fix(tasks): don't allow adding the same assignee multiple times

See https://community.vikunja.io/t/task-can-be-assigned-twice-or-more-to-the-same-user/883

src/components/tasks/partials/editAssignees.vue

@@ -28,7 +28,7 @@
 </template>
 
 <script setup lang="ts">
-import {ref, shallowReactive, watch, type PropType} from 'vue'
+import {ref, shallowReactive, watch, nextTick, type PropType} from 'vue'
 import {useI18n} from 'vue-i18n'
 
 import User from '@/components/misc/user.vue'
@@ -43,22 +43,22 @@ import {useTaskStore} from '@/stores/tasks'
 import type {IUser} from '@/modelTypes/IUser'
 
 const props = defineProps({
-		taskId: {
-			type: Number,
-			required: true,
-		},
-		listId: {
-			type: Number,
-			required: true,
-		},
-		disabled: {
-			default: false,
-		},
-		modelValue: {
-			type: Array as PropType<IUser[]>,
-			default: () => [],
-		},
-	})
+	taskId: {
+		type: Number,
+		required: true,
+	},
+	listId: {
+		type: Number,
+		required: true,
+	},
+	disabled: {
+		default: false,
+	},
+	modelValue: {
+		type: Array as PropType<IUser[]>,
+		default: () => [],
+	},
+})
 const emit = defineEmits(['update:modelValue'])
 
 const taskStore = useTaskStore()
@@ -67,6 +67,7 @@ const {t} = useI18n({useScope: 'global'})
 const listUserService = shallowReactive(new ListUserService())
 const foundUsers = ref([])
 const assignees = ref<IUser[]>([])
+let isAdding = false
 
 watch(
 	() => props.modelValue,
@@ -80,9 +81,19 @@ watch(
 )
 
 async function addAssignee(user: IUser) {
-	await taskStore.addAssignee({user: user, taskId: props.taskId})
-	emit('update:modelValue', assignees.value)
-	success({message: t('task.assignee.assignSuccess')})
+	if (isAdding) {
+		return
+	}
+
+	try {
+		nextTick(() => isAdding = true)
+
+		await taskStore.addAssignee({user: user, taskId: props.taskId})
+		emit('update:modelValue', assignees.value)
+		success({message: t('task.assignee.assignSuccess')})
+	} finally {
+		nextTick(() => isAdding = false)
+	}
 }
 
 async function removeAssignee(user: IUser) {
@@ -119,6 +130,7 @@ function clearAllFoundUsers() {
 }
 
 const multiselect = ref()
+
 function focus() {
 	multiselect.value.focus()
 }

src/stores/tasks.ts

@@ -171,32 +171,39 @@ export const useTaskStore = defineStore('task', {
 			user: IUser,
 			taskId: ITask['id']
 		}) {
-			const kanbanStore = useKanbanStore()
-			const taskAssigneeService = new TaskAssigneeService()
-			const r = await taskAssigneeService.create(new TaskAssigneeModel({
-				userId: user.id,
-				taskId: taskId,
-			}))
-			const t = kanbanStore.getTaskById(taskId)
-			if (t.task === null) {
-				// Don't try further adding a label if the task is not in kanban
-				// Usually this means the kanban board hasn't been accessed until now.
-				// Vuex seems to have its difficulties with that, so we just log the error and fail silently.
-				console.debug('Could not add assignee to task in kanban, task not found', t)
+			const cancel = setModuleLoading(this)
+			
+			try {
+				const kanbanStore = useKanbanStore()
+				const taskAssigneeService = new TaskAssigneeService()
+				const r = await taskAssigneeService.create(new TaskAssigneeModel({
+					userId: user.id,
+					taskId: taskId,
+				}))
+				const t = kanbanStore.getTaskById(taskId)
+				if (t.task === null) {
+					// Don't try further adding a label if the task is not in kanban
+					// Usually this means the kanban board hasn't been accessed until now.
+					// Vuex seems to have its difficulties with that, so we just log the error and fail silently.
+					console.debug('Could not add assignee to task in kanban, task not found', t)
+					return r
+				}
+
+				kanbanStore.setTaskInBucketByIndex({
+					...t,
+					task: {
+						...t.task,
+						assignees: [
+							...t.task.assignees,
+							user,
+						],
+					},
+				})
+
 				return r
+			} finally {
+				cancel()
 			}
-
-			kanbanStore.setTaskInBucketByIndex({
-				...t,
-				task: {
-					...t.task,
-					assignees: [
-						...t.task.assignees,
-						user,
-					],
-				},
-			})
-			return r
 		},
 
 		async removeAssignee({