[Concurrency][Linux] Fix WASI build.

This doesn't actually add proper WASI support - it just fixes the
build so that we're no worse off than we were.

rdar://141348916

stdlib/public/Concurrency/CMakeLists.txt

@@ -93,9 +93,12 @@ set(SWIFT_RUNTIME_CONCURRENCY_C_SOURCES
   linker-support/magic-symbols-for-install-name.c
 )
 
+set(SWIFT_RUNTIME_CONCURRENCY_EXECUTOR_SOURCES)
+if("${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR}" STREQUAL "dispatch")
   set(SWIFT_RUNTIME_CONCURRENCY_EXECUTOR_SOURCES
     DispatchGlobalExecutor.cpp
   )
+endif()
 
 set(LLVM_OPTIONAL_SOURCES
   CooperativeGlobalExecutor.cpp
@@ -168,9 +171,11 @@ set(SWIFT_RUNTIME_CONCURRENCY_SWIFT_SOURCES
   TaskSleepDuration.swift
   DispatchExecutor.swift
   CFExecutor.swift
+  DummyExecutor.swift
   PlatformExecutorDarwin.swift
   PlatformExecutorLinux.swift
   PlatformExecutorWindows.swift
+  PlatformExecutorWASI.swift
 )
 
 set(SWIFT_RUNTIME_CONCURRENCY_NONEMBEDDED_SWIFT_SOURCES

stdlib/public/Concurrency/DispatchExecutor.swift

@@ -10,7 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if !$Embedded
+#if !$Embedded && !os(WASI)
 
 import Swift
 
@@ -200,4 +200,4 @@ extension DispatchGlobalTaskExecutor: DispatchExecutorProtocol {
 extension DispatchMainExecutor: DispatchExecutorProtocol {
 }
 
-#endif // !$Embedded
+#endif // !$Embedded && !os(WASI)

stdlib/public/Concurrency/DummyExecutor.swift

@@ -0,0 +1,51 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2020 - 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Swift
+
+// .. Main Executor ............................................................
+
+@available(SwiftStdlib 6.2, *)
+public class DummyMainExecutor: MainExecutor, @unchecked Sendable {
+  public init() {}
+
+  public func run() throws {
+    fatalError("There is no executor implementation active")
+  }
+
+  public func stop() {
+    fatalError("There is no executor implementation active")
+  }
+
+  public func enqueue(_ job: consuming ExecutorJob) {
+    fatalError("There is no executor implementation active")
+  }
+
+  public var isMainExecutor: Bool { true }
+
+  public func checkIsolated() {
+    // Do nothing
+  }
+}
+
+// .. Task Executor ............................................................
+
+@available(SwiftStdlib 6.2, *)
+public class DummyTaskExecutor: TaskExecutor, @unchecked Sendable {
+  public init() {}
+
+  public func enqueue(_ job: consuming ExecutorJob) {
+    fatalError("There is no executor implementation active")
+  }
+
+  public var isMainExecutor: Bool { false }
+}

stdlib/public/Concurrency/ExecutorBridge.cpp

@@ -10,7 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if !SWIFT_CONCURRENCY_EMBEDDED
+#if SWIFT_CONCURRENCY_USES_DISPATCH
 #include <dispatch/dispatch.h>
 #endif
 
@@ -119,38 +119,7 @@ void *swift_job_getExecutorPrivateData(Job *job) {
   return &job->SchedulerPrivate[0];
 }
 
-#if !SWIFT_CONCURRENCY_EMBEDDED
-extern "C" SWIFT_CC(swift)
-void *swift_createDispatchEventC(void (*handler)(void *), void *context) {
-  dispatch_source_t source = dispatch_source_create(DISPATCH_SOURCE_TYPE_DATA_OR,
-                                                    0, 0,
-                                                    dispatch_get_main_queue());
-  dispatch_source_set_event_handler_f(source, handler);
-  dispatch_activate(source);
-
-  return source;
-}
-
-extern "C" SWIFT_CC(swift)
-void swift_destroyDispatchEventC(void *event) {
-  dispatch_source_t source = (dispatch_source_t)event;
-
-  dispatch_source_cancel(source);
-  dispatch_release(source);
-}
-
-extern "C" SWIFT_CC(swift)
-void *swift_getDispatchEventContext(void *event) {
-  return dispatch_get_context((dispatch_source_t)event);
-}
-
-extern "C" SWIFT_CC(swift)
-void swift_signalDispatchEvent(void *event) {
-  dispatch_source_t source = (dispatch_source_t)event;
-
-  dispatch_source_merge_data(source, 1);
-}
-
+#if SWIFT_CONCURRENCY_USES_DISPATCH
 extern "C" SWIFT_CC(swift) __attribute__((noreturn))
 void swift_dispatchMain() {
   dispatch_main();
@@ -160,7 +129,6 @@ extern "C" SWIFT_CC(swift)
 void swift_dispatchAssertMainQueue() {
   dispatch_assert_queue(dispatch_get_main_queue());
 }
-
-#endif // !SWIFT_CONCURRENCY_EMBEDDED
+#endif // SWIFT_CONCURRENCY_ENABLE_DISPATCH
 
 #pragma clang diagnostic pop

stdlib/public/Concurrency/ExecutorBridge.swift

@@ -112,49 +112,3 @@ internal func _dispatchEnqueueWithDeadline(_ global: CBool,
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("swift_dispatchAssertMainQueue")
 internal func _dispatchAssertMainQueue()
-
-@available(SwiftStdlib 6.2, *)
-@_silgen_name("swift_createDispatchEventC")
-internal func _createDispatchEventC(
-  handler: @convention(c) @escaping (UnsafeMutableRawPointer) -> (),
-  context: UnsafeMutableRawPointer
-) -> OpaquePointer
-
-fileprivate class DispatchEventHandlerBox {
-  var handler: @Sendable () -> ()
-  init(handler: @escaping @Sendable () -> ()) {
-    self.handler = handler
-  }
-}
-
-@available(SwiftStdlib 6.2, *)
-internal func _createDispatchEvent(handler: @escaping @Sendable () -> ()) -> OpaquePointer {
-  let boxed = DispatchEventHandlerBox(handler: handler)
-  let opaqueHandlerBox = unsafe Unmanaged.passRetained(boxed).toOpaque()
-  return unsafe _createDispatchEventC(
-    handler: { context in
-      let unmanaged = unsafe Unmanaged<DispatchEventHandlerBox>.fromOpaque(context)
-      unsafe unmanaged.takeUnretainedValue().handler()
-    },
-    context: opaqueHandlerBox
-  )
-}
-
-@available(SwiftStdlib 6.2, *)
-@_silgen_name("swift_destroyDispatchEventC")
-internal func _destroyDispatchEventC(_ event: OpaquePointer)
-
-@available(SwiftStdlib 6.2, *)
-@_silgen_name("swift_getDispatchEventContext")
-internal func _getDispatchEventContext(_ event: OpaquePointer) -> UnsafeMutableRawPointer
-
-@available(SwiftStdlib 6.2, *)
-internal func _destroyDispatchEvent(_ event: OpaquePointer) {
-  let context = unsafe _getDispatchEventContext(event)
-  unsafe Unmanaged<DispatchEventHandlerBox>.fromOpaque(context).release()
-  unsafe _destroyDispatchEventC(event)
-}
-
-@available(SwiftStdlib 6.2, *)
-@_silgen_name("swift_signalDispatchEvent")
-internal func _signalDispatchEvent(_ event: OpaquePointer)

stdlib/public/Concurrency/PlatformExecutorWASI.swift

@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2020 - 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#if os(WASI)
+
+import Swift
+
+// The default executors for now are Dispatch-based
+@available(SwiftStdlib 6.2, *)
+public struct PlatformExecutorFactory: ExecutorFactory {
+  public static let mainExecutor: any MainExecutor = DummyMainExecutor()
+  public static let defaultExecutor: any TaskExecutor
+    = DummyTaskExecutor()
+}
+
+#endif // os(WASI)