Question about DEFSYSTEM-DEPENDS-ON

[Faré]

On Wed, Sep 21, 2016 at 9:22 AM, Robert Goldman <rpgoldman at sift.net> wrote:
> Per my recent post to launchpad, I don't think dependency updating is
> the fatal flaw in D-D-O.  D-D-O's bad interaction with the package
> system is worse.
>
> Specifically, D-D-O cannot be used to introduce ASDF extensions unless
> those ASDF extensions live in the ASDF package.  Otherwise, by the time
> a DEFSYSTEM form is read, the enclosing package's imports are already
> established.  This means that ASDF has no protection against namespace
> pollution, since extenders are practically forced to add symbols to ASDF.
>
> For example, we have a FIVEAM-ASDF extension that introduces a new
> defsystem class that has features for using 5AM as an implementation for
> the TEST-OP.  But we cannot put a DEFSYSTEM-DEPENDS-ON for FIVEAM-ASDF
> in a system and reference FIVEAM-ASDF:FIVEAM-TESTER-SYSTEM as the system
> class, because the FIVEAM-ASDF package does not (in general) exist when
> the enclosing DEFSYSTEM is read.
>
> I can think of three ways of handling this:
>
> 1. Deprecate and remove D-D-O.  This seems undesirable, since D-D-O is
> commonly used.
>
> 2. Replace the use of the lisp reader for processing DEFSYSTEM forms,
> and introduce some kind of parser.  This seems like an enormous amount
> of work and difficult to get right.
>
> 3. In some way extend the keyword-processing features of DEFSYSTEM to
> allow it to reference symbols that are not only in the current package
> and ASDF, but also programmer-specified packages.  Unfortunately,
> processing of keyword symbols in DEFSYSTEM is very case-specific -- we
> know particular locations where there use is permitted, and handle each
> one specifically.  Without a cleaner way to handle this, we are likely
> to simply be backing ourselves into alternative #2.  OTOH, if we *could*
> do this, it would be a great solution, because it would maintain the
> maximal amount of backwards-compatibility.
>
> This is the problem I would most like to see solved in ASDF.
>
(defsystem "foo-test"
  :defsystem-depends-on ("fiveam") :depends-on ("foo")
  :class "fiveam-asdf:fiveam-tester-system"
  :components (("some-system:its-component-class" "myfile" ...) ...) ...)

This has been working since 2.31.4.

IIRC, it was Stelian who prodded me to get D-D-O working properly.

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