Fix document symbols regression

This appears to have been accidentally removed in
17f6568, the `children` field is
optional in the LSP spec.

Change-Id: I1055658c8f09873279d676fee0daff02fa59e3f8

Author: DavidGoldman

Sources/LanguageServerProtocol/Requests/DocumentSymbolRequest.swift

@@ -91,7 +91,7 @@ public struct DocumentSymbol: Hashable, Codable {
   public var selectionRange: Range<Position>
 
   /// Children of this symbol, e.g. properties of a class.
-  public var children: [DocumentSymbol]
+  public var children: [DocumentSymbol]?
 
   public init(
     name: String,
@@ -100,7 +100,7 @@ public struct DocumentSymbol: Hashable, Codable {
     deprecated: Bool? = nil,
     range: Range<Position>,
     selectionRange: Range<Position>,
-    children: [DocumentSymbol] = [])
+    children: [DocumentSymbol]? = nil)
   {
     self.name = name
     self.detail = detail

Tests/LanguageServerProtocolTests/CodingTests.swift

@@ -333,9 +333,6 @@ final class CodingTests: XCTestCase {
     checkCoding(DocumentSymbolResponse.documentSymbols([DocumentSymbol(name: "mySymbol", kind: .function, range: range, selectionRange: range)]), json: """
       [
         {
-          "children" : [
-
-          ],
           "kind" : 12,
           "name" : "mySymbol",
           "range" : \(rangejson.indented(4, skipFirstLine: true)),

Tests/SourceKitLSPTests/LocalClangTests.swift

@@ -38,12 +38,18 @@ final class LocalClangTests: XCTestCase {
 
     connection = TestSourceKitServer()
     sk = connection.client
+    let documentSymbol = TextDocumentClientCapabilities.DocumentSymbol(
+      dynamicRegistration: nil,
+      symbolKind: nil,
+      hierarchicalDocumentSymbolSupport: true
+    )
+    let textDocument = TextDocumentClientCapabilities(documentSymbol: documentSymbol)
     _ = try! sk.sendSync(InitializeRequest(
         processId: nil,
         rootPath: nil,
         rootURI: nil,
         initializationOptions: nil,
-        capabilities: ClientCapabilities(workspace: nil, textDocument: nil),
+        capabilities: ClientCapabilities(workspace: nil, textDocument: textDocument),
         trace: .off,
         workspaceFolders: nil))
   }
@@ -139,6 +145,35 @@ final class LocalClangTests: XCTestCase {
     XCTAssertNil(resp)
   }
 
+  func testDocumentSymbols() throws {
+    guard haveClangd else { return }
+    let url = URL(fileURLWithPath: "/a.cpp")
+
+    sk.send(DidOpenTextDocumentNotification(textDocument: TextDocumentItem(
+      uri: DocumentURI(url),
+      language: .cpp,
+      version: 1,
+      text: """
+      struct S {
+        void foo() {
+          int local = 1;
+        }
+      };
+      """)))
+
+    guard let resp = try! sk.sendSync(DocumentSymbolRequest(textDocument: TextDocumentIdentifier(url))) else {
+      XCTFail("Invalid document symbol response")
+      return
+    }
+    guard case let .documentSymbols(syms) = resp else {
+      XCTFail("Expected a [DocumentSymbol] but got \(resp)")
+      return
+    }
+    XCTAssertEqual(syms.count, 1)
+    XCTAssertEqual(syms.first?.name, "S")
+    XCTAssertEqual(syms.first?.children?.first?.name, "foo")
+  }
+
   func testClangStdHeaderCanary() throws {
     guard let ws = try staticSourceKitTibsWorkspace(name: "ClangStdHeaderCanary") else { return }
     if ToolchainRegistry.shared.default?.clangd == nil { return }