[Swift] Swift IPC handlers should return their reply and may be async [reland] - #76310

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[Swift] Swift IPC handlers should return their reply and may be async [reland]
https://bugs.webkit.org/show_bug.cgi?id=324524

Reviewed by Richard Robinson

A handler for a message with a reply now returns it, and any handler may be async. For instance,
IPCTesterReceiver's deferred reply no longer deals with WTF::CompletionHandler and becomes
simply:

    func deferredReplyMessage(connection: IPC.Connection, arg1: UInt32) async -> UInt64 {
        deferredReplyArgument = arg1
        return await withCheckedContinuation { pendingDeferredReply = $0 }
    }

so the reply is whatever the handler returns, whenever it returns. It cannot forget to
reply or reply twice, and no C++ reply type appears in its signature.

Async or not, throwing or not, all four combinations go through one generated call, since a
single `await` and a single `try` each cover a whole expression:

    let reply = try await mayThrowInvalidMessage(target.foo(connection: connection, ...))

Nothing in .messages.in says whether a handler is async: handleMessageSynchronous moves the
reply encoder into the completion handler, so Synchronous only means the sender blocks, and
deferring is the receiver's choice. A handler without a reply may need to await too, so every
message is dispatched the same way.

Everything runs on the main thread. Handlers are @MainActor. @MainActor functions are not
exposed to C++, so the generated wrapper stays synchronous, enters the actor with
MainActor.assumeIsolated - which also asserts IPC dispatched us on the main thread - and
starts the handler with Task.immediate, which runs it inline until its first suspension and
inherits the actor, so the remainder stays on the main thread too. Running inline is what keeps
Swift-handled messages in order with C++-handled ones; Task.init would not. The body lives in a
@MainActor static method because a typed `catch` inside a closure widens to `any Error`.
mayThrowInvalidMessage's async overload is nonisolated(nonsending), without which awaiting it
would send the reply out of the actor.

Adds -Werror RegionIsolation, without which none of this is checked: data-race diagnostics
are only warnings when a C++ type is involved, because C++ modules carry no concurrency
annotations. That is most of our Swift.

None of this crosses a real boundary - it is one thread and one stack frame - but the wrapper
must be nonisolated for C++ to call it, because swiftc silently omits @MainActor members from
the generated C++ header.

Everything under Scripts/webkit/tests/ is messages_unittest.py -r output, except
TestWithSwift.messages.in, which gains a message with an empty reply.

This is a reland; the previous version hit a Swift compiler bug rdar://189495426 on Windows
alone. This is worked around in this version by packing the function arguments into a struct.

* Source/WebKit/Platform/IPC/MessageCheck.swift:
(mayThrowInvalidMessage(_:)):
(Task.immediateOnMainActor(_:)):
(InvalidMessage.markMessageInvalid(_:on:)): Deleted.
* Source/WebKit/Scripts/webkit/messages.py:
(swift_reply_completion_argument):
(generate_swift_message_handler):
(swift_dispatch_target_and_function):
* Source/WebKit/Scripts/webkit/tests/TestWithStreamSwiftEnabledByMessageReceiver.swift:
* Source/WebKit/Scripts/webkit/tests/TestWithStreamSwiftMessageReceiver.swift:
* Source/WebKit/Scripts/webkit/tests/TestWithSwiftConditionallyAndEnabledByMessageReceiver.swift:
* Source/WebKit/Scripts/webkit/tests/TestWithSwiftConditionallyMessageReceiver.swift:
* Source/WebKit/Scripts/webkit/tests/TestWithSwiftMessageReceiver.swift:
* Source/WebKit/Shared/IPCTesterReceiver.swift:
(IPCTesterReceiver.asyncMessage):
(IPCTesterReceiver.deferredReplyMessage):
(IPCTesterReceiver.completeDeferredReply(connection:arg1:)):
(IPCTesterReceiver.pendingDeferredReply):
(IPCTesterReceiver.deferredReply): Deleted.
(IPCTesterReceiver.completeDeferredReply(_:arg1:)):
* Source/WebKit/UIProcess/WebBackForwardList.swift:
(WebBackForwardList.backForwardAddItem):
(WebBackForwardList.backForwardSetChildItem):
(WebBackForwardList.backForwardClearChildren):
(WebBackForwardList.backForwardUpdateItem):
(WebBackForwardList.backForwardGoToItem):
(WebBackForwardList.backForwardListContainsItem):
(WebBackForwardList.backForwardAllItems):
(WebBackForwardList.backForwardItemAtIndexForWebContent):
(WebBackForwardList.backForwardListCounts):
* Source/cmake/WebKitSwiftFlags.cmake:
* Source/WTF/wtf/PlatformHave.h:
* Source/WebKit/Configurations/AllowedSPI.toml:
* Source/WebKit/Platform/spi/Cocoa/_Concurrency_SPI.swiftinterface: Added.
* Source/WebKit/Scripts/webkit/tests/MessageArgumentDescriptions.cpp:
(IPC::jsValueForArguments):
(IPC::jsValueForReplyArguments):
(IPC::messageArgumentDescriptions):
(IPC::messageReplyArgumentDescriptions):
* Source/WebKit/Scripts/webkit/tests/MessageNames.cpp:
* Source/WebKit/Scripts/webkit/tests/MessageNames.h:
* Source/WebKit/Scripts/webkit/tests/TestWithSwift.messages.in:
* Source/WebKit/Scripts/webkit/tests/TestWithSwiftMessageReceiver.cpp:
(WebKit::TestWithSwiftMessageForwarder::didReceiveMessage):
(CompletionHandlers::TestWithSwift::completeWithDefaultReply):
(IPC::jsValueForDecodedMessage<MessageName::TestWithSwift_TestMessageWithEmptyReply>):
(IPC::jsValueForDecodedMessageReply<MessageName::TestWithSwift_TestMessageWithEmptyReply>):
(IPC::jsValueForDecodedMessage<MessageName::TestWithSwift_TestMessageWithEmptyReplyReply>):
* Source/WebKit/Scripts/webkit/tests/TestWithSwiftMessages.h:
(Messages::TestWithSwift::TestMessageWithEmptyReply::name):
(Messages::TestWithSwift::TestMessageWithEmptyReply::asyncMessageReplyName):
(Messages::TestWithSwift::TestMessageWithEmptyReply::TestMessageWithEmptyReply):
(Messages::TestWithSwift::TestMessageWithEmptyReply::encode):
(Messages::TestWithSwift::TestMessageWithEmptyReplyReply::name):
(Messages::TestWithSwift::TestMessageWithEmptyReplyReply::TestMessageWithEmptyReplyReply):
(Messages::TestWithSwift::TestMessageWithEmptyReplyReply::encode):
* Configurations/CommonBase.xcconfig:
* Source/WebKit/CMakeLists.txt:
* Source/WebKit/Shared/Concurrency+Extras.swift: Added.
(Task.immediateOnMainActor(_:)):
* Source/WebKit/WebKit.xcodeproj/project.pbxproj:

Canonical link: https://commits.webkit.org/323222@main

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