Add Base.active_manifest()

[IanButterworth]

Closes #57924

julia> Base.active_project()
"/Users/ian/.julia/environments/v1.13/Project.toml"

julia> Base.active_manifest()
"/Users/ian/.julia/environments/v1.13/Manifest.toml"

(@v1.13) pkg> activate --temp
  Activating new project at `/var/folders/1z/jf841bdj73bdj3vk7kc7f_3w0000gn/T/jl_SCVFBB`

julia> Base.active_project()
"/var/folders/1z/jf841bdj73bdj3vk7kc7f_3w0000gn/T/jl_SCVFBB/Project.toml"

julia> Base.active_manifest()

julia>

I'm holding off adding tests because I wasn't sure whether that last case should match active_project and return a path to a nonexistant file? i.e. the temp Project.toml doesn't exist, nor manifest.

[KristofferC]

Maybe it should optionally take a project and give the manifest for that (defaulting to the active project).

[bvdmitri]

A test for these changes would be nice, especially because (edit: ops I'm blind) the code has a bug and spells @something as @someting

[IanButterworth]

See the label and

I'm holding off adding tests because I wasn't sure whether that last case should match active_project and return a path to a nonexistant file? i.e. the temp Project.toml doesn't exist, nor manifest.

[DilumAluthge]

I'm holding off adding tests because I wasn't sure whether that last case should match active_project and return a path to a nonexistant file? i.e. the temp Project.toml doesn't exist, nor manifest.

IMO it makes sense to return nothing (which it looks like is what you currently do).

[DilumAluthge]

How does this function behave with regards to versioned manifest filenames?

[DilumAluthge]

I'm holding off adding tests because I wasn't sure whether that last case should match active_project and return a path to a nonexistant file? i.e. the temp Project.toml doesn't exist, nor manifest.

IMO it makes sense to return nothing (which it looks like is what you currently do).

To clarify my opinion, I think it's good that this PR currently returns nothing in this case. I don't think this PR should return a path to the non-existent path.

[DilumAluthge]

I still think that this would be nice to have. @IanButterworth @KristofferC What do you think?

[IanButterworth]

Feel free to take it over

[DilumAluthge]

Ah, I should have left in "draft" - still needs tests.

[DilumAluthge]

Has tests now.