+    still erroneously included in the expected token list.  We are
+    currently working on a fix to eliminate this problem and to
+    eliminate the need for canonical LR.

 
 ** Destructor calls fixed for lookaheads altered in semantic actions.
 
 
 ** Destructor calls fixed for lookaheads altered in semantic actions.
 


@@ -266,7 +266,52 @@ Bison News
   determine which destructor to call for the lookahead upon a syntax
   error or upon parser return.  This bug has been fixed.
 
   determine which destructor to call for the lookahead upon a syntax
   error or upon parser return.  This bug has been fixed.
 

-* Changes in version 2.4.3 (????-??-??):
+** C++ parsers use YYRHSLOC
+
+  Similarly to the C parsers, the C++ parsers now define the YYRHSLOC
+  macro and use it in the default YYLLOC_DEFAULT.  You are encouraged
+  to use it.  If, for instance, your location structure has "first"
+  and "last" members, instead of
+
+      # define YYLLOC_DEFAULT(Current, Rhs, N)                             \
+        do                                                                 \
+          if (N)                                                           \
+            {                                                              \
+              (Current).first = (Rhs)[1].location.first;                   \
+              (Current).last  = (Rhs)[N].location.last;                    \
+            }                                                              \
+          else                                                             \
+            {                                                              \
+              (Current).first = (Current).last = (Rhs)[0].location.last;   \
+            }                                                              \
+        while (false)
+
+  use:
+
+      # define YYLLOC_DEFAULT(Current, Rhs, N)                             \
+        do                                                                 \
+          if (N)                                                           \
+            {                                                              \
+              (Current).first = YYRHSLOC (Rhs, 1).first;                   \
+              (Current).last  = YYRHSLOC (Rhs, N).last;                    \
+            }                                                              \
+          else                                                             \
+            {                                                              \
+              (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last;   \
+            }                                                              \
+        while (false)
+
+** YYLLOC_DEFAULT in C++
+
+  The default implementation of YYLLOC_DEFAULT used to be issued in
+  the header file.  It is now output in the implementation file, after
+  the user %code sections so that its #ifndef guard does not try to
+  override the user's YYLLOC_DEFAULT if provided.
+
+* Changes in version 2.4.3 (2010-08-05):
+
+** Bison now obeys -Werror and --warnings=error for warnings about
+   grammar rules that are useless in the parser due to conflicts.

 
 ** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
    been fixed.
 
 ** Problems with spawning M4 on at least FreeBSD 8 and FreeBSD 9 have
    been fixed.


@@ -281,6 +326,8 @@ Bison News
    errors in Bison 2.5.  They will remain warnings, which should be
    sufficient for POSIX while avoiding backward compatibility issues.
 
    errors in Bison 2.5.  They will remain warnings, which should be
    sufficient for POSIX while avoiding backward compatibility issues.
 

+** Minor documentation fixes.
+

 * Changes in version 2.4.2 (2010-03-20):
 
 ** Some portability problems that resulted in failures and livelocks
 * Changes in version 2.4.2 (2010-03-20):
 
 ** Some portability problems that resulted in failures and livelocks


@@ -1422,7 +1469,9 @@ End:
 
 -----
 
 
 -----
 

-Copyright (C) 1995-2010 Free Software Foundation, Inc.
+Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
+2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation,
+Inc.

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