webpack: Accept a function for filename (#38989)

https://webpack.js.org/configuration/output/#outputfilename

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

types/webpack/index.d.ts

@@ -17,6 +17,7 @@
 //                 Kyle Uehlein <https://github.com/kuehlein>
 //                 Grgur Grisogono <https://github.com/grgur>
 //                 Rubens Pinheiro Gonçalves Cavalcante <https://github.com/rubenspgcavalcante>
+//                 Anders Kaseorg <https://github.com/andersk>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.3
 
@@ -153,7 +154,7 @@ declare namespace webpack {
         /** When used in tandem with output.library and output.libraryTarget, this option allows users to insert comments within the export wrapper. */
         auxiliaryComment?: string | AuxiliaryCommentObject;
         /** The filename of the entry chunk as relative path inside the output.path directory. */
-        filename?: string;
+        filename?: string | ((chunkData: ChunkData) => string);
         /** The filename of non-entry chunks as relative path inside the output.path directory. */
         chunkFilename?: string;
         /** Number of milliseconds before chunk request expires, defaults to 120,000. */
@@ -234,6 +235,10 @@ declare namespace webpack {
 
     type AuxiliaryCommentObject = { [P in LibraryTarget]: string };
 
+    interface ChunkData {
+        chunk: compilation.Chunk;
+    }
+
     interface Module {
         /** A array of applied pre loaders. */
         preLoaders?: RuleSetRule[];

types/webpack/webpack-tests.ts

@@ -989,3 +989,12 @@ webpack.Template.renderChunkModules(
   [],
   'a',
 );
+
+// https://webpack.js.org/configuration/output/#outputfilename
+configuration = {
+    output: {
+        filename: chunkData => {
+            return chunkData.chunk.name === 'main' ? '[name].js' : '[name]/[name].js';
+        },
+    },
+};