Mark target preparation out-of-date when it has changed in the build server

Sources/SemanticIndex/SemanticIndexManager.swift

@@ -413,6 +413,38 @@ package final actor SemanticIndexManager {
     )
   }
 
+  package func buildTargetsChanged(_ changes: [BuildTargetEvent]?) async {
+    let targets = changes?.map(\.target)
+
+    if let targets {
+      var targetsAndDependencies = targets
+      targetsAndDependencies += await buildSystemManager.targets(dependingOn: Set(targets))
+      if !targetsAndDependencies.isEmpty {
+        logger.info(
+          """
+          Marking dependent targets as out-of-date: \
+          \(String(targetsAndDependencies.map(\.uri.stringValue).joined(separator: ", ")))
+          """
+        )
+        await preparationUpToDateTracker.markOutOfDate(targetsAndDependencies)
+      }
+    } else {
+      await preparationUpToDateTracker.markAllKnownOutOfDate()
+    }
+
+    await orLog("Scheduling re-indexing of changed targets") {
+      var sourceFiles = try await self.buildSystemManager.sourceFiles(includeNonBuildableFiles: false)
+      if let targets {
+        sourceFiles = sourceFiles.filter { !$0.value.targets.isDisjoint(with: targets) }
+      }
+      _ = await scheduleIndexing(
+        of: sourceFiles.keys,
+        indexFilesWithUpToDateUnit: false,
+        priority: .low
+      )
+    }
+  }
+
   /// Returns the files that should be indexed to get up-to-date index information for the given files.
   ///
   /// If `files` contains a header file, this will return a `FileToIndex` that re-indexes a main file which includes the

Sources/SourceKitLSP/Workspace.swift

@@ -435,20 +435,7 @@ package final class Workspace: Sendable, BuildSystemManagerDelegate {
 
   package func buildTargetsChanged(_ changes: [BuildTargetEvent]?) async {
     await sourceKitLSPServer?.fileHandlingCapabilityChanged()
-    await orLog("Scheduling re-indexing of changed targets") {
-      var sourceFiles = try await self.buildSystemManager.sourceFiles(includeNonBuildableFiles: false)
-      if let changes {
-        let changedTargets = changes.map(\.target)
-        sourceFiles = sourceFiles.filter {
-          !$0.value.targets.isDisjoint(with: changedTargets)
-        }
-      }
-      _ = await semanticIndexManager?.scheduleIndexing(
-        of: sourceFiles.keys,
-        indexFilesWithUpToDateUnit: false,
-        priority: .low
-      )
-    }
+    await semanticIndexManager?.buildTargetsChanged(changes)
     await orLog("Scheduling syntactic test re-indexing") {
       let testFiles = try await buildSystemManager.testFiles()
       await syntacticTestIndex.listOfTestFilesDidChange(testFiles)

Tests/SourceKitLSPTests/BackgroundIndexingTests.swift

@@ -1977,6 +1977,69 @@ final class BackgroundIndexingTests: XCTestCase {
       return true
     }
   }
+
+  func testRePrepareTargetsWhenBuildServerChanges() async throws {
+    let project = try await SwiftPMTestProject(
+      files: [
+        "LibA/LibA.swift": """
+        #if ENABLE_FOO
+        public func foo() {}
+        #endif
+        """,
+        "LibB/LibB.swift": """
+        import LibA
+
+        func test() {
+          1️⃣foo()
+        }
+        """,
+      ],
+      manifest: """
+        // swift-tools-version: 5.7
+
+        import PackageDescription
+
+        let package = Package(
+          name: "MyLibrary",
+          targets: [
+           .target(name: "LibA"),
+           .target(name: "LibB", dependencies: ["LibA"]),
+          ]
+        )
+        """,
+      enableBackgroundIndexing: true
+    )
+
+    let (uri, positions) = try project.openDocument("LibB.swift")
+    let hoverWithMissingDependencyDeclaration = try await project.testClient.send(
+      HoverRequest(textDocument: TextDocumentIdentifier(uri), position: positions["1️⃣"])
+    )
+    XCTAssertNil(hoverWithMissingDependencyDeclaration)
+
+    let manifestUri = try project.uri(for: "Package.swift")
+    try """
+    // swift-tools-version: 5.7
+
+    import PackageDescription
+
+    let package = Package(
+      name: "MyLibrary",
+      targets: [
+       .target(name: "LibA", swiftSettings: [.define("ENABLE_FOO")]),
+       .target(name: "LibB", dependencies: ["LibA"]),
+      ]
+    )
+    """.write(to: XCTUnwrap(project.uri(for: "Package.swift").fileURL), atomically: true, encoding: .utf8)
+
+    project.testClient.send(DidChangeWatchedFilesNotification(changes: [FileEvent(uri: manifestUri, type: .changed)]))
+
+    try await repeatUntilExpectedResult {
+      let hoverAfterAddingDependencyDeclaration = try await project.testClient.send(
+        HoverRequest(textDocument: TextDocumentIdentifier(uri), position: positions["1️⃣"])
+      )
+      return hoverAfterAddingDependencyDeclaration != nil
+    }
+  }
 }
 
 extension HoverResponseContents {