Using auto-accessor with readonly or declare should raise an error

[fwienber]

Bug Report

🔎 Search Terms

auto accessor readonly declare

🕗 Version & Regression Information

Version 4.9.3

• I was unable to test this on prior versions because the auto-accessor feature is new in 4.9

⏯ Playground Link

Playground link with relevant code

💻 Code

class Foo {
    accessor readonly foo: number = 5;
    //       ^ no error here
    accessor declare bar: string;
    //       ^ no error here
}

const myc = new Foo();
myc.foo = 6;
// property is not read-only, which is correct because trying to
// define it read-only as above should be an error in the first place

🙁 Actual behavior

No TypeScript error is shown, neither for readonly nor for declare.
readonly is completely ignored, i.e. writing to the property also does not result in an error.

🙂 Expected behavior

In the auto-accessor PR description, it is explicitly stated that

• accessor cannot be used with readonly or declare on the same field declaration.

So I'd expect a corresponding TypeScript error message for both accessor declarations in the example above.
Once using readonly on an accessor raises an error, it is correct to ignore this for further analysis, so the current behavior to not report an error when trying to write to the property is correct and should remain as-is.

[fatcerberus]

I'm a bit confused why declare accessor wouldn't be legal, but accessor declare is just weird and looks like an oversight in the parser.

[RyanCavanaugh]

Yeah, modifier order is always enforced. This is a bug.

[fwienber]

That was fast! 👍