Add support for inlay hints using CollectExpressionType

- Add UID for CollectExpressionType request
- Add ExpressionTypeInfo structure
- Add keys to support sourcekitd's CollectExpressionType
- Implement CollectExpressionType request
- Add SwiftLanguageServer.expressionTypeInfos
- Add InlayHint and supporting types
- Add InlayHintsRequest
- Add inlayHints handler stub
- Implement inlay hints request
- Update InlayHint to follow the current proposal
- # This is the commit message #11:
- ...as described in the LSP proposal
- Update doc comment on InlayHintsRequest
- Map inlay hints lazily
- Fix minor style issue
- Add new files to CMakeLists.txt
- Specify commit of the current inlay hints proposal state
- Add public, memberwise initializer for InlayHintsRequest
- assert(false) if deserializing ExpressionTypeInfos fails
- Add dispatch precondition to _expressionTypeInfos
- Add InlayHintsRequest to the builtinRequests
- Factor out function for querying document symbols for URI
- Only render inlay hints after variable bindings
- Test inlay hints on empty document
- Test inlay hints for some simple bindings
- Test ranged inlay hint requests
- Make sure that inlay hints are unique per position
- Test inlay hints for fields
- Apply various PR suggestions regarding inlay hints
- Update inlay hint tests and add case with explicit type annotations
- Continue iterating if an ExpressionTypeInfo fails to deserialize

Author: fwcd

Sources/LanguageServerProtocol/CMakeLists.txt

@@ -41,6 +41,7 @@ add_library(LanguageServerProtocol
   Requests/HoverRequest.swift
   Requests/ImplementationRequest.swift
   Requests/InitializeRequest.swift
+  Requests/InlayHintsRequest.swift
   Requests/PollIndexRequest.swift
   Requests/ReferencesRequest.swift
   Requests/RegisterCapabilityRequest.swift
@@ -63,6 +64,7 @@ add_library(LanguageServerProtocol
   SupportTypes/FileEvent.swift
   SupportTypes/FileSystemWatcher.swift
   SupportTypes/FoldingRangeKind.swift
+  SupportTypes/InlayHint.swift
   SupportTypes/Language.swift
   SupportTypes/Location.swift
   SupportTypes/LocationLink.swift

Sources/LanguageServerProtocol/Messages.swift

@@ -47,6 +47,7 @@ public let builtinRequests: [_RequestType.Type] = [
 
   SymbolInfoRequest.self,
   PollIndexRequest.self,
+  InlayHintsRequest.self,
 ]
 
 /// The set of known notifications.

Sources/LanguageServerProtocol/Requests/InlayHintsRequest.swift

@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+/// Request for inline annotations to be displayed in the editor **(LSP Extension)**.
+/// 
+/// This implements the proposed `textDocument/inlayHints` API from
+/// https://github.com/microsoft/language-server-protocol/pull/1249 (commit: `d55733d`)
+///
+/// - Parameters:
+///   - textDocument: The document for which to provide the inlay hints.
+///
+/// - Returns: InlayHints for the entire document
+public struct InlayHintsRequest: TextDocumentRequest, Hashable {
+  public static let method: String = "sourcekit-lsp/inlayHints"
+  public typealias Response = [InlayHint]
+
+  /// The document for which to provide the inlay hints.
+  public var textDocument: TextDocumentIdentifier
+
+  /// The range the inlay hints are requested for. If nil,
+  /// hints for the entire document are requested.
+  @CustomCodable<PositionRange?>
+  public var range: Range<Position>?
+
+  /// The categories of hints that are interesting to the client
+  /// and should be filtered.
+  public var only: [InlayHintCategory]?
+
+  public init(
+    textDocument: TextDocumentIdentifier,
+    range: Range<Position>? = nil,
+    only: [InlayHintCategory]? = nil
+  ) {
+    self.textDocument = textDocument
+    self._range = CustomCodable(wrappedValue: range)
+    self.only = only
+  }
+}

Sources/LanguageServerProtocol/SupportTypes/InlayHint.swift

@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+/// Represents an inline annotation displayed by the editor in a source file.
+public struct InlayHint: ResponseType, Codable, Hashable {
+  /// The position within the code that this hint is attached to.
+  public var position: Position
+
+  /// The hint's kind, used for more flexible client-side styling.
+  public let category: InlayHintCategory?
+
+  /// The hint's text, e.g. a printed type
+  public let label: String
+
+  public init(
+    position: Position,
+    category: InlayHintCategory? = nil,
+    label: String
+  ) {
+    self.position = position
+    self.category = category
+    self.label = label
+  }
+}
+
+/// A hint's kind, used for more flexible client-side styling.
+public struct InlayHintCategory: RawRepresentable, Codable, Hashable {
+  public var rawValue: String
+
+  public init(rawValue: String) {
+    self.rawValue = rawValue
+  }
+
+  /// A parameter label. Note that this case is not used by
+  /// Swift, since Swift already has explicit parameter labels.
+  public static let parameter: InlayHintCategory = InlayHintCategory(rawValue: "parameter")
+  /// An inferred type.
+  public static let type: InlayHintCategory = InlayHintCategory(rawValue: "type")
+}

Sources/SourceKitD/sourcekitd_uids.swift

@@ -33,6 +33,10 @@ public struct sourcekitd_keys {
   public let educational_note_paths: sourcekitd_uid_t
   public let endcolumn: sourcekitd_uid_t
   public let endline: sourcekitd_uid_t
+  public let expression_length: sourcekitd_uid_t
+  public let expression_offset: sourcekitd_uid_t
+  public let expression_type: sourcekitd_uid_t
+  public let expression_type_list: sourcekitd_uid_t
   public let filepath: sourcekitd_uid_t
   public let fixits: sourcekitd_uid_t
   public let id: sourcekitd_uid_t
@@ -94,6 +98,10 @@ public struct sourcekitd_keys {
     educational_note_paths = api.uid_get_from_cstr("key.educational_note_paths")!
     endcolumn = api.uid_get_from_cstr("key.endcolumn")!
     endline = api.uid_get_from_cstr("key.endline")!
+    expression_length = api.uid_get_from_cstr("key.expression_length")!
+    expression_offset = api.uid_get_from_cstr("key.expression_offset")!
+    expression_type = api.uid_get_from_cstr("key.expression_type")!
+    expression_type_list = api.uid_get_from_cstr("key.expression_type_list")!
     filepath = api.uid_get_from_cstr("key.filepath")!
     fixits = api.uid_get_from_cstr("key.fixits")!
     id = api.uid_get_from_cstr("key.id")!
@@ -146,6 +154,7 @@ public struct sourcekitd_requests {
   public let codecomplete_update: sourcekitd_uid_t
   public let codecomplete_close: sourcekitd_uid_t
   public let cursorinfo: sourcekitd_uid_t
+  public let expression_type: sourcekitd_uid_t
   public let relatedidents: sourcekitd_uid_t
   public let semantic_refactoring: sourcekitd_uid_t
 
@@ -159,6 +168,7 @@ public struct sourcekitd_requests {
     codecomplete_update = api.uid_get_from_cstr("source.request.codecomplete.update")!
     codecomplete_close = api.uid_get_from_cstr("source.request.codecomplete.close")!
     cursorinfo = api.uid_get_from_cstr("source.request.cursorinfo")!
+    expression_type = api.uid_get_from_cstr("source.request.expression.type")!
     relatedidents = api.uid_get_from_cstr("source.request.relatedidents")!
     semantic_refactoring = api.uid_get_from_cstr("source.request.semantic.refactoring")!
   }

Sources/SourceKitLSP/CMakeLists.txt

@@ -24,6 +24,7 @@ target_sources(SourceKitLSP PRIVATE
   Swift/CursorInfo.swift
   Swift/Diagnostic.swift
   Swift/EditorPlaceholder.swift
+  Swift/ExpressionTypeInfo.swift
   Swift/SemanticRefactorCommand.swift
   Swift/SemanticRefactoring.swift
   Swift/SourceKitD+ResponseError.swift

Sources/SourceKitLSP/Clang/ClangLanguageServer.swift

@@ -490,6 +490,13 @@ extension ClangLanguageServerShim {
     forwardRequestToClangdOnQueue(req)
   }
 
+  func inlayHints(_ req: Request<InlayHintsRequest>) {
+    // FIXME: Currently a Swift-specific, non-standard request.
+    // Once inlay hints have been upstreamed to LSP, forward
+    // them to clangd.
+    req.reply(.success([]))
+  }
+
   func foldingRange(_ req: Request<FoldingRangeRequest>) {
     queue.async {
       if self.capabilities?.foldingRangeProvider?.isSupported == true {

Sources/SourceKitLSP/SourceKitServer.swift

@@ -99,6 +99,7 @@ public final class SourceKitServer: LanguageServer {
     registerToolchainTextDocumentRequest(SourceKitServer.documentSemanticTokensRange, nil)
     registerToolchainTextDocumentRequest(SourceKitServer.colorPresentation, [])
     registerToolchainTextDocumentRequest(SourceKitServer.codeAction, nil)
+    registerToolchainTextDocumentRequest(SourceKitServer.inlayHints, [])
   }
 
   /// Register a `TextDocumentRequest` that requires a valid `Workspace`, `ToolchainLanguageServer`,
@@ -942,6 +943,14 @@ extension SourceKitServer {
     languageService.codeAction(request)
   }
 
+  func inlayHints(
+    _ req: Request<InlayHintsRequest>,
+    workspace: Workspace,
+    languageService: ToolchainLanguageServer
+  ) {
+    languageService.inlayHints(req)
+  }
+
   func definition(
     _ req: Request<DefinitionRequest>,
     workspace: Workspace,

Sources/SourceKitLSP/Swift/ExpressionTypeInfo.swift

@@ -0,0 +1,117 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Dispatch
+import LanguageServerProtocol
+import SourceKitD
+
+/// A typed expression as returned by sourcekitd's CollectExpressionType.
+///
+/// A detailed description of the structure returned by sourcekitd can be found
+/// here: https://github.com/apple/swift/blob/main/tools/SourceKit/docs/Protocol.md#expression-type
+struct ExpressionTypeInfo {
+  /// Range of the expression in the source file.
+  var range: Range<Position>
+  /// The printed type of the expression.
+  var printedType: String
+
+  init?(_ dict: SKDResponseDictionary, in snapshot: DocumentSnapshot) {
+    let keys = dict.sourcekitd.keys
+
+    guard let offset: Int = dict[keys.expression_offset],
+          let length: Int = dict[keys.expression_length],
+          let startIndex = snapshot.positionOf(utf8Offset: offset),
+          let endIndex = snapshot.positionOf(utf8Offset: offset + length),
+          let printedType: String = dict[keys.expression_type] else {
+      return nil
+    }
+    
+    self.range = startIndex..<endIndex
+    self.printedType = printedType
+  }
+}
+
+enum ExpressionTypeInfoError: Error, Equatable {
+  /// The given URL is not a known document.
+  case unknownDocument(DocumentURI)
+
+  /// The underlying sourcekitd request failed with the given error.
+  case responseError(ResponseError)
+}
+
+extension SwiftLanguageServer {
+  /// Must be called on self.queue.
+  private func _expressionTypeInfos(
+    _ uri: DocumentURI,
+    _ completion: @escaping (Swift.Result<[ExpressionTypeInfo], ExpressionTypeInfoError>) -> Void
+  ) {
+    if #available(macOS 10.12, *) {
+      dispatchPrecondition(condition: .onQueue(queue))
+    }
+
+    guard let snapshot = documentManager.latestSnapshot(uri) else {
+      return completion(.failure(.unknownDocument(uri)))
+    }
+
+    let keys = self.keys
+
+    let skreq = SKDRequestDictionary(sourcekitd: sourcekitd)
+    skreq[keys.request] = requests.expression_type
+    skreq[keys.sourcefile] = snapshot.document.uri.pseudoPath
+
+    // FIXME: SourceKit should probably cache this for us.
+    if let compileCommand = self.commandsByFile[uri] {
+      skreq[keys.compilerargs] = compileCommand.compilerArgs
+    }
+
+    let handle = self.sourcekitd.send(skreq, self.queue) { result in
+      guard let dict = result.success else {
+        return completion(.failure(.responseError(ResponseError(result.failure!))))
+      }
+
+      guard let skExpressionTypeInfos: SKDResponseArray = dict[keys.expression_type_list] else {
+        return completion(.success([]))
+      }
+
+      var expressionTypeInfos: [ExpressionTypeInfo] = []
+      expressionTypeInfos.reserveCapacity(skExpressionTypeInfos.count)
+
+      skExpressionTypeInfos.forEach { (_, skExpressionTypeInfo) -> Bool in
+        guard let info = ExpressionTypeInfo(skExpressionTypeInfo, in: snapshot) else {
+          assert(false, "ExpressionTypeInfo failed to deserialize")
+          return true
+        }
+        expressionTypeInfos.append(info)
+        return true
+      }
+
+      completion(.success(expressionTypeInfos))
+    }
+
+    // FIXME: cancellation
+    _ = handle
+  }
+
+  /// Provides typed expressions in a document.
+  ///
+  /// - Parameters:
+  ///   - url: Document URL in which to perform the request. Must be an open document.
+  ///   - completion: Completion block to asynchronously receive the ExpressionTypeInfos, or error.
+  func expressionTypeInfos(
+    _ uri: DocumentURI,
+    _ completion: @escaping (Swift.Result<[ExpressionTypeInfo], ExpressionTypeInfoError>) -> Void
+  ) {
+    queue.async {
+      self._expressionTypeInfos(uri, completion)
+    }
+  }
+}