`buildTarget/inverseSources` is not required to be implemented by BSP servers and we have almost all information needed for it in `BuildSystemManager`.
This also makes sure that `buildTarget/sources` and `buildTarget/inverseSources` actually match each other. Before this change, we had source files like `Package.swift` for which we returned a target from `buildTarget/inverseSources` but that weren’t part of that target’s sources retrieved using `buildTarget/sources`.
The implementation of which file’s dependencies have been updated is common across all build systems and thus build systems shouldn’t need to implement this logic. This also allows us to remove `BuildSystemDelegate`.
This finalizes the move of `BuiltInBuildSystem` creation into `BuiltInBuildSystemAdapter` and means that we can set the message handler of the `BuiltInBuildSystem` during initialization instead of using a setter method.
This allows us to create the build system from a `BuiltInBuildSystemAdapter` when it receives an `InitializeRequest`, which will be done in a follow-up commit.
We were making the initial `generateBuildGraph` call in `SourceKitLSPServer` from a `Task`. This means that `generateBuildGraph` could be executed after `waitForUpToDateBuildGraph` was called by `SemanticIndexManager`. Thus `waitForUpToDateBuildGraph` returned immediately and no files were background indexed.
Make `generateBuildGraph` immediately schedule a package reload for SwiftPM build systems instead of doing the hop through a `Task`, fixing the race condition.
rdar://135551812
We currently load the entire package before generating a `SwiftPMBuildSystem`. That means that the initialize request to SourceKit-LSP is blocked until the package has been loaded, preventing us from offering any sort of functionality, including syntactic functionality like formatting.
Decouple build system creation and build graph generation (aka. package loading for SwiftPM). We can operate with fallback build settings until the build graph has been loaded and reopen the document once the proper build settings are available.
rdar://126644596
Do one of the following for every `FIXME` or `TODO` comment
- Add an issue that tracks the task
- Remove the comment if we are not planning to address it
