[PATCH 00/12] {master} explicit empty right-hand side of a rule

[Akim Demaille]

Joel wrote:
> How about the following proposal?
> 
> 1. -Wall will continue to mean all warnings rather than trying to mimic 
> gcc's -Wall.  If someone specifies -Wall, he has no right to complain that 
> it enables a warning (such as -Wempty-rule) that he doesn't find useful.  
> He explicitly requested all warnings that Bison provides and might ever 
> provide.
> 
> 2. -Wempty-rule will be off by default for now because it would likely be 
> too noisy for projects not ready to rewrite for %empty.  A use of %empty 
> will enable it by default.
> 
> 3. Yacc mode should have no influence on whether -Wempty-rule is enabled.  
> That is, because existing Yacc-compatible grammars don't use %empty, they 
> won't produce the warnings unless the user has requested them.

This is a nice summary, and that's what I implemented.  

It's funny how a single character can influence your mind: as long as
I wanted to use "$empty", I saw it as a pseudo-symbol, and meant to
treat it as a symbol (appended to the rule by the parser).  Many
complications follow from that (in both checking valid uses of %empty,
and when stripping %empty when building the tables).

But once you suggested "%empty", I started to see it as an "adjective"
about rules, much like %prec and other %dprecs.  The implementation is
then much simpler, and more consistent with the other directives.

This batch of commits relies on previous changes that were made so
that we could implement "if %empty is used then enable -Wempty-rule,
unless -Wno-empty-rule":

http://lists.gnu.org/archive/html/bison-patches/2013-02/msg00043.html

One question is whether the documentation should be moved to use
%empty.  I decided to do forward and use it everywhere, but of course
to leave a note about compatibility with Yacc.

The last three patches are boring, and should be sent in a separate
thread, but I feel lazy...

Akim Demaille (12):
  grammar: introduce %empty
  parser: use %empty
  regen
  tests: use %empty
  -Wempty-rule: diagnose empty rules without %empty
  diagnostics: %empty enables -Wempty-rule
  report: use %empty to denote empty rules
  doc: introduce %empty and -Wempty-rule
  doc: use %empty instead of /* empty */
  style: no longer use backquotes in messages
  style: no longer use backquotes
  style: no longer use backquotes

 NEWS                    |  22 ++
 README                  |   2 +-
 REFERENCES              |   2 +-
 THANKS                  |   1 +
 TODO                    |   8 +-
 configure.ac            |   2 +-
 data/README             |   2 +-
 data/bison.m4           |   6 +-
 data/c++.m4             |   4 +-
 data/c.m4               |   4 +-
 data/java.m4            |   2 +-
 data/lalr1.cc           |   2 +-
 data/lalr1.java         |   2 +-
 data/yacc.c             |  12 +-
 doc/bison.texi          | 159 +++++++++-----
 doc/local.mk            |   2 +-
 etc/bench.pl.in         |   4 +-
 lib/libiberty.h         |   2 +-
 lib/timevar.h           |   2 +-
 src/complain.c          |  11 +
 src/complain.h          |   5 +
 src/conflicts.c         |   2 +-
 src/files.c             |  26 +--
 src/getargs.c           |  49 ++---
 src/gram.c              |   6 +-
 src/gram.h              |  12 +-
 src/lalr.c              |   2 +-
 src/location.c          |   2 +-
 src/location.h          |   2 +-
 src/muscle-tab.c        |   8 +-
 src/muscle-tab.h        |   2 +-
 src/output.c            |   2 +-
 src/parse-gram.c        | 552 +++++++++++++++++++++++++-----------------------
 src/parse-gram.h        |   8 +-
 src/parse-gram.y        |  30 +--
 src/print-xml.c         |   2 +-
 src/print.c             |   4 +-
 src/reader.c            |  37 +++-
 src/reader.h            |   2 +
 src/reduce.c            |   2 +-
 src/scan-gram.l         |   1 +
 src/scan-skel.l         |   6 +-
 src/symlist.c           |   1 +
 src/symlist.h           |   4 +
 src/symtab.h            |   6 +-
 src/system.h            |   2 +-
 src/tables.c            |  14 +-
 tests/actions.at        | 116 +++++++++-
 tests/atlocal.in        |   2 +-
 tests/c++.at            |   4 +-
 tests/calc.at           |  40 ++--
 tests/conflicts.at      |  22 +-
 tests/existing.at       |  93 ++++++--
 tests/glr-regression.at |   8 +-
 tests/input.at          |  90 ++++----
 tests/java.at           |  16 +-
 tests/local.at          |  14 +-
 tests/reduce.at         |   6 +-
 tests/regression.at     |  14 +-
 tests/sets.at           |  10 +-
 tests/synclines.at      |   2 +-
 61 files changed, 901 insertions(+), 576 deletions(-)

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1.8.1.3