Merge pull request #9624 from xedin/rdar-32101765

[QoI] Improve diagnostics for Smart KeyPath

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -445,6 +445,9 @@ ERROR(expr_swift_keypath_invalid_component,none,
       "invalid component of Swift key path", ())
 ERROR(expr_swift_keypath_not_starting_with_type,none,
       "a Swift key path must begin with a type", ())
+ERROR(expr_smart_keypath_value_covert_to_contextual_type,none,
+      "KeyPath value type %0 cannot be converted to contextual type %1",
+      (Type, Type))
 
 // Selector expressions.
 ERROR(expr_selector_no_objc_runtime,none,