Fix async XCTest execution on Darwin when the runner's main is `a…

…sync`.

There is what appears to be a strange bug on Darwin platforms here. If the calling context (e.g., `main`) is `async` and there are any `async` tests in the suite to be run, calling `XCTestSuite.run()` will cause the test process to terminate abnormally with the error "freed pointer was not the last allocation" out of the Swift runtime. We "avoid" (work around) this by wrapping the call in a detached task and then awaiting its result. The task must be detached so that we don't block the main actor, which the tests may also be depending on.

PiperOrigin-RevId: 662944537

tools/test_discoverer/ObjcTestPrinter.swift

@@ -34,12 +34,22 @@ struct ObjcTestPrinter {
           let description: String
         }
 
-        static func run() throws {
+        static func run() async throws {
           try loadXCTest()
           XCTestObservationCenter.shared.addTestObserver(BazelXMLTestObserver.default)
-          var testCollector = try ShardingFilteringTestCollector()
-          let shardedSuite = testCollector.shard(XCTestSuite.default)
-          shardedSuite.run()
+
+          // There is what appears to be a strange bug on Darwin platforms here. If the calling
+          // context (e.g., `main`) is `async` and there are any `async` tests in the suite to be
+          // run, calling `shardedSuite.run()` below will cause the test process to terminate
+          // abnormally with the error "freed pointer was not the last allocation" out of the Swift
+          // runtime. We "avoid" (work around) this by wrapping the call in a detached task and then
+          // awaiting its result. The task must be detached so that we don't block the main actor,
+          // which the tests may also be depending on.
+          _ = try await Task.detached {
+            var testCollector = try ShardingFilteringTestCollector()
+            let shardedSuite = testCollector.shard(XCTestSuite.default)
+            shardedSuite.run()
+          }.value
         }
 
         private static func loadXCTest() throws {

tools/test_discoverer/TestDiscoverer.swift

@@ -109,9 +109,9 @@ struct TestDiscoverer: ParsableCommand {
       \(availabilityAttribute)
       @main
       struct Main {
-        static func main() {
+        static func main() async {
           do {
-            try XCTestRunner.run()
+            try await XCTestRunner.run()
 
             try XUnitTestRecorder.shared.writeXML()
             guard !XUnitTestRecorder.shared.hasFailure else {