Add fmt compatibility for interface types

Author: tmadlener

python/templates/Interface.h.jinja2

@@ -14,6 +14,8 @@
 #include "podio/utilities/TypeHelpers.h"
 #include "podio/detail/OrderKey.h"
 
+#include <fmt/ostream.h>
+
 #include <memory>
 #include <ostream>
 #include <stdexcept>
@@ -196,4 +198,7 @@ struct std::hash<{{ class.full_type }}> {
   }
 };
 
+template <>
+struct fmt::formatter<{{ class.full_type }}> : fmt::ostream_formatter {};
+
 #endif

tests/unittests/interface_types.cpp

@@ -195,3 +195,14 @@ TEST_CASE("InterfaceType extension model", "[interface-types][extension]") {
   REQUIRE(wrapper.isA<iextension::AnotherHit>());
   REQUIRE(wrapper.as<iextension::AnotherHit>().energy() == 4.2f);
 }
+
+TEST_CASE("InterfaceType formatting", "[interface-types][basics][formatting]") {
+  auto iface = iextension::EnergyInterface::makeEmpty();
+  auto formatted = fmt::format("{}", iface);
+  REQUIRE(formatted == "[not available]");
+
+  iface = ExampleCluster{};
+  formatted = fmt::format("{}", iface);
+  REQUIRE_FALSE(formatted.empty());
+  REQUIRE(formatted != "[not available]");
+}