diff --git a/Sources/SKCore/BuildServerBuildSystem.swift b/Sources/SKCore/BuildServerBuildSystem.swift
index 19d7270f..7bd9a500 100644
--- a/Sources/SKCore/BuildServerBuildSystem.swift
+++ b/Sources/SKCore/BuildServerBuildSystem.swift
@@ -317,14 +317,14 @@ extension BuildServerBuildSystem: BuildSystem {
     return .unhandled
   }
 
-  public func testFiles() async -> [DocumentURI] {
-    // BuildServerBuildSystem does not support syntactic test discovery
+  public func sourceFiles() async -> [SourceFileInfo] {
+    // BuildServerBuildSystem does not support syntactic test discovery or background indexing.
     // (https://github.com/apple/sourcekit-lsp/issues/1173).
     return []
   }
 
-  public func addTestFilesDidChangeCallback(_ callback: @escaping () async -> Void) {
-    // BuildServerBuildSystem does not support syntactic test discovery
+  public func addSourceFilesDidChangeCallback(_ callback: @escaping () async -> Void) {
+    // BuildServerBuildSystem does not support syntactic test discovery or background indexing.
     // (https://github.com/apple/sourcekit-lsp/issues/1173).
   }
 }
diff --git a/Sources/SKCore/BuildSystem.swift b/Sources/SKCore/BuildSystem.swift
index e9756023..a0954fd1 100644
--- a/Sources/SKCore/BuildSystem.swift
+++ b/Sources/SKCore/BuildSystem.swift
@@ -27,6 +27,22 @@ public enum FileHandlingCapability: Comparable, Sendable {
   case handled
 }
 
+public struct SourceFileInfo: Sendable {
+  /// The URI of the source file.
+  public let uri: DocumentURI
+
+  /// Whether the file might contain test cases. This property is an over-approximation. It might be true for files
+  /// from non-test targets or files that don't actually contain any tests. Keeping this list of files with
+  /// `mayContainTets` minimal as possible helps reduce the amount of work that the syntactic test indexer needs to
+  /// perform.
+  public let mayContainTests: Bool
+
+  public init(uri: DocumentURI, mayContainTests: Bool) {
+    self.uri = uri
+    self.mayContainTests = mayContainTests
+  }
+}
+
 /// Provider of FileBuildSettings and other build-related information.
 ///
 /// The primary role of the build system is to answer queries for
@@ -88,17 +104,13 @@ public protocol BuildSystem: AnyObject, Sendable {
 
   func fileHandlingCapability(for uri: DocumentURI) async -> FileHandlingCapability
 
-  /// Returns the list of files that might contain test cases.
-  ///
-  /// The returned file list is an over-approximation. It might contain tests from non-test targets or files that don't
-  /// actually contain any tests. Keeping this list as minimal as possible helps reduce the amount of work that the
-  /// syntactic test indexer needs to perform.
-  func testFiles() async -> [DocumentURI]
+  /// Returns the list of source files in the project.
+  func sourceFiles() async -> [SourceFileInfo]
 
-  /// Adds a callback that should be called when the value returned by `testFiles()` changes.
+  /// Adds a callback that should be called when the value returned by `sourceFiles()` changes.
   ///
-  /// The callback might also be called without an actual change to `testFiles`.
-  func addTestFilesDidChangeCallback(_ callback: @Sendable @escaping () async -> Void) async
+  /// The callback might also be called without an actual change to `sourceFiles`.
+  func addSourceFilesDidChangeCallback(_ callback: @Sendable @escaping () async -> Void) async
 }
 
 public let buildTargetsNotSupported =
diff --git a/Sources/SKCore/BuildSystemManager.swift b/Sources/SKCore/BuildSystemManager.swift
index 0e03e6b2..926037f0 100644
--- a/Sources/SKCore/BuildSystemManager.swift
+++ b/Sources/SKCore/BuildSystemManager.swift
@@ -191,8 +191,17 @@ extension BuildSystemManager {
     )
   }
 
+  public func sourceFiles() async -> [SourceFileInfo] {
+    return await buildSystem?.sourceFiles() ?? []
+  }
+
   public func testFiles() async -> [DocumentURI] {
-    return await buildSystem?.testFiles() ?? []
+    return await sourceFiles().compactMap { (info: SourceFileInfo) -> DocumentURI? in
+      guard info.mayContainTests else {
+        return nil
+      }
+      return info.uri
+    }
   }
 }
 
diff --git a/Sources/SKCore/CompilationDatabaseBuildSystem.swift b/Sources/SKCore/CompilationDatabaseBuildSystem.swift
index 929110f2..5e0e2fe7 100644
--- a/Sources/SKCore/CompilationDatabaseBuildSystem.swift
+++ b/Sources/SKCore/CompilationDatabaseBuildSystem.swift
@@ -192,11 +192,16 @@ extension CompilationDatabaseBuildSystem: BuildSystem {
     }
   }
 
-  public func testFiles() async -> [DocumentURI] {
-    return compdb?.allCommands.map { DocumentURI($0.url) } ?? []
+  public func sourceFiles() async -> [SourceFileInfo] {
+    guard let compdb else {
+      return []
+    }
+    return compdb.allCommands.map {
+      SourceFileInfo(uri: DocumentURI($0.url), mayContainTests: true)
+    }
   }
 
-  public func addTestFilesDidChangeCallback(_ callback: @escaping () async -> Void) async {
+  public func addSourceFilesDidChangeCallback(_ callback: @escaping () async -> Void) async {
     testFilesDidChangeCallbacks.append(callback)
   }
 }
diff --git a/Sources/SKSwiftPMWorkspace/SwiftPMBuildSystem.swift b/Sources/SKSwiftPMWorkspace/SwiftPMBuildSystem.swift
index 4bb6ee64..c4599607 100644
--- a/Sources/SKSwiftPMWorkspace/SwiftPMBuildSystem.swift
+++ b/Sources/SKSwiftPMWorkspace/SwiftPMBuildSystem.swift
@@ -437,17 +437,22 @@ extension SwiftPMBuildSystem: SKCore.BuildSystem {
     }
   }
 
-  public func testFiles() -> [DocumentURI] {
-    return fileToTarget.compactMap { (path, target) -> DocumentURI? in
+  public func sourceFiles() -> [SourceFileInfo] {
+    return fileToTarget.compactMap { (path, target) -> SourceFileInfo? in
       guard target.isPartOfRootPackage else {
         // Don't consider files from package dependencies as possible test files.
         return nil
       }
-      return DocumentURI(path.asURL)
+      // We should only set mayContainTests to `true` for files from test targets
+      // (https://github.com/apple/sourcekit-lsp/issues/1174).
+      return SourceFileInfo(
+        uri: DocumentURI(path.asURL),
+        mayContainTests: true
+      )
     }
   }
 
-  public func addTestFilesDidChangeCallback(_ callback: @Sendable @escaping () async -> Void) async {
+  public func addSourceFilesDidChangeCallback(_ callback: @Sendable @escaping () async -> Void) async {
     testFilesDidChangeCallbacks.append(callback)
   }
 }
diff --git a/Sources/SourceKitLSP/Workspace.swift b/Sources/SourceKitLSP/Workspace.swift
index bba836a3..50ec6a49 100644
--- a/Sources/SourceKitLSP/Workspace.swift
+++ b/Sources/SourceKitLSP/Workspace.swift
@@ -97,7 +97,7 @@ public final class Workspace {
     await indexDelegate?.addMainFileChangedCallback { [weak self] in
       await self?.buildSystemManager.mainFilesChanged()
     }
-    await underlyingBuildSystem?.addTestFilesDidChangeCallback { [weak self] in
+    await underlyingBuildSystem?.addSourceFilesDidChangeCallback { [weak self] in
       guard let self else {
         return
       }
diff --git a/Tests/SKCoreTests/BuildSystemManagerTests.swift b/Tests/SKCoreTests/BuildSystemManagerTests.swift
index 156a2f1c..96ec6890 100644
--- a/Tests/SKCoreTests/BuildSystemManagerTests.swift
+++ b/Tests/SKCoreTests/BuildSystemManagerTests.swift
@@ -469,11 +469,11 @@ class ManualBuildSystem: BuildSystem {
     }
   }
 
-  func testFiles() async -> [DocumentURI] {
+  func sourceFiles() async -> [SourceFileInfo] {
     return []
   }
 
-  func addTestFilesDidChangeCallback(_ callback: @escaping () async -> Void) {}
+  func addSourceFilesDidChangeCallback(_ callback: @escaping () async -> Void) {}
 }
 
 /// A `BuildSystemDelegate` setup for testing.
diff --git a/Tests/SourceKitLSPTests/BuildSystemTests.swift b/Tests/SourceKitLSPTests/BuildSystemTests.swift
index c0ac9f0d..092520dd 100644
--- a/Tests/SourceKitLSPTests/BuildSystemTests.swift
+++ b/Tests/SourceKitLSPTests/BuildSystemTests.swift
@@ -61,11 +61,11 @@ final class TestBuildSystem: BuildSystem {
     }
   }
 
-  func testFiles() async -> [DocumentURI] {
+  func sourceFiles() async -> [SourceFileInfo] {
     return []
   }
 
-  func addTestFilesDidChangeCallback(_ callback: @escaping () async -> Void) async {}
+  func addSourceFilesDidChangeCallback(_ callback: @escaping () async -> Void) async {}
 }
 
 final class BuildSystemTests: XCTestCase {