Preferences for `Main`?

[MilesCranmer]

I wanted to set preferences for Main so that I can control behavior in my REPL. But seems like it requires a UUID to store it in the cache:

        uuid = Base.PkgId(m).uuid
        if uuid === nothing
            throw(ArgumentError("Module $(m) does not correspond to a loaded package!"))
        end

(from src/utils.jl)

All I really want is to write

[Main]
my_preference = true

Is this possible?

[StefanKarpinski]

Any thoughts on this, @staticfloat?

[DilumAluthge]

Can you say a little more about your use case? How are you consuming the preference value?

[StefanKarpinski]

I'm imagining this would be for doing things like setting how many float decimal points you want to print or whatever. A few options:

1. Give Main a UUID
2. Use REPL instead, which has a UUID since it's a stdlib
3. Use the julia UUID

[DilumAluthge]

At first glance, option 2 (use REPL's UUID) seems to make the most sense, especially if the only use case is the REPL.

[StefanKarpinski]

I agree that if the use case is controlling behavior of the REPL (which seems like a good application), then it should be a REPL preference. There could be a use case for using Preferences to control Julia itself, in which case I think the third option might be the way to go.

[DilumAluthge]

Or perhaps identify a different relevant stdlib, based on the use case? E.g. for non-REPL sessions, if the user wants to customize logging behavior, then using the UUID of the Logging stdlib would likely make sense.

[MilesCranmer]

I basically want to set preferences for DispatchDoctor.jl in the REPL to control the codegen for local functions defined as @stable without needing to pass it in the macro. When I am running DispatchDoctor in the REPL, it appears to check the preferences for Main, although that does not map to a UUID, so there’s no way for me to control it from a preferences file.

DispatchDoctor.jl uses load_preferences(uuid, key) to load a preference: https://github.com/MilesCranmer/DispatchDoctor.jl/blob/94ce9de50e2da51917fcac0d1125e0a251386a5e/src/preferences.jl#L60. But it falls back to UUID(0) outside of registered packages as it errored when getting Main UUID. However, there’s no way I can pass preferences for this fallback UUID.

[MilesCranmer]

Note that DispatchDoctor macros hit Main rather than REPL because it reads the module with __module__: https://github.com/MilesCranmer/DispatchDoctor.jl/blob/94ce9de50e2da51917fcac0d1125e0a251386a5e/src/macros.jl#L84

[staticfloat]

I think this is a case where you just don’t want to use the preferences macros and instead want to explicitly list which package to load the preferences from. In this case, you want to associate the preferences with DisparchDoctor, right?

[MilesCranmer]

DispatchDoctor is used inside different libraries. You wouldn’t want to control its behavior globally. It needs different behavior per library it is applied to.

[MilesCranmer]

Similar to how PrecompileTools.jl is used with the precompile_workload preference key. You don’t want to apply this preference to PrecompileTools itself; you want to set it per module.

Difference here is that I’d like to apply a preference to the top level module of an interactive session.

[staticfloat]

I see. In that case I would suggest that we just sub out REPL for Main. We can do that by writing a wrapper that uses REPL instead of module in the preference load.