Sure, feel free to upload a patch on Gerrit. Wikibase/Installation might be useful to set up a local wiki where you can test the behavior.

I would love to see this improved. I often get this generic error when an empty string is passed with a string property. I would also really like to know which property was related to the input error so I don't have to scan through tens of properties to find the anomaly manually.

@gabbyprecious: Hi! This task has been assigned to you a while ago. Could you maybe share an update? Do you still plan to work on this task, or do you need any help?

@Lucas_Werkmeister_WMDE I think we can add problematic part of a property as a parameter to the API response? UI can also highlight the issue with the input as well. I don't know if it's a good idea to add it as a parameter though.

Example:

{
    "error": {
        "code": "wikibase-validator-malformed-value",
        "info": "Malformed input: hmm\u00a0"
    },
    "results": [
        {
            "raw": "hmm\u00a0",
            "value": {
                "text": "hmm\u00a0",
                "language": "en"
            },
            "type": "monolingualtext",
            "error": "ValidationError",
            "messages": [
                {
                    "name": "wikibase-validator-malformed-value",
                    "parameters": [
                        "hmm\u00a0",
                        "\u00a0"
                    ],
                    "html": {
                        "*": "Malformed input: hmm "
                    }
                }
            ],
            "validation-errors": [
                "malformed-value"
            ]
        }
    ]
}

I think we should use the existing RegexValidator error reporting, just with a custom error code instead of the default 'malformed-value'.

In T304943#8274994, @Lucas_Werkmeister_WMDE wrote:

I think we should use the existing RegexValidator error reporting, just with a custom error code instead of the default 'malformed-value'.

malformed-value is not a wrong error message, but it needs more detail. We already have some additional details in API response, like escaped original string, but I don't know if we add a new custom error code or do something else.

Change 841529 had a related patch set uploaded (by Hasan Akgün (WMDE); author: Hasan Akgün (WMDE)):

[mediawiki/extensions/Wikibase@master] Make Wikibase error message "Malformed input" more meaningful

https://gerrit.wikimedia.org/r/841529

Change 841529 merged by jenkins-bot:

[mediawiki/extensions/Wikibase@master] Make Wikibase error message "Malformed input" more meaningful

https://gerrit.wikimedia.org/r/841529