Picked up the exceptions from protobuf JSON parser to give more informative config errors (#158)

Co-authored-by: Calvin Leng <calvinl@science.xyz>

Author: calvinleng-science

synapse/utils/proto.py

@@ -1,4 +1,4 @@
-from google.protobuf.json_format import Parse
+from google.protobuf.json_format import Parse, ParseError
 from synapse.api.device_pb2 import DeviceConfiguration
 from synapse.api.app_pb2 import AppManifest
 import synapse as syn
@@ -8,20 +8,35 @@ def load_device_config(path_to_json, console):
     # We support either a manifest or a device configuration.
     # First, try to load a device configuration
     try:
-        json_text = open(path_to_json, "r").read()
+        with open(path_to_json, "r") as f:
+            json_text = f.read()
+    except FileNotFoundError:
+        raise ValueError(f"File not found: {path_to_json}")
+    except PermissionError:
+        raise ValueError(f"Permission denied reading: {path_to_json}")
+    except Exception as e:
+        raise ValueError(f"Failed to read {path_to_json}: {e}")
+
+    errors = []
+    try:
         cfg_proto = Parse(json_text, DeviceConfiguration())
         return syn.Config.from_proto(cfg_proto)
-    except Exception:
-        pass
+    except ParseError as e:
+        errors.append(f"DeviceConfiguration: {str(e)}")
+    except Exception as e:
+        errors.append(f"DeviceConfiguration: {type(e).__name__}: {str(e)}")
 
     # We couldn't load a device configuration, so try to load a manifest
     try:
         json_text = open(path_to_json, "r").read()
         manifest_proto = Parse(json_text, AppManifest())
         return syn.Config.from_proto(manifest_proto.device_config)
+    except ParseError as e:
+        errors.append(f"AppManifest: {str(e)}")
     except Exception:
-        raise ValueError(
-            f"Could not parse {path_to_json} as either device configuration or manifest"
-        )
+        errors.append(f"AppManifest: {type(e).__name__}: {str(e)}")
 
-    return None
+    # Only reached here when we've failed to parse
+    error_msg = f"Could not parse {path_to_json} as either format:\n"
+    error_msg += "\n".join(f"  - {error}" for error in errors)
+    raise ValueError(error_msg)