feat(@ngtools/webpack): disable sourcefile cache when not in watch mode

Requires Webpack 4.23.0+

Author: clydin

packages/ngtools/webpack/src/angular_compiler_plugin.ts

@@ -585,7 +585,10 @@ export class AngularCompilerPlugin {
   }
 
   // Registration hook for webpack plugin.
-  apply(compiler: Compiler) {
+  apply(compiler: Compiler & { watchMode?: boolean }) {
+    // only present for webpack 4.23.0+, assume true otherwise
+    const watchMode = compiler.watchMode === undefined ? true : compiler.watchMode;
+
     // Decorate inputFileSystem to serve contents of CompilerHost.
     // Use decorated inputFileSystem in watchFileSystem.
     compiler.hooks.environment.tap('angular-compiler', () => {
@@ -629,6 +632,7 @@ export class AngularCompilerPlugin {
         this._compilerOptions,
         this._basePath,
         host,
+        watchMode,
       );
 
       // Create and set a new WebpackResourceLoader.

packages/ngtools/webpack/src/compiler_host.ts

@@ -45,6 +45,7 @@ export class WebpackCompilerHost implements ts.CompilerHost {
     private _options: ts.CompilerOptions,
     basePath: string,
     host: virtualFs.Host,
+    private readonly cacheSourceFiles: boolean,
   ) {
     this._syncHost = new virtualFs.SyncDelegateHost(host);
     this._memoryHost = new virtualFs.SyncDelegateHost(new virtualFs.SimpleMemoryHost());
@@ -260,7 +261,10 @@ export class WebpackCompilerHost implements ts.CompilerHost {
       const content = this.readFile(fileName);
       if (content !== undefined) {
         const sf = ts.createSourceFile(workaroundResolve(fileName), content, languageVersion, true);
-        this._sourceFileCache.set(p, sf);
+
+        if (this.cacheSourceFiles) {
+          this._sourceFileCache.set(p, sf);
+        }
 
         return sf;
       }

packages/ngtools/webpack/src/transformers/ast_helpers.ts

@@ -62,6 +62,7 @@ export function createTypescriptContext(content: string) {
     compilerOptions,
     basePath,
     new virtualFs.SimpleMemoryHost(),
+    false,
   );
 
   // Add a dummy file to host content.

packages/ngtools/webpack/src/type_checker.ts

@@ -53,6 +53,7 @@ export class TypeChecker {
       _compilerOptions,
       _basePath,
       host,
+      true,
     );
     // We don't set a async resource loader on the compiler host because we only support
     // html templates, which are the only ones that can throw errors, and those can be loaded