Resurrect proposed Fix #13553: add Symbol#tpe method

[neko-kai]

by @cchantep
This seems to have been erroneously submitted as a feature request and then closed lampepfl/dotty-feature-requests#247
I suspect that simply exposing def tpe: TypeRepr = self.denot.info is sufficient to fix the bulk of the issue, so I'm reopening it as a PR.

[odersky]

I think the consensus was that we should go through the thisType of the owner instead? Is that exposed in the API?

The reason not to have a Symbol#tpe method is not that it's impossible (in fact it is trivial) but that it is wrong in most cases. People will be tempted use this method (because it is so straightforward!) and then be surprised that more advanced cases won't work. We had this happen literally hundreds of times in the compiler. Newbies will fall into this trap with close to 100% probability.

[cchantep]

How it's possible to get a symbol for a TypeRepr using ThisType ?

[odersky]

@cchantep It should be something like

sym.owner.thisType.memberType(sym)

That assumes there is a thisType. I don't know the details. (I only know the compiler).

[cchantep]

@cchantep It should be something like

sym.owner.thisType.memberType(sym)

That assumes there is a thisType. I don't know the details. (I only know the compiler).

And also assume there is already a Symbol, starting from a TypeRepr (or even Type[T]), I don't think that's possible.

[neko-kai]

That assumes there is a thisType

Adding thisType would also solve #13553. As is, there's a recommendation in memberType doc to use it with the owner type, but no way to retrieve the owner type except via .tree.tpe

[neko-kai]

Fixed in #14124