From 3fa4e8109e10c3b60b73d333ca4932775ab85e63 Mon Sep 17 00:00:00 2001
From: Kefu Chai <kchai@redhat.com>
Date: Fri, 3 Nov 2017 16:10:07 +0800
Subject: [PATCH] denc: support enum with underlying type

Signed-off-by: Kefu Chai <kchai@redhat.com>
---
 src/include/denc.h   | 10 +++++++++-
 src/test/encoding.cc | 27 +++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/include/denc.h b/src/include/denc.h
index 823da640860b7..9dc1b7b5f4c6a 100644
--- a/src/include/denc.h
+++ b/src/include/denc.h
@@ -231,6 +231,13 @@ namespace _denc {
     std::true_type,
     is_any_of<T, Tail...>>::type
   {};
+  template<typename T, typename=void> struct underlying_type {
+    using type = T;
+  };
+  template<typename T> struct underlying_type<
+    T, typename std::enable_if<std::is_enum<T>::value>::type> {
+    using type = typename std::underlying_type<T>::type;
+  };
 }
 
 
@@ -238,7 +245,8 @@ template<typename T>
 struct denc_traits<
   T,
   typename std::enable_if<
-    _denc::is_any_of<T, ceph_le64, ceph_le32, ceph_le16, uint8_t
+    _denc::is_any_of<typename _denc::underlying_type<T>::type,
+		     ceph_le64, ceph_le32, ceph_le16, uint8_t
 #ifndef _CHAR_IS_SIGNED
 		     , int8_t
 #endif
diff --git a/src/test/encoding.cc b/src/test/encoding.cc
index af3346e1a0916..21e31d4fab9f4 100644
--- a/src/test/encoding.cc
+++ b/src/test/encoding.cc
@@ -264,6 +264,23 @@ void encode<ceph_le64, denc_traits<ceph_le64>>(const ceph_le64&,
   ASSERT_TRUE(false);
 }
 
+namespace {
+  // search `underlying_type` in denc.h for supported underlying types
+  enum class Colour : int8_t { R,G,B };
+  ostream& operator<<(ostream& os, Colour c) {
+    switch (c) {
+    case Colour::R:
+      return os << "Colour::R";
+    case Colour::G:
+      return os << "Colour::G";
+    case Colour::B:
+      return os << "Colour::B";
+    default:
+      return os << "Colour::???";
+    }
+  }
+}
+
 TEST(EncodingRoundTrip, Integers) {
   // int types
   {
@@ -288,6 +305,16 @@ TEST(EncodingRoundTrip, Integers) {
     i = 42;
     test_encode_and_decode(i);
   }
+  // enum
+  {
+    test_encode_and_decode(Colour::R);
+    // this should not build, as the size of unsigned is not the same on
+    // different archs, that's why denc_traits<> intentionally leaves
+    // `int` and `unsigned int` out of supported types.
+    //
+    // enum E { R, G, B };
+    // test_encode_and_decode(R);
+  }
 }
 
 const char* expected_what[] = {
-- 
2.39.5