fix(build): do not copy polyfills to the dist OT unless building es5

Prior to this change Stencil will copy polyfills to the `dist` output
target whether or not the user has indicated they'll be necessary.

The polyfills comprise two things: copying the polyfills themselves into
the 'loader' path, and adding code to the lazy-loader entry points which
loads those polyfills. Instead of just assuming that the user wants
this, we now gate this behavior on whether `buildEs5` is set on the
Stencil configuration.

fixes #5416
STENCIL-1288

src/compiler/output-targets/dist-lazy/generate-esm.ts

@@ -58,14 +58,25 @@ export const generateEsm = async (
         '',
       );
 
-      await copyPolyfills(config, compilerCtx, esmOutputs);
+      if (config.buildEs5) {
+        await copyPolyfills(config, compilerCtx, esmOutputs);
+      }
       await generateShortcuts(config, compilerCtx, outputTargets, output);
     }
   }
 
   return { name: 'esm', buildCtx };
 };
 
+/**
+ * Copy polyfills from `$INSTALL_DIR/internal/client/polyfills` to the lazy
+ * loader output directory where $INSTALL_DIR is the directory in which the
+ * `@stencil/core` package is installed.
+ *
+ * @param config a validated Stencil configuration
+ * @param compilerCtx the current compiler context
+ * @param outputTargets dist-lazy output targets
+ */
 const copyPolyfills = async (
   config: d.ValidatedConfig,
   compilerCtx: d.CompilerCtx,

src/compiler/output-targets/output-lazy-loader.ts

@@ -44,26 +44,33 @@ const generateLoader = async (
     2,
   );
 
+  const polyfillsEntryPoint = join(es2017Dir, 'polyfills/index.js');
+  const polyfillsExport = `export * from '${relative(loaderPath, polyfillsEntryPoint)}';`;
+
   const es5EntryPoint = join(es5Dir, 'loader.js');
+  const indexContent = filterAndJoin([
+    generatePreamble(config),
+    es5HtmlElement,
+    config.buildEs5 ? polyfillsExport : null,
+    `export * from '${relative(loaderPath, es5EntryPoint)}';`,
+  ]);
+
   const es2017EntryPoint = join(es2017Dir, 'loader.js');
-  const polyfillsEntryPoint = join(es2017Dir, 'polyfills/index.js');
+  const indexES2017Content = filterAndJoin([
+    generatePreamble(config),
+    config.buildEs5 ? polyfillsExport : null,
+    `export * from '${relative(loaderPath, es2017EntryPoint)}';`,
+  ]);
+
   const cjsEntryPoint = join(cjsDir, 'loader.cjs.js');
-  const polyfillsExport = `export * from '${relative(loaderPath, polyfillsEntryPoint)}';`;
-  const indexContent = `${generatePreamble(config)}
-${es5HtmlElement}
-${polyfillsExport}
-export * from '${relative(loaderPath, es5EntryPoint)}';
-`;
-  const indexES2017Content = `${generatePreamble(config)}
-${polyfillsExport}
-export * from '${relative(loaderPath, es2017EntryPoint)}';
-`;
-  const indexCjsContent = `${generatePreamble(config)}
-module.exports = require('${relative(loaderPath, cjsEntryPoint)}');
-module.exports.applyPolyfills = function() { return Promise.resolve() };
-`;
+  const indexCjsContent = filterAndJoin([
+    generatePreamble(config),
+    `module.exports = require('${relative(loaderPath, cjsEntryPoint)}');`,
+    config.buildEs5 ? `module.exports.applyPolyfills = function() { return Promise.resolve() };` : null,
+  ]);
 
   const indexDtsPath = join(loaderPath, 'index.d.ts');
+
   await Promise.all([
     compilerCtx.fs.writeFile(join(loaderPath, 'package.json'), packageJsonContent),
     compilerCtx.fs.writeFile(join(loaderPath, 'index.d.ts'), generateIndexDts(indexDtsPath, outputTarget.componentDts)),
@@ -98,3 +105,18 @@ export declare function applyPolyfills(): Promise<void>;
 export declare function setNonce(nonce: string): void;
 `;
 };
+
+/**
+ * Given an array of 'parts' which can be assembled into a string 1) filter
+ * out any parts that are `null` and 2) join the remaining strings into a single
+ * output string
+ *
+ * @param parts an array of parts to filter and join
+ * @returns the joined string
+ */
+function filterAndJoin(parts: (string | null)[]): string {
+  return parts
+    .filter((part) => part !== null)
+    .join('\n')
+    .trim();
+}

src/compiler/output-targets/test/output-lazy-loader.spec.ts

@@ -0,0 +1,73 @@
+import type * as d from '@stencil/core/declarations';
+import { mockBuildCtx, mockCompilerCtx, mockCompilerSystem, mockValidatedConfig } from '@stencil/core/testing';
+import { DIST, resolve } from '@utils';
+
+import { validateDist } from '../../config/outputs/validate-dist';
+import { outputLazyLoader } from '../output-lazy-loader';
+
+function setup(configOverrides: Partial<d.ValidatedConfig> = {}) {
+  const sys = mockCompilerSystem();
+  const config: d.ValidatedConfig = mockValidatedConfig({
+    ...configOverrides,
+    configPath: '/testing-path',
+    buildAppCore: true,
+    namespace: 'TestApp',
+    outputTargets: [
+      {
+        type: DIST,
+        dir: 'my-test-dir',
+      },
+    ],
+    srcDir: '/src',
+    sys,
+  });
+
+  config.outputTargets = validateDist(config, config.outputTargets);
+
+  const compilerCtx = mockCompilerCtx(config);
+  const writeFileSpy = jest.spyOn(compilerCtx.fs, 'writeFile');
+  const buildCtx = mockBuildCtx(config, compilerCtx);
+
+  return { config, compilerCtx, buildCtx, writeFileSpy };
+}
+
+describe('Lazy Loader Output Target', () => {
+  let config: d.ValidatedConfig;
+  let compilerCtx: d.CompilerCtx;
+  let writeFileSpy: jest.SpyInstance;
+
+  afterEach(() => {
+    writeFileSpy.mockRestore();
+  });
+
+  it('should write code for initializing polyfills when buildEs5=true', async () => {
+    ({ config, compilerCtx, writeFileSpy } = setup({ buildEs5: true }));
+    await outputLazyLoader(config, compilerCtx);
+
+    const expectedIndexOutput = `export * from '../esm/polyfills/index.js';
+export * from '../esm-es5/loader.js';`;
+    expect(writeFileSpy).toHaveBeenCalledWith(resolve('/my-test-dir/loader/index.js'), expectedIndexOutput);
+
+    const expectedCjsIndexOutput = `module.exports = require('../cjs/loader.cjs.js');
+module.exports.applyPolyfills = function() { return Promise.resolve() };`;
+    expect(writeFileSpy).toHaveBeenCalledWith(resolve('/my-test-dir/loader/index.cjs.js'), expectedCjsIndexOutput);
+
+    const expectedES2017Output = `export * from '../esm/polyfills/index.js';
+export * from '../esm/loader.js';`;
+    expect(writeFileSpy).toHaveBeenCalledWith(resolve('/my-test-dir/loader/index.es2017.js'), expectedES2017Output);
+  });
+
+  it('should exclude polyfill code when buildEs5=false', async () => {
+    ({ config, compilerCtx, writeFileSpy } = setup({ buildEs5: false }));
+    await outputLazyLoader(config, compilerCtx);
+
+    const expectedIndexOutput = `export * from '../esm/loader.js';`;
+    expect(writeFileSpy).toHaveBeenCalledWith(resolve('/my-test-dir/loader/index.js'), expectedIndexOutput);
+
+    const expectedCjsIndexOutput = `module.exports = require('../cjs/loader.cjs.js');`;
+    expect(writeFileSpy).toHaveBeenCalledWith(resolve('/my-test-dir/loader/index.cjs.js'), expectedCjsIndexOutput);
+
+    const expectedES2017Output = `export * from '../esm/loader.js';`;
+    expect(writeFileSpy).toHaveBeenCalledWith(resolve('/my-test-dir/loader/index.es2017.js'), expectedES2017Output);
+  });
+});