Great! I did expect it to be rather uncontroversial since it's pretty much just mirroring SwiftPM's conceptual model — there are possibly some nuances with system library targets and binary targets, though this proposal exposes pretty much what's there already, so if more is needed, the manifest might need be extended as well, in a separate proposal. I do expect that future proposals that modify SwiftPM's data model should include a section on how the plugin API evolves along with it.
That's good feedback — in general I would expect that the tools that the plugin would look up would be the ones that it has itself declared a dependency on, but this might indeed be worth exposing in the API. We could also do that by making the name-to-tool mapping available without a lookup function, and then let the plugin just do a subscripted lookup?
Right, I've been thinking the same thing, though in this proposal I wanted to focus entirely on extending the API (though that's not a requirement, I guess).
The original intent in SE-0303 was to try to avoid assumptions about what build tools wanted to look at as their inputs, and thereby unintentionally limiting them. But it's certainly very common for a build tool in particular to want to process files matching a particular naming pattern. In that case perhaps the main entry point should pass those input files up-front so that the tool doesn't have to find them.
I'm also mildly concerned about the performance of making all the inputs available to all build tools, only for the build tool to ignore most of them. I think that can be mitigated in the implementation, and is one reason why the API is an iterator, but it would be even more efficient to just state it up-front rather than filter it later.
I'm concerned about adding more complexity back to the manifest declaration, though. Ideally I think it would make sense to use annotated properties on the plugin type to convey this kind of information, in the manner of SwiftArgumentParser. This could be used for custom parameters to the plugin and also perhaps to declare input filters etc. SwiftPM could then look at those annotations, perhaps even syntactically before even running the plugin if they are literals.
But those are just future ideas. Do you think that, in the immediate term, there should be an optional file name pattern on the
.buildTool() capability declaration in the manifest?