[Concurrency] Fix priority implementation

Author: ktoso

stdlib/public/Concurrency/Task.swift

@@ -45,7 +45,12 @@ extension Task {
   /* @instantaneous */
   public static func currentPriority() async -> Priority {
     let task = Builtin.getCurrentAsyncTask()
-    return getPriority(task)
+    let p = getPriority(task)
+    if let priority = Priority(rawValue: p) {
+      return priority
+    } else {
+      fatalError("Unknown priority: \(p)")
+    }
   }
 
   /// Task priority may inform decisions an `Executor` makes about how and when
@@ -417,7 +422,7 @@ extension Task {
 public func runTask(_ task: __owned Builtin.NativeObject)
 
 @_silgen_name("swift_task_getPriority")
-public func getPriority(_ task: __owned Builtin.NativeObject) -> Task.Priority
+func getPriority(_ task: __owned Builtin.NativeObject) -> Int
 
 public func runAsync(_ asyncFun: @escaping () async -> ()) {
   let childTask = Builtin.createAsyncTask(0, nil, asyncFun)

test/Concurrency/Runtime/async_task_priority_basic.swift

@@ -25,9 +25,9 @@ extension DispatchQueue {
 func test_getPriority() {
   _ = DispatchQueue.main.async { () async in
     let p = await Task.currentPriority()
-    // CHECK: priority: userInteractive
+    // CHECK: priority: default
     print("priority: \(p)")
-    assert(p == Task.Priority.userInteractive)
+    assert(p == Task.Priority.default)
     exit(0)
   }
 }