feat(@angular-devkit/core): Remove dep on chokidar

It is unused within our code, as webpack will do the file watching.
This removes 1.4 MB from the download size of the package.
See https://codepen.io/alexeagle/full/zbZWRM

BREAKING CHANGE:
Users who rely on angular-devkit/core to do the file watching must add chokidar to their devDependencies.

Author: alexeagle

packages/angular_devkit/core/BUILD

@@ -72,7 +72,6 @@ jasmine_node_test(
     deps = [
         "@npm//jasmine",
         "@npm//source-map",
-        "@npm//chokidar",
     ],
 )
 

packages/angular_devkit/core/node/host.ts

@@ -38,8 +38,24 @@ interface ChokidarWatcher {
   close(): void;
 }
 
-const { FSWatcher }: { FSWatcher: ChokidarWatcher } = require('chokidar');
-
+// This will only be initialized if the watch() method is called.
+// Otherwise chokidar appears only in type positions, and shouldn't be referenced
+// in the JavaScript output.
+let FSWatcher: ChokidarWatcher;
+function loadFSWatcher() {
+  if (!FSWatcher) {
+    try {
+      // tslint:disable-next-line:no-implicit-dependencies
+      FSWatcher = require('chokidar').FSWatcher;
+    } catch (e) {
+      if (e.code !== 'MODULE_NOT_FOUND') {
+        throw new Error('As of angular-devkit version 8.0, the "chokidar" package ' +
+            'must be installed in order to use watch() features.');
+      }
+      throw e;
+    }
+  }
+}
 
 type FsFunction0<R> = (cb: (err?: Error, result?: R) => void) => void;
 type FsFunction1<R, T1> = (p1: T1, cb: (err?: Error, result?: R) => void) => void;
@@ -180,6 +196,7 @@ export class NodeJsAsyncHost implements virtualFs.Host<fs.Stats> {
     _options?: virtualFs.HostWatchOptions,
   ): Observable<virtualFs.HostWatchEvent> | null {
     return new Observable<virtualFs.HostWatchEvent>(obs => {
+      loadFSWatcher();
       const watcher = new FSWatcher({ persistent: true }).add(getSystemPath(path));
 
       watcher
@@ -365,6 +382,7 @@ export class NodeJsSyncHost implements virtualFs.Host<fs.Stats> {
   ): Observable<virtualFs.HostWatchEvent> | null {
     return new Observable<virtualFs.HostWatchEvent>(obs => {
       const opts = { persistent: false };
+      loadFSWatcher();
       const watcher = new FSWatcher(opts).add(getSystemPath(path));
 
       watcher

packages/angular_devkit/core/package.json

@@ -9,7 +9,6 @@
   ],
   "dependencies": {
     "ajv": "6.10.0",
-    "chokidar": "2.1.2",
     "fast-json-stable-stringify": "2.0.0",
     "rxjs": "6.4.0",
     "source-map": "0.7.3"

packages/angular_devkit/schematics/BUILD

@@ -61,7 +61,6 @@ jasmine_node_test(
     name = "schematics_test",
     srcs = [":schematics_test_lib"],
     deps = [
-        "@npm//chokidar",
         "@npm//jasmine",
         "@npm//source-map",
     ],
@@ -159,7 +158,6 @@ jasmine_node_test(
     deps = [
         "@npm//jasmine",
         "@npm//source-map",
-        "@npm//chokidar",
     ],
 )
 
@@ -225,7 +223,6 @@ jasmine_node_test(
     deps = [
         "@npm//jasmine",
         "@npm//source-map",
-        "@npm//chokidar",
     ],
 )
 

packages/schematics/angular/BUILD

@@ -102,7 +102,6 @@ jasmine_node_test(
     deps = [
         "@npm//jasmine",
         "@npm//source-map",
-        "@npm//chokidar",
         "//packages/schematics/angular/third_party/github.com/Microsoft/TypeScript",
     ],
 )

packages/schematics/update/BUILD

@@ -83,7 +83,6 @@ jasmine_node_test(
     deps = [
         "@npm//jasmine",
         "@npm//source-map",
-        "@npm//chokidar",
         "@npm//npm-registry-client",
     ],
 )