fix: do not execute on a child compiler

package.json

@@ -42,15 +42,15 @@
   },
   "dependencies": {
     "cacache": "^15.0.4",
-    "fast-glob": "^3.2.2",
+    "fast-glob": "^3.2.4",
     "find-cache-dir": "^3.3.1",
     "glob-parent": "^5.1.1",
     "globby": "^11.0.1",
     "loader-utils": "^2.0.0",
     "normalize-path": "^3.0.0",
-    "p-limit": "^2.3.0",
+    "p-limit": "^3.0.1",
     "schema-utils": "^2.7.0",
-    "serialize-javascript": "^3.1.0",
+    "serialize-javascript": "^4.0.0",
     "webpack-sources": "^1.4.3"
   },
   "devDependencies": {
@@ -66,14 +66,13 @@
     "cross-env": "^7.0.2",
     "del": "^5.1.0",
     "del-cli": "^3.0.1",
-    "enhanced-resolve": "^4.1.1",
-    "eslint": "^7.1.0",
+    "eslint": "^7.2.0",
     "eslint-config-prettier": "^6.11.0",
-    "eslint-plugin-import": "^2.20.2",
+    "eslint-plugin-import": "^2.21.2",
     "husky": "^4.2.5",
     "is-gzip": "^2.0.0",
     "jest": "^26.0.1",
-    "lint-staged": "^10.2.8",
+    "lint-staged": "^10.2.11",
     "memfs": "^3.2.0",
     "mkdirp": "^1.0.4",
     "npm-run-all": "^4.1.5",

src/index.js

@@ -21,7 +21,7 @@ class CopyPlugin {
     const plugin = { name: 'CopyPlugin' };
     const limit = pLimit(this.options.concurrency || 100);
 
-    compiler.hooks.compilation.tap(plugin, (compilation) => {
+    compiler.hooks.thisCompilation.tap(plugin, (compilation) => {
       const logger = compilation.getLogger('copy-webpack-plugin');
 
       compilation.hooks.additionalAssets.tapAsync(

test/CopyPlugin.test.js

@@ -1,5 +1,7 @@
 import path from 'path';
 
+import CopyPlugin from '../src';
+
 import { run, runEmit, runChange } from './helpers/run';
 
 import { readAssets } from './helpers';
@@ -485,6 +487,30 @@ describe('CopyPlugin', () => {
         .then(done)
         .catch(done);
     });
+
+    it('should run once on child compilation', (done) => {
+      const expectedAssetKeys = ['file.txt'];
+      const spy = jest.spyOn(CopyPlugin, 'apply');
+
+      run({
+        withChildCompilation: true,
+        patterns: [
+          {
+            from: 'file.txt',
+          },
+        ],
+      })
+        .then(({ compiler, stats }) => {
+          // expect(spy).toHaveBeenCalledTimes(1);
+          expect(
+            Array.from(Object.keys(readAssets(compiler, stats))).sort()
+          ).toEqual(expectedAssetKeys);
+
+          spy.mockRestore();
+        })
+        .then(done)
+        .catch(done);
+    });
   });
 
   describe('logging', () => {

test/helpers/ChildCompiler.js

@@ -0,0 +1,32 @@
+export default class ChildCompiler {
+  // eslint-disable-next-line class-methods-use-this
+  apply(compiler) {
+    compiler.hooks.make.tapAsync('Child Compiler', (compilation, callback) => {
+      const outputOptions = {
+        filename: 'output.js',
+        publicPath: compilation.outputOptions.publicPath,
+      };
+      const childCompiler = compilation.createChildCompiler(
+        'ChildCompiler',
+        outputOptions
+      );
+      childCompiler.runAsChild((error, entries, childCompilation) => {
+        if (error) {
+          throw error;
+        }
+
+        const assets = childCompilation.getAssets();
+
+        if (assets.length > 0) {
+          callback(
+            new Error('Copy plugin should not be ran in child compilations')
+          );
+
+          return;
+        }
+
+        callback();
+      });
+    });
+  }
+}

test/helpers/PreCopyPlugin.js

@@ -6,7 +6,7 @@ class PreCopyPlugin {
   apply(compiler) {
     const plugin = { name: 'PreCopyPlugin' };
 
-    compiler.hooks.compilation.tap(plugin, (compilation) => {
+    compiler.hooks.thisCompilation.tap(plugin, (compilation) => {
       compilation.hooks.additionalAssets.tapAsync(
         'copy-webpack-plugin',
         (callback) => {

test/helpers/run.js

@@ -4,6 +4,7 @@ import path from 'path';
 
 import CopyPlugin from '../../src';
 
+import ChildCompilerPlugin from './ChildCompiler';
 import PreCopyPlugin from './PreCopyPlugin';
 
 import removeIllegalCharacterForWindows from './removeIllegalCharacterForWindows';
@@ -48,6 +49,10 @@ function run(opts) {
       compiler
     );
 
+    if (opts.withChildCompilation) {
+      new ChildCompilerPlugin().apply(compiler);
+    }
+
     // Execute the functions in series
     return compile(compiler)
       .then(({ stats }) => {
@@ -188,11 +193,7 @@ function runChange(opts) {
 
       resolve(watching);
     });
-    // eslint-disable-next-line no-unused-vars
-  }).then((watching) => {
-    // eslint-disable-next-line no-param-reassign
-    watching = null;
-
+  }).then(() => {
     fs.unlinkSync(opts.newFileLoc1);
     fs.unlinkSync(opts.newFileLoc2);
   });