fix: Make charge smearing optional in digi config

Currently, the JSON reading for digitization configurations
unconditionally reads the charge smearing data, but this need not
necessarily be present; the geometric config for the ODD, for example,
does not have this data. As a result, parser was failing to parse the
geometric ODD digitization config. This commit makes the reading
conditional and adds tests to ensure the ODD config reading remains
functional.

Examples/Io/Json/src/JsonDigitizationConfig.cpp

@@ -139,7 +139,9 @@ void ActsExamples::to_json(nlohmann::json& j,
   j["thickness"] = gdc.thickness;
   j["threshold"] = gdc.threshold;
   j["digital"] = gdc.digital;
-  to_json(j["charge-smearing"], gdc.chargeSmearer);
+  if (j.find("charge-smearing") != j.end()) {
+    to_json(j["charge-smearing"], gdc.chargeSmearer);
+  }
 }
 
 void ActsExamples::from_json(const nlohmann::json& j,
@@ -161,7 +163,9 @@ void ActsExamples::from_json(const nlohmann::json& j,
       gdc.varianceMap[idx] = vars;
     }
   }
-  from_json(j["charge-smearing"], gdc.chargeSmearer);
+  if (j.find("charge-smearing") != j.end()) {
+    from_json(j["charge-smearing"], gdc.chargeSmearer);
+  }
 }
 
 void ActsExamples::to_json(nlohmann::json& j,

Examples/Python/tests/test_examples.py

@@ -1000,6 +1000,40 @@ def test_digitization_example(trk_geo, tmp_path, assert_root_hash, digi_config_f
     assert_root_hash(root_file.name, root_file)
 
 
+@pytest.mark.parametrize(
+    "digi_config_file",
+    [
+        DIGI_SHARE_DIR / "default-smearing-config-generic.json",
+        DIGI_SHARE_DIR / "default-geometric-config-generic.json",
+        pytest.param(
+            (
+                getOpenDataDetectorDirectory()
+                / "config"
+                / "odd-digi-smearing-config.json"
+            ),
+            marks=[
+                pytest.mark.odd,
+            ],
+        ),
+        pytest.param(
+            (
+                getOpenDataDetectorDirectory()
+                / "config"
+                / "odd-digi-geometric-config.json"
+            ),
+            marks=[
+                pytest.mark.odd,
+            ],
+        ),
+    ],
+    ids=["smeared", "geometric", "odd-smeared", "odd-geometric"],
+)
+def test_digitization_example_input_parsing(digi_config_file):
+    from acts.examples import readDigiConfigFromJson
+
+    acts.examples.readDigiConfigFromJson(str(digi_config_file))
+
+
 @pytest.mark.parametrize(
     "digi_config_file",
     [