From 323f7e076acf58269ce1816c617b8037b7e49f8e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vladim=C3=ADr=20Vondru=C5=A1?= <mosra@centrum.cz>
Date: Mon, 2 Apr 2018 00:03:13 +0200
Subject: [PATCH] external: better diagnostics for the std::optional
 compatiblity test.

---
 .../Optional/Test/StdOptionalTest.cpp             | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/MagnumExternal/Optional/Test/StdOptionalTest.cpp b/src/MagnumExternal/Optional/Test/StdOptionalTest.cpp
index 3bab115a0..bf0de87bf 100644
--- a/src/MagnumExternal/Optional/Test/StdOptionalTest.cpp
+++ b/src/MagnumExternal/Optional/Test/StdOptionalTest.cpp
@@ -55,6 +55,21 @@ StdOptionalTest::StdOptionalTest() {
 #endif
 void StdOptionalTest::conversion() {
     Debug{} << "Using C++ version" << CORRADE_CXX_STANDARD;
+    #ifdef __has_include
+    Debug{} << "__has_include is supported";
+    #if __has_include(<optional>)
+    Debug{} << "<optional> header is present";
+    #else
+    Debug{} << "<optional> header is not present";
+    #endif
+    #if __has_include(<experimental/optional>)
+    Debug{} << "<experimental/optional> header is present";
+    #else
+    Debug{} << "<experimental/optional> header is not present";
+    #endif
+    #else
+    Debug{} << "__has_include is not supported";
+    #endif
     #ifdef _MAGNUM_HAS_STD_OPTIONAL
     Debug{} << "Using a conversion to std::optional, C++17 should be present";
     CORRADE_VERIFY(CORRADE_CXX_STANDARD >= 201703L);