keepClasName was introduced in swc v1.2.50. But there was a bug at configuration merging, and it didn't work.
It's now fixed.
Arrow functions without parenthesis in arguments like
async foo => 0; is now handled properly.
Previsouly, swc break the code like
await (bar = Promise.resolve(2)); by removing parens.
This is now fixed and it works properly.
Previously swc miscompiled
which is wrong. swc now emits
swc now compiles
regardless of target version.