TOML support

[czechboy0]

I think it'd be great for there to be a TOML provider. Now, I don't think we should add it to this core package, but using this issue to help coordinate interested parties.

@finnvoor created https://github.com/finnvoor/swift-configuration-toml

@dduan maintains https://github.com/dduan/TOMLDecoder and is interested in a provider being added directly to that repo, dduan/TOMLDecoder#88

Connecting you folks in case you'd like to collaborate on a single implementation.

Once there is one based on Swift Configuration 1.0, I'd like to link to it from Swift Configuration's README and docs, from a section "Community Providers".

[czechboy0]

Whichever implementation y'all decide to embrace, it'd probably be valuable to use FileProvider/ReloadingFileProvider, as that'll let you avoid reimplementing a lot of boilerplate and just implement the file parsing.

For details: https://swiftpackageindex.com/apple/swift-configuration/main/documentation/configuration/sco-0001

[czechboy0]

More specifically - any TOML provider really just needs to vend a type conforming to FileProviderSnapshot (https://swiftpackageindex.com/apple/swift-configuration/1.0.0/documentation/configuration/fileconfigsnapshot) and adopters will use it with FileProvider/ReloadingFileProvider.

Meaning the TOML repo can depend on Swift Configuration with traits: [], which will minimize the dependencies.

[mattt]

Hi @czechboy0. I built one here: https://github.com/mattt/swift-configuration-toml. For your consideration ✌️

[czechboy0]

Looks great, @mattt! Once you have a release, I'll link to it from the README.

That applies to other alternatives, too - I'll add a Community Providers section to the README and it's totally okay if we have multiple alternatives, I'll link to all if them.

[czechboy0]

Btw, @mattt, you don't need the separate TOMLProvider type at all, you could just offer the TOMLSnapshot, as your current TOMLProvider is equivalent to FileProvider<TOMLSnapshot>. If you wanted to make it super discoverable, just add public typealias TOMLProvider = FileProvider<TOMLSnapshot>

[mattt]

You don't need the separate TOMLProvider type at all, you could just offer the TOMLSnapshot, as your current TOMLProvider is equivalent to FileProvider<TOMLSnapshot>. If you wanted to make it super discoverable, just add public typealias TOMLProvider = FileProvider<TOMLSnapshot>

Thanks for the pro tip! That definitely made for a simpler implementation. Along the way, I bumped on some confusion about testability, and opened an issue to track that here: #127

After making those changes, I went ahead and cut a 1.0.0 release for the project. Let me know if you need anything else to feature this as a community provider implementation, or have any suggestions for how to improve it.

[czechboy0]

@mattt looks great, one addition you could make:

public typealias ReloadingTOMLProvider = ReloadingFileProvider<TOMLSnapshot>

Let me add a link to your project to a new Community Providers section.

[czechboy0]

#129

[mattt]

@mattt looks great, one addition you could make:

public typealias ReloadingTOMLProvider = ReloadingFileProvider

Thank you for that recommendation. I just opened a PR making that change here. Lemme know if that looks right.

[czechboy0]

I'm not 100%, but I don't think that'll work - the Reloading trait is specific to Swift Configuration, and isn't visible to downstream dependencies.

So you have two options:

1. Do not add this typealias, and just mention that folks can still do ReloadingFileProvider<TOMLSnapshot> in their code.
2. Add a trait to swift-configuration-toml, also called Reloading, which is disabled by default, and in your dependency on Swift Configuration, add a conditional trait like:

.package(
    url: "https://github.com/apple/swift-configuration",
    from: "1.0.0",
    traits: [.defaults, .trait(name: "Reloading", condition: .when(traits: ["Reloading"]))]
)

What this will do is only show the Reloading type alias if your users enable the Reloading trait on your package, which in turn will turn on Swift Configuration's Reloading trait, which provides ReloadingFileProvider.

The fact that they're called the same name is purely for convenience, you can call your trait anything else.

[mattt]

@czechboy0 Thank you for calling that out. I just implemented that and cut a 1.1.0 release.

[czechboy0]

@mattt looks great!