Generic class expressions in JS should issue an error

[weswigham]

TypeScript Version: 3.4.0-dev.201xxxxx

Search Terms:

Code

// @ts-check
class Foo {
	static Bar = class<T> {
		/** @type {number} */
		x;
	};
}

Expected behavior:
Error on <T>

Actual behavior:
No error.

getJSSyntacticDiagnosticsForFile in program.ts seems to be missing something.

[tanhauhau]

Can I have a try on this?

[RyanCavanaugh]

@tanhauhau sure!

[fatcerberus]

Out of curiosity what does TS do with the type parameter here? Just ignore it? Or does it actually contribute to type inference/checking?

[karthikkp]

@weswigham @RyanCavanaugh can you point to a mdn doc that talks about this? Just so that the context is clear.

[weswigham]

For clarity: we parse & check most TS constructs even in .js files, but we're supposed to isssue a "X are not valid in a JavaScript file" error, where in this case, X is "Type parameters".

[karthikkp]

@weswigham You mean, when the typescript compiler is used against a .js file which contains a generic class expression should throw an error?

[weswigham]

Report a diagnostic, similar to what we do when we find type parameters on a call expression. I referenced the function which needs adjustment in the OP.