Don't pass Python Future objects to QML

Returning a Future doesn't work on Windows for some reason
(https://github.com/thp/pyotherside/issues/116).

Instead of using these objects from QML to cancel running coroutines,
call a Python QMLBridge function that takes a coroutine UUID and will
take care of the cancelling.

src/gui/PythonBridge/Future.qml

@@ -1,26 +0,0 @@
-// Copyright Mirage authors & contributors <https://github.com/mirukana/mirage>
-// SPDX-License-Identifier: LGPL-3.0-or-later
-
-import QtQuick 2.12
-
-QtObject {
-    id: future
-
-    property PythonBridge bridge
-
-    readonly property QtObject privates: QtObject {
-        property var pythonFuture: null
-        property bool cancelPending: false
-
-        onPythonFutureChanged: if (cancelPending) future.cancel()
-    }
-
-    function cancel() {
-        if (! privates.pythonFuture) {
-            privates.cancelPending = true
-            return
-        }
-
-        bridge.call(bridge.getattr(privates.pythonFuture, "cancel"))
-    }
-}

src/gui/PythonBridge/PythonBridge.qml

@@ -11,48 +11,39 @@ Python {
 
     readonly property var pendingCoroutines: Globals.pendingCoroutines
 
-    function makeFuture(callback) {
-        return Qt.createComponent("Future.qml").createObject(py, {bridge: py})
-    }
-
     function setattr(obj, attr, value, callback=null) {
         py.call(py.getattr(obj, "__setattr__"), [attr, value], callback)
     }
 
     function callCoro(name, args=[], onSuccess=null, onError=null) {
-        const uuid   = name + "." + CppUtils.uuid()
-        const future = makeFuture()
+        const uuid = name + "." + CppUtils.uuid()
 
-        Globals.pendingCoroutines[uuid] = {future, onSuccess, onError}
+        Globals.pendingCoroutines[uuid] = {onSuccess, onError}
         Globals.pendingCoroutinesChanged()
-        // if (name  === "models.ensure_exists_from_qml") { print("r");  return}
 
-        call("BRIDGE.call_backend_coro", [name, uuid, args], pyFuture => {
-            future.privates.pythonFuture = pyFuture
-        })
-
-        return future
+        call("BRIDGE.call_backend_coro", [name, uuid, args])
+        return uuid
     }
 
     function callClientCoro(
         accountId, name, args=[], onSuccess=null, onError=null
     ) {
-        const future = makeFuture()
+        const uuid = accountId + "." + name + "." + CppUtils.uuid()
 
+        Globals.pendingCoroutines[uuid] = {onSuccess, onError}
+        Globals.pendingCoroutinesChanged()
+
+        // Ensure the client exists or wait for it to exist
         callCoro("get_client", [accountId, [name, args]], () => {
-            const uuid = accountId + "." + name + "." + CppUtils.uuid()
-
-            Globals.pendingCoroutines[uuid] = {onSuccess, onError}
-            Globals.pendingCoroutinesChanged()
-
-            const call_args = [accountId, name, uuid, args]
-
-            call("BRIDGE.call_client_coro", call_args, pyFuture => {
-                future.privates.pythonFuture = pyFuture
-            })
+            // Now that we're sure it won't error, run that client's function
+            call("BRIDGE.call_client_coro", [accountId, name, uuid, args])
         })
 
-        return future
+        return uuid
+    }
+
+    function cancelCoro(uuid) {
+        call("BRIDGE.cancel_coro", [uuid])
     }
 
     function saveConfig(backend_attribute, data, callback=null) {