How to detect duplicate keys?

[ulgens]

Coming from https://gitlab.com/bmares/check-json5/-/issues/1, I was wondering if there is anything similar to object_pairs_hook from

import json5
json5.load(f, object_pairs_hook=...)

I checked the source code, the documentation and the issues but couldn't find anything related to duplicate key detection. It looks like decode automatically deduplicates the keys and doesn't raise/return any error.

[maresb]

A little more context: check-json5 is a pre-commit hook for validating JSON5 files, and we'd like to switch to pyjson5 for the performance benefits over dpranke's implementation.

From the validation perspective, duplicate keys often (but technically not always) indicate a mistake in the original file. Thus to not lose any functionality, we'd like some way to raise an exception in the case of duplicate keys, and the current implementation using dpranke's code relies on setting object_pairs_hook to detect and raise on duplicate keys.