From 72a7bc0d225d75560c30f295e0a2a0b5ff5802d9 Mon Sep 17 00:00:00 2001
From: Alan Agius <alan.agius4@gmail.com>
Date: Fri, 21 May 2021 13:33:22 +0200
Subject: [PATCH] perf(@angular-devkit/build-angular): disable CSS optimization
 parallelism for components styles

Since we rely on child compilations to compile components CSS, using the `parallel` option will cause a significant overhead because each compilation will need to spawn a worker, in this mode the worker limit is not be honored because `css-minimizer-webpack-plugin` spawn and calulators workers during the optimization phase of a compilation and not globally per instance hence causes OOM because a large number of workers to be spawned simultaneously.

Closes #20883

(cherry picked from commit 1ab2ef9a3f3d416241db9f34e285da265d9cc27f)
---
 .../src/webpack/configs/common.ts             | 24 ----------
 .../src/webpack/configs/styles.ts             | 44 +++++++++++++++++++
 2 files changed, 44 insertions(+), 24 deletions(-)

diff --git a/packages/angular_devkit/build_angular/src/webpack/configs/common.ts b/packages/angular_devkit/build_angular/src/webpack/configs/common.ts
index 851f566192b2..774e5c50b45b 100644
--- a/packages/angular_devkit/build_angular/src/webpack/configs/common.ts
+++ b/packages/angular_devkit/build_angular/src/webpack/configs/common.ts
@@ -313,30 +313,6 @@ export function getCommonConfig(wco: WebpackConfigOptions): Configuration {
   }
 
   const extraMinimizers = [];
-  if (stylesOptimization.minify) {
-    const CssMinimizerPlugin = require('css-minimizer-webpack-plugin');
-    extraMinimizers.push(
-      new CssMinimizerPlugin({
-        // component styles retain their original file name
-        test: /\.(?:css|scss|sass|less|styl)$/,
-        parallel: maxWorkers,
-        minify: [CssMinimizerPlugin.cssnanoMinify],
-        minimizerOptions: {
-          preset: [
-            'default',
-            {
-              // Disable SVG optimizations, as this can cause optimizations which are not compatible in all browsers.
-              svgo: false,
-              // Disable `calc` optimizations, due to several issues. #16910, #16875, #17890
-              calc: false,
-              // Disable CSS rules sorted due to several issues #20693, https://github.com/ionic-team/ionic-framework/issues/23266 and https://github.com/cssnano/cssnano/issues/1054
-              cssDeclarationSorter: false,
-            },
-          ],
-        },
-      }),
-    );
-  }
 
   if (scriptsOptimization) {
     const TerserPlugin = require('terser-webpack-plugin');
diff --git a/packages/angular_devkit/build_angular/src/webpack/configs/styles.ts b/packages/angular_devkit/build_angular/src/webpack/configs/styles.ts
index 918bb5f1eb82..7fd4acb089db 100644
--- a/packages/angular_devkit/build_angular/src/webpack/configs/styles.ts
+++ b/packages/angular_devkit/build_angular/src/webpack/configs/styles.ts
@@ -13,6 +13,7 @@ import { ExtraEntryPoint } from '../../browser/schema';
 import { SassWorkerImplementation } from '../../sass/sass-service';
 import { BuildBrowserFeatures } from '../../utils/build-browser-features';
 import { WebpackConfigOptions } from '../../utils/build-options';
+import { maxWorkers } from '../../utils/environment-options';
 import {
   AnyComponentStyleBudgetChecker,
   PostcssCliResources,
@@ -402,11 +403,54 @@ export function getStylesConfig(wco: WebpackConfigOptions): webpack.Configuratio
     });
   }
 
+  const extraMinimizers = [];
+  if (buildOptions.optimization.styles.minify) {
+    const CssMinimizerPlugin = require('css-minimizer-webpack-plugin');
+    const minimizerOptions = {
+      preset: [
+        'default',
+        {
+          // Disable SVG optimizations, as this can cause optimizations which are not compatible in all browsers.
+          svgo: false,
+          // Disable `calc` optimizations, due to several issues. #16910, #16875, #17890
+          calc: false,
+          // Disable CSS rules sorted due to several issues #20693, https://github.com/ionic-team/ionic-framework/issues/23266 and https://github.com/cssnano/cssnano/issues/1054
+          cssDeclarationSorter: false,
+        },
+      ],
+    };
+
+    const globalBundlesRegExp = new RegExp(
+      `^(${Object.keys(entryPoints).join('|')})(\.[0-9a-f]{20})?.css$`,
+    );
+
+    extraMinimizers.push(
+      new CssMinimizerPlugin({
+        // Component styles retain their original file name
+        test: /\.(?:css|scss|sass|less|styl)$/,
+        parallel: false,
+        exclude: globalBundlesRegExp,
+        minify: [CssMinimizerPlugin.cssnanoMinify],
+        minimizerOptions,
+      }),
+      new CssMinimizerPlugin({
+        test: /\.css$/,
+        include: globalBundlesRegExp,
+        parallel: maxWorkers,
+        minify: [CssMinimizerPlugin.cssnanoMinify],
+        minimizerOptions,
+      }),
+    );
+  }
+
   return {
     entry: entryPoints,
     module: {
       rules: [...fileLanguageRules, ...inlineLanguageRules],
     },
+    optimization: {
+      minimizer: extraMinimizers,
+    },
     plugins: extraPlugins,
   };
 }