duplicates:

• SR-1420 Provide compiler warning when shadowing generic type

relates to:

• SR-8524 Shadowing in protocols leads to difficult to find bugs

Issue Description:

Is it normal to want to shadow generic type parameter names? If not, can we make it a compiler warning?

I recently helped someone with Swift who was confused by code like this:

struct Foo<T: Hashable> {
var t: T
func foo<T>() -> Int { return t.hashValue }
}
t.swift:3:12: error: generic parameter 'T' is not used in function signature
func foo<T>() -> Int { return t.hashValue }
^

The error message was unhelpful to them. They didn't realize that they were shadowing the class's generic parameter.

We only need a warning here that would show up before any subsequent diagnostics. Since a warning doesn't break code, I don't know that this needs to go through evolution.

<rdar://problem/26899805> QoI Warn when shadowing generic type parameters