fix: use CommonJS import for webpack-sources (#314)

webpack-sources is a CommonJS module and requires default import syntax
in ESM. This fixes the package import to work with Node's ESM loader.

Fixes #313

Author: dcsaszar

src/hooks.ts

@@ -5,13 +5,15 @@ import { SyncWaterfallHook } from 'tapable';
 import type { Compiler, Module, Compilation, LoaderContext } from 'webpack';
 // Note: This was the old delcaration. It appears to be Webpack v3 compat.
 // const { RawSource } = (webpack as any).sources || require('webpack-sources');
-import { RawSource } from 'webpack-sources';
+import webpackSources from 'webpack-sources';
 
 import type { EmitCountMap, InternalOptions } from './index.js';
 
 import type { CompilationAsset, FileDescriptor } from './helpers.js';
 import { generateManifest, reduceAssets, reduceChunk, transformFiles } from './helpers.js';
 
+const { RawSource } = webpackSources;
+
 interface BeforeRunHookArgs {
   emitCountMap: EmitCountMap;
   manifestFileName: string;

test/integration/usage.ts

@@ -0,0 +1,14 @@
+import { execSync } from 'node:child_process';
+
+import test from '../helpers/ava-compat';
+
+// make implicit dependency explicit:
+import '../../src/index';
+
+test.before(() => execSync('pnpm build'));
+
+test('can be used as documented', (t) => {
+  const readmeCode = "import { WebpackManifestPlugin } from 'webpack-manifest-plugin'";
+
+  t.deepEqual(execSync(`node -e "${readmeCode}"`, { encoding: 'utf-8' }), '');
+});