[rmattes]

That's an interesting point. If you're using a language that adds more rules to the API compatibility than the language that a module is released in, it's probably not possible to rely on semver in the general case. Unless the author is aware of those issues and versioning accordingly, any minor release could be breaking.

[iopq]

Even in the same language, how do you prove that your changes didn't break things like type inference? Any change to the signature of a function (even accepting MORE types than before) can potentially break someone's code.

[rmattes]

If you can't definitively prove that a class of changes won't break things, then you probably have to treat that class of changes as breaking and version accordingly, no?