maint: run "make update-copyright".

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 5799790572eb10a4496e356915f62c666bf105cc..5c2783f93a04833175c6892c040debf726ab9be9 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -6,7 +6,7 @@ Bison News
 ** 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

-  and yyparse.  The %lex-param, %parse-param, and %param directive
+  and yyparse.  The %lex-param, %parse-param, and %param directives

   support one or more arguments.  Instead of
 
       %lex-param   {arg1_type *arg1}
   support one or more arguments.  Instead of
 
       %lex-param   {arg1_type *arg1}


@@ -51,9 +51,32 @@ 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".
 

-* Changes in version 2.5 (????-??-??):
+** Semantic predicates

 
 

-** Named References Support
+  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 2.5.1 (????-??-??):
+
+** Some portability problems in the test suite have been fixed.
+
+** Minor improvements have been made to the manual.
+
+* Changes in version 2.5 (2011-05-14):
+
+** Grammar symbol names can now contain non-initial dashes:
+
+  Consistently with directives (such as %error-verbose) and with
+  %define variables (e.g. push-pull), grammar symbol names may contain
+  dashes in any position except the beginning.  This is a GNU
+  extension over POSIX Yacc.  Thus, use of this extension is reported
+  by -Wyacc and rejected in Yacc mode (--yacc).
+
+** Named references:

 
   Historically, Yacc and Bison have supported positional references
   ($n, $$) to allow access to symbol values from inside of semantic
 
   Historically, Yacc and Bison have supported positional references
   ($n, $$) to allow access to symbol values from inside of semantic


@@ -63,12 +86,12 @@ Bison News
   When no ambiguity is possible, original symbol names may be used
   as named references:
 
   When no ambiguity is possible, original symbol names may be used
   as named references:
 

-    if_stmt : 'if' cond_expr 'then' then_stmt ';'
+    if_stmt : "if" cond_expr "then" then_stmt ';'

     { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
 
   In the more common case, explicit names may be declared:
 
     { $if_stmt = mk_if_stmt($cond_expr, $then_stmt); }
 
   In the more common case, explicit names may be declared:
 

-    stmt[res] : 'if' expr[cond] 'then' stmt[then] 'else' stmt[else] ';'
+    stmt[res] : "if" expr[cond] "then" stmt[then] "else" stmt[else] ';'

     { $res = mk_if_stmt($cond, $then, $else); }
 
   Location information is also accessible using @name syntax.  When
     { $res = mk_if_stmt($cond, $then, $else); }
 
   Location information is also accessible using @name syntax.  When


@@ -78,13 +101,13 @@ 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.
 

-** IELR(1) and Canonical LR(1) Support
+** IELR(1) and canonical LR(1):

 
   IELR(1) is a minimal LR(1) parser table generation algorithm.  That
   is, given any context-free grammar, IELR(1) generates parser tables
 
   IELR(1) is a minimal LR(1) parser table generation algorithm.  That
   is, given any context-free grammar, IELR(1) generates parser tables

-  with the full language recognition power of canonical LR(1) but with
-  nearly the same number of parser states as LALR(1).  This reduction in
-  parser states is often an order of magnitude.  More importantly,
+  with the full language-recognition power of canonical LR(1) but with
+  nearly the same number of parser states as LALR(1).  This reduction
+  in parser states is often an order of magnitude.  More importantly,

   because canonical LR(1)'s extra parser states may contain duplicate
   conflicts in the case of non-LR(1) grammars, the number of conflicts
   for IELR(1) is often an order of magnitude less as well.  This can
   because canonical LR(1)'s extra parser states may contain duplicate
   conflicts in the case of non-LR(1) grammars, the number of conflicts
   for IELR(1) is often an order of magnitude less as well.  This can


@@ -99,24 +122,58 @@ Bison News
     %define lr.type ielr
     %define lr.type canonical-lr
 
     %define lr.type ielr
     %define lr.type canonical-lr
 

-  The default reduction optimization in the parser tables can also be
-  adjusted using `%define lr.default-reductions'.  See the documentation
-  for `%define lr.type' and `%define lr.default-reductions' in the
-  section `Bison Declaration Summary' in the Bison manual for the
-  details.
+  The default-reduction optimization in the parser tables can also be
+  adjusted using `%define lr.default-reductions'.  For details on both
+  of these features, see the new section `Tuning LR' in the Bison
+  manual.

 
   These features are experimental.  More user feedback will help to
   stabilize them.
 
 
   These features are experimental.  More user feedback will help to
   stabilize them.
 

-** Unrecognized %code qualifiers are now an error not a warning.
+** LAC (Lookahead Correction) for syntax error handling:

 
 

-** %define improvements.
+  Canonical LR, IELR, and LALR can suffer from a couple of problems
+  upon encountering a syntax error.  First, the parser might perform
+  additional parser stack reductions before discovering the syntax
+  error.  Such reductions can perform user semantic actions that are
+  unexpected because they are based on an invalid token, and they
+  cause error recovery to begin in a different syntactic context than
+  the one in which the invalid token was encountered.  Second, when
+  verbose error messages are enabled (with %error-verbose or the
+  obsolete `#define YYERROR_VERBOSE'), the expected token list in the
+  syntax error message can both contain invalid tokens and omit valid
+  tokens.

 
 

-*** Unrecognized variables are now an error not a warning.
+  The culprits for the above problems are %nonassoc, default
+  reductions in inconsistent states, and parser state merging.  Thus,
+  IELR and LALR suffer the most.  Canonical LR can suffer only if
+  %nonassoc is used or if default reductions are enabled for
+  inconsistent states.

 
 

-*** Multiple invocations for any variable is now an error not a warning.
+  LAC is a new mechanism within the parsing algorithm that solves
+  these problems for canonical LR, IELR, and LALR without sacrificing
+  %nonassoc, default reductions, or state merging.  When LAC is in
+  use, canonical LR and IELR behave almost exactly the same for both
+  syntactically acceptable and syntactically unacceptable input.
+  While LALR still does not support the full language-recognition
+  power of canonical LR and IELR, LAC at least enables LALR's syntax
+  error handling to correctly reflect LALR's language-recognition
+  power.

 
 

-*** Can now be invoked via the command line.
+  Currently, LAC is only supported for deterministic parsers in C.
+  You can enable LAC with the following directive:
+
+    %define parse.lac full
+
+  See the new section `LAC' in the Bison manual for additional
+  details including a few caveats.
+
+  LAC is an experimental feature.  More user feedback will help to
+  stabilize it.
+
+** %define improvements:
+
+*** Can now be invoked via the command line:

 
   Each of these command-line options
 
 
   Each of these command-line options
 


@@ -133,9 +190,9 @@ Bison News
   except that the manner in which Bison processes multiple definitions
   for the same NAME differs.  Most importantly, -F and --force-define
   quietly override %define, but -D and --define do not.  For further
   except that the manner in which Bison processes multiple definitions
   for the same NAME differs.  Most importantly, -F and --force-define
   quietly override %define, but -D and --define do not.  For further

-  details, see the section "Bison Options" in the Bison manual.
+  details, see the section `Bison Options' in the Bison manual.

 
 

-*** Variables renamed.
+*** Variables renamed:

 
   The following %define variables
 
 
   The following %define variables
 


@@ -150,7 +207,7 @@ Bison News
   The old names are now deprecated but will be maintained indefinitely
   for backward compatibility.
 
   The old names are now deprecated but will be maintained indefinitely
   for backward compatibility.
 

-*** Values no longer need to be quoted in grammar file.
+*** Values no longer need to be quoted in the grammar file:

 
   If a %define value is an identifier, it no longer needs to be placed
   within quotations marks.  For example,
 
   If a %define value is an identifier, it no longer needs to be placed
   within quotations marks.  For example,


@@ -161,15 +218,75 @@ Bison News
 
     %define api.push-pull push
 
 
     %define api.push-pull push
 

-** Symbol names.
+*** Unrecognized variables are now errors not warnings.
+
+*** Multiple invocations for any variable is now an error not a warning.
+
+** Unrecognized %code qualifiers are now errors not warnings.
+
+** Character literals not of length one:

 
 

-  Consistently with directives (such as %error-verbose) and variables
-  (e.g. push-pull), symbol names may include dashes in any position,
-  similarly to periods and underscores.  This is GNU extension over
-  POSIX Yacc whose use is reported by -Wyacc, and rejected in Yacc
-  mode (--yacc).
+  Previously, Bison quietly converted all character literals to length
+  one.  For example, without warning, Bison interpreted the operators in
+  the following grammar to be the same token:
+
+    exp: exp '++'
+       | exp '+' exp
+       ;
+
+  Bison now warns when a character literal is not of length one.  In
+  some future release, Bison will start reporting an error instead.

 
 

-** YYFAIL now produces warnings and Java parsers no longer implement it.
+** Destructor calls fixed for lookaheads altered in semantic actions:
+
+  Previously for deterministic parsers in C, if a user semantic action
+  altered yychar, the parser in some cases used the old yychar value to
+  determine which destructor to call for the lookahead upon a syntax
+  error or upon parser return.  This bug has been fixed.
+
+** 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.
+
+** YYFAIL now produces warnings and Java parsers no longer implement it:

 
   YYFAIL has existed for many years as an undocumented feature of
   deterministic parsers in C generated by Bison.  More recently, it was
 
   YYFAIL has existed for many years as an undocumented feature of
   deterministic parsers in C generated by Bison.  More recently, it was


@@ -180,7 +297,7 @@ Bison News
   discussion of how to suppress C preprocessor warnings about YYFAIL
   being unused, see the Bison 2.4.2 NEWS entry.
 
   discussion of how to suppress C preprocessor warnings about YYFAIL
   being unused, see the Bison 2.4.2 NEWS entry.
 

-** Temporary hack for adding a semicolon to the user action.
+** Temporary hack for adding a semicolon to the user action:

 
   Previously, Bison appended a semicolon to every user action for
   reductions when the output language defaulted to C (specifically, when
 
   Previously, Bison appended a semicolon to every user action for
   reductions when the output language defaulted to C (specifically, when


@@ -201,36 +318,133 @@ Bison News
   about a missing semicolon where it did not before.  Future releases of
   Bison will cease to append semicolons entirely.
 
   about a missing semicolon where it did not before.  Future releases of
   Bison will cease to append semicolons entirely.
 

-** Character literals not of length one.
+** Verbose syntax error message fixes:

 
 

-  Previously, Bison quietly converted all character literals to length
-  one.  For example, without warning, Bison interpreted the operators in
-  the following grammar to be the same token:
+  When %error-verbose or the obsolete `#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 a more complete fix requires LAC, described above:

 
 

-    exp: exp '++'
-       | exp '+' exp
-       ;
+*** 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.

 
 

-  Bison now warns when a character literal is not of length one.  In
-  some future release, Bison will report an error instead.
+*** 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.

 
 

-** Verbose error messages fixed for nonassociative tokens.
+*** Expected token lists are still often wrong due to state merging
+    (from LALR or IELR) and default reductions, which can both add
+    invalid tokens 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.  Bison's new LAC implementation,
+    described above, eliminates this problem and the need for
+    canonical LR.  However, LAC is still experimental and is disabled
+    by default.

 
 

-  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.
+** Java skeleton fixes:

 
 

-** Destructor calls fixed for lookaheads altered in semantic actions.
+*** A location handling bug has been fixed.

 
 

-  Previously for deterministic parsers in C, if a user semantic action
-  altered yychar, the parser in some cases used the old yychar value to
-  determine which destructor to call for the lookahead upon a syntax
-  error or upon parser return.  This bug has been fixed.
+*** The top element of each of the value stack and location stack is now
+    cleared when popped so that it can be garbage collected.
+
+*** Parser traces now print the top element of the stack.
+
+** -W/--warnings fixes:
+
+*** Bison now properly recognizes the `no-' versions of categories:
+
+  For example, given the following command line, Bison now enables all
+  warnings except warnings for incompatibilities with POSIX Yacc:
+
+    bison -Wall,no-yacc gram.y
+
+*** Bison now treats S/R and R/R conflicts like other warnings:
+
+  Previously, conflict reports were independent of Bison's normal
+  warning system.  Now, Bison recognizes the warning categories
+  `conflicts-sr' and `conflicts-rr'.  This change has important
+  consequences for the -W and --warnings command-line options.  For
+  example:
+
+    bison -Wno-conflicts-sr gram.y  # S/R conflicts not reported
+    bison -Wno-conflicts-rr gram.y  # R/R conflicts not reported
+    bison -Wnone            gram.y  # no conflicts are reported
+    bison -Werror           gram.y  # any conflict is an error
+
+  However, as before, if the %expect or %expect-rr directive is
+  specified, an unexpected number of conflicts is an error, and an
+  expected number of conflicts is not reported, so -W and --warning
+  then have no effect on the conflict report.
+
+*** The `none' category no longer disables a preceding `error':
+
+  For example, for the following command line, Bison now reports
+  errors instead of warnings for incompatibilities with POSIX Yacc:
+
+    bison -Werror,none,yacc gram.y
+
+*** The `none' category now disables all Bison warnings:
+
+  Previously, the `none' category disabled only Bison warnings for
+  which there existed a specific -W/--warning category.  However,
+  given the following command line, Bison is now guaranteed to
+  suppress all warnings:
+
+    bison -Wnone gram.y
+
+** Precedence directives can now assign token number 0:
+
+  Since Bison 2.3b, which restored the ability of precedence
+  directives to assign token numbers, doing so for token number 0 has
+  produced an assertion failure.  For example:
+
+    %left END 0
+
+  This bug has been fixed.
+
+* 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.
+
+** Failures in the test suite for GCC 4.5 have been fixed.
+
+** Failures in the test suite for some versions of Sun Studio C++ have
+   been fixed.
+
+** Contrary to Bison 2.4.2's NEWS entry, it has been decided that
+   warnings about undefined %prec identifiers will not be converted to
+   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):

 
 

-* Changes in version 2.4.2 (????-??-??):
+** Some portability problems that resulted in failures and livelocks
+   in the test suite on some versions of at least Solaris, AIX, HP-UX,
+   RHEL4, and Tru64 have been addressed.  As a result, fatal Bison
+   errors should no longer cause M4 to report a broken pipe on the
+   affected platforms.

 
 ** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately.
 
 
 ** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately.
 


@@ -241,6 +455,8 @@ Bison News
   %prec directive.  It is now restored.  However, for backward
   compatibility with recent Bison releases, it is only a warning for
   now.  In Bison 2.5 and later, it will return to being an error.
   %prec directive.  It is now restored.  However, for backward
   compatibility with recent Bison releases, it is only a warning for
   now.  In Bison 2.5 and later, it will return to being an error.

+  [Between the 2.4.2 and 2.4.3 releases, it was decided that this
+  warning will not be converted to an error in Bison 2.5.]

 
 ** Detection of GNU M4 1.4.6 or newer during configure is improved.
 
 
 ** Detection of GNU M4 1.4.6 or newer during configure is improved.
 


@@ -680,26 +896,26 @@ Bison News
   if the symbols have destructors.  For instance:
 
      exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
   if the symbols have destructors.  For instance:
 
      exp: exp "?" exp ":" exp { $1 ? $1 : $3; }

-       | exp "+" exp
-       ;
+        | exp "+" exp
+        ;

 
   will trigger a warning about $$ and $5 in the first rule, and $3 in
   the second ($1 is copied to $$ by the default rule).  This example
   most likely contains three errors, and could be rewritten as:
 
      exp: exp "?" exp ":" exp
 
   will trigger a warning about $$ and $5 in the first rule, and $3 in
   the second ($1 is copied to $$ by the default rule).  This example
   most likely contains three errors, and could be rewritten as:
 
      exp: exp "?" exp ":" exp

-           { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
-       | exp "+" exp
-           { $$ = $1 ? $1 : $3; if ($1) free ($3); }
-       ;
+            { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
+        | exp "+" exp
+            { $$ = $1 ? $1 : $3; if ($1) free ($3); }
+        ;

 
   However, if the original actions were really intended, memory leaks
   and all, the warnings can be suppressed by letting Bison believe the
   values are used, e.g.:
 
      exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
 
   However, if the original actions were really intended, memory leaks
   and all, the warnings can be suppressed by letting Bison believe the
   values are used, e.g.:
 
      exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }

-       | exp "+" exp         { $$ = $1; (void) $3; }
-       ;
+        | exp "+" exp         { $$ = $1; (void) $3; }
+        ;

 
   If there are mid-rule actions, the warning is issued if no action
   uses it.  The following triggers no warning: $1 and $3 are used.
 
   If there are mid-rule actions, the warning is issued if no action
   uses it.  The following triggers no warning: $1 and $3 are used.


@@ -943,16 +1159,16 @@ Bison News
   In agreement with POSIX and with other Yaccs, leaving a default
   action is valid when $$ is untyped, and $1 typed:
 
   In agreement with POSIX and with other Yaccs, leaving a default
   action is valid when $$ is untyped, and $1 typed:
 

-       untyped: ... typed;
+        untyped: ... typed;

 
   but the converse remains an error:
 
 
   but the converse remains an error:
 

-       typed: ... untyped;
+        typed: ... untyped;

 
 ** Values of mid-rule actions
   The following code:
 
 
 ** Values of mid-rule actions
   The following code:
 

-       foo: { ... } { $$ = $1; } ...
+        foo: { ... } { $$ = $1; } ...

 
   was incorrectly rejected: $1 is defined in the second mid-rule
   action, and is equal to the $$ of the first mid-rule action.
 
   was incorrectly rejected: $1 is defined in the second mid-rule
   action, and is equal to the $$ of the first mid-rule action.


@@ -1363,8 +1579,7 @@ End:
 
 -----
 
 
 -----
 

-Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
-2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
+Copyright (C) 1995-2012 Free Software Foundation, Inc.

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