bug#65665: package-mapping with #:deep? #t doesn't get all the implicit inputs

[Maxim Cournoyer]

Hello Ulf,

Ulf Herrman <striness@tilde.club> writes:

> #:deep? #t currently works by interposing a dummy build system that
> lowers the package to a bag using the original build system, then
> applies the supplied transformation to all of the bag's inputs, then
> returns a new bag with the new inputs.
>
> The problem with this approach is that it doesn't affect the bag
> arguments.  This means that packages passed in as arguments may still
> end up being used without being transformed.  Worse still, packages
> *not* passed in as arguments may end up being used *unless one is
> explicitly passed in as an argument*, as is the case with
> qt-build-system's #:qtbase argument.
>
> In short, the current approach of having the build-system lower
> procedure leave the arguments mostly unchanged and letting the
> bag->derivation procedure (the "bag builder") fill in lots of defaults
> means that there are implicit inputs that cannot be touched at the
> package level without adding special logic for every single build system
> that does something like this.

This is indeed sub-optimal!

> I propose that we have the build system lower procedure (that is, the
> one that converts from package to bag) completely fill in the argument
> list with all defaults, and we modify build-system-with-package-mapping
> to transform all arguments that look like a package or a list of
> packages (or maybe even a tree containing packages).

[...]

> What do you think?

Like Csepp, I like your proposition!  I'm CC'ing the core team, in case
they have something to add to it, but otherwise, we only need a
volunteer to turn it into code :-).

-- 
Thanks,
Maxim