[Bug c++/33255] A warning for "unused" typedefs?

["dodji at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33255

--- Comment #15 from Dodji Seketeli <dodji at gcc dot gnu.org> 2011-07-24 21:57:47 UTC ---
Created attachment 24820
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24820
Work in progress patch

This works only on the C++ FE (not on the C FE yet) for now and has been
lightly tested so far.

I ran it on libstdc++ and so far it fell short only on the use of
PB_DS_STATIC_ASSERT (and friends) which defines a typedef.  When this macro is
expanded in a function that doesn't use the typedef it defines, the patch
warns.  Normally, it shouldn't warn b/c the macro is defined in a system
header.  But with the current (libcpp) infrastructure, we cannot tell the
difference between a typedef defined in a system header macro that is expanded
in a local function, and a typedef that is directly defined in the function. 
Normally with the work being done on PR proprocessor/7263 this patch should not
warn in those case.  At least if my understanding of the issue is correct.

The warning option is -Wunused-local-typedefs and is activated by -Wall
-Wextra, or -Wunused -Wextra.

I am putting it here for now in case someone has interesting test cases to add.