feat(HMR): apply changes in application styles at runtime

Expose `HmrContext` interface.
Apply changes in `app.css` instantly.
Avoid navigation on livesync when changes in `app.css` have been made.
Apply changes in `app.css` on back navigation.

tns-core-modules/application/application-common.ts

@@ -70,11 +70,11 @@ export function setApplication(instance: iOSApplication | AndroidApplication): v
     app = instance;
 }
 
-export function livesync() {
+export function livesync(context?: HmrContext) {
     events.notify(<EventData>{ eventName: "livesync", object: app });
     const liveSyncCore = global.__onLiveSyncCore;
     if (liveSyncCore) {
-        liveSyncCore();
+        liveSyncCore(context);
     }
 }
 

tns-core-modules/application/application.android.ts

@@ -212,12 +212,12 @@ export function getNativeApplication(): android.app.Application {
     return nativeApp;
 }
 
-global.__onLiveSync = function () {
+global.__onLiveSync = function __onLiveSync(context?: HmrContext) {
     if (androidApp && androidApp.paused) {
         return;
     }
 
-    livesync();
+    livesync(context);
 };
 
 function initLifecycleCallbacks() {

tns-core-modules/application/application.ios.ts

@@ -18,6 +18,7 @@ export * from "./application-common";
 import { createViewFromEntry } from "../ui/builder";
 import { ios as iosView, View } from "../ui/core/view";
 import { Frame, NavigationEntry } from "../ui/frame";
+import { loadCss } from "../ui/styling/style-scope";
 import * as utils from "../utils/utils";
 import { profile, level as profilingLevel, Level } from "../profiling";
 
@@ -225,12 +226,23 @@ class IOSApplication implements IOSApplicationDefinition {
         }
     }
 
-    public _onLivesync(): void {
+    public _onLivesync(context?: HmrContext): void {
+        let executeLivesync = true;
+        // HMR has context, livesync does not
+        if (context) {
+            if (context.module === getCssFileName()) {
+                loadCss(context.module);
+                this._rootView._onCssStateChange();
+                executeLivesync = false;
+            }
+        }
+        if (executeLivesync) {
             // If view can't handle livesync set window controller.
             if (!this._rootView._onLivesync()) {
                 this.setWindowContent();
             }
         }
+    }
 
     public setWindowContent(view?: View): void {
         if (this._rootView) {
@@ -264,8 +276,8 @@ exports.ios = iosApp;
 setApplication(iosApp);
 
 // attach on global, so it can be overwritten in NativeScript Angular
-(<any>global).__onLiveSyncCore = function () {
-    iosApp._onLivesync();
+(<any>global).__onLiveSyncCore = function __onLiveSyncCore(context?: HmrContext) {
+    iosApp._onLivesync(context);
 }
 
 let mainEntry: NavigationEntry;
@@ -373,10 +385,10 @@ function setViewControllerView(view: View): void {
     }
 }
 
-global.__onLiveSync = function () {
+global.__onLiveSync = function __onLiveSync(context?: HmrContext) {
     if (!started) {
         return;
     }
 
-    livesync();
+    livesync(context);
 }

tns-core-modules/module.d.ts

@@ -51,8 +51,8 @@ declare namespace NodeJS {
         __native?: any;
         __inspector?: any;
         __extends: any;
-        __onLiveSync: () => void;
-        __onLiveSyncCore: () => void;
+        __onLiveSync: (context?: { type: string, module: string }) => void;
+        __onLiveSyncCore: (context?: { type: string, module: string }) => void;
         __onUncaughtError: (error: NativeScriptError) => void;
         TNS_WEBPACK?: boolean;
         __requireOverride?: (name: string, dir: string) => any;
@@ -64,6 +64,27 @@ declare function clearTimeout(timeoutId: number): void;
 declare function setInterval(callback: (...args: any[]) => void, ms: number, ...args: any[]): number;
 declare function clearInterval(intervalId: number): void;
 
+declare enum HmrType {
+    markup = "markup",
+    script = "script",
+    style = "style"
+}
+
+/**
+ * Define a context for Hot Module Replacement.
+ */
+interface HmrContext {
+    /**
+     * The type of module for replacement.
+     */
+    type: HmrType;
+
+    /**
+     * The module for replacement.
+     */
+    module: string;
+}
+
 /**
  * An extended JavaScript Error which will have the nativeError property initialized in case the error is caused by executing platform-specific code.
  */

tns-core-modules/ui/frame/frame.android.ts

@@ -17,6 +17,7 @@ import {
     _updateTransitions, _reverseTransitions, _clearEntry, _clearFragment, AnimationType
 } from "./fragment.transitions";
 
+import { loadCss } from "../styling/style-scope";
 import { profile } from "../../profiling";
 
 // TODO: Remove this and get it from global to decouple builder for angular
@@ -82,14 +83,25 @@ function getAttachListener(): android.view.View.OnAttachStateChangeListener {
     return attachStateChangeListener;
 }
 
-export function reloadPage(): void {
+export function reloadPage(context?: HmrContext): void {
     const activity = application.android.foregroundActivity;
     const callbacks: AndroidActivityCallbacks = activity[CALLBACKS];
     const rootView: View = callbacks.getRootView();
 
+    let executeLivesync = true;
+    // HMR has context, livesync does not
+    if (context) {
+        if (context.module === application.getCssFileName()) {
+            loadCss(context.module);
+            rootView._onCssStateChange();
+            executeLivesync = false;
+        }
+    }
+    if (executeLivesync) {
         if (!rootView || !rootView._onLivesync()) {
             callbacks.resetActivityContent(activity);
         }
+    }
 }
 
 // attach on global, so it can be overwritten in NativeScript Angular

tns-core-modules/ui/page/page-common.ts

@@ -103,6 +103,10 @@ export class PageBase extends ContentView implements PageDefinition {
     public onNavigatingTo(context: any, isBackNavigation: boolean, bindingContext?: any) {
         this._navigationContext = context;
 
+        if (!this._cssState.isSelectorsLatestVersionApplied()) {
+            this._onCssStateChange();
+        }
+
         //https://github.com/NativeScript/NativeScript/issues/731
         if (!isBackNavigation && bindingContext !== undefined && bindingContext !== null) {
             this.bindingContext = bindingContext;

tns-core-modules/ui/styling/style-scope.d.ts

@@ -19,6 +19,11 @@ export class CssState {
      * Gets the static selectors that match the view and the dynamic selectors that may potentially match the view.
      */
     public changeMap: ChangeMap<ViewBase>;
+
+    /**
+     * Checks whether style scope and CSS state selectors are in sync.
+     */
+    public isSelectorsLatestVersionApplied(): boolean
 }
 
 export class StyleScope {
@@ -29,6 +34,9 @@ export class StyleScope {
     public static createSelectorsFromImports(tree: SyntaxTree, keyframes: Object): RuleSet[];
     public ensureSelectors(): number;
 
+    public isApplicationCssSelectorsLatestVersionApplied(): boolean;
+    public isLocalCssSelectorsLatestVersionApplied(): boolean;
+
     public applySelectors(view: ViewBase): void
     public query(options: Node): SelectorCore[];
 

tns-core-modules/ui/styling/style-scope.ts

@@ -307,7 +307,7 @@ function onLiveSync(args: applicationCommon.CssChangedEventData): void {
     loadCss(applicationCommon.getCssFileName());
 }
 
-const loadCss = profile(`"style-scope".loadCss`, (cssFile: string) => {
+export const loadCss = profile(`"style-scope".loadCss`, (cssFile: string) => {
     if (!cssFile) {
         return undefined;
     }
@@ -343,6 +343,7 @@ export class CssState {
     _appliedChangeMap: Readonly<ChangeMap<ViewBase>>;
     _appliedPropertyValues: Readonly<{}>;
     _appliedAnimations: ReadonlyArray<kam.KeyframeAnimation>;
+    _appliedSelectorsVersion: number;
 
     _match: SelectorsMatch<ViewBase>;
     _matchInvalid: boolean;
@@ -367,6 +368,15 @@ export class CssState {
         }
     }
 
+    public isSelectorsLatestVersionApplied(): boolean {
+        if (this._appliedSelectorsVersion && this.view._styleScope) {
+            this.view._styleScope.ensureSelectors();
+            return this.view._styleScope._getSelectorsVersion() === this._appliedSelectorsVersion;
+        } else {
+            return true;
+        }
+    }
+
     public onLoaded(): void {
         if (this._matchInvalid) {
             this.updateMatch();
@@ -381,6 +391,7 @@ export class CssState {
 
     @profile
     private updateMatch() {
+        this._appliedSelectorsVersion = this.view._styleScope._getSelectorsVersion();
         this._match = this.view._styleScope ? this.view._styleScope.matchSelectors(this.view) : CssState.emptyMatch;
         this._matchInvalid = false;
     }
@@ -597,8 +608,8 @@ export class StyleScope {
     }
 
     public ensureSelectors(): number {
-        if (this._applicationCssSelectorsAppliedVersion !== applicationCssSelectorVersion ||
-            this._localCssSelectorVersion !== this._localCssSelectorsAppliedVersion ||
+        if (!this.isApplicationCssSelectorsLatestVersionApplied() ||
+            !this.isLocalCssSelectorsLatestVersionApplied() ||
             !this._mergedCssSelectors) {
 
             this._createSelectors();
@@ -607,6 +618,14 @@ export class StyleScope {
         return this._getSelectorsVersion();
     }
 
+    public isApplicationCssSelectorsLatestVersionApplied(): boolean {
+        return this._applicationCssSelectorsAppliedVersion === applicationCssSelectorVersion;
+    }
+
+    public isLocalCssSelectorsLatestVersionApplied(): boolean {
+        return this._localCssSelectorsAppliedVersion === this._localCssSelectorVersion;
+    }
+
     @profile
     private _createSelectors() {
         let toMerge: RuleSet[][] = [];