Is there a TypeScript parser written in Chevrotain yet?

[trusktr]

Thinking to start a project if it doesn't exist, or re-use one if it does.

Any thoughts on using Chevrotain vs something else in terms of easy in defining the grammar?

[trusktr]

This issue shows a sample of TypeScript-like generic type syntax.

#917

Does the lack of left-recursion make it challenging?

[msujew]

We have some documentation on this over at Langium which explains how to deal with left-recursion in LL parsers using tree-rewriting actions. Given that Langium is using Chevrotain, writing something like this in pure Chevrotain should be feasible as well.

[bd82]

ECMAScript (The basis for TypeScript) has an ambiguity between division operator and regular expressions.

• https://stackoverflow.com/questions/4726295/division-regexp-conflict-while-tokenizing-javascript

This is normally resolved by lexing on the fly(lexerless) rather than using distinct lexing and parsing steps.
Unfortunately, By default Chevrotain does not support a lexerless flow, so this is one significant gap.

It is probably possible to modifying Chevrotain to support a lexerless flow, but I doubt all the features would be 100% compatible with this, in particular error recovery related features.

Anyhow: for what purpose do you need another TypeScript parser implemented in a JavaScript runtime?

Beyond TSC itself I believe Babel also has a set of plugins that enable support for TypeScript syntax, e.g:

• https://babeljs.io/docs/en/babel-plugin-transform-typescript
• Is this how the prettier project formats TypeScript source code?

[trusktr]

Anyhow: for what purpose do you need another TypeScript parser implemented in a JavaScript runtime?

Some folks and I are interested in taking TypeScript's syntax (but that's about all) and making custom type checking (probably compatible, maybe optionally not? but definitely strict, probably beneficial for TypeScript tooling to function, but we add additional checking) and custom output (f.e. to native or wasm).

Specifically wanting to do it in JavaScript isn't a requirement, but after having read about Chevro, it sounds great (for example debugging a parser in debugger, rather than having a level of indirection with a parser grammar language and generator, plus the speed and comparisons with other parser projects). Plus Chevro is currently maintained and moving along, has great docs that provide nice entry points into further things to research, while some other options I looked at are dormant or unmaintained.

If you were specifically making a new compiler for TypeScript source code, what tools would you use?

[msujew]

As long as you are purely concerned about (a subset of) TypeScript and no superset, I would probably recommend using the typescript package as well to parse your project. You can always implement a custom type checker and code generation on top, but it does give you a lot of the box.

[bd82]

If you were specifically making a new compiler for TypeScript source code, what tools would you use?

Assuming I needed a new parser for TypeScript my starting point would be Chevrotain, but I would
evaluate if the "harder" syntax (regexp vs division / generics (?) / other) can be supported first.

I will also keep in mind that long term an hand-crafted parser may be needed for maximum control / performance / feature set.

Generally I would try very hard to avoid re-implementing a parser for TypeScript,
particularly due to the fact it does not seem to have an up-to-date specification...