[SR-1306] Inconsistent behavior with labeled type parameters

[natecook1000]

Previous ID	SR-1306
Radar	None
Original Reporter	@natecook1000
Type	Bug
Status	Resolved
Resolution	Duplicate

Environment

Swift 2.2 and Swift 3 master branch

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, TypeChecker
Assignee	None
Priority	Medium

md5: 109c04a65b17188a6ae294c4a3e1ae14

duplicates:

• SR-899 .self can be omitted if a function has only one parameter

Issue Description:

When a metatype type is used as a function parameter, whether or not the passed type requires ".self" depends on whether the parameter has an external label.

func foo<T>(type: T.Type) {
    print(T)
}

func bar<T>(baz type: T.Type) {
    print(T)
}

foo(String.self)        // ok
foo(String)             // ok
bar(baz: String.self)   // ok
bar(baz: String)        // error

The error output looks like this:

<REPL Input>:1:5: error: cannot create a single-element tuple with an element label
bar(baz: String)        // error
    ^~~~~
    
<REPL Input>:1:4: error: missing argument label 'baz:' in call
bar(baz: String)        // error
   ^
   baz: 

Whatever the correct behavior is should be consistent between foo(_:) and bar(baz:).