Add support for specifying external helpers to avoid patching SWC

[xand3r40r93]

Currently, in order to enable externalHelpers for legacy decorators in SWC, users need to manually patch swc.transformFile. It would be helpful if tsup provided a way to specify this option without requiring modifications to SWC itself.

Example workaround:

const transformFile = swc.transformFile;
swc.transformFile = (filePath, options) => {
  if (options?.jsc?.transform?.legacyDecorator) options.jsc.externalHelpers = true;
  return transformFile.call(this, filePath, options);
};

Proposed solution:

Introduce an option in tsup to allow enabling externalHelpers when using decorators, eliminating the need for manual patches.

[Romakita]

Almost the issue related to swc configuration:
#1104

[melroy89]

To be honest.. If something goes wrong in my code.. Instead of showing me the correct error message, I will get:

node:internal/modules/run_main:123
    triggerUncaughtException(
    ^

Error [ERR_MODULE_NOT_FOUND]: Cannot find package '@swc/helpers' imported from /home/melroy/my/project/path/dist/index.js
Did you mean to import "@swc/helpers/esm/_extends.js"?
    at Object.getPackageJSONURL (node:internal/modules/package_json_reader:266:9)
    at packageResolve (node:internal/modules/esm/resolve:767:81)
    at moduleResolve (node:internal/modules/esm/resolve:853:18)
    at defaultResolve (node:internal/modules/esm/resolve:983:11)
    at #cachedDefaultResolve (node:internal/modules/esm/loader:731:20)
    at ModuleLoader.resolve (node:internal/modules/esm/loader:708:38)
    at ModuleLoader.getModuleJobForImport (node:internal/modules/esm/loader:310:38)
    at ModuleJob._link (node:internal/modules/esm/module_job:183:49) {
  code: 'ERR_MODULE_NOT_FOUND'
}

I'm using tsup with esm..

tsup.config.ts config looks like this:

import { defineConfig, type Options } from 'tsup'

export default defineConfig((options: Options) => ({
  entry: ['src/**/*'],
  clean: true,
  format: ['esm'],
  ...options
}))

I'm using pnpm.. I believe @swc/helpers needs to be added to the package dependency explicitly or did I miss something in my setup?

Currently I only have tsup as my devDepedencies in my package.json file. Nothing regarding any swc package.

Does the tsup project need to add @swc/helpers to your peer deps? Or.. maybe this helper is not working with esm!? I have no clue anymore.

[melroy89]

Currently I only have tsup as my devDepedencies in my package.json file. Nothing regarding any swc package.

Does the tsup project need to add @swc/helpers to your peer deps? Or.. maybe this helper is not working with esm!? I have no clue anymore.

So I notice the problem came from another package (since I'm using a monorepo with multiple packages with pnpm). I just add @swc/helpers dev package to this second package. Which resolved the issue, in case somebody else might have this issue with tsup.