From 2a4682263d45c7615a53e84694da9189de5d19ba Mon Sep 17 00:00:00 2001
From: Yuta Saito <kateinoigakukun@gmail.com>
Date: Tue, 12 Mar 2024 20:50:48 +0000
Subject: [PATCH] Remove DispatchShims.swift and replace it with a conditional
 typealias

The use of DispatchQueue in XCTest is now very limited, and it's only used
in a single place in XCTestCase.swift.
---
 CMakeLists.txt                             |  1 -
 Sources/XCTest/Private/DispatchShims.swift | 47 ----------------------
 Sources/XCTest/Public/XCTestCase.swift     | 18 ++++++++-
 3 files changed, 17 insertions(+), 49 deletions(-)
 delete mode 100644 Sources/XCTest/Private/DispatchShims.swift

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 75fd3da4..14ecd0fe 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -38,7 +38,6 @@ add_library(XCTest
   Sources/XCTest/Private/WaiterManager.swift
   Sources/XCTest/Private/IgnoredErrors.swift
   Sources/XCTest/Private/XCTestCase.TearDownBlocksState.swift
-  Sources/XCTest/Private/DispatchShims.swift
   Sources/XCTest/Public/XCTestRun.swift
   Sources/XCTest/Public/XCTestMain.swift
   Sources/XCTest/Public/XCTestCase.swift
diff --git a/Sources/XCTest/Private/DispatchShims.swift b/Sources/XCTest/Private/DispatchShims.swift
deleted file mode 100644
index 55ce8b68..00000000
--- a/Sources/XCTest/Private/DispatchShims.swift
+++ /dev/null
@@ -1,47 +0,0 @@
-// This source file is part of the Swift.org open source project
-//
-// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
-// Licensed under Apache License v2.0 with Runtime Library Exception
-//
-// See http://swift.org/LICENSE.txt for license information
-// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
-//
-//
-//  NoThreadDispatchShims.swift
-//
-
-// This file is a shim for platforms that don't have libdispatch and do assume a single-threaded environment.
-
-// NOTE: We can't use use `#if canImport(Dispatch)` because Dispatch Clang module is placed directly in the resource
-// directory, and not split into target-specific directories. This means that the module is always available, even on
-// platforms that don't have libdispatch. Thus, we need to check for the actual platform.
-#if os(WASI)
-
-/// No-op shim function
-func dispatchPrecondition(condition: DispatchPredicate) {}
-
-struct DispatchPredicate {
-    static func onQueue<X>(_: X) -> Self {
-        return DispatchPredicate()
-    }
-
-    static func notOnQueue<X>(_: X) -> Self {
-        return DispatchPredicate()
-    }
-}
-
-extension XCTWaiter {
-    /// Single-threaded queue without any actual queueing
-    struct DispatchQueue {
-        init(label: String) {}
-
-        func sync<T>(_ body: () -> T) -> T {
-            body()
-        }
-        func async(_ body: @escaping () -> Void) {
-            body()
-        }
-    }
-}
-
-#endif
diff --git a/Sources/XCTest/Public/XCTestCase.swift b/Sources/XCTest/Public/XCTestCase.swift
index 1f2ab76a..2d899b91 100644
--- a/Sources/XCTest/Public/XCTestCase.swift
+++ b/Sources/XCTest/Public/XCTestCase.swift
@@ -54,7 +54,23 @@ open class XCTestCase: XCTest {
         return 1
     }
 
-    internal static let subsystemQueue = DispatchQueue(label: "org.swift.XCTestCase")
+    #if DISABLE_XCTWAITER && os(WASI)
+    /// Single-threaded queue without any actual queueing
+    struct SubsystemQueue {
+        init(label: String) {}
+
+        func sync<T>(_ body: () -> T) -> T {
+            body()
+        }
+        func async(_ body: @escaping () -> Void) {
+            body()
+        }
+    }
+    #else
+    typealias SubsystemQueue = DispatchQueue
+    #endif
+
+    internal static let subsystemQueue = SubsystemQueue(label: "org.swift.XCTestCase")
 
     #if !DISABLE_XCTWAITER
     @MainActor