Use dynamic registration for folding range options

Sources/LanguageServerProtocol/SupportTypes/RegistrationOptions.swift

@@ -74,6 +74,23 @@ public struct CompletionRegistrationOptions: RegistrationOptions, TextDocumentRe
   }
 }
 
+/// Folding range registration options.
+public struct FoldingRangeRegistrationOptions: RegistrationOptions, TextDocumentRegistrationOptionsProtocol, Hashable {
+  public var textDocumentRegistrationOptions: TextDocumentRegistrationOptions
+  public var foldingRangeOptions: FoldingRangeOptions
+
+  public init(documentSelector: DocumentSelector? = nil, foldingRangeOptions: FoldingRangeOptions) {
+    self.textDocumentRegistrationOptions =
+        TextDocumentRegistrationOptions(documentSelector: documentSelector)
+    self.foldingRangeOptions = foldingRangeOptions
+  }
+
+  public func encodeIntoLSPAny(dict: inout [String: LSPAny]) {
+    textDocumentRegistrationOptions.encodeIntoLSPAny(dict: &dict)
+    // foldingRangeOptions is currently empty.
+  }
+}
+
 public struct SemanticTokensRegistrationOptions: RegistrationOptions, TextDocumentRegistrationOptionsProtocol, Hashable {
   /// Method for registration, which defers from the actual requests' methods
   /// since this registration handles multiple requests.

Sources/LanguageServerProtocol/SupportTypes/ServerCapabilities.swift

@@ -275,6 +275,11 @@ public struct CompletionOptions: Codable, Hashable {
   }
 }
 
+public struct FoldingRangeOptions: Codable, Hashable {
+  /// Currently empty in the spec.
+  public init() {}
+}
+
 public struct SignatureHelpOptions: Codable, Hashable {
   /// The characters that trigger signature help automatically.
   public var triggerCharacters: [String]?

Sources/SourceKitLSP/CapabilityRegistry.swift

@@ -23,6 +23,9 @@ public final class CapabilityRegistry {
   /// Dynamically registered completion options.
   private var completion: [CapabilityRegistration: CompletionRegistrationOptions] = [:]
 
+  /// Dynamically registered folding range options.
+  private var foldingRange: [CapabilityRegistration: FoldingRangeRegistrationOptions] = [:]
+
   /// Dynamically registered semantic tokens options.
   private var semanticTokens: [CapabilityRegistration: SemanticTokensRegistrationOptions] = [:]
 
@@ -36,6 +39,10 @@ public final class CapabilityRegistry {
     clientCapabilities.textDocument?.completion?.dynamicRegistration == true
   }
 
+  public var clientHasDynamicFoldingRangeRegistration: Bool {
+    clientCapabilities.textDocument?.foldingRange?.dynamicRegistration == true
+  }
+
   public var clientHasDynamicSemanticTokensRegistration: Bool {
     clientCapabilities.textDocument?.semanticTokens?.dynamicRegistration == true
   }
@@ -68,6 +75,34 @@ public final class CapabilityRegistry {
     registerOnClient(registration)
   }
 
+  /// Dynamically register folding range capabilities if the client supports it and
+  /// we haven't yet registered any folding range capabilities for the given
+  /// languages.
+  public func registerFoldingRangeIfNeeded(
+    options: FoldingRangeOptions,
+    for languages: [Language],
+    registerOnClient: ClientRegistrationHandler
+  ) {
+    guard clientHasDynamicFoldingRangeRegistration else { return }
+    if let registration = registration(for: languages, in: foldingRange) {
+      if options != registration.foldingRangeOptions {
+        log("Unable to register new folding range options \(options) for " +
+            "\(languages) due to pre-existing options \(registration.foldingRangeOptions)", level: .warning)
+      }
+      return
+    }
+    let registrationOptions = FoldingRangeRegistrationOptions(
+      documentSelector: self.documentSelector(for: languages),
+      foldingRangeOptions: options)
+    let registration = CapabilityRegistration(
+      method: FoldingRangeRequest.method,
+      registerOptions: self.encode(registrationOptions))
+
+    self.foldingRange[registration] = registrationOptions
+
+    registerOnClient(registration)
+  }
+
   /// Dynamically register semantic tokens capabilities if the client supports
   /// it and we haven't yet registered any semantic tokens capabilities for the
   /// given languages.

Sources/SourceKitLSP/SourceKitServer.swift

@@ -546,7 +546,7 @@ extension SourceKitServer {
         supportsCodeActions: true
       )),
       colorProvider: .bool(true),
-      foldingRangeProvider: .bool(true),
+      foldingRangeProvider: .bool(!registry.clientHasDynamicFoldingRangeRegistration),
       executeCommandProvider: ExecuteCommandOptions(
         commands: builtinSwiftCommands // FIXME: Clangd commands?
       )
@@ -563,6 +563,11 @@ extension SourceKitServer {
         self.dynamicallyRegisterCapability($0, registry)
       }
     }
+    if server.foldingRangeProvider?.isSupported == true {
+      registry.registerFoldingRangeIfNeeded(options: FoldingRangeOptions(), for: languages) {
+        self.dynamicallyRegisterCapability($0, registry)
+      }
+    }
     if let semanticTokensOptions = server.semanticTokensProvider {
       registry.registerSemanticTokensIfNeeded(options: semanticTokensOptions, for: languages) {
         self.dynamicallyRegisterCapability($0, registry)