Add testcase for @_implements typechecking diagnostics.

Author: graydon

test/attr/attr_implements_bad_types.swift

@@ -0,0 +1,25 @@
+// RUN: %target-swift-frontend -typecheck -verify %s
+
+protocol NeedsF0 {
+  func f0() // expected-note {{protocol requires function 'f0()' with type '() -> ()'; do you want to add a stub?}}
+}
+
+struct S0 : NeedsF0 {  // expected-error {{type 'S0' does not conform to protocol 'NeedsF0'}}
+  @_implements(NeedsF0, f0())
+  func g0() -> Bool {  // expected-note {{candidate has non-matching type '() -> Bool'}}
+    return true
+  }
+
+  @_implements(NeedsF0, ff0()) // expected-error {{protocol 'NeedsF0' has no member 'ff0()'}}
+  func gg0() {
+  }
+
+  @_implements(Int, zz) // expected-error {{non-protocol type in @_implements attribute}}
+  static func gg1(x:S0, y:S0) -> Bool {
+  }
+
+  @_implements(Equatable, ==(_:_:)) // expected-error {{containing type 'S0' does not conform to protocol 'Equatable'}}
+  static func gg2(x:S0, y:S0) -> Bool {
+  }
+}
+