Add a SourceKit-LSP API to get the output paths of a clang target (#8317)

To facilitate swiftlang/sourcekit-lsp#2017.

Author: ahoppen

Sources/SourceKitLSPAPI/BuildDescription.swift

@@ -27,6 +27,11 @@ public enum BuildDestination {
     case target
 }
 
+public enum BuildTargetCompiler {
+    case swift
+    case clang
+}
+
 public protocol BuildTarget {
     /// Source files in the target
     var sources: [URL] { get }
@@ -46,13 +51,18 @@ public protocol BuildTarget {
     /// The name of the target. It should be possible to build a target by passing this name to `swift build --target`
     var name: String { get }
 
+    /// The compiler that is responsible for building this target.
+    var compiler: BuildTargetCompiler { get }
+
     var destination: BuildDestination { get }
 
     /// Whether the target is part of the root package that the user opened or if it's part of a package dependency.
     var isPartOfRootPackage: Bool { get }
 
     var isTestTarget: Bool { get }
 
+    var outputPaths: [URL] { get throws }
+
     func compileArguments(for fileURL: URL) throws -> [String]
 }
 
@@ -100,10 +110,19 @@ private struct WrappedClangTargetBuildDescription: BuildTarget {
         return description.clangTarget.name
     }
 
+    var compiler: BuildTargetCompiler { .clang }
+
+
     public var destination: BuildDestination {
         return description.destination == .host ? .host : .target
     }
 
+    var outputPaths: [URL] {
+       get throws {
+           return try description.compilePaths().map(\.object.asURL)
+       }
+    }
+
     public func compileArguments(for fileURL: URL) throws -> [String] {
         let filePath = try resolveSymlinks(try Basics.AbsolutePath(validating: fileURL.path))
         let commandLine = try description.emitCommandLine(for: filePath)
@@ -127,6 +146,8 @@ private struct WrappedSwiftTargetBuildDescription: BuildTarget {
         return description.target.name
     }
 
+    var compiler: BuildTargetCompiler { .swift }
+
     public var destination: BuildDestination {
         return description.destination == .host ? .host : .target
     }
@@ -155,6 +176,15 @@ private struct WrappedSwiftTargetBuildDescription: BuildTarget {
         return others.map(\.asURL)
     }
 
+    var outputPaths: [URL] {
+        get throws {
+            struct NotSupportedError: Error, CustomStringConvertible {
+                var description: String { "Getting output paths for a Swift target is not supported" }
+            }
+            throw NotSupportedError()
+        }
+    }
+
     func compileArguments(for fileURL: URL) throws -> [String] {
         // Note: we ignore the `fileURL` here as the expectation is that we get a command line for the entire target
         // in case of Swift.

Sources/SourceKitLSPAPI/PluginTargetBuildDescription.swift

@@ -54,11 +54,22 @@ struct PluginTargetBuildDescription: BuildTarget {
         return target.name
     }
 
+    var compiler: BuildTargetCompiler { .swift }
+
     var destination: BuildDestination {
         // Plugins are always built for the host.
         .host
     }
 
+    var outputPaths: [URL] {
+        get throws {
+            struct NotSupportedError: Error, CustomStringConvertible {
+                var description: String { "Getting output paths for a plugin target is not supported" }
+            }
+            throw NotSupportedError()
+        }
+    }
+
     func compileArguments(for fileURL: URL) throws -> [String] {
         // FIXME: This is very odd and we should clean this up by merging `ManifestLoader` and `DefaultPluginScriptRunner` again.
         var args = ManifestLoader.interpreterFlags(for: self.toolsVersion, toolchain: toolchain)

Tests/SourceKitLSPAPITests/SourceKitLSPAPITests.swift

@@ -319,6 +319,51 @@ final class SourceKitLSPAPITests: XCTestCase {
             )
         }
     }
+
+    func testClangOutputPaths() async throws {
+        let fs = InMemoryFileSystem(emptyFiles:
+            "/Pkg/Sources/lib/include/lib.h",
+            "/Pkg/Sources/lib/lib.cpp",
+        )
+
+        let observability = ObservabilitySystem.makeForTesting()
+        let graph = try loadModulesGraph(
+            fileSystem: fs,
+            manifests: [
+                Manifest.createRootManifest(
+                    displayName: "Pkg",
+                    path: "/Pkg",
+                    toolsVersion: .v5_10,
+                    targets: [
+                        TargetDescription(
+                            name: "lib",
+                            dependencies: []
+                        )
+                    ]),
+            ],
+            observabilityScope: observability.topScope
+        )
+        XCTAssertNoDiagnostics(observability.diagnostics)
+        let plan = try await BuildPlan(
+            destinationBuildParameters: mockBuildParameters(
+                destination: .target,
+                shouldLinkStaticSwiftStdlib: true
+            ),
+            toolsBuildParameters: mockBuildParameters(
+                destination: .host,
+                shouldLinkStaticSwiftStdlib: true
+            ),
+            graph: graph,
+            fileSystem: fs,
+            observabilityScope: observability.topScope
+        )
+        let description = BuildDescription(buildPlan: plan)
+
+        let target = try XCTUnwrap(description.getBuildTarget(for: XCTUnwrap(graph.module(for: "lib")), destination: .target))
+        XCTAssertEqual(target.compiler, .clang)
+        XCTAssertEqual(try target.outputPaths.count, 1)
+        XCTAssertEqual(try target.outputPaths.last?.lastPathComponent, "lib.cpp.o")
+    }
 }
 
 extension SourceKitLSPAPI.BuildDescription {