fix(@ngtools/webpack): improve resource loader caching

This change reduces the complexity of the component resource loader caching as well as moves the caching check earlier in the workflow to further minimize the amount of processing needed.

(cherry picked from commit f0abae5)

Author: clydin

packages/ngtools/webpack/src/resource_loader.ts

@@ -22,39 +22,39 @@ const SingleEntryPlugin = require('webpack/lib/SingleEntryPlugin');
 interface CompilationOutput {
   outputName: string;
   source: string;
+  success: boolean;
 }
 
 export class WebpackResourceLoader {
   private _parentCompilation: any;
-  private _context = '';
   private _fileDependencies = new Map<string, Set<string>>();
   private _reverseDependencies = new Map<string, Set<string>>();
-  private _cachedSources = new Map<string, string>();
-  private _cachedEvaluatedSources = new Map<string, RawSource>();
 
-  public changedFiles?: Iterable<string>;
+  private cache = new Map<string, string>();
+  private modifiedResources = new Set<string>();
 
-  update(parentCompilation: import('webpack').compilation.Compilation, changedFiles?: Iterable<string>) {
+  update(
+    parentCompilation: import('webpack').compilation.Compilation,
+    changedFiles?: Iterable<string>,
+  ) {
     this._parentCompilation = parentCompilation;
-    this._context = parentCompilation.context;
 
-    // Update changed file list
-    this.changedFiles = changedFiles;
+    // Update resource cache and modified resources
+    this.modifiedResources.clear();
+    if (changedFiles) {
+      for (const changedFile of changedFiles) {
+        for (const affectedResource of this.getAffectedResources(changedFile)) {
+          this.cache.delete(normalizePath(affectedResource));
+          this.modifiedResources.add(affectedResource);
+        }
+      }
+    } else {
+      this.cache.clear();
+    }
   }
 
   getModifiedResourceFiles() {
-    const modifiedResources = new Set<string>();
-    if (!this.changedFiles) {
-      return modifiedResources;
-    }
-
-    for (const changedFile of this.changedFiles) {
-      this.getAffectedResources(
-        changedFile,
-      ).forEach((affected: string) => modifiedResources.add(affected));
-    }
-
-    return modifiedResources;
+    return this.modifiedResources;
   }
 
   getResourceDependencies(filePath: string) {
@@ -70,7 +70,6 @@ export class WebpackResourceLoader {
   }
 
   private async _compile(filePath: string): Promise<CompilationOutput> {
-
     if (!this._parentCompilation) {
       throw new Error('WebpackResourceLoader cannot be used without parentCompilation');
     }
@@ -83,39 +82,25 @@ export class WebpackResourceLoader {
     }
 
     const outputOptions = { filename: filePath };
-    const relativePath = path.relative(this._context || '', filePath);
+    const context = this._parentCompilation.context;
+    const relativePath = path.relative(context || '', filePath);
     const childCompiler = this._parentCompilation.createChildCompiler(relativePath, outputOptions);
-    childCompiler.context = this._context;
+    childCompiler.context = context;
 
     new NodeTemplatePlugin(outputOptions).apply(childCompiler);
     new NodeTargetPlugin().apply(childCompiler);
-    new SingleEntryPlugin(this._context, filePath).apply(childCompiler);
+    new SingleEntryPlugin(context, filePath).apply(childCompiler);
     new LibraryTemplatePlugin('resource', 'var').apply(childCompiler);
 
     childCompiler.hooks.thisCompilation.tap('ngtools-webpack', (compilation: any) => {
-      compilation.hooks.additionalAssets.tapAsync('ngtools-webpack',
-      (callback: (err?: Error) => void) => {
-        if (this._cachedEvaluatedSources.has(compilation.fullHash)) {
-          const cachedEvaluatedSource = this._cachedEvaluatedSources.get(compilation.fullHash);
-          compilation.assets[filePath] = cachedEvaluatedSource;
-          callback();
-
+      compilation.hooks.additionalAssets.tapPromise('ngtools-webpack', async () => {
+        const asset = compilation.assets[filePath];
+        if (!asset) {
           return;
         }
 
-        const asset = compilation.assets[filePath];
-        if (asset) {
-          this._evaluate({ outputName: filePath, source: asset.source() })
-            .then(output => {
-              const evaluatedSource = new RawSource(output);
-              this._cachedEvaluatedSources.set(compilation.fullHash, evaluatedSource);
-              compilation.assets[filePath] = evaluatedSource;
-              callback();
-            })
-            .catch(err => callback(err));
-        } else {
-          callback();
-        }
+        const output = await this._evaluate(filePath, asset.source());
+        compilation.assets[filePath] = new RawSource(output);
       });
     });
 
@@ -139,13 +124,13 @@ export class WebpackResourceLoader {
       this._parentCompilation.errors.push(...errors);
     }
 
-    Object.keys(childCompilation.assets).forEach(assetName => {
+    Object.keys(childCompilation.assets).forEach((assetName) => {
       // Add all new assets to the parent compilation, with the exception of
       // the file we're loading and its sourcemap.
       if (
-        assetName !== filePath
-        && assetName !== `${filePath}.map`
-        && this._parentCompilation.assets[assetName] == undefined
+        assetName !== filePath &&
+        assetName !== `${filePath}.map` &&
+        this._parentCompilation.assets[assetName] == undefined
       ) {
         this._parentCompilation.assets[assetName] = childCompilation.assets[assetName];
       }
@@ -163,34 +148,40 @@ export class WebpackResourceLoader {
       }
     }
 
-    const compilationHash = childCompilation.fullHash;
-    const maybeSource = this._cachedSources.get(compilationHash);
-    if (maybeSource) {
-      return { outputName: filePath, source: maybeSource };
-    } else {
-      const source = childCompilation.assets[filePath].source();
-      this._cachedSources.set(compilationHash, source);
+    const finalOutput = childCompilation.assets[filePath]?.source();
 
-      return { outputName: filePath, source };
-    }
+    return { outputName: filePath, source: finalOutput ?? '', success: !errors?.length };
   }
 
-  private async _evaluate({ outputName, source }: CompilationOutput): Promise<string> {
-      // Evaluate code
-      const context: { resource?: string | { default?: string } } = {};
-      vm.runInNewContext(source, context, { filename: outputName });
+  private async _evaluate(filename: string, source: string): Promise<string> {
+    // Evaluate code
+    const context: { resource?: string | { default?: string } } = {};
+    vm.runInNewContext(source, context, { filename });
 
-      if (typeof context.resource === 'string') {
-        return context.resource;
-      } else if (typeof context.resource?.default === 'string') {
-        return context.resource.default;
-      }
+    if (typeof context.resource === 'string') {
+      return context.resource;
+    } else if (typeof context.resource?.default === 'string') {
+      return context.resource.default;
+    }
 
-      throw new Error(`The loader "${outputName}" didn't return a string.`);
+    throw new Error(`The loader "${filename}" didn't return a string.`);
   }
 
-  get(filePath: string): Promise<string> {
-    return this._compile(filePath)
-      .then((result: CompilationOutput) => result.source);
+  async get(filePath: string): Promise<string> {
+    const normalizedFile = normalizePath(filePath);
+    let data = this.cache.get(normalizedFile);
+
+    if (data === undefined) {
+      // cache miss so compile resource
+      const compilationResult = await this._compile(filePath);
+      data = compilationResult.source;
+
+      // Only cache if compilation was successful
+      if (compilationResult.success) {
+        this.cache.set(normalizedFile, data);
+      }
+    }
+
+    return data;
   }
 }