Loose the Neuropod backend version match about neuropod HOT 2 OPEN

This is a good suggestion and something I've thought about a bit. Unfortunately, it's kinda tricky to do correctly.

The backends depend on code compiled into libneuropod.so. For example, all the backends use code in /internal and some use code in /bindings and /core as well. This effectively means that it's quite likely that a header file change almost anywhere will break ABI compatibility for backends.

We can use tools to track this and ensure we don't break ABI compatibility for backends within a {MAJOR/MINOR}¹ version, but since most header file changes are likely to break it, this approach might not be particularly useful at the moment. Header only/templated classes make finding accidental breakages much more complex as well. This also requires deciding on a versioning strategy and the guarantees we're willing to stick to (e.g. a backend will work with all Neuropod libraries within a specific {MAJOR/MINOR}¹ version, there will be a release with breaking changes at most once a quarter, etc). This also significantly impacts backend loading logic so we have to be thoughtful about our approach.

All of the above also will likely make our CI tooling more complex as well.

Adding version mismatch flexibility will be fairly complex to do (and test) correctly so we need to figure out if it's worth it. Maybe there's another solution that's simpler (e.g. mount backends as a docker volume at runtime instead of building them into the image, inject them the same way you inject the .jar file, etc.).

¹ This depends on if we want to follow semver or not. For example, PyTorch does a minor release every quarter (~90 days), but these minor releases contain backwards incompatible changes (which goes against semver rules): https://github.com/pytorch/pytorch/releases

from neuropod.

This effectively means that it's quite likely that a header file change almost anywhere will break ABI compatibility for backends.

To clarify, we haven't changed a header file in a way that should impact ABI compatibility since June of last year. However, the point of the quote above is that it would be very easy to accidentally break ABI compatibility.

from neuropod.