[m-rev.] Where to check foreign_proc attributes?

[Ben Schmidt]

Hi,

I need to implement some checking of foreign_proc attributes. Certain 
combinations of attributes need to generate compile-time warnings or 
errors. They should be errors in agc grades and warnings in other 
grades. They don't really depend on anything except for the list of 
attributes and the grade. So...

1. It could probably be done at parsing-time, while conflicting 
attributes are checked for (prog_io_pragma.m), except there isn't a way 
to access globals there, so I couldn't differentiate between warnings 
and errors based on the gc method, or at least, not as far as I can 
tell. And actually, I'm not sure warnings can be output at all at this 
stage.

2. It could be done at code-generation time (while converting 
HLDS->MLDS; ml_code_gen.m), but that's not really the right place to be 
detecting errors, and they won't be detected at all unless the right 
backend is being used.

3. They could be done as checks on the HLDS...but where should they be 
incorporated (submodule of check_hlds.m)? They are not type, mode or 
determinism checks, nor are they various code simplifications or 
module-level checks. One thought is to incorporate them in 
clause_to_proc.m, as they are essentially procedure-based 
checks...but...as that operation is abstracted away from implementation 
detail, the globals and hence gc method aren't available there either, 
so the warning/error distinction can't be drawn.

4. Maybe they could be done in an optimisation pass 
(transform_hlds.m)--but is there an appropriate one which can't be 
turned off (or can all of them be turned off), as they are semantic 
errors that need to be picked up? dead_proc_elim.m is potentially a 
place it could be done, I think, but it may be turned off. I don't think 
the tiny amount of checking that needs to be done warrants an extra pass.

So...I'm a bit stuck as to where is the best place to slot this in. 
Anyone have any ideas?

Ben.


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