[Bug]: Adding js extensions for index resolution

[Timeless0911]

Details

input

// folder/index.ts
export const folder = 'folder';

// index.ts
import { folder } from './folder';

export const text = folder;

Output

import * as __WEBPACK_EXTERNAL_MODULE__folder_js__ from "./folder.js";
const src_text = __WEBPACK_EXTERNAL_MODULE__folder_js__.folder;
export { src_text as text };

rslib/packages/core/src/config.ts

Lines 693 to 721 in 600937c

	if (data.contextInfo.issuer) {
	// Node.js ECMAScript module loader does no extension searching.
	// Add a file extension according to autoExtension config
	// when data.request is a relative path and do not have an extension.
	// If data.request already have an extension, we replace it with new extension
	// This may result in a change in semantics,
	// user should use copy to keep origin file or use another separate entry to deal this
	let request = data.request;
	if (request[0] === '.') {
	if (extname(request)) {
	if (JS_EXTENSIONS_PATTERN.test(request)) {
	request = request.replace(/\.[^.]+$/, jsExtension);
	} else {
	// If it does not match jsExtensionsPattern, we should do nothing, eg: ./foo.png
	return callback();
	}
	} else {
	request = `${request}${jsExtension}`;
	}
	}
	return callback(null, request);
	}
	callback();
	},
	],
	},
	};
	};

In line 710, we directly add a jsExtension in bundless mode to make bundleless esm outputs work.

rslib/packages/core/src/config.ts

Line 710 in 600937c

request = `${request}${jsExtension}`;

• Modern.js Module forces user to add /index in bundleless mode.
• Tsup do not add js extensions automatically, it forces user to write extensions in sourcecode

Index resolution is a standard behaviour which takes effects in both nodejs and ts, and Rslib now use default resolve.mainFiles: ['index'] of Rspack.

We should handle when ./folder/index.ts and ./folder.ts exists at the same time, there may also be .ts, .tsx, .jsx existing.

[fi3ework]

Feeling like we really need getResolve param in function external type.