Implement cancelling python coros from QML

This was needed to implement the cancel button featue on the login
screen

src/python/app.py

@@ -54,7 +54,7 @@ class App:
         return asyncio.run_coroutine_threadsafe(coro, self.loop)
 
 
-    def _call_coro(self, coro: Coroutine, uuid: str) -> None:
+    def _call_coro(self, coro: Coroutine, uuid: str) -> Future:
         def on_done(future: Future) -> None:
             result = exception = trace = None
 
@@ -66,21 +66,23 @@ class App:
 
             CoroutineDone(uuid, result, exception, trace)
 
-        self.run_in_loop(coro).add_done_callback(on_done)
+        future = self.run_in_loop(coro)
+        future.add_done_callback(on_done)
+        return future
 
 
     def call_backend_coro(self, name: str, uuid: str, args: Sequence[str] = (),
-                         ) -> None:
-        self._call_coro(attrgetter(name)(self.backend)(*args), uuid)
+                         ) -> Future:
+        return self._call_coro(attrgetter(name)(self.backend)(*args), uuid)
 
 
     def call_client_coro(self,
                          account_id: str,
                          name:       str,
                          uuid:       str,
-                         args:       Sequence[str] = ()) -> None:
+                         args:       Sequence[str] = ()) -> Future:
         client = self.backend.clients[account_id]
-        self._call_coro(attrgetter(name)(client)(*args), uuid)
+        return self._call_coro(attrgetter(name)(client)(*args), uuid)
 
 
     def pdb(self, additional_data: Sequence = ()) -> None:

src/qml/Pages/AddAccount/SignIn.qml

@@ -31,7 +31,7 @@ HBox {
 
             signInTimeout.restart()
 
-            py.callCoro("login_client", args, userId => {
+            loginFuture = py.callCoro("login_client", args, userId => {
                 signInTimeout.stop()
                 errorMessage.text = ""
                 button.loading    = false
@@ -48,9 +48,14 @@ HBox {
                 )
 
             }, type => {
-                if (type === "CancelledError") return
-
                 signInTimeout.stop()
+
+                if (type === "CancelledError") {
+                    loginFuture    = null
+                    button.loading = false
+                    return
+                }
+
                 let txt = qsTr("Invalid request or login type")
 
                 if (type === "MatrixForbidden")
@@ -64,11 +69,14 @@ HBox {
             })
         },
 
-        cancel: button => {}
+        cancel: button => { if (loginFuture) loginFuture.cancel() }
     })
 
 
+    property var loginFuture: null
+
     property string signInWith: "username"
+
     readonly property bool canSignIn:
         serverField.text && idField.text && passwordField.text &&
         ! serverField.error

src/qml/Python.qml

@@ -1,15 +1,40 @@
 import QtQuick 2.12
-import QtQuick.Controls 2.12
 import io.thp.pyotherside 1.5
 import "event_handlers.js" as EventHandlers
 
 Python {
     id: py
 
+
     property bool ready: false
     property bool startupAnyAccountsSaved: false
     property var pendingCoroutines: ({})
 
+
+    function newQmlFuture() {
+        return {
+            _pyFuture: null,
+
+            get pyFuture() { return this._pyFuture },
+
+            set pyFuture(value) {
+                this._pyFuture = value
+                if (this.cancelPending) this.cancel()
+            },
+
+            cancelPending: false,
+
+            cancel: function() {
+                if (! this.pyFuture) {
+                    this.cancelPending = true
+                    return
+                }
+
+                py.call(py.getattr(this.pyFuture, "cancel"))
+            },
+        }
+    }
+
     function setattr(obj, attr, value, callback=null) {
         py.call(py.getattr(obj, "__setattr__"), [attr, value], callback)
     }
@@ -22,27 +47,43 @@ Python {
         let uuid = name + "." + CppUtils.uuid()
 
         pendingCoroutines[uuid] = {onSuccess, onError}
-        call("APP.call_backend_coro", [name, uuid, args])
+
+        let qmlFuture = py.newQmlFuture()
+
+        call("APP.call_backend_coro", [name, uuid, args], pyFuture => {
+            qmlFuture.pyFuture = pyFuture
+        })
+
+        return qmlFuture
     }
 
     function callClientCoro(
         accountId, name, args=[], onSuccess=null, onError=null
     ) {
+        let qmlFuture = py.newQmlFuture()
+
         callCoro("wait_until_client_exists", [accountId], () => {
             let uuid = accountId + "." + name + "." + CppUtils.uuid()
 
             pendingCoroutines[uuid] = {onSuccess, onError}
-            call("APP.call_client_coro", [accountId, name, uuid, args])
+
+            let call_args = [accountId, name, uuid, args]
+
+            call("APP.call_client_coro", call_args, pyFuture => {
+                qmlFuture.pyFuture = pyFuture
             })
+        })
+
+        return qmlFuture
     }
 
     function saveConfig(backend_attribute, data, callback=null) {
         if (! py.ready) { return }  // config not loaded yet
-        callCoro(backend_attribute + ".write", [data], callback)
+        return callCoro(backend_attribute + ".write", [data], callback)
     }
 
     function loadSettings(callback=null) {
-        callCoro("load_settings", [], ([settings, uiState, theme]) => {
+        return callCoro("load_settings", [], ([settings, uiState, theme]) => {
             window.settings = settings
             window.uiState  = uiState
             window.theme    = Qt.createQmlObject(theme, window, "theme")