Allow querying the build system for the language of a document

The build system has potentially  more information about a document's language than we do based on the file’s extension.

Author: ahoppen

Sources/SKCore/BuildServerBuildSystem.swift

@@ -267,6 +267,10 @@ extension BuildServerBuildSystem: BuildSystem {
     return buildSettings[document]
   }
 
+  public func defaultLanguage(for document: DocumentURI) async -> Language? {
+    return nil
+  }
+
   public func registerForChangeNotifications(for uri: DocumentURI) {
     let request = RegisterForChanges(uri: uri, action: .register)
     _ = self.buildServer?.send(request) { result in

Sources/SKCore/BuildSystem.swift

@@ -87,6 +87,13 @@ public protocol BuildSystem: AnyObject, Sendable {
   /// file or if it hasn't computed build settings for the file yet.
   func buildSettings(for document: DocumentURI, language: Language) async throws -> FileBuildSettings?
 
+  /// If the build system has knowledge about the language that this document should be compiled in, return it.
+  ///
+  /// This is used to determine the language in which a source file should be background indexed.
+  ///
+  /// If `nil` is returned, the language based on the file's extension.
+  func defaultLanguage(for document: DocumentURI) async -> Language?
+
   /// Register the given file for build-system level change notifications, such
   /// as command line flag changes, dependency changes, etc.
   ///
@@ -113,5 +120,4 @@ public protocol BuildSystem: AnyObject, Sendable {
   func addSourceFilesDidChangeCallback(_ callback: @Sendable @escaping () async -> Void) async
 }
 
-public let buildTargetsNotSupported =
-  ResponseError.methodNotFound(BuildTargets.method)
+public let buildTargetsNotSupported = ResponseError.methodNotFound(BuildTargets.method)

Sources/SKCore/BuildSystemManager.swift

@@ -106,6 +106,22 @@ extension BuildSystemManager {
     self.mainFilesProvider = mainFilesProvider
   }
 
+  /// Returns the language that a document should be interpreted in for background tasks where the editor doesn't
+  /// specify the document's language.
+  public func defaultLanguage(for document: DocumentURI) async -> Language? {
+    if let defaultLanguage = await buildSystem?.defaultLanguage(for: document) {
+      return defaultLanguage
+    }
+    switch document.fileURL?.pathExtension {
+    case "c": return .c
+    case "cpp", "cc", "cxx": return .cpp
+    case "m": return .objective_c
+    case "mm", "h": return .objective_cpp
+    case "swift": return .swift
+    default: return nil
+    }
+  }
+
   private func buildSettings(
     for document: DocumentURI,
     language: Language

Sources/SKCore/CompilationDatabaseBuildSystem.swift

@@ -114,6 +114,10 @@ extension CompilationDatabaseBuildSystem: BuildSystem {
     )
   }
 
+  public func defaultLanguage(for document: DocumentURI) async -> Language? {
+    return nil
+  }
+
   public func registerForChangeNotifications(for uri: DocumentURI) async {
     self.watchedFiles.insert(uri)
   }

Sources/SKSwiftPMWorkspace/SwiftPMBuildSystem.swift

@@ -341,6 +341,11 @@ extension SwiftPMBuildSystem: SKCore.BuildSystem {
     return nil
   }
 
+  public func defaultLanguage(for document: DocumentURI) async -> Language? {
+    // TODO (indexing): Query The SwiftPM build system for the document's language
+    return nil
+  }
+
   public func registerForChangeNotifications(for uri: DocumentURI) async {
     self.watchedFiles.insert(uri)
   }

Tests/SKCoreTests/BuildSystemManagerTests.swift

@@ -449,6 +449,10 @@ class ManualBuildSystem: BuildSystem {
     return map[uri]
   }
 
+  public func defaultLanguage(for document: DocumentURI) async -> Language? {
+    return nil
+  }
+
   func registerForChangeNotifications(for uri: DocumentURI) async {
   }
 

Tests/SourceKitLSPTests/BuildSystemTests.swift

@@ -43,6 +43,10 @@ final class TestBuildSystem: BuildSystem {
     return buildSettingsByFile[document]
   }
 
+  public func defaultLanguage(for document: DocumentURI) async -> Language? {
+    return nil
+  }
+
   func registerForChangeNotifications(for uri: DocumentURI) async {
     watchedFiles.insert(uri)
   }