transformer: tsc vs babel on enum transformation

[Boshen]

Discussed in #8341

^{Originally posted by branchseer January 8, 2025}
oxc-transform currently follows babel's rules on enum transformation. IMHO it's a little bit weird about whether an identifier should be resolved to the enum member:

https://playground.oxc.rs/#eNqNkcFqwzAMhl9F+NIEwroOdunooD0Udhh7gVycREkNjlRsp11X8u6Tk6UbXRk7+Zcs/f+HfValWqqckiSF1TOccwI4aAdrWMFsh9by7Cn2kLoWtszjBAz3i2zUG9HrDOZz6RoPDj3bA1YQGMIOx9UW2wIdmBpMmHkomXzQFKJBn1OfJqnE/BNjIxc/MF512N05TRW3SfoL6U0Q3NF4zGRYiK7puAvC5Uveo3AVhipDzTVWTl/BH2Pw7djv0Jc6ervoSHw7IhsfQjfa0F9PJhQ5qUyxWp6V6yge/kRBv6tlcB1myhoKkx5CLsWpLdhOVRBWX7Nrx0afqb12Hp0Yio4mk75MDg0VtGtQEhT6h/vFo5KJkitsMLJI0RoytZmW5WeDY7u1fIzLB3QFe0GqtfXY9/0nDIDKdw==

In contrast, tsc has a simpler rule:

https://www.typescriptlang.org/play/?#code/PTAEEFQSwZ1BDANgd3gTzgJwKYwPaIBu2AJqAC54UAW2o2AdgK4C2oL2LARtpgHQAoIQAphASlABeAHygA3gNChC8TBCmgA5AHNEeLkk0BuRfWZsAYnioKlSyJNABGADSmlAIQ3gXoUwF8BfzFxEwFRCRl5UxU1By1dfUMTJUZWUA9VaLt1RwBZeHJqPkx4BhI8FnE3HK9HHwCgkLEwgTS2TIAvbNzQAqKSsoqqsRqM7zdAoA

Would it be better to switch to tsc's rule?

[overlookmotel]

Confirmed that this weird behavior is also present in Babel. Babel REPL

I am no TypeScript expert, so I may be wrong, but my understanding is: TSC is the "source of truth" on TypeScript transforms, and Babel's TS transform should replicate TSC's behavior. If it doesn't, then that's a bug in Babel.

@branchseer May I suggest raising an issue on Babel? That would help "flush out" answer on whether they diverged from TSC for any good reason, or if it's simply a bug.

[branchseer]

issue logged for Babel: babel/babel#17049

[branchseer]

The Babel team acknowledged the bug and has merged the fix.

@Dunqing I can draft a fix for oxc if no one is working on it.

[overlookmotel]

Great! Thank you. #8508 updates our transformer test fixtures to latest from Babel, which includes the test case you added in babel/babel#17050 (obviously, that test is failing currently).

I'll let @Dunqing come back on whether he plans to work on it, or if he has any thoughts, but as far as I'm aware he's currently working on other things, and a PR would be very welcome.