Updated Bad diagnostic errors

[dk-talks]

Fixes #64903

I have updated the error messages which were not very clear to the user.

Environment
Swift version 5.9-dev (LLVM 6a04c4848990c70, Swift f2bac1a22939a4d)

This is my first pull request on this project. Please scold me if I have made any mistake.

[dk-talks]

Hey @LucianoPAlmeida I have committed the new changes you suggested, please have a look

[LucianoPAlmeida]

Sorry, been a bit busy lately with work so I just glanced on the basics when commenting.
Now was trying to get more context I see that the exercise here is to try to make the wording of diagnostic to be clear on what the language rule is and tell that to the user.
Here are a few things to think about:

struct SS<T> : T { } // expected-error{{cannot inherit from non-protocol type 'T'}}

It is still not clear what cannot inherit from not protocol types. So you can start thinking about the rules about inheritance for struct types and how to describe that in a succinct, but clear way.

Same applies to other cases, so you can start with questions such as:
What is the language rules for inheritance of each construct class, struct, enum and extensions of each of those?
And how improve the current diagnostics to express that in a more clear way?

[xedin]

I think we need to split this into multiple diagnostics and change phrasing. There are a couple of issues here which are not clearly stated by the diagnostic:

• There are only curtain types allowed in inheritance clause, this could be fixed by splitting diagnostic into multiple ones;
• Inheritance in extension is even more restricted to protocols only;
• Message is not very clear about the why to give actionable guidance to the developer how to fix the problem;
  • I think it might be useful to separate type kind + name information into a note and give error more information about what is going on here;