Undo new-build support for convenience libraries.

[ezyang]

The previous approach I took, though correct, was quite
confusing. If I refactor InstallPlan to operate on a
per-component basis, then we'll automatically get support
for convenience libraries, which will ultimately cleaner.
(While we won't be able to get rid of support for whole
package installs, it will be safe to assume packages
using convenience libraries also support one-shot
configure.)

I think this may fix #3637.

Signed-off-by: Edward Z. Yang ezyang@cs.stanford.edu

[hvr]

Just for the record, this doesn't fix #3637 yet, as with this patch applied to master, and trying to build exe:cabal with it:

$ cabal new-build exe:cabal
In order, the following will be built (use -v for more details):
cabal-install-1.25.0.0
rebuildTarget: unexpected package status
CallStack (from HasCallStack):
error, called at ./Distribution/Client/ProjectBuilding.hs:676:23 in
main:Distribution.Client.ProjectBuilding

[23Skidoo]

If I refactor InstallPlan to operate on a
per-component basis, then we'll automatically get support
for convenience libraries, which will ultimately cleaner.

SGTM.

[ezyang]

Actually, I am feeling a little regretful about this patch, because component-izing the new-build code was quite involved, and I'm not sure I want to do it again for the old codepath (install). So I think maybe I'll revert half this patch, keeping the old implementation for the legacy codepath (which hopefully is going away soon.)

[23Skidoo]

(which hopefully is going away soon.)

Well, it will still be around in the next release for sure.

[ezyang]

Going to redo the patch to only drop this codepath for new-build.