ensure plugins don't interact negatively with clean-webpack-plugin

packages/kbn-optimizer/src/common/bundle.ts

@@ -81,7 +81,7 @@ export class Bundle {
     this.banner = spec.banner;
     this.pageLoadAssetSizeLimit = spec.pageLoadAssetSizeLimit;
 
-    this.cache = new BundleCache(Path.resolve(this.outputDir, '.kbn-optimizer-cache'));
+    this.cache = new BundleCache(this.outputDir);
   }
 
   /**

packages/kbn-optimizer/src/common/bundle_cache.test.ts

@@ -25,12 +25,12 @@ beforeEach(() => {
 });
 
 it(`doesn't complain if files are not on disk`, () => {
-  const cache = new BundleCache('/foo/bar.json');
+  const cache = new BundleCache('/foo');
   expect(cache.get()).toEqual({});
 });
 
 it(`updates files on disk when calling set()`, () => {
-  const cache = new BundleCache('/foo/bar.json');
+  const cache = new BundleCache('/foo');
   cache.set(SOME_STATE);
   expect(mockReadFileSync).not.toHaveBeenCalled();
   expect(mockMkdirSync.mock.calls).toMatchInlineSnapshot(`
@@ -46,7 +46,7 @@ it(`updates files on disk when calling set()`, () => {
   expect(mockWriteFileSync.mock.calls).toMatchInlineSnapshot(`
     Array [
       Array [
-        "/foo/bar.json",
+        "/foo/.kbn-optimizer-cache",
         "{
       \\"cacheKey\\": \\"abc\\",
       \\"files\\": [
@@ -61,7 +61,7 @@ it(`updates files on disk when calling set()`, () => {
 });
 
 it(`serves updated state from memory`, () => {
-  const cache = new BundleCache('/foo/bar.json');
+  const cache = new BundleCache('/foo');
   cache.set(SOME_STATE);
   jest.clearAllMocks();
 
@@ -72,7 +72,7 @@ it(`serves updated state from memory`, () => {
 });
 
 it('reads state from disk on get() after refresh()', () => {
-  const cache = new BundleCache('/foo/bar.json');
+  const cache = new BundleCache('/foo');
   cache.set(SOME_STATE);
   cache.refresh();
   jest.clearAllMocks();
@@ -83,15 +83,15 @@ it('reads state from disk on get() after refresh()', () => {
   expect(mockReadFileSync.mock.calls).toMatchInlineSnapshot(`
     Array [
       Array [
-        "/foo/bar.json",
+        "/foo/.kbn-optimizer-cache",
         "utf8",
       ],
     ]
   `);
 });
 
 it('provides accessors to specific state properties', () => {
-  const cache = new BundleCache('/foo/bar.json');
+  const cache = new BundleCache('/foo');
 
   expect(cache.getModuleCount()).toBe(undefined);
   expect(cache.getReferencedFiles()).toEqual(undefined);

packages/kbn-optimizer/src/common/bundle_cache.ts

@@ -9,6 +9,9 @@
 import Fs from 'fs';
 import Path from 'path';
 
+import webpack from 'webpack';
+import { RawSource } from 'webpack-sources';
+
 export interface State {
   optimizerCacheKey?: unknown;
   cacheKey?: unknown;
@@ -20,13 +23,17 @@ export interface State {
 
 const DEFAULT_STATE: State = {};
 const DEFAULT_STATE_JSON = JSON.stringify(DEFAULT_STATE);
+const CACHE_FILENAME = '.kbn-optimizer-cache';
 
 /**
  * Helper to read and update metadata for bundles.
  */
 export class BundleCache {
   private state: State | undefined = undefined;
-  constructor(private readonly path: string | false) {}
+  private readonly path: string | false;
+  constructor(outputDir: string | false) {
+    this.path = outputDir === false ? false : Path.resolve(outputDir, CACHE_FILENAME);
+  }
 
   refresh() {
     this.state = undefined;
@@ -63,6 +70,7 @@ export class BundleCache {
 
   set(updated: State) {
     this.state = updated;
+
     if (this.path) {
       const directory = Path.dirname(this.path);
       Fs.mkdirSync(directory, { recursive: true });
@@ -107,4 +115,16 @@ export class BundleCache {
       }
     }
   }
+
+  public writeWebpackAsset(compilation: webpack.compilation.Compilation) {
+    if (!this.path) {
+      return;
+    }
+
+    const source = new RawSource(JSON.stringify(this.state, null, 2));
+
+    // see https://github.com/jantimon/html-webpack-plugin/blob/33d69f49e6e9787796402715d1b9cd59f80b628f/index.js#L266
+    // @ts-expect-error undocumented, used to add assets to the output
+    compilation.emitAsset(CACHE_FILENAME, source);
+  }
 }

packages/kbn-optimizer/src/worker/emit_stats_plugin.ts

@@ -17,11 +17,18 @@ export class EmitStatsPlugin {
   constructor(private readonly bundle: Bundle) {}
 
   public apply(compiler: webpack.Compiler) {
-    compiler.hooks.done.tap('EmitStatsPlugin', (stats) => {
-      Fs.writeFileSync(
-        Path.resolve(this.bundle.outputDir, 'stats.json'),
-        JSON.stringify(stats.toJson())
-      );
-    });
+    compiler.hooks.done.tap(
+      {
+        name: 'EmitStatsPlugin',
+        // run at the very end, ensure that it's after clean-webpack-plugin
+        stage: 10,
+      },
+      (stats) => {
+        Fs.writeFileSync(
+          Path.resolve(this.bundle.outputDir, 'stats.json'),
+          JSON.stringify(stats.toJson())
+        );
+      }
+    );
   }
 }

packages/kbn-optimizer/src/worker/populate_bundle_cache_plugin.ts

@@ -123,6 +123,9 @@ export class PopulateBundleCachePlugin {
           workUnits,
           files,
         });
+
+        // write the cache to the compilation so that it isn't cleaned by clean-webpack-plugin
+        bundle.cache.writeWebpackAsset(compilation);
       }
     );
   }