pkg> add for a weakdep package does not permanently install package

[topolarity]

If you pkg> add a package that's already in your Project.toml as a weakdep, Pkg gets mildly indecisive and installs all of the package + deps only to remove them on the next package operation.

MWE:

$ cat Foo/Project.toml
name = "Foo"
uuid = "721b2572-63d0-4bb6-a91e-fe9952250d90"
authors = ["Cody Tapscott <topolarity@tapscott.me>"]
version = "0.1.0"

[weakdeps]
CUDA = "052768ef-5323-5732-b1bb-66c8b64840ba"

[compat]
CUDA = "4"
$ julia --project=Foo -q
(Foo) pkg> add CUDA
<adds a ton of CUDA + dependent packages>
(Foo) pkg> add TOML
<immediately removes all of CUDA + its dependent packages>

It is a bit concerning that > add Foo can have an inconsistent concept of the state after an add versus the rest of Pkg.

[KristofferC]

The reason for this is that when Pkg reads a project and sees that it is both a weakdep and a dep it ignores the dep entry (so that extensions can be used in a backwards compatible manner).

The solution here might be to just delete the weak dep entry when an explicit add is made.

[KristofferC]

But on the other hand, having extensions while having strong deps on the triggers for those extensions is very likely to run into a cycle analogous to JuliaLang/julia#52511 (comment).