hygiene: Do not treat Self ctor as a local variable

[petrochenkov]

Fixes#57523

[Centril]

r? @alexreg

[Centril]

Apparently bors hasn't rebooted yet...

@bors delegate=alexreg

[bors]

✌️ @alexreg can now approve this pull request

[alexreg]

This is a small delta and looks totally fine to me, so I'm going to go ahead and r+ it. Travis would fail before Bors gets around to it anyway...

@bors r+

[bors]

📌 Commit 805099c has been approved by alexreg

[varkor]

@petrochenkov: are these still necessary now?

rust/src/librustc_resolve/lib.rs

Lines 3410 to 3419 in 0e1402d

	(Def::SelfTy(..), _)if ns == ValueNS => {
	err.span_label(span, fallback_label);
	err.note("can't use `Self` as a constructor, you must use the \
	implemented struct");
	return(err, candidates);
	}
	(Def::TyAlias(_), _) | (Def::AssociatedTy(..), _)if ns == ValueNS => {
	err.note("can't use a type alias as a constructor");
	return(err, candidates);
	}

[petrochenkov]

@varkor
The type alias case is necessary.
The SelfTy case is necessary only in corner cases when we have Self in type namespace, but not in value namespace (i.e. probably not necessary in practice).