feat(@angular-devkit/build-ng-packagr): add support for watch when building a library

`ng-packagr` version `4.0.0-rc.3`, lands the incremental builds feature.

More info:  https://github.com/dherges/ng-packagr/blob/master/CHANGELOG.md#400-rc2-2018-06-23

`enableResourceInlining` needs to be enabled for libraries that contain components

Closes: #10643

Author: alan-agius4

package-lock.json

@@ -11,7 +11,8 @@
   "dependencies": {
     "@angular-devkit/architect": "0.0.0",
     "@angular-devkit/core": "0.0.0",
-    "rxjs": "^6.0.0"
+    "rxjs": "^6.0.0",
+    "semver": "^5.3.0"
   },
   "peerDependencies": {
     "ng-packagr": "^2.2.0 || ^3.0.0 || ^4.0.0"

packages/angular_devkit/build_ng_packagr/package.json

@@ -12,20 +12,55 @@ import {
   BuilderConfiguration,
   BuilderContext,
 } from '@angular-devkit/architect';
-import { getSystemPath, normalize, resolve } from '@angular-devkit/core';
+import { getSystemPath, normalize, resolve, tags } from '@angular-devkit/core';
+import * as fs from 'fs';
 import * as ngPackagr from 'ng-packagr';
-import { Observable } from 'rxjs';
+import { EMPTY, Observable } from 'rxjs';
+import { catchError, tap } from 'rxjs/operators';
+import * as semver from 'semver';
+
+const NEW_NG_PACKAGR_VERSION = '4.0.0-rc.3';
 
 // TODO move this function to architect or somewhere else where it can be imported from.
 // Blatantly copy-pasted from 'require-project-module.ts'.
 function requireProjectModule(root: string, moduleName: string) {
   return require(require.resolve(moduleName, { paths: [root] }));
 }
 
+function resolveProjectModule(root: string, moduleName: string) {
+  return require.resolve(moduleName, { paths: [root] });
+}
 
 export interface NgPackagrBuilderOptions {
   project: string;
   tsConfig?: string;
+  watch?: boolean;
+}
+
+function checkNgPackagrVersion(projectRoot: string): boolean {
+  let ngPackagrJsonPath;
+
+  try {
+    ngPackagrJsonPath = resolveProjectModule(projectRoot, 'ng-packagr/package.json');
+  } catch {
+    // ng-packagr is not installed
+    throw new Error(tags.stripIndent`
+    ng-packagr is not installed. Run \`npm install ng-packagr --save-dev\` and try again.
+  `);
+  }
+
+  const ngPackagrPackageJson = fs.readFileSync(ngPackagrJsonPath).toString();
+  const ngPackagrVersion = JSON.parse(ngPackagrPackageJson)['version'];
+
+  if (!semver.gte(ngPackagrVersion, NEW_NG_PACKAGR_VERSION)) {
+    throw new Error(tags.stripIndent`
+    The installed version of ng-packagr is ${ngPackagrVersion}. The watch feature
+    requires ng-packagr version to satisfy ${NEW_NG_PACKAGR_VERSION}.
+    Please upgrade your ng-packagr version.
+  `);
+  }
+
+  return true;
 }
 
 export class NgPackagrBuilder implements Builder<NgPackagrBuilderOptions> {
@@ -53,12 +88,30 @@ export class NgPackagrBuilder implements Builder<NgPackagrBuilderOptions> {
         ngPkgProject.withTsConfig(tsConfigPath);
       }
 
-      ngPkgProject.build()
-        .then(() => {
-          obs.next({ success: true });
-          obs.complete();
-        })
-        .catch((e) => obs.error(e));
+      if (options.watch) {
+        checkNgPackagrVersion(getSystemPath(root));
+
+        const ngPkgSubscription = ngPkgProject
+          .watch()
+          .pipe(
+            tap(() => obs.next({ success: true })),
+            catchError(e => {
+              obs.error(e);
+
+              return EMPTY;
+            }),
+          )
+          .subscribe();
+
+        return () => ngPkgSubscription.unsubscribe();
+      } else {
+        ngPkgProject.build()
+          .then(() => {
+            obs.next({ success: true });
+            obs.complete();
+          })
+          .catch(e => obs.error(e));
+      }
     });
   }
 

packages/angular_devkit/build_ng_packagr/src/build/index.ts

@@ -10,6 +10,11 @@
     "tsConfig": {
       "type": "string",
       "description": "The file path of the TypeScript configuration file."
+    },
+    "watch": {
+      "type": "boolean",
+      "description": "Run build when files change.",
+      "default": false
     }
   },
   "additionalProperties": false,