[feature request] Better error messages for decorators (they are completely not understandable)

Search Terms

"Unable to resolve signature of property decorator when called as an expression"

Suggestion

The error message I received was error TS1240: Unable to resolve signature of property decorator when called as an expression.

This leaves absolutely no clue what is wrong.

Examples

To fix the issue, I had to change the signature of one of my functions from

export function attribute(
	prototype: any
	propName: string,
	descriptor: PropertyDescriptor | undefined,
): any

to

export function attribute(
	prototype: any
	propName: string,
	descriptor?: PropertyDescriptor | undefined,
): any

The difference is subtle: the descriptor arg isn't always passed to a decorator (depends on whether it is used on a property or on an accessor or method).

It'd be better if the message said something like The 'descriptor' argument to a property decorator should not be required.

Similar for other cases that trigger the same unhelpful error message.

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.