[Sema] Don't look through CoerceExprs in markDirectCallee

Doing so prevented the coercion of a function with argument labels to a
user-written function type, as the latter cannot contain argument
labels. This commit changes the behaviour such that the referenced
function is considered to be unapplied, meaning it has its argument
labels stripped, therefore allowing the coercion.

Resolves SR-11429.

Author: hamishknight

lib/Sema/TypeCheckConstraints.cpp

@@ -897,12 +897,6 @@ namespace {
         continue;
       }
 
-      // Coercions can be used for disambiguation.
-      if (auto coerce = dyn_cast<CoerceExpr>(callee)) {
-        callee = coerce->getSubExpr();
-        continue;
-      }
-
       // We're done.
       break;
     }

test/Sema/suppress-argument-labels-in-types.swift

@@ -204,3 +204,21 @@ class C0 {
 
 // Check diagnostics changes.
 let _ = min(Int(3), Float(2.5)) // expected-error{{cannot convert value of type 'Float' to expected argument type 'Int'}}
+
+// SR-11429
+func testIntermediateCoercions() {
+  _ = (f1 as (Int, Int) -> Int)(a: 0, b: 1) // expected-error {{extraneous argument labels 'a:b:' in call}}
+  _ = (f1 as (Int, Int) -> Int)(0, 1)
+
+  typealias Magic<T> = T
+  _ = (f1 as Magic)(a: 0, b: 1) // expected-error {{extraneous argument labels 'a:b:' in call}}
+  _ = (f1 as Magic)(0, 1)
+
+  _ = (f4 as (Int, Int) -> Int)(0, 0)
+  _ = (f4 as (Double, Double) -> Double)(0, 0)
+
+  func iuoReturning() -> Int! {}
+  _ = (iuoReturning as () -> Int?)()
+  _ = (iuoReturning as Magic)()
+  _ = (iuoReturning as () -> Int)() // expected-error {{'() -> Int?' is not convertible to '() -> Int'; did you mean to use 'as!' to force downcast?}}
+}