fix: concurrency writing assets (#484)

Author: evilebottnawi

src/index.js

@@ -38,7 +38,7 @@ class CopyPlugin {
           };
 
           try {
-            await Promise.all(
+            const assets = await Promise.all(
               this.patterns.map((pattern) =>
                 limit(async () => {
                   const patternAfterPreProcess = await preProcessPattern(
@@ -70,6 +70,54 @@ class CopyPlugin {
               )
             );
 
+            // Avoid writing assets inside `p-limit`, because it creates concurrency.
+            // It could potentially lead to an error - "Multiple assets emit different content to the same filename"
+            assets
+              .reduce((acc, val) => acc.concat(val), [])
+              .filter(Boolean)
+              .forEach((asset) => {
+                const {
+                  absoluteFrom,
+                  targetPath,
+                  webpackTo,
+                  source,
+                  force,
+                } = asset;
+
+                // For old version webpack 4
+                /* istanbul ignore if */
+                if (typeof compilation.emitAsset !== 'function') {
+                  // eslint-disable-next-line no-param-reassign
+                  compilation.assets[targetPath] = source;
+
+                  return;
+                }
+
+                if (compilation.getAsset(targetPath)) {
+                  if (force) {
+                    logger.log(
+                      `force updating '${webpackTo}' to compilation assets from '${absoluteFrom}'`
+                    );
+
+                    compilation.updateAsset(targetPath, source);
+
+                    return;
+                  }
+
+                  logger.log(
+                    `skipping '${webpackTo}', because it already exists`
+                  );
+
+                  return;
+                }
+
+                logger.log(
+                  `writing '${webpackTo}' to compilation assets from '${absoluteFrom}'`
+                );
+
+                compilation.emitAsset(targetPath, source);
+              });
+
             logger.debug('end to adding additional assets');
 
             callback();

src/postProcessPattern.js

@@ -7,7 +7,6 @@ import cacache from 'cacache';
 import serialize from 'serialize-javascript';
 import findCacheDir from 'find-cache-dir';
 import normalizePath from 'normalize-path';
-
 import { RawSource } from 'webpack-sources';
 
 import { version } from '../package.json';
@@ -148,36 +147,10 @@ export default async function postProcessPattern(globalRef, pattern, file) {
     );
   }
 
-  const targetPath = normalizePath(file.webpackTo);
-  const source = new RawSource(content);
-
-  // For old version webpack 4
-  /* istanbul ignore if */
-  if (typeof compilation.emitAsset !== 'function') {
-    compilation.assets[targetPath] = source;
-
-    return;
-  }
-
-  if (compilation.getAsset(targetPath)) {
-    if (pattern.force) {
-      logger.log(
-        `force updating '${file.webpackTo}' to compilation assets from '${file.absoluteFrom}'`
-      );
-
-      compilation.updateAsset(targetPath, source);
-
-      return;
-    }
-
-    logger.log(`skipping '${file.webpackTo}', because it already exists`);
-
-    return;
-  }
-
-  logger.log(
-    `writing '${file.webpackTo}' to compilation assets from '${file.absoluteFrom}'`
-  );
+  file.source = new RawSource(content);
+  file.targetPath = normalizePath(file.webpackTo);
+  file.force = pattern.force;
 
-  compilation.emitAsset(targetPath, source);
+  // eslint-disable-next-line consistent-return
+  return file;
 }