refactor: Force custom enum conversion in Json Plugin (#3144)

Since we had the same enum conversion problem a second time I propose to disable the default enum serialization via `JSON_DISABLE_ENUM_SERIALIZATION`.

This results in a compile error instead of runtime errors when we actually try to read strings as integers.

I set the flag `PRIVATE` in cmake so it does not sneak into user codebases but the user might face the same problems if the includes are not done correctly.

Not having the enum and the `NLOHMANN_JSON_SERIALIZE_ENUM` in the same place results in these kind of issues. I wonder if we should rather bring them together and use preprocessor flags. That would also guarantee that the right conversion function will be visible all the time.

References:
 - https://json.nlohmann.me/api/macros/json_disable_enum_serialization/
 - https://json.nlohmann.me/api/macros/nlohmann_json_serialize_enum/

Related PRs and issues:
 - #3142
 - #2333
 - #2331

Plugins/Json/CMakeLists.txt

@@ -28,6 +28,9 @@ target_link_libraries(
   ActsPluginJson PUBLIC ActsCore)
 acts_target_link_libraries_system(
   ActsPluginJson PUBLIC nlohmann_json::nlohmann_json)
+target_compile_definitions(
+  ActsPluginJson
+  PRIVATE JSON_DISABLE_ENUM_SERIALIZATION=1)
 
 install(
   TARGETS ActsPluginJson

Plugins/Json/include/Acts/Plugins/Json/GridJsonConverter.hpp

@@ -18,6 +18,24 @@
 // Custom Json encoder/decoders.
 namespace Acts {
 
+namespace detail {
+
+/// @cond
+NLOHMANN_JSON_SERIALIZE_ENUM(Acts::detail::AxisBoundaryType,
+                             {{Acts::detail::AxisBoundaryType::Bound, "Bound"},
+                              {Acts::detail::AxisBoundaryType::Open, "Open"},
+                              {Acts::detail::AxisBoundaryType::Closed,
+                               "Closed"}})
+
+NLOHMANN_JSON_SERIALIZE_ENUM(Acts::detail::AxisType,
+                             {{Acts::detail::AxisType::Equidistant,
+                               "Equidistant"},
+                              {Acts::detail::AxisType::Variable, "Variable"}})
+
+/// @endcond
+
+}  // namespace detail
+
 namespace AxisJsonConverter {
 
 /// Convert an axis to json
@@ -269,19 +287,4 @@ auto fromJson(const nlohmann::json& jGrid,
 }
 
 }  // namespace GridJsonConverter
-
-/// @cond
-NLOHMANN_JSON_SERIALIZE_ENUM(Acts::detail::AxisBoundaryType,
-                             {{Acts::detail::AxisBoundaryType::Bound, "Bound"},
-                              {Acts::detail::AxisBoundaryType::Open, "Open"},
-                              {Acts::detail::AxisBoundaryType::Closed,
-                               "Closed"}})
-
-NLOHMANN_JSON_SERIALIZE_ENUM(Acts::detail::AxisType,
-                             {{Acts::detail::AxisType::Equidistant,
-                               "Equidistant"},
-                              {Acts::detail::AxisType::Variable, "Variable"}})
-
-/// @endcond
-
 }  // namespace Acts

Plugins/Json/include/Acts/Plugins/Json/VolumeBoundsJsonConverter.hpp

@@ -25,8 +25,6 @@
 // can not match our naming guidelines.
 namespace Acts {
 
-class VolumeBounds;
-
 void to_json(nlohmann::json& j, const VolumeBounds& bounds);
 
 namespace VolumeBoundsJsonConverter {

Plugins/Json/src/ProtoDetectorJsonConverter.cpp

@@ -11,6 +11,7 @@
 #include "Acts/Detector/ProtoDetector.hpp"
 #include "Acts/Geometry/Extent.hpp"
 #include "Acts/Plugins/Json/ExtentJsonConverter.hpp"
+#include "Acts/Plugins/Json/SurfaceJsonConverter.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Utilities/BinningData.hpp"
 
@@ -42,7 +43,7 @@ void Acts::to_json(nlohmann::json& j, const Acts::ProtoVolume& pv) {
     auto& its = pv.internal.value();
     nlohmann::json jinternal;
     if (its.layerType != Surface::SurfaceType::Other) {
-      jinternal["layerType"] = static_cast<int>(its.layerType);
+      jinternal["layerType"] = its.layerType;
     }
     if (!its.surfaceBinning.empty()) {
       writeBinning(jinternal, its.surfaceBinning, "surfaceBinning");

Tests/UnitTests/Plugins/Json/ProtoDetectorJsonConverterTests.cpp

@@ -12,6 +12,7 @@
 #include "Acts/Detector/ProtoDetector.hpp"
 #include "Acts/Geometry/Extent.hpp"
 #include "Acts/Plugins/Json/ProtoDetectorJsonConverter.hpp"
+#include "Acts/Plugins/Json/SurfaceJsonConverter.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Utilities/BinningData.hpp"
 #include "Acts/Utilities/BinningType.hpp"