Migrate to upstream LSP inlay hints

- Use official textDocument/inlayHint request
- Rename InlayHintCategory to InlayHintKind
- Additionally, represent it using an Int, as in the proposed LSP API.
- Add inlay hint client capabilities
- Add inlay hint server capabilities
- Add dynamic registration of inlay hint request
- Rename InlayHintsRequest -> InlayHintRequest
  This is to be consistent with the request itself being named in singular
  in LSP and the other requests (e.g. DocumentSymbolRequest).
- Forward inlay hint requests to clangd
- Add colon before inlay hints
- Add other properties to InlayHint
- Add InlayHintLabel structures
- Conform InlayHintLabel to ExpressibleByStringX protocols
- Attach TextEdit to inlay hints for committing them
- Add InlayHint.data
- Fix InlayHintTests
  We need to include text edits in the expected inlay hints.

Sources/LanguageServerProtocol/CMakeLists.txt

@@ -41,7 +41,7 @@ add_library(LanguageServerProtocol STATIC
   Requests/HoverRequest.swift
   Requests/ImplementationRequest.swift
   Requests/InitializeRequest.swift
-  Requests/InlayHintsRequest.swift
+  Requests/InlayHintRequest.swift
   Requests/PollIndexRequest.swift
   Requests/PrepareRenameRequest.swift
   Requests/ReferencesRequest.swift

Sources/LanguageServerProtocol/Messages.swift

@@ -47,12 +47,12 @@ public let builtinRequests: [_RequestType.Type] = [
   RenameRequest.self,
   RegisterCapabilityRequest.self,
   UnregisterCapabilityRequest.self,
+  InlayHintRequest.self,
 
   // MARK: LSP Extension Requests
 
   SymbolInfoRequest.self,
   PollIndexRequest.self,
-  InlayHintsRequest.self,
 ]
 
 /// The set of known notifications.

Sources/LanguageServerProtocol/Requests/InlayHintsRequest.swift → Sources/LanguageServerProtocol/Requests/InlayHintRequest.swift

@@ -10,17 +10,17 @@
 //
 //===----------------------------------------------------------------------===//
 
-/// Request for inline annotations to be displayed in the editor **(LSP Extension)**.
+/// Request for inline annotations to be displayed in the editor.
 /// 
-/// This implements the proposed `textDocument/inlayHints` API from
+/// This implements the proposed `textDocument/inlayHint` 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 struct InlayHintRequest: TextDocumentRequest, Hashable {
+  public static let method: String = "textDocument/inlayHint"
   public typealias Response = [InlayHint]
 
   /// The document for which to provide the inlay hints.
@@ -33,12 +33,12 @@ public struct InlayHintsRequest: TextDocumentRequest, Hashable {
 
   /// The categories of hints that are interesting to the client
   /// and should be filtered.
-  public var only: [InlayHintCategory]?
+  public var only: [InlayHintKind]?
 
   public init(
     textDocument: TextDocumentIdentifier,
     range: Range<Position>? = nil,
-    only: [InlayHintCategory]? = nil
+    only: [InlayHintKind]? = nil
   ) {
     self.textDocument = textDocument
     self._range = CustomCodable(wrappedValue: range)

Sources/LanguageServerProtocol/SupportTypes/ClientCapabilities.swift

@@ -499,6 +499,33 @@ public struct TextDocumentClientCapabilities: Hashable, Codable {
     }
   }
 
+  /// Capabilities specific to 'textDocument/inlayHint'.
+  public struct InlayHint: Hashable, Codable {
+    /// Properties a client can resolve lazily.
+    public struct ResolveSupport: Hashable, Codable {
+      /// The properties that a client can resolve lazily.
+      public var properties: [String]
+
+      public init(properties: [String] = []) {
+        self.properties = properties
+      }
+    }
+
+    /// Whether inlay hints support dynamic registration.
+    public var dynamicRegistration: Bool?
+
+    /// Indicates which properties a client can resolve lazily on an inlay hint.
+    public var resolveSupport: ResolveSupport?
+
+    public init(
+      dynamicRegistration: Bool? = nil,
+      resolveSupport: ResolveSupport? = nil
+    ) {
+      self.dynamicRegistration = dynamicRegistration
+      self.resolveSupport = resolveSupport
+    }
+  }
+
   // MARK: Properties
 
   public var synchronization: Synchronization? = nil
@@ -547,6 +574,8 @@ public struct TextDocumentClientCapabilities: Hashable, Codable {
 
   public var semanticTokens: SemanticTokens? = nil
 
+  public var inlayHint: InlayHint? = nil
+
   public init(synchronization: Synchronization? = nil,
               completion: Completion? = nil,
               hover: Hover? = nil,
@@ -569,7 +598,8 @@ public struct TextDocumentClientCapabilities: Hashable, Codable {
               publishDiagnostics: PublishDiagnostics? = nil,
               foldingRange: FoldingRange? = nil,
               callHierarchy: DynamicRegistrationCapability? = nil,
-              semanticTokens: SemanticTokens? = nil) {
+              semanticTokens: SemanticTokens? = nil,
+              inlayHint: InlayHint? = nil) {
     self.synchronization = synchronization
     self.completion = completion
     self.hover = hover
@@ -593,5 +623,6 @@ public struct TextDocumentClientCapabilities: Hashable, Codable {
     self.foldingRange = foldingRange
     self.callHierarchy = callHierarchy
     self.semanticTokens = semanticTokens
+    self.inlayHint = inlayHint
   }
 }

Sources/LanguageServerProtocol/SupportTypes/InlayHint.swift

@@ -16,33 +16,126 @@ public struct InlayHint: ResponseType, Codable, Hashable {
   public var position: Position
 
   /// The hint's kind, used for more flexible client-side styling.
-  public let category: InlayHintCategory?
+  public let kind: InlayHintKind?
 
   /// The hint's text, e.g. a printed type
-  public let label: String
+  public let label: InlayHintLabel
+
+  /// Optional text edits that are performed when accepting this inlay hint.
+  public let textEdits: [TextEdit]?
+
+  /// The tooltip text displayed when the inlay hint is hovered.
+  public let tooltip: MarkupContent?
+
+  /// Whether to render padding before the hint.
+  public let paddingLeft: Bool?
+
+  /// Whether to render padding after the hint.
+  public let paddingRight: Bool?
+
+  /// A data entry field that is present between a `textDocument/inlayHint`
+  /// and a `inlayHint/resolve` request.
+  public let data: LSPAny?
 
   public init(
     position: Position,
-    category: InlayHintCategory? = nil,
-    label: String
+    kind: InlayHintKind? = nil,
+    label: InlayHintLabel,
+    textEdits: [TextEdit]? = nil,
+    tooltip: MarkupContent? = nil,
+    paddingLeft: Bool? = nil,
+    paddingRight: Bool? = nil,
+    data: LSPAny? = nil
   ) {
     self.position = position
-    self.category = category
+    self.kind = kind
     self.label = label
+    self.textEdits = textEdits
+    self.tooltip = tooltip
+    self.paddingLeft = paddingLeft
+    self.paddingRight = paddingRight
+    self.data = data
   }
 }
 
 /// A hint's kind, used for more flexible client-side styling.
-public struct InlayHintCategory: RawRepresentable, Codable, Hashable {
-  public var rawValue: String
+public struct InlayHintKind: RawRepresentable, Codable, Hashable {
+  public var rawValue: Int
 
-  public init(rawValue: String) {
+  public init(rawValue: Int) {
     self.rawValue = rawValue
   }
 
+  /// A type annotation.
+  public static let type: InlayHintKind = InlayHintKind(rawValue: 1)
   /// 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")
+  public static let parameter: InlayHintKind = InlayHintKind(rawValue: 2)
+}
+
+/// A hint's label, either being a single string or a composition of parts.
+public enum InlayHintLabel: Codable, Hashable {
+  case parts([InlayHintLabelPart])
+  case string(String)
+
+  public init(from decoder: Decoder) throws {
+    if let parts = try? [InlayHintLabelPart](from: decoder) {
+      self = .parts(parts)
+    } else if let string = try? String(from: decoder) {
+      self = .string(string)
+    } else {
+      let context = DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Expected [InlayHintLabelPart] or String")
+      throw DecodingError.dataCorrupted(context)
+    }
+  }
+
+  public func encode(to encoder: Encoder) throws {
+    switch self {
+    case let .parts(parts):
+      try parts.encode(to: encoder)
+    case let .string(string):
+      try string.encode(to: encoder)
+    }
+  }
+}
+
+extension InlayHintLabel: ExpressibleByStringLiteral {
+  public init(stringLiteral value: String) {
+    self = .string(value)
+  }
+}
+
+extension InlayHintLabel: ExpressibleByStringInterpolation {
+  public init(stringInterpolation interpolation: DefaultStringInterpolation) {
+    self = .string(.init(stringInterpolation: interpolation))
+  }
+}
+
+/// A part of an interactive or composite inlay hint label.
+public struct InlayHintLabelPart: Codable, Hashable {
+  /// The value of this label part.
+  public let value: String
+
+  /// The tooltip to show when the part is hovered.
+  public let tooltip: MarkupContent?
+
+  /// An optional source code location representing this part.
+  /// Used by the editor for hover and code navigation, e.g.
+  /// by making the part a clickable link to the given position.
+  public let location: Location?
+
+  /// An optional command for this label part.
+  public let command: Command?
+
+  public init(
+    value: String,
+    tooltip: MarkupContent? = nil,
+    location: Location? = nil,
+    command: Command? = nil
+  ) {
+    self.value = value
+    self.tooltip = tooltip
+    self.location = location
+    self.command = command
+  }
 }

Sources/LanguageServerProtocol/SupportTypes/RegistrationOptions.swift

@@ -136,6 +136,26 @@ public struct SemanticTokensRegistrationOptions: RegistrationOptions, TextDocume
   }
 }
 
+public struct InlayHintRegistrationOptions: RegistrationOptions, TextDocumentRegistrationOptionsProtocol, Hashable {
+  public var textDocumentRegistrationOptions: TextDocumentRegistrationOptions
+  public var inlayHintOptions: InlayHintOptions
+
+  public init(
+    documentSelector: DocumentSelector? = nil,
+    inlayHintOptions: InlayHintOptions
+  ) {
+    textDocumentRegistrationOptions = TextDocumentRegistrationOptions(documentSelector: documentSelector)
+    self.inlayHintOptions = inlayHintOptions
+  }
+
+  public func encodeIntoLSPAny(dict: inout [String: LSPAny]) {
+    textDocumentRegistrationOptions.encodeIntoLSPAny(dict: &dict)
+    if let resolveProvider = inlayHintOptions.resolveProvider {
+      dict["resolveProvider"] = .bool(resolveProvider)
+    }
+  }
+}
+
 /// Describe options to be used when registering for file system change events.
 public struct DidChangeWatchedFilesRegistrationOptions: RegistrationOptions {
   /// The watchers to register.

Sources/LanguageServerProtocol/SupportTypes/ServerCapabilities.swift

@@ -89,6 +89,9 @@ public struct ServerCapabilities: Codable, Hashable {
   /// requests.
   public var semanticTokensProvider: SemanticTokensOptions?
 
+  /// Whether the server supports the `textDocument/inlayHint` family of requests.
+  public var inlayHintProvider: InlayHintOptions?
+
   public var experimental: LSPAny?
 
   public init(
@@ -117,6 +120,7 @@ public struct ServerCapabilities: Codable, Hashable {
     workspace: WorkspaceServerCapabilities? = nil,
     callHierarchyProvider: ValueOrBool<TextDocumentAndStaticRegistrationOptions>? = nil,
     semanticTokensProvider: SemanticTokensOptions? = nil,
+    inlayHintProvider: InlayHintOptions? = nil,
     experimental: LSPAny? = nil
   )
   {
@@ -145,6 +149,7 @@ public struct ServerCapabilities: Codable, Hashable {
     self.workspace = workspace
     self.callHierarchyProvider = callHierarchyProvider
     self.semanticTokensProvider = semanticTokensProvider
+    self.inlayHintProvider = inlayHintProvider
     self.experimental = experimental
   }
 }
@@ -505,6 +510,16 @@ public struct SemanticTokensOptions: Codable, Hashable {
   }
 }
 
+public struct InlayHintOptions: Codable, Hashable {
+  /// The server provides support to resolve additional information
+  /// for an inlay hint item.
+  public var resolveProvider: Bool?
+
+  public init(resolveProvider: Bool? = nil) {
+    self.resolveProvider = resolveProvider
+  }
+}
+
 public struct WorkspaceServerCapabilities: Codable, Hashable {
   public struct WorkspaceFolders: Codable, Hashable {
     /// The server has support for workspace folders

Sources/SourceKitLSP/CapabilityRegistry.swift

@@ -29,6 +29,9 @@ public final class CapabilityRegistry {
   /// Dynamically registered semantic tokens options.
   private var semanticTokens: [CapabilityRegistration: SemanticTokensRegistrationOptions] = [:]
 
+  /// Dynamically registered inlay hint options.
+  private var inlayHint: [CapabilityRegistration: InlayHintRegistrationOptions] = [:]
+
   /// Dynamically registered file watchers.
   private var didChangeWatchedFiles: DidChangeWatchedFilesRegistrationOptions?
 
@@ -53,6 +56,10 @@ public final class CapabilityRegistry {
     clientCapabilities.textDocument?.semanticTokens?.dynamicRegistration == true
   }
 
+  public var clientHasDynamicInlayHintRegistration: Bool {
+    clientCapabilities.textDocument?.inlayHint?.dynamicRegistration == true
+  }
+
   public var clientHasDynamicExecuteCommandRegistration: Bool {
     clientCapabilities.workspace?.executeCommand?.dynamicRegistration == true
   }
@@ -167,6 +174,34 @@ public final class CapabilityRegistry {
     registerOnClient(registration)
   }
 
+  /// Dynamically register inlay hint capabilities if the client supports
+  /// it and we haven't yet registered any inlay hint capabilities for the
+  /// given languages.
+  public func registerInlayHintIfNeeded(
+    options: InlayHintOptions,
+    for languages: [Language],
+    registerOnClient: ClientRegistrationHandler
+  ) {
+    guard clientHasDynamicInlayHintRegistration else { return }
+    if let registration = registration(for: languages, in: inlayHint) {
+      if options != registration.inlayHintOptions {
+        log("Unable to register new inlay hint options \(options) for " +
+            "\(languages) due to pre-existing options \(registration.inlayHintOptions)", level: .warning)
+      }
+      return
+    }
+    let registrationOptions = InlayHintRegistrationOptions(
+      documentSelector: self.documentSelector(for: languages),
+      inlayHintOptions: options)
+    let registration = CapabilityRegistration(
+      method: InlayHintRequest.method,
+      registerOptions: self.encode(registrationOptions))
+
+    self.inlayHint[registration] = registrationOptions
+
+    registerOnClient(registration)
+  }
+
   /// Dynamically register executeCommand with the given IDs if the client supports
   /// it and we haven't yet registered the given command IDs yet.
   public func registerExecuteCommandIfNeeded(

Sources/SourceKitLSP/Clang/ClangLanguageServer.swift

@@ -493,11 +493,8 @@ 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 inlayHint(_ req: Request<InlayHintRequest>) {
+    forwardRequestToClangdOnQueue(req)
   }
 
   func foldingRange(_ req: Request<FoldingRangeRequest>) {