Fix module definition jumping in Swift interface files

Sources/LanguageServerProtocolExtensions/Language+Inference.swift

@@ -39,7 +39,7 @@ extension Language {
     case "cpp", "cc", "cxx", "hpp": self = .cpp
     case "m": self = .objective_c
     case "mm", "h": self = .objective_cpp
-    case "swift": self = .swift
+    case "swift", "swiftinterface": self = .swift
     default: return nil
     }
   }

Sources/SKTestSupport/Utils.swift

@@ -32,7 +32,7 @@ extension Language {
     case "cpp": self = .cpp
     case "m": self = .objective_c
     case "mm": self = .objective_cpp
-    case "swift": self = .swift
+    case "swift", "swiftinterface": self = .swift
     case "md": self = .markdown
     case "tutorial": self = .tutorial
     default: return nil

Sources/SourceKitLSP/SourceKitLSPServer.swift

@@ -553,7 +553,7 @@ package actor SourceKitLSPServer {
     }
 
     let toolchain = await workspace.buildServerManager.toolchain(
-      for: uri,
+      for: uri.buildSettingsFile,
       in: workspace.buildServerManager.canonicalTarget(for: uri),
       language: language
     )
@@ -1850,10 +1850,24 @@ extension SourceKitLSPServer {
     languageService: LanguageService
   ) async throws -> [Location] {
     // If this symbol is a module then generate a textual interface
-    if symbol.kind == .module, let name = symbol.name {
+    if symbol.kind == .module {
+      // For module symbols, prefer using systemModule information if available
+      let moduleName: String
+      let groupName: String?
+
+      if let systemModule = symbol.systemModule {
+        moduleName = systemModule.moduleName
+        groupName = systemModule.groupName
+      } else if let name = symbol.name {
+        moduleName = name
+        groupName = nil
+      } else {
+        return []
+      }
+
       let interfaceLocation = try await self.definitionInInterface(
-        moduleName: name,
-        groupName: nil,
+        moduleName: moduleName,
+        groupName: groupName,
         symbolUSR: nil,
         originatorUri: uri,
         languageService: languageService
@@ -2051,9 +2065,36 @@ extension SourceKitLSPServer {
     originatorUri: DocumentURI,
     languageService: LanguageService
   ) async throws -> Location {
+    // Check if we're already in the target interface with the same module/group/symbol
+    if let referenceDoc = try? ReferenceDocumentURL(from: originatorUri),
+       case .generatedInterface(let interfaceData) = referenceDoc,
+       interfaceData.moduleName == moduleName && interfaceData.groupName == groupName {
+
+      // If we have a specific symbol USR, try to find its position in the current interface
+      if let symbolUSR = symbolUSR,
+         let swiftLanguageService = languageService as? SwiftLanguageService {
+        do {
+          let position = try await swiftLanguageService.generatedInterfaceManager.position(
+            ofUsr: symbolUSR, 
+            in: interfaceData
+          )
+          return Location(uri: originatorUri, range: Range(position))
+        } catch {
+          // If we can't find the symbol, just return the top of the current interface
+          return Location(uri: originatorUri, range: Range(Position(line: 0, utf16index: 0)))
+        }
+      } else {
+        // No specific symbol, just return the current interface location
+        return Location(uri: originatorUri, range: Range(Position(line: 0, utf16index: 0)))
+      }
+    }
+
+    // If the originator URI is already a generated interface, use its primary file for build settings
+    let documentForBuildSettings = originatorUri.primaryFile ?? originatorUri
+
     guard
       let interfaceDetails = try await languageService.openGeneratedInterface(
-        document: originatorUri,
+        document: documentForBuildSettings,
         moduleName: moduleName,
         groupName: groupName,
         symbolUSR: symbolUSR

Sources/SourceKitLSP/Swift/GeneratedInterfaceManager.swift

@@ -92,7 +92,13 @@ actor GeneratedInterfaceManager {
     incrementingRefCount: Bool
   ) async throws -> OpenGeneratedInterfaceDocumentDetails {
     func loadFromCache() -> OpenGeneratedInterfaceDocumentDetails? {
-      guard let cachedIndex = openInterfaces.firstIndex(where: { $0.url == document }) else {
+      // Cache by module name and group name, not the full document data
+      // This allows reuse across different buildSettingsFrom URIs
+      guard let cachedIndex = openInterfaces.firstIndex(where: { 
+        $0.url.moduleName == document.moduleName && 
+        $0.url.groupName == document.groupName &&
+        $0.url.sourcekitdDocumentName == document.sourcekitdDocumentName
+      }) else {
         return nil
       }
       if incrementingRefCount {
@@ -160,7 +166,11 @@ actor GeneratedInterfaceManager {
   }
 
   private func decrementRefCount(for document: GeneratedInterfaceDocumentURLData) {
-    guard let cachedIndex = openInterfaces.firstIndex(where: { $0.url == document }) else {
+    guard let cachedIndex = openInterfaces.firstIndex(where: { 
+      $0.url.moduleName == document.moduleName && 
+      $0.url.groupName == document.groupName &&
+      $0.url.sourcekitdDocumentName == document.sourcekitdDocumentName
+    }) else {
       logger.fault(
         "Generated interface document for \(document.moduleName) is not open anymore. Unbalanced retain and releases?"
       )

Sources/SourceKitLSP/Swift/OpenInterface.swift

@@ -21,10 +21,18 @@ extension SwiftLanguageService {
     groupName: String?,
     symbolUSR symbol: String?
   ) async throws -> GeneratedInterfaceDetails? {
+    // Generate a deterministic document name based on module name and group name
+    // This ensures we reuse the same interface for the same module/group combination
+    let documentName = if let groupName {
+      "\(moduleName)-\(groupName.replacingOccurrences(of: "/", with: "-"))"
+    } else {
+      moduleName
+    }
+
     let urlData = GeneratedInterfaceDocumentURLData(
       moduleName: moduleName,
       groupName: groupName,
-      sourcekitdDocumentName: "\(moduleName)-\(UUID())",
+      sourcekitdDocumentName: documentName,
       primaryFile: document
     )
     let position: Position? =

Sources/SourceKitLSP/Swift/ReferenceDocumentURL.swift

@@ -165,13 +165,14 @@ extension DocumentURI {
       return referenceDocument.buildSettingsFile
     }
     return self
+  }  /// Convert sourcekit-lsp:// URIs to actual file system paths when possible.
+  /// For generated Swift interfaces, this returns the path where the interface file
+  /// would be stored in the GeneratedInterfaces directory.
+  var actualFileSystemPath: DocumentURI {
+    return self
   }
 }
 
 package struct ReferenceDocumentURLError: Error, CustomStringConvertible {
   package var description: String
-
-  init(description: String) {
-    self.description = description
-  }
 }

Sources/SourceKitLSP/Workspace.swift

@@ -432,11 +432,12 @@ package final class Workspace: Sendable, BuildServerManagerDelegate {
   /// document is returned.
   func setDocumentService(for uri: DocumentURI, _ newLanguageService: any LanguageService) -> LanguageService {
     return documentService.withLock { service in
-      if let languageService = service[uri] {
+      let key = uri.buildSettingsFile
+      if let languageService = service[key] {
         return languageService
       }
 
-      service[uri] = newLanguageService
+      service[key] = newLanguageService
       return newLanguageService
     }
   }