feat: added transformAll option

README.md

@@ -87,6 +87,7 @@ module.exports = {
 |            [`force`](#force)            |     `{Boolean}`      |                     `false`                     | Overwrites files already in `compilation.assets` (usually added by other plugins/loaders).                                                             |
 |         [`priority`](#priority)         |      `{Number}`      |                       `0`                       | Allows you to specify the copy priority.                                                                                                               |
 |        [`transform`](#transform)        |      `{Object}`      |                   `undefined`                   | Allows to modify the file contents. Enable `transform` caching. You can use `{ transform: {cache: { key: 'my-cache-key' }} }` to invalidate the cache. |
+|     [`transformAll`](#transformAll)     |     `{Function}`     |                   `undefined`                   | Allows you to modify the contents of multiple files and save the result to one file.                                                                   |
 | [`noErrorOnMissing`](#noerroronmissing) |     `{Boolean}`      |                     `false`                     | Doesn't generate an error on missing file(s).                                                                                                          |
 |             [`info`](#info)             | `{Object\|Function}` |                   `undefined`                   | Allows to add assets info.                                                                                                                             |
 
@@ -730,6 +731,45 @@ module.exports = {
 };
 ```
 
+#### `transformAll`
+
+Type: `Function`
+Default: `undefined`
+
+Allows you to modify the contents of multiple files and save the result to one file.
+
+> ℹ️ The `to` option must specify to a file. It is allowed to use only `[contenthash]` and `[fullhash]` template strings.
+
+**webpack.config.js**
+
+```js
+module.exports = {
+  plugins: [
+    new CopyPlugin({
+      patterns: [
+        {
+          from: "src/**/*.txt",
+          to: "dest/file.txt",
+          // The `assets` argument is an assets array for the pattern.from ("src/**/*.txt")
+          transformAll(assets) {
+            const result = assets.reduce((accumulator, asset) => {
+              // The asset content can be obtained from `asset.source` using `source` method.
+              // The asset content is a [`Buffer`](https://nodejs.org/api/buffer.html) object, it could be converted to a `String` to be processed using `content.toString()`
+              const content = asset.source.source();
+
+              accumulator = `${accumulator}${content}\n`;
+              return accumulator;
+            }, "");
+
+            return result;
+          },
+        },
+      ],
+    }),
+  ],
+};
+```
+
 ### `noErrorOnMissing`
 
 Type: `Boolean`

src/index.js

@@ -69,6 +69,27 @@ class CopyPlugin {
     });
   }
 
+  static getContentHash(compiler, compilation, source) {
+    const { outputOptions } = compilation;
+    const {
+      hashDigest,
+      hashDigestLength,
+      hashFunction,
+      hashSalt,
+    } = outputOptions;
+    const hash = compiler.webpack.util.createHash(hashFunction);
+
+    if (hashSalt) {
+      hash.update(hashSalt);
+    }
+
+    hash.update(source);
+
+    const fullContentHash = hash.digest(hashDigest);
+
+    return fullContentHash.slice(0, hashDigestLength);
+  }
+
   static async runPattern(
     compiler,
     compilation,
@@ -338,6 +359,7 @@ class CopyPlugin {
             filename,
             force: pattern.force,
             info,
+            toType,
           };
 
           // If this came from a glob or dir, add it to the file dependencies
@@ -526,23 +548,11 @@ class CopyPlugin {
               `interpolating template '${filename}' for '${sourceFilename}'...`
             );
 
-            const { outputOptions } = compilation;
-            const {
-              hashDigest,
-              hashDigestLength,
-              hashFunction,
-              hashSalt,
-            } = outputOptions;
-            const hash = compiler.webpack.util.createHash(hashFunction);
-
-            if (hashSalt) {
-              hash.update(hashSalt);
-            }
-
-            hash.update(result.source.source());
-
-            const fullContentHash = hash.digest(hashDigest);
-            const contentHash = fullContentHash.slice(0, hashDigestLength);
+            const contentHash = CopyPlugin.getContentHash(
+              compiler,
+              compilation,
+              result.source.source()
+            );
             const ext = path.extname(result.sourceFilename);
             const base = path.basename(result.sourceFilename);
             const name = base.slice(0, base.length - ext.length);
@@ -634,6 +644,86 @@ class CopyPlugin {
                 }
 
                 if (assets && assets.length > 0) {
+                  if (item.transformAll) {
+                    assets.sort((a, b) =>
+                      a.absoluteFilename > b.absoluteFilename
+                        ? 1
+                        : a.absoluteFilename < b.absoluteFilename
+                        ? -1
+                        : 0
+                    );
+
+                    const mergedEtag =
+                      assets.length === 1
+                        ? cache.getLazyHashedEtag(assets[0].source.source())
+                        : assets.reduce((accumulator, asset, ind) => {
+                            // eslint-disable-next-line no-param-reassign
+                            accumulator = cache.mergeEtags(
+                              ind === 1
+                                ? cache.getLazyHashedEtag(
+                                    accumulator.source.source()
+                                  )
+                                : accumulator,
+                              cache.getLazyHashedEtag(asset.source.source())
+                            );
+
+                            return accumulator;
+                          });
+
+                    const cacheKeys = `transformAll|${serialize({
+                      version,
+                      transform: item.transformAll,
+                    })}`;
+                    const eTag = cache.getLazyHashedEtag(mergedEtag);
+                    const cacheItem = cache.getItemCache(cacheKeys, eTag);
+                    let transformedAsset = await cacheItem.getPromise();
+
+                    if (!transformedAsset) {
+                      const { RawSource } = compiler.webpack.sources;
+
+                      transformedAsset = {};
+
+                      try {
+                        transformedAsset.source = new RawSource(
+                          await item.transformAll(assets)
+                        );
+                      } catch (error) {
+                        compilation.errors.push(error);
+
+                        return;
+                      }
+
+                      let mergedFilename = assets[0].filename;
+
+                      if (assets[0].toType === "template") {
+                        const mergedContentHash = CopyPlugin.getContentHash(
+                          compiler,
+                          compilation,
+                          transformedAsset.source.source()
+                        );
+                        const { contenthash: oldContentHash } = assets[0].info;
+                        const regExp = new RegExp(oldContentHash, "gi");
+
+                        mergedFilename = mergedFilename.replace(
+                          regExp,
+                          mergedContentHash
+                        );
+
+                        transformedAsset.info = {
+                          contenthash: mergedContentHash,
+                          fullhash: assets[0].info.fullhash,
+                        };
+                      }
+
+                      transformedAsset.force = item.force;
+                      transformedAsset.filename = mergedFilename;
+
+                      await cacheItem.storePromise(transformedAsset);
+                    }
+
+                    assets = [transformedAsset];
+                  }
+
                   const priority = item.priority || 0;
 
                   if (!assetMap.has(priority)) {

src/options.json

@@ -27,6 +27,9 @@
         "filter": {
           "instanceof": "Function"
         },
+        "transformAll": {
+          "instanceof": "Function"
+        },
         "toType": {
           "enum": ["dir", "file", "template"]
         },

test/__snapshots__/transformAll-option.test.js.snap

@@ -0,0 +1,21 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`cache should work with the "memory" cache: assets 1`] = `
+Object {
+  "file.txt": "new::directory/nested/deep-nested/deepnested.txt::directory/nested/nestedfile.txt::",
+}
+`;
+
+exports[`cache should work with the "memory" cache: assets 2`] = `
+Object {
+  "file.txt": "new::directory/nested/deep-nested/deepnested.txt::directory/nested/nestedfile.txt::",
+}
+`;
+
+exports[`cache should work with the "memory" cache: errors 1`] = `Array []`;
+
+exports[`cache should work with the "memory" cache: errors 2`] = `Array []`;
+
+exports[`cache should work with the "memory" cache: warnings 1`] = `Array []`;
+
+exports[`cache should work with the "memory" cache: warnings 2`] = `Array []`;