use Pkg.precompile during loading via Pkg hook

[IanButterworth]

Closes #48259

Previously

julia> using CSV
[ Info: Precompiling CSV [336ed68f-0bac-5ca0-87d4-7b16caf5d00b]

julia> 

This PR

julia> using CSV
Precompiling CSV
  20 dependencies successfully precompiled in 30 seconds. 1 already precompiled.

julia> 

Note that errors and warnings will be shown, including warnings about precompilation waiting for tasks to finish etc. so this should be quite safe. But a switch could be added to turn it off.

Requires:

• Precompile: pass precompile to new Base loading hook Pkg.jl#3433

Also two minor bug fixes:

• precompile: include extensions when packages are specified Pkg.jl#3432
• precompile: fix minor print bug Pkg.jl#3431

[vtjnash]

We are in the imminent process of removing Pkg, so this seems unwise to merge now

[vtjnash]

There was also an issue with Pkg.precompile suppressing warnings and other similar messages, which means this PR would harm usability and development until that fix is merged.

[ericphanson]

There was also an issue with Pkg.precompile suppressing warnings and other similar messages, which means this PR would harm usability and development until that fix is merged.

I believe Ian has already addressed this in Pkg.jl. See also his message:

Note that errors and warnings will be shown, including warnings about precompilation waiting for tasks to finish etc. so this should be quite safe. But a switch could be added to turn it off.

---

We are in the imminent process of removing Pkg, so this seems unwise to merge now

This just adds a hook, so it seems fine? If you load Pkg, it populates the hook, and switches you to parallel precompilation.

[KristofferC]

We are in the imminent process of removing Pkg, so this seems unwise to merge now

We might want to move the parallel precompile code to Base. It doesn't really have anything to do with the package manager itself. You would want parallel precompile without having to load Pkg.

[vtjnash]

The issue seems to be still open #48371?

[IanButterworth]

Oops. Just closed that

[vtjnash]

Gotcha, yeah that makes more sense.

[IanButterworth]

Should this be merged before Pkg.precompile is moved to Base? It might be helpful to try it out and if it's ok aim to move it over for 1.10?

[KristofferC]

IMO it's fine to merge it in the current state (using Pkg) so the whole concept gets tested.

[IanButterworth]

Won't be functional until Pkg has been bumped with JuliaLang/Pkg.jl#3433