More user-friendly error when writing unchecked to declare an unchecked user-defined operator

[Rekkonnect]

Just tried the checked user-defined operator feature out, and I think it would be nice to have a more specific error when a user types:

public static int operator unchecked +(int left, int right);
//                         ~~~~~~~~~

Saying that unchecked operators do not require the modifier. Currently, multiple unrelated errors are being shown, and parsing breaks miserably:

Originally posted here

[jcouv]

That'll definitely be better.
Closing as duplicate of #60394

[Rekkonnect]

By the way, shouldn't this be added to the test plan for this feature? That's where I looked for to find whether the issue is known.

[jcouv]

@alfasgd Added link in test plan. Working on a fix now