Changing internal functions is not considered a "breaking change" by anyone I know. You're allowed to refactor code internally, which definitely includes changing the structure of the internal functions.
Other coders who are also working inside the same module/API boundary will have their edits broken by this change. The original developer cannot fix their code because it's not checked in yet.
> rather why they're so eager to change a function signature without following up and either fixing the things they break, or flagging those things up to the people who require it.
I already explained why they can't follow up - because the code that needs the follow up is in their codevelopers' working trees. Flagging here would be silly. Almost every single commit would be "flagged for fixing breakage", since every single commit can refactor/change internal function signatures.
> If there's an error, somebody made a mistake. Some mistakes are stupid, others are subtle. Changing a method signature and then not doing something about the callers is a stupid mistake.
Yes, and we are all human so sometimes, despite heroic efforts, we will all make stupid mistakes as well as subtle mistakes.
Now, once we made the mistake, do we want our tool to insidiously hide this mistake from us, making it as expensive as possible to punish us for our mistake? Or do we want a tool that tells me ASAP "Hey dude, you made a stupid mistake over there"?
> but your job is to minimise the frequency and severity of those errors.
And to do this job, I have tools like languages that help me find those mistakes quickly.
> There's no excuse for sloppiness
Making mistakes isn't "sloppiness", it's human.
> Call it whatever you like, but a shitty broken codebase is only the fault of the developers, not the language
If one language makes writing a non-shitty codebase harder than a different language, it is also the fault of that language.