"introduce no new bootstrap warning" criteria. was: Loop iv debugging patch

[Akim Demaille]

>>>>> "Robert" == Robert Dewar <dewar@gnat.com> writes:

Robert> In GNAT, we have a compiler option to make all warnings fatal,
Robert> and we always use this option for all builds. We have also
Robert> adopted a zero warnings tolerance for all our C code.

In forthcoming Autoconf 2.50 we have introduced support for a new
hopefully standard envvar, WARNINGS.  I plan to propagate its support
in several tools, the ultimate goals being to make it possible to run
say a test suite with an ultra severe environment, something which is
extremely useful in the development of Autoconf for instance.

Bison is next on my list, and it would be great if GCC could support
it too.

Here is the documentation provided with Autoconf:

   `autoconf' accepts the following options:

[--- CUT ---]

`--warnings=CATEGORY'
`-W CATEGORY'
     Report the warnings related to CATEGORY (which can actually be a
     comma separated list).  *Note Reporting Messages::, macro
     `AC_DIAGNOSE', for a comprehensive list of categories.  Special
     values include:

    `all'
          report all the warnings

    `none'
          report none

    `error'
          treats warnings as errors

    `no-CATEGORY'
          disable warnings falling into CATEGORY

     Warnings about `syntax' are enabled by default, and the environment
     variable `WARNINGS', a comma separated list of categories, is
     honored. `autoconf' will actually behave as if you had run

          autoconf --warnings=syntax,$WARNINGS,CATEGORIES

     If you want to disable `autoconf''s defaults and `WARNING' but
     enable the warnings about obsolete constructs, use `-W
     none,obsolete'.

     `autoconf' displays a back trace for errors, but not for warnings;
     if you want them, just pass `-W error'.  For instance on this
     `configure.ac':

          AC_DEFUN([INNER],
          [AC_TRY_RUN([true])])
          
          AC_DEFUN([OUTTER],
          [INNER])
          
          AC_INIT
          OUTTER

     you get:

          /tmp % ace -Wcross
          configure.ac:8: warning: AC_TRY_RUN called without default \
          to allow cross compiling
          /tmp % ace -Wcross,error
          configure.ac:8: error: AC_TRY_RUN called without default \
          to allow cross compiling
          acgeneral.m4:3044: AC_TRY_RUN is expanded from...
          configure.ac:2: INNER is expanded from...
          configure.ac:5: OUTTER is expanded from...
          configure.ac:8: the top level