[m-rev.] for review: new machinery in make.dependencies.m

[Julien Fischer]

On Sat, 30 Sep 2023, Zoltan Somogyi wrote:

> For review by anyone. I am particularly seeking feedback
> on whether you guys think the few test cases for which the
> old/new comparison in the diff detected changes are
> indicative of a problem with this diff, or not. (I have looked
> at it and couldn't decide, maybe you have some ideas
> I have overlooked. The failure reports for two of the
> test cases are attached; the others are similar.)
>
> I am also depending on you guys to test out this diff
> on real code, since you work with code bases using mmc --make,
> which I don't do. I would also like to know whether you want to
> do such tryouts before this diff is committed, or after.

I will test it after the diff is committed; the obvious test case for me
is to use G12, but I will need to update that from Mercury 22.01.

> Implement new machinery in make.dependencies.m.
> 
> compiler/make.dependencies.m:
>     The task of this module is to find which are the source files
>     needed to build each target file of an "mmc --make" invocation.
>     The original machinery used for this purpose used three-level towers
>     of closures, which made code the hard to read and to understand, and
>     also made it effectively impossible to change the argument list
>     of any of the predicates involved without also making the same change
>     to all the other predicates used at the same level tower level.

Delete the first "level there.

The diff looks fine to me; that said, I'm not really the right person
to be reviewing it in the first place. Peter should be able to comment
on things like caching with more authority.

Julien.