Roadmap

[yyx990803]

This roadmap outlines the high-level milestones that we intend to follow as we progress with Rolldown's development, but is subject to frequent adjustment as things go.

Milestone 1: Basic Bundling

• Goal: to be able to use Rolldown instead of esbuild to perform dependency pre-bundling in Vite.
• Key features needed:
  • Basic code splitting for multiple entrypoints
  • cjs / esm mixed bundling
  • Basic plugin support

Milestone 2: Advanced Bundling

• Goal: to be able to use Rolldown for production builds in Vite.
• Key features needed:
  • Treeshaking
  • Basic CLI & config file support ^{by @kazupon}
  • Source map ^@underfin
  • Chunk hashing ^@hyf0
  • Full Rollup plugin compatibility ^{WIP by @hyf0 & @underfin} Tracking issue
  • Advanced chunk splitting
  • Module Federation
  • Built-in CSS bundling

Milestone 3: Transform Features

• Goal: to be able to use Rolldown for all current esbuild usage in Vite.
• These features will be relying on oxc which is developed in parallel to Rolldown. We want these integrated in Rolldown so we can reuse the same AST as much as possible.
• Key features needed:
  • Built-in Typescript / JSX transform (via oxc)
  • Built-in minification (via oxc)
  • Syntax lowering (via oxc)

Milestone 4: Deeper Vite Integration

• Goal: improve Vite core performance by leveraging Rolldown
• Items here are mostly tentative!
  • Expose plugin container as a Rolldown API
  • Introduce Rust in Vite core, using Rolldown as dependency
  • Port perf-critical Vite internal plugins to Rust. This will be done pragmatically - we will need to consider the perf gain vs. the loss of iteration flexibility caused by moving from TS to Rust for each internal plugin. The candidate will be those that are relatively stable but will yield the most perf gains.
  • Port Vite's SSR transform (used in ssrLoadModule) to Rust, eliminate SSR externals
  • Full bundled mode in Vite (for cases with too many modules)

Side Features

Don't fit in a specific milestone but good to be tackled whenever possible

• WASM build ^{WIP by @Brooooooklyn}
• Playground
• Built-in profiling / build observability
• Opinionated, zero config TypeScript library bundling
• DTS generation + bundling (requires isolatedDeclarations)
• CSS processing by leveraging Lightning CSS.

[kazupon]

@yyx990803
I have a question.

I found out vite-compatible open source project called farm, which is implemented in Rust.
That is similar to rolldown's goals, does rolldown have any plans to collaborate?

https://github.com/farm-fe

[yyx990803]

The problem with Farm is that it is designed more like a complete build tool like Vite, instead of a lower-level bundler that supports it. This makes it difficult for us to envision a future where it can be integrated into applications using Vite today. We've talked to the author previously, I think there might be a chance to have him collaborate on Rolldown in the future.

[montoyaaguirre]

Congrats on the progress so far 💪

I remember that you addressed the lack of first party module federation support during your 2023 keynote "The State of Vite".
Will this be worked on during one of these 4 stages?

[yyx990803]

Yes, forgot to add it to this roadmap! (just edited)

[zackarychapple]

Very much looking forward to MF support.

[benmccann]

Exciting! I'd love to try it out soon. One thing that would be great is some sort of repl / playground like rollup, esbuild, and oxc have

[yyx990803]

There is a already a playground in place but we need to fix a few issues to get the wasm build working.

[NMinhNguyen]

Is "bundled" mode meant to be on the roadmap as well? See https://twitter.com/youyuxi/status/1730412728333025635?s=46 for context. Or more specifically https://x.com/youyuxi/status/1730855549863178698?s=46. It's common to have packages in a monorepo that export lots of code from a single entry point (instead of requiring deep imports into the package which would sort of work like manual tree shaking). In my app, I was hoping to make use of lazy loading to help with unnecessary modules getting loaded, but importing just a single thing from a fat monorepo package ended up pulling in everything 🥲

[yyx990803]

Yes, added it to the last milestone.

[Dooblr]

One pain point with Vite+Rollup currently is using libraries that require polyfilling and resolving Node global variables like Process, Buffer, Crypto, etc.

We have some dependencies that worked fine with Webpack polyfill plugins but spent a fair amount of time working on implementing Vite & Rollup plugins, aliases, and updating our own libraries to make it work.

If this seems like something worth addressing I can provide specific examples.

[yyx990803]

Our general stance is that it's bad practice to rely on Node globals when you are targeting browsers, so it is intentional that we don't provide this as a core / default feature in Vite in order to push new users away from dependencies that do this.

For users migrating from old codebases that already have such dependencies and can't easily migrate away, there are already community solutions: https://www.npmjs.com/package/vite-plugin-node-polyfills

For Rolldown, the community plugin should continue to work so it won't be high priority. But it should be trivial to have this ported as a Rust native plugin and become a built-in option, if necessary.

[zhang2657977442]

What is the difference between Rolldown and Rspack

[zackarychapple]

Rolldown is the rust rewrite of Rollup
Rspack is the rust rewrite of webpack

[OskarLebuda]

What about the HMR? As I know the HRM not exists in rollup at all. Will Rolldown supports this feature from the beginning out of the box? Or it still will be esbuild?

[OskarLebuda]

@yyx990803 ? :)

[benmccann]

I don't think HMR and esbuild have anything to do with each other in Vite currently

[franmc01]

I love that this considers Module Federation, but you know that I also see it as necessary, something solid that brings out the best of vite to integrate with Single SPA

[zackarychapple]

💯

[franmc01]

https://github.com/module-federation/vite

[zackarychapple]

@franmc01 have you been able to use it in production? Would love feedback.

[benmccann]

I thought I'd mention that for milestone 3, the team here might need to help contribute some improvements to oxc before switching to it for minification. I did a bit of testing between oxc and esbuild and found that esbuild produces smaller output today. The oxc team stated that they currently don't have the bandwidth to work on minification and closed my issues, so I'm guessing the gap won't get closed without some efforts from this side. oxc-project/oxc#2646 for reference (note that in this issue esbuild does not produce optimal output either, but there are others where esbuild excels relative to oxc)

[yyx990803]

We are working closely with the oxc team and already contributing to oxc (e.g. recent sourcemap optimizations).

[ghost]

A minifier is mentioned in oxc website as one feature they want to implement.

At the same time, CSS processing by leveraging Lightning CSS is considered in the development of rolldown.

As I understand, you plan to develop CSS minifier and CSS transformation in rolldown with lightningCSS, while resorting to oxc for minifying and transforming JavaScript. Is that correct?

[yyx990803]

That is the current plan, yes.

[trymeouteh]

Will the css bundling be done by having a CSS entry file such as index.css, or will be done using a JS entry file such as index.js using import method?

[BitTechDeveloper]

will you provide the feature to preserve the complete folder structure between src/ and dist/ in rolldown by default with any required configuration?
I mean if I've 4 to 5 level nested folder structure in src/ for html css js and images and I want this to retain in my dist/ exactly and want this to be default behaviour so I don't need to configure anything,
will you porvide this feature when rolldown becomes the underlying technology for vite?

[hyf0]

It' might be better that you explain your requirements in more details.

• Does other bundler supports your needs?
• What's the context?
• How is it useful?

[BitTechDeveloper]

Other bundlers I tried doesn't support this feature except vite. but it support it for only html files. and mostly it's enough.

the main context is url structure issue in multipage application. for example in development we organise files in src/ according to url structure need but when we build, it all goes in the same folder in dist/ this way we can't control the url structure for individual files, but that's not the case for vite and I'm glad vite solved this.

It's also useful when we need to manage some small but distinct project in the same repository because creating a separate repository for each small project is headache.

for other assets like css js and image it does't matter a lot but it would better if we have this feature too.