Re: Adding load-only source files to ASDF

Richard M Kreuter <[email protected]> writes:
> Richard M Kreuter <[email protected]> writes:
>
>> In fact, if you're willing to use just a class, I think you can
>> implement the functionality as an extension using asdf's protocols...
>
> ...maybe the right way to implement a load-only component would be
> to have load-op depend on load-source-op for such components...

The code in my last post in this thread was broken.  I deleted some
defmethod forms, but forgot to remove the methods from the Lisp I was
working in.  Sorry about that.

However, in working on fixing it, I noticed a problem: COMPILE-OPs and
LOAD-OPs still get PERFORMed on the load-only file.  Even if the
default primary methods of COMPILE-OP and LOAD-OP do nothing, that
they are PERFORMed at all is arguably a flaw: subclasses of COMPILE-OP
or LOAD-OP can have methods that probably shouldn't be run at all on
load-only files.  For example, subclasses' methods might assume that
fasls exist after COMPILE-OP or before LOAD-OP on generalized
instances of CL-SOURCE-FILE, but this will be false for load-only
instances implemented as has been discussed.

For COMPILE-OP, the solution is easy: have OPERATION-DONE-P return
true for COMPILE-OP and LOAD-ONLY-CL-SOURCE-FILE, and TRAVERSE will
prune out that operation/component pair.

For LOAD-OP, the situation is trickier, whether LOAD-OP'ing a
LOAD-ONLY-CL-SOURCE-FILE depends on a LOAD-SOURCE-OP or loads the file
itself, a LOAD-OP will still be performed, and so subclasses and
auxiliary methods will run, and so potential badness.

I can think of a couple ways of dealing with the LOAD-OP case:

* make LOAD-ONLY-CL-SOURCE-FILE a subclass of SOURCE-FILE but not
  CL-SOURCE-FILE.  This way, methods specializing on LOAD-OP and
  CL-SOURCE-FILE won't get run for LOAD-ONLY-CL-SOURCE-FILE, but
  generalized instances of LOAD-ONLY-CL-SOURCE-FILE won't
  inherit behavior from CL-SOURCE-FILE.

* Add a protocol function, say, COMPONENT-DELEGATES-TO, which TRAVERSE
  can use to substitute one operation/component pair for another, and
  have a method of this function specializing on LOAD-OP and
  LOAD-ONLY-CL-SOURCE-FILE that returns a LOAD-SOURCE-OP and the
  component.  (This function would be similar to COMPONENT-DEPENDS-ON,
  except that whereas C-D-O means "do that in addition to this", C-D-T
  would mean "do that instead of this".)  This way, the LOAD-OP won't
  be present in the traversal, but maybe this will make the operation
  protocol harder to understand than it is already.

Any thoughts?

--
RmK


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