[ASTGen] Fix ReferenceOwnershipAttr modifier

Similar to 7dd8944. Modifier argument is not parsed as a keyword.

Author: rintaro

lib/ASTGen/Sources/ASTGen/DeclAttrs.swift

@@ -2066,17 +2066,18 @@ extension ASTGenVisitor {
       kind = .weak
       guard node.detail == nil else {
         // TODO: Diagnose.
-        return nil
+        fatalError("invalid argument for 'weak' modifier")
       }
     case .unowned:
-      switch node.detail?.detail.keywordKind {
-      case .safe, nil:
+      switch node.detail?.detail.rawText {
+      case "safe", nil:
         kind = .unowned
-      case .unsafe:
+      case "unsafe":
         kind = .unmanaged
-      case _?:
+      case let text?:
         // TODO: Diagnose
-        kind = .unowned
+        _ = text
+        fatalError("invalid argument for 'unowned' modifier")
       }
     default:
       preconditionFailure("ReferenceOwnership modifier must be 'weak' or 'unowned'")

test/ASTGen/attrs.swift

@@ -227,3 +227,10 @@ func testNonIsolated(actor: MyActor) {
   _ = actor.constFlag
   _ = actor.mutableFlag
 }
+
+struct ReferenceOwnershipModifierTest<X: AnyObject> {
+    weak var weakValue: X?
+    unowned var unownedValue: X
+    unowned(safe) var unownedSafeValue: X
+    unowned(unsafe) var unmanagedValue: X
+}