Add a new test project type that uses a custom build server

[ahoppen]

This allows us to more easily test behavior for build servers that have different behavior than SwiftPM and compile commands without having to implement the build server in Python.

[ahoppen]

Not to self: If this gets merged before #2032, then we can update that PR to use the following test case, using the new build server test infrastructure.

Updated test

func testUseResponseFileIfTooManyArguments() async throws {
  // The build system returns too many arguments to fit them into a command line invocation, so we need to use a
  // response file to invoke the indexer.

  final class BuildServer: CustomBuildServer {
    private let projectRoot: URL
    private var testFileURL: URL { projectRoot.appendingPathComponent("Test File.swift") }

    init(projectRoot: URL, connectionToSourceKitLSP: any LanguageServerProtocol.Connection) {
      self.projectRoot = projectRoot
    }

    func initializeBuildRequest(_ request: InitializeBuildRequest) async throws -> InitializeBuildResponse {
      return initializationResponse(
        initializeData: SourceKitInitializeBuildResponseData(
          indexDatabasePath: try projectRoot.appendingPathComponent("index-db").filePath,
          indexStorePath: try projectRoot.appendingPathComponent("index-store").filePath,
          prepareProvider: true,
          sourceKitOptionsProvider: true
        )
      )
    }

    func buildTargetSourcesRequest(_ request: BuildTargetSourcesRequest) async throws -> BuildTargetSourcesResponse {
      return BuildTargetSourcesResponse(items: [
        SourcesItem(
          target: .dummy,
          sources: [
            SourceItem(uri: URI(testFileURL), kind: .file, generated: false)
          ]
        )
      ])
    }

    func textDocumentSourceKitOptionsRequest(
      _ request: TextDocumentSourceKitOptionsRequest
    ) async throws -> TextDocumentSourceKitOptionsResponse? {
      var arguments =
        [try testFileURL.filePath] + (0..<50_000).map { "-DTHIS_IS_AN_OPTION_THAT_CONTAINS_MANY_BYTES_\($0)" }
      if let defaultSDKPath {
        arguments += ["-sdk", defaultSDKPath]
      }
      return TextDocumentSourceKitOptionsResponse(
        compilerArguments: arguments
      )
    }

  }

  let project = try await CustomBuildServerTestProject(
    files: [
      // File name contains a space to ensure we escape it in the response file.
      "Test File.swift": """
      func 1️⃣myTestFunc() {}
      """
    ],
    buildServer: BuildServer.self,
    enableBackgroundIndexing: true
  )
  try await project.testClient.send(PollIndexRequest())

  let symbols = try await project.testClient.send(WorkspaceSymbolsRequest(query: "myTestFunc"))
  XCTAssertEqual(
    symbols,
    [
      .symbolInformation(
        SymbolInformation(
          name: "myTestFunc()",
          kind: .function,
          location: try project.location(from: "1️⃣", to: "1️⃣", in: "Test File.swift")
        )
      )
    ]
  )
}

[ahoppen]

@swift-ci Please test

[ahoppen]

@swift-ci Please test

[hamishknight]

2025, right? :)

[ahoppen]

Yeah… Probably from some copy-pasting

[ahoppen]

@swift-ci Please test Windows

[ahoppen]

@swift-ci Please test Windows