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Issue Description:

I've just done a bit of refactoring and this happened a lot: I frequently had code like function bar

func foo(_ body: () -> ()) {
}

func bar() {
    foo {
        try print("hello world")
    }
}

clearly, I can just remove the unnecessary try in bar and everything's good. However I didn't spot the try straight away and then I get a compilation error that I'm turning a throwing function into a non-throwing function.

test.swift:5:9: error: invalid conversion from throwing function of type '() throws -> ()' to non-throwing function type '() -> ()'
    foo {
        ^
test.swift:6:9: warning: no calls to throwing functions occur within 'try' expression
        try print("hello world")
        ^

It shows both. But if there's errors, Xcode and possibly other IDEs prefer to show you the errors first and you can't spot the warning at all (see attached screenshot).

Given that the compiler already figured out that the try is unnecessary, it shouldn't infer the closure's type to have a throws.

Even if I help the type checker by telling it the full type

func foo(_ body: () -> ()) {
}

func bar() {
    foo { () -> () in
        try print("hello world")
    }
}

it still shows the same error 🙁

test.swift:5:9: error: invalid conversion from throwing function of type '() throws -> ()' to non-throwing function type '() -> ()'
    foo { () -> () in
        ^~~~~~~~~~~~~
test.swift:6:9: warning: no calls to throwing functions occur within 'try' expression
        try print("hello world")
        ^