Add TypeDecoder test

Author: jckarter

test/TypeDecoder/opaque_return_type.swift

@@ -0,0 +1,17 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-build-swift -emit-executable %s -g -o %t/opaque_return_type -emit-module
+// RUN: sed -ne '/\/\/ *DEMANGLE: /s/\/\/ *DEMANGLE: *//p' < %s > %t/input
+// RUN: %lldb-moduleimport-test %t/opaque_return_type -type-from-mangled=%t/input | %FileCheck %s
+
+protocol P {}
+extension Int: P {}
+
+func foo() -> some P { return 0 }
+var prop: some P { return 0 }
+
+// DEMANGLE: $s18opaque_return_type3fooQryFQOyQo_
+// CHECK: some P
+
+// DEMANGLE: $s18opaque_return_type4propQrvpQOyQo_
+// CHECK: some P