What's the ugliest bug you've hit migrating a module between major Odoo versions?

[leo-puk]

Hi, I'm Leo — undergrad thesis student in Computer/Informatics Engineering. I'm building a framework to make custom-module migration across major Odoo versions more predictable (combining static analysis with LLM-assisted resolution, validated against OCA's own peer-reviewed migrations as ground truth).

I'd love to hear real war stories: what version jump were you migrating, was the break in Python (API/ORM), in XML views, in data/manifest, or something else entirely unexpected.

If you have a link to the actual issue/PR/commit where it happened, even better — that's exactly the kind of verifiable case I'm trying to collect. I'll only quote or reference specific comments in my thesis with your permission, and I'm happy to share results back with the community once I'm done.

[zeroheure]

There is already a framework build by OCA. Look at the OpenUpgrade repo.