feat(repl): Type stripping in the REPL

[dsherret]

This is part of the implementation for #1158. It allows TypeScript to be inputted in the REPL and it will transpile it to JS for execution.

[dsherret]

Example

[dsherret]

A side effect of this is when the transformed AST gets printed the line numbers will no longer match.

For example, before (note line number is 2):

And after (now it's 5):

Is there a way we can fix this easily with the source map since swc can provides that? I'm not super familiar with this, but can look into it if someone believes it's worthwhile.

[bartlomieju]

Is there a way we can fix this easily with the source map since swc can provides that? I'm not super familiar with this, but can look into it if someone believes it's worthwhile.

I don't think it would be that simple - we'd have to store related source map for the last evaluated expression and perform ad-hoc mapping on errors. I think we can skip it for the first pass?

[bartlomieju]

Very impressed how little code is required to provide this functionality!

[caspervonb]

Class expressions throw parse errors:

class {
  foo() {
  }
  
  bar() {
  }
}

Edit:

Actually, never mind that's consistent with the current behaviour anyway.

[dsherret]

@caspervonb it's the case currently in deno 1.11 as well:

[caspervonb]

@caspervonb it's the case currently in deno 1.11 as well:

Yeah never mind that note 👍

[caspervonb]

Got a panic

> namespace Foo { bar: String }
undefined
> namespace Foo { bar: String }
undefined
> namespace Foo { bar: String = "32" }
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', cli/tools/repl.rs:529:45
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[dsherret]

@caspervonb interesting! I've opened #10938 to discuss that there (note that bar: is a label in a labeled statement, so what's being done here is re-assigning the String function to "32").

[caspervonb]

I'm thinking we should be respecting the media-type as a flag here (e.g, via --ext).
There are some (albeit rare) cases where TypeScript isn't a superset of JavaScript.

[caspervonb]

Store this as last error?

[dsherret]

I'm not sure it's worth the trouble since it's not a thrown error.

[caspervonb]

Things that would've been SyntaxError's and stored in _ today are caught at this point so.
If we don't store it's somewhat of a regression.

[dsherret]

I'm thinking we should be respecting the media-type as a flag here (e.g, via --ext).
There are some (albeit rare) cases where TypeScript isn't a superset of JavaScript.

Do you have an example? It might be handled by swc.

[bartlomieju]

LGTM 🚀