TypeScript: x < y >= z is incorrectly interpreted as a type argument list

[evanw]

Describe the bug

SWC's interpretation of type arguments in TypeScript code is different than the TypeScript compiler, which can cause SWC to generate incorrect JavaScript.

Input code

fn(x < y, x >= y)

Config

(I only ran SWC via the playground)

Playground link

https://play.swc.rs/?version=1.3.57&code=H4sIAAAAAAAAA0vL06hQsFGo1FGoULCzVajU5AIAIT%2B1gxIAAAA%3D&config=H4sIAAAAAAAAA1VPOw7DIAzdOQXy3CHK0KF36CEQdSIqfsKOVBTl7oUE0maz38fveRVSwps0PORaxrJElQjTuReEsmf1KQhwjkg6mchw6yxTpSZlCXdoOxhglWbk6kIah3FoDrAhEHZHw5zxZsr%2FmTq4mJDoKqxS5WeL10TRUsGF17KT7Zfa92hwh5%2Boh52HwdCzOzktKLYvIO%2B2AhcBAAA%3D

Expected behavior

SWC should produce this to match the TypeScript compiler:

fn(x < y, x >= y);

Actual behavior

SWC produces this instead, which is incorrect:

fn(x = y);

Version

1.3.57

Additional context

Specifically TypeScript's parseTypeArgumentsInExpression function backtracks unless the trailing > comes from a > real token. This is subtle because TypeScript's type argument parser normally strips off the leading > from a token, which is why >> works in a<b<c>>(d). But it turns out that should only be done when you're in a type context. When you're in an expression context, the trailing > must not come from a token that has anything else after it. So for example a<b<c>>=(d) should not be considered a type argument list because parseTypeArgumentsInExpression encounters a >= token.

I just fixed this bug in esbuild: evanw/esbuild#3111. I'm reporting it here because SWC appears to also have this issue. The bug does not introduce a syntax error, which means the problematic output might be missed before releasing it, so I considered this bug to be higher severity.

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.