refactor(@angular-devkit/build-angular): gate Ivy-only plugin behind feature flag

The new Ivy Webpack plugin is considered experimental and can only be used by enabling the `NG_BUILD_IVY_EXPERIMENTAL` environment variable.

Author: clydin

.circleci/config.yml

@@ -199,6 +199,14 @@ jobs:
       - run:
           name: Execute CLI E2E Tests
           command: PATH=~/.npm-global/bin:$PATH node ./tests/legacy-cli/run_e2e --nb-shards=${CIRCLE_NODE_TOTAL} --shard=${CIRCLE_NODE_INDEX} <<# parameters.ve >>--ve<</ parameters.ve >> <<# parameters.snapshots >>--ng-snapshots<</ parameters.snapshots >> --tmpdir=/mnt/ramdisk
+      - unless:
+          condition: << parameters.ve >>
+          steps:
+            - run:
+                name: Execute CLI E2E Test Subset for Ivy-only plugin
+                command: |
+                  rm -rf /mnt/ramdisk/*test-project
+                  PATH=~/.npm-global/bin:$PATH NG_BUILD_IVY_EXPERIMENTAL=1 node ./tests/legacy-cli/run_e2e --nb-shards=${CIRCLE_NODE_TOTAL} --shard=${CIRCLE_NODE_INDEX} <<# parameters.snapshots >>--ng-snapshots<</ parameters.snapshots >> --tmpdir=/mnt/ramdisk --glob="{tests/basic/**,tests/build/**}"
 
   e2e-cli-node-10:
     executor:

packages/angular_devkit/build_angular/src/webpack/configs/typescript.ts

@@ -26,31 +26,48 @@ function canUseIvyPlugin(wco: WebpackConfigOptions): boolean {
     return false;
   }
 
-  // Allow fallback to legacy build system via environment variable ('NG_BUILD_IVY_LEGACY=1')
-  const flag = process.env['NG_BUILD_IVY_LEGACY'];
-  if (flag !== undefined && flag !== '0' && flag.toLowerCase() !== 'false') {
-    wco.logger.warn(
-      '"NG_BUILD_IVY_LEGACY" environment variable detected. Using legacy Ivy build system.',
-    );
-
+  // Allow new ivy build system via environment variable ('NG_BUILD_IVY_EXPERIMENTAL=1')
+  // TODO: Remove this section and adjust warnings below once the Ivy plugin is the default
+  const flag = process.env['NG_BUILD_IVY_EXPERIMENTAL'];
+  if (flag === undefined || flag === '0' || flag.toLowerCase() === 'false') {
     return false;
   }
 
+  // Allow fallback to legacy build system via environment variable ('NG_BUILD_IVY_LEGACY=1')
+  // TODO: Enable this section once the Ivy plugin is the default
+  // const flag = process.env['NG_BUILD_IVY_LEGACY'];
+  // if (flag !== undefined && flag !== '0' && flag.toLowerCase() !== 'false') {
+  //   wco.logger.warn(
+  //     '"NG_BUILD_IVY_LEGACY" environment variable detected. Using legacy Ivy build system.',
+  //   );
+
+  //   return false;
+  // }
+
   // Lazy modules option uses the deprecated string format for lazy routes which is not supported
   if (wco.buildOptions.lazyModules && wco.buildOptions.lazyModules.length > 0) {
     wco.logger.warn(
-      '"lazyModules" option is deprecated and not supported by the new Ivy build system. ' +
-        'Using legacy Ivy build system.'
+      '"lazyModules" option is deprecated and not supported by the experimental Ivy build system. ' +
+        'Using existing Ivy build system.'
     );
 
     return false;
   }
 
   // This pass relies on internals of the original plugin
   if (wco.buildOptions.experimentalRollupPass) {
+    wco.logger.warn(
+      'The experimental rollup pass is not supported by the experimental Ivy build system. ' +
+        'Using existing Ivy build system.'
+    );
+
     return false;
   }
 
+  wco.logger.warn(
+    '"NG_BUILD_IVY_EXPERIMENTAL" environment variable detected. Using experimental Ivy build system.',
+  );
+
   return true;
 }