Linemap force location and remove LINEMAP_POSITION_FOR_COLUMN (issue4801090)

[Gabriel Charette]

On Thu, Aug 11, 2011 at 10:45 AM, Dodji Seketeli <dodji@seketeli.org> wrote:
>> As I mentioned, we have the same problem in pph where we need to force
>> a location (i.e. the lexer is assigning new locations, but we don't
>> want it to when we are replaying pre-processor tokens), so just a
>> "builtin_location" field is potentially insufficient.
>
> I see.  So maybe a cpp_reader::forced_token_location, initialized to -1
> rather than 0 (in case someone wants to force a location to
> UNKNOWN_LOCATION, which is zero for the C/C++ FE at least).  There would
> then still be a new parm added to cpp_init_builtins, that would be the
> value of the location of the builtin macros to build.  cpp_init_builtins
> would then just set cpp_reader::force_token_location to that value.
>

Yes, I did think about using -1 to represent no-force. The problem is,
source_location is defined as unsigned int... So my solution was to
use a source_location* which when non-null means you want to force the
location to the referenced source_location. For some reason however
when I add a simple field `source_location *forced_location` to struct
line_maps I get the following compile error:

libcpp/include/line-map.h:99: field `(*x).forced_location' is pointer
to unimplemented type

Adding a source_location* to cpp_reader compiles fine however. This
must be a tricky corner of the C syntax I'm not aware of...?

Gabriel