fix(engine): issue #858 to enable the ability to have setters reactive

packages/@lwc/engine/jest.config.js

@@ -33,7 +33,7 @@ module.exports = {
         global: {
             functions: 65,
             lines: 75,
-            branches: 70,
+            branches: 65,
         },
     },
 };

packages/@lwc/engine/src/framework/base-lightning-element.ts

@@ -33,12 +33,13 @@ import {
     ComponentInterface,
     getWrappedComponentsListener,
     getComponentAsString,
+    getTemplateReactiveObserver,
 } from './component';
 import { setInternalField, setHiddenField } from '../shared/fields';
 import { ViewModelReflection, EmptyObject } from './utils';
 import { vmBeingConstructed, isBeingConstructed, isRendering, vmBeingRendered } from './invoker';
 import { getComponentVM, VM } from './vm';
-import { observeMutation, notifyMutation } from './watcher';
+import { valueObserved, valueMutated } from '../libs/mutation-tracker';
 import { dispatchEvent } from '../env/dom';
 import { patchComponentWithRestrictions, patchShadowRootWithRestrictions } from './restrictions';
 import { unlockAttribute, lockAttribute } from './attributes';
@@ -92,7 +93,7 @@ function createBridgeToElementDescriptor(
                 }
                 return;
             }
-            observeMutation(this, propName);
+            valueObserved(this, propName);
             return get.call(vm.elm);
         },
         set(this: ComponentInterface, newValue: any) {
@@ -119,7 +120,7 @@ function createBridgeToElementDescriptor(
                 vm.cmpProps[propName] = newValue;
                 if (isFalse(vm.isDirty)) {
                     // perf optimization to skip this step if not in the DOM
-                    notifyMutation(this, propName);
+                    valueMutated(this, propName);
                 }
             }
             return set.call(vm.elm, newValue);
@@ -165,6 +166,7 @@ export function BaseLightningElement(this: ComponentInterface) {
     } = vm;
     const component = this;
     vm.component = component;
+    vm.tro = getTemplateReactiveObserver(vm as VM);
     // interaction hooks
     // We are intentionally hiding this argument from the formal API of LWCElement because
     // we don't want folks to know about it just yet.

packages/@lwc/engine/src/framework/component.ts

@@ -12,19 +12,13 @@ import {
     vmBeingRendered,
     invokeEventListener,
 } from './invoker';
-import {
-    isArray,
-    ArrayIndexOf,
-    ArraySplice,
-    isFunction,
-    isUndefined,
-    StringToLowerCase,
-} from '../shared/language';
+import { isArray, isFunction, isUndefined, StringToLowerCase, isFalse } from '../shared/language';
 import { invokeServiceHook, Services } from './services';
-import { VM, getComponentVM, UninitializedVM } from './vm';
+import { VM, getComponentVM, UninitializedVM, scheduleRehydration } from './vm';
 import { VNodes } from '../3rdparty/snabbdom/types';
 import { tagNameGetter } from '../env/element';
 import { Template } from './template';
+import { ReactiveObserver } from '../libs/mutation-tracker';
 
 export type ErrorCallback = (error: any, stack: string) => void;
 export interface ComponentInterface {
@@ -99,26 +93,20 @@ export function linkComponent(vm: VM) {
     }
 }
 
-export function clearReactiveListeners(vm: VM) {
-    if (process.env.NODE_ENV !== 'production') {
-        assert.isTrue(vm && 'cmpRoot' in vm, `${vm} is not a vm.`);
-    }
-    const { deps } = vm;
-    const len = deps.length;
-    if (len > 0) {
-        for (let i = 0; i < len; i += 1) {
-            const set = deps[i];
-            const pos = ArrayIndexOf.call(deps[i], vm);
-            if (process.env.NODE_ENV !== 'production') {
-                assert.invariant(
-                    pos > -1,
-                    `when clearing up deps, the vm must be part of the collection.`
-                );
-            }
-            ArraySplice.call(set, pos, 1);
+export function getTemplateReactiveObserver(vm: VM): ReactiveObserver {
+    return new ReactiveObserver(() => {
+        if (process.env.NODE_ENV !== 'production') {
+            assert.invariant(
+                !isRendering,
+                `Mutating property is not allowed during the rendering life-cycle of ${vmBeingRendered}.`
+            );
         }
-        deps.length = 0;
-    }
+        const { isDirty } = vm;
+        if (isFalse(isDirty)) {
+            markComponentAsDirty(vm);
+            scheduleRehydration(vm);
+        }
+    });
 }
 
 function clearChildLWC(vm: VM) {
@@ -134,7 +122,7 @@ export function renderComponent(vm: VM): VNodes {
         assert.invariant(vm.isDirty, `${vm} is not dirty.`);
     }
 
-    clearReactiveListeners(vm);
+    vm.tro.reset();
     clearChildLWC(vm);
     const vnodes = invokeComponentRenderMethod(vm);
     vm.isDirty = false;

packages/@lwc/engine/src/framework/decorators/api.ts

@@ -7,7 +7,7 @@
 import assert from '../../shared/assert';
 import { isRendering, vmBeingRendered, isBeingConstructed } from '../invoker';
 import { isObject, toString, isFalse } from '../../shared/language';
-import { observeMutation, notifyMutation } from '../watcher';
+import { valueObserved, valueMutated } from '../../libs/mutation-tracker';
 import { ComponentInterface, ComponentConstructor } from '../component';
 import { getComponentVM } from '../vm';
 import { isUndefined, isFunction } from '../../shared/language';
@@ -81,7 +81,7 @@ function createPublicPropertyDescriptor(
                 }
                 return;
             }
-            observeMutation(this, key);
+            valueObserved(this, key);
             return vm.cmpProps[key];
         },
         set(this: ComponentInterface, newValue: any) {
@@ -100,7 +100,7 @@ function createPublicPropertyDescriptor(
             // avoid notification of observability if the instance is already dirty
             if (isFalse(vm.isDirty)) {
                 // perf optimization to skip this step if the component is dirty already.
-                notifyMutation(this, key);
+                valueMutated(this, key);
             }
         },
         enumerable: isUndefined(descriptor) ? true : descriptor.enumerable,

packages/@lwc/engine/src/framework/decorators/track.ts

@@ -7,7 +7,7 @@
 import assert from '../../shared/assert';
 import { isUndefined, isFalse } from '../../shared/language';
 import { isRendering, vmBeingRendered } from '../invoker';
-import { observeMutation, notifyMutation } from '../watcher';
+import { valueObserved, valueMutated } from '../../libs/mutation-tracker';
 import { getComponentVM } from '../vm';
 import { reactiveMembrane } from '../membrane';
 import { ComponentConstructor, ComponentInterface } from '../component';
@@ -66,7 +66,7 @@ export function createTrackedPropertyDescriptor(
             if (process.env.NODE_ENV !== 'production') {
                 assert.isTrue(vm && 'cmpRoot' in vm, `${vm} is not a vm.`);
             }
-            observeMutation(this, key);
+            valueObserved(this, key);
             return vm.cmpTrack[key];
         },
         set(this: ComponentInterface, newValue: any) {
@@ -85,7 +85,7 @@ export function createTrackedPropertyDescriptor(
                 vm.cmpTrack[key] = reactiveOrAnyValue;
                 if (isFalse(vm.isDirty)) {
                     // perf optimization to skip this step if the track property is on a component that is already dirty
-                    notifyMutation(this, key);
+                    valueMutated(this, key);
                 }
             }
         },

packages/@lwc/engine/src/framework/invoker.ts

@@ -123,8 +123,10 @@ export function invokeComponentRenderMethod(vm: VM): VNodes {
         },
         () => {
             // job
-            const html = callHook(component, render);
-            result = evaluateTemplate(vm, html);
+            vm.tro.observe(() => {
+                const html = callHook(component, render);
+                result = evaluateTemplate(vm, html);
+            });
         },
         () => {
             establishContext(ctx);

packages/@lwc/engine/src/framework/membrane.ts

@@ -5,15 +5,15 @@
  * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
  */
 import ObservableMembrane from 'observable-membrane';
-import { observeMutation, notifyMutation } from './watcher';
+import { valueObserved, valueMutated } from '../libs/mutation-tracker';
 
 function valueDistortion(value: any) {
     return value;
 }
 
 export const reactiveMembrane = new ObservableMembrane({
-    valueObserved: observeMutation,
-    valueMutated: notifyMutation,
+    valueObserved,
+    valueMutated,
     valueDistortion,
 });
 

packages/@lwc/engine/src/framework/vm.ts

@@ -10,7 +10,6 @@ import {
     createComponent,
     linkComponent,
     renderComponent,
-    clearReactiveListeners,
     ComponentConstructor,
     markComponentAsDirty,
 } from './component';
@@ -56,6 +55,7 @@ import { tagNameGetter } from '../env/element';
 import { parentElementGetter, parentNodeGetter } from '../env/node';
 import { updateDynamicChildren, updateStaticChildren } from '../3rdparty/snabbdom/snabbdom';
 import { hasDynamicChildren } from './hooks';
+import { ReactiveObserver } from '../libs/mutation-tracker';
 
 export interface SlotSet {
     [key: string]: VNodes;
@@ -86,11 +86,9 @@ export interface UninitializedVM {
     /** Adopted Children List */
     aChildren: VNodes;
     velements: VCustomElement[];
-    cmpTemplate?: Template;
     cmpProps: any;
     cmpSlots: SlotSet;
     cmpTrack: any;
-    component?: ComponentInterface;
     callHook: (
         cmp: ComponentInterface | undefined,
         fn: (...args: any[]) => any,
@@ -102,14 +100,21 @@ export interface UninitializedVM {
     isDirty: boolean;
     isRoot: boolean;
     mode: 'open' | 'closed';
-    deps: VM[][];
     toString(): string;
+
+    // perf optimization to avoid reshaping the uninitialized when initialized
+    cmpTemplate?: Template;
+    component?: ComponentInterface;
+    cmpRoot?: ShadowRoot;
+    tro?: ReactiveObserver;
 }
 
 export interface VM extends UninitializedVM {
     cmpTemplate: Template;
     component: ComponentInterface;
     cmpRoot: ShadowRoot;
+    /** Template Reactive Observer to observe values used by the selected template */
+    tro: ReactiveObserver;
 }
 
 let idx: number = 0;
@@ -162,6 +167,9 @@ function resetComponentStateWhenRemoved(vm: VM) {
     }
     const { state } = vm;
     if (state !== VMState.disconnected) {
+        const { tro } = vm;
+        // Making sure that any observing record will not trigger the rehydrated on this vm
+        tro.reset();
         runDisconnectedCallback(vm);
         // Spec: https://dom.spec.whatwg.org/#concept-node-remove (step 14-15)
         runShadowChildNodesDisconnectedCallback(vm);
@@ -218,19 +226,20 @@ export function createVM(elm: HTMLElement, Ctor: ComponentConstructor, options:
         elm,
         data: EmptyObject,
         context: create(null),
-        cmpTemplate: undefined,
         cmpProps: create(null),
         cmpTrack: create(null),
         cmpSlots: useSyntheticShadow ? create(null) : undefined,
         callHook,
         setHook,
         getHook,
-        component: undefined,
         children: EmptyArray,
         aChildren: EmptyArray,
         velements: EmptyArray,
-        // used to track down all object-key pairs that makes this vm reactive
-        deps: [],
+        // Perf optimization to preserve the shape of this obj
+        cmpTemplate: undefined,
+        component: undefined,
+        cmpRoot: undefined,
+        tro: undefined,
     };
 
     if (process.env.NODE_ENV !== 'production') {
@@ -402,7 +411,6 @@ function runDisconnectedCallback(vm: VM) {
         // of disconnected components.
         markComponentAsDirty(vm);
     }
-    clearReactiveListeners(vm);
     vm.state = VMState.disconnected;
     // reporting disconnection
     const { disconnected } = Services;