Make it possible to disable code splitting

[tats-u]

Clear and concise description of the problem

tsup can disable code splitting by the following config:

import { defineConfig } from "tsup";

export default defineConfig({
  entry: ["./src"],
  format: "esm",
  splitting: false, // !!!!!! HERE !!!!!
  dts: true,
  target: "es2021",
});

However, tsdown doesn't have such a splitting property.
Disabling code splitting improves readability and analyzability of output JS code.

tsup's doc: https://tsup.egoist.dev/#code-splitting

Suggested solution

Support splitting property

Alternative

Use tsup instead of tsdown. tsup has already been able to disable splitting.

Additional context

I tried tsdown in my packages in https://github.com/tats-u/markdown-cjk-friendly/, but gave up due to the lack of this feature.

Validations

• Follow our Code of Conduct
• Read the Contributing Guide.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[sxzz]

Now unsupported because of Rolldown

[tats-u]

I see.

[tats-u]

I found it's not supported in Rollup either.

rollup/rollup#2756

[sxzz]

Is there any use cases that need disabling code splitting?

[tats-u]

remarkjs/remark#1422

It looks like one of the main maintainers of remark prefer to keep .ts source and built .d.ts/.js 1:1 (one pair of .d.ts/.js per .ts).
He wants library authors to keep the published package source easily-analyzable/debuggable.

[tats-u]

I personally prefer to bundle source files into single pair of .d.ts and .js.

By this, a JS runtime has only to open and parse just one JS file.

[sxzz]

Maybe preserveModules is more like you needed (but Rolldown haven't implement preserveModules yet)

[tats-u]

Is it a Rollup's option? I can't try it today because tsup is basically esbuild-powered. I couldn't find such an option in tsup's website.

[lishaduck]

Is it a Rollup's option?

Yeah, it's this: https://rollupjs.org/configuration-options/#output-preservemodules

[tats-u]

I googled it and it looks like what I've wanted. However I can't try it today unfortunately because I don't use Vite or Rollup to build my libraries.

[pcfreak30]

Im assuming this would prevent distX.js files (x = number) from being generated? preservemodules doesn't seem to be in tsdown.

[TheAlexLichter]

As @sxzz mentioned, it isn't available in Rolldown yet.

[sxzz]

Track rolldown/rolldown#4437

[sxzz]

As mentioned in rolldown/rolldown#4437, unbundle mode will be landed in the next release.

[sxzz]

The documentation has been published: https://tsdown.dev/options/unbundle

[tats-u]

I'll try it in https://github.com/tats-u/markdown-cjk-friendly later. Thank you.

[tats-u]

The single-file bundle mode (just code splitting disabled) seems to be missing... (I don't use it for a while though)
I think tsup's splitting: false is the single-file bundle mode.

[sxzz]

splitting: false is not fully supported at this time. As a workaround, you can specify a single entry point and enable outputOptions.inlineDynamicImports to approximate the desired behavior.

Also track rolldown/rolldown#4437 and rolldown/rolldown#3986 for future updates!

[sxzz]

BTW, I have carefully reviewed your requirement (to generate one pair of .js and .d.ts files for each .ts file), and I can confirm that the unbundle feature already meets your needs.

Additionally, the issue title does not accurately reflect the proposed solution. To clarify: we currently recommend enabling the unbundle option to achieve the behavior of generating one pair of .js and .d.ts files for each .ts file. For information on fully disabling code splitting, please refer to rolldown/rolldown#3986 (comment).