[TypeCheckEffects] AbstractFunction: Parameter types should be mapped into context

Parameter type could be represented by an associated type which is
bound to a concrete type by an extension, `AbstractFunction::getType()`
should map it into context before returning because the construct is
that it always produces a function type.

Resolves: rdar://156955193

Author: xedin

lib/Sema/TypeCheckEffects.cpp

@@ -395,7 +395,10 @@ class AbstractFunction {
     }
     case Kind::Closure: return getClosure()->getType();
     case Kind::Parameter:
-      return getParameter()->getInterfaceType()->lookThroughAllOptionalTypes();
+      auto *param = getParameter();
+      auto *dc = param->getDeclContext();
+      return dc->mapTypeIntoContext(param->getInterfaceType())
+          ->lookThroughAllOptionalTypes();
     }
     llvm_unreachable("bad kind");
   }

validation-test/Sema/type_checker_crashers_fixed/rdar156955193.swift

@@ -0,0 +1,25 @@
+// RUN: %target-typecheck-verify-swift
+
+protocol Definition {
+  associatedtype Delegate
+}
+
+enum Kind {
+  case normal
+  case other
+}
+
+struct Payload {
+}
+
+extension Definition where Delegate == ((Kind, Payload) -> Void) {
+  static func invokeDelegate(_ delegate: Delegate, kind: Kind, payload: Payload) {
+    delegate(kind, payload)
+  }
+}
+
+extension Definition where Delegate == ((Kind, Payload) -> Void)? {
+  static func invokeOptionalDelegate(_ delegate: Delegate, kind: Kind, payload: Payload) {
+    delegate?(kind, payload)
+  }
+}