Can't emit types for subclassed abstract class: error TS4094

[paulmillr]

🔎 Search Terms

ts4094, abstract, class, property, protected, private

🕗 Version & Regression Information

• This is a crash
• Happens in the 5.6-dev, 5.x, 4.x, etc

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.6.0-dev.20240708#code/JYWwDg9gTgLgBAbzgZwBYEMBMBWAbHdZOAfTSzzgF84AzKCEOAcgAEA7CAIwBsBTAegxpeyfmRy4mAbgBQvAB6RYcAMYQ2yeOIoBeEttxSgA

💻 Code

Cloneable repo: https://github.com/paulmillr/ts-bug-4094.

So there's abstract class which declares protected property (https://github.com/paulmillr/noble-hashes/blob/main/src/_md.ts#L33):

export abstract class HashMD<T extends HashMD<T>> extends Hash<T> {
  protected buffer: Uint8Array;
}

The class is subclassed (https://github.com/paulmillr/noble-hashes/blob/e804a2f9eff77c92e21705f876d99c3069037988/src/sha256.ts#L31C1-L32C1):

class SHA256 extends HashMD<SHA256> {}

The protected buffer property is not used as emit type anywhere.

https://github.com/paulmillr/noble-hashes/blob/e804a2f9eff77c92e21705f876d99c3069037988/src/_md.ts#L33

🙁 Actual behavior

It doesn't compile, error emitted: TS4094: Property 'buffer' of exported class expression may not be private or protected

🙂 Expected behavior

It should compile

Additional information about the issue

No response

[paulmillr]

I think it's because SHA256 is not exported, but the error is not clear.

[weswigham]

Yeah, correct - because SHA256 isn't exported, we try to write an anonymous type for it in the output, but can't because of the protected properties in the class type, hence the errors.