The various projects that say something is deprecated but then don't give a removal timeline or keep delaying the removal (or even explicitly say it won't be removed, just remain deprecated) are the cause of this problem.

IMO, any deprecation should go in the following steps:

1. Decide that you want to deprecate the thing. This also includes steps on how to migrate away from the thing, what to use instead, and how to keep the existing behaviour if needed. This step would also decide on the overall timeline, starting with the decision and ending with the removal.

2. Make the code give out big warnings for the deprecation. If there's a standard build system, it should have support for deprecation warnings.

3. Break the build in an easy to fix way. If there is too much red tape to take one of the recommended steps, the old API is still there, just under a `deprecated` flag or path. Importantly, this means that at this step, 'fixing' the build doesn't require any change in dependencies or (big) change in code. This should be a one line change to make it work.

4. Remove the deprecated thing. This step is NOT optional! Actually remove it. Keep it part of your compiler / library / etc in a way to give an error but still delete it. Fixing the build now requires some custom code or extra dependency. It is no longer a trivial fix (as trivial as the previous step at least).

Honestly, the build system should provide the tools for this. Being able to say that some item is deprecated and should warn or it is deprecated and should only be accessible if a flag is set or it is removed and the error message should say "function foo() was removed in v1.4.5. Refer to the following link:..." instead of just "function foo() not found"

If the build system has the option to treat warnings as errors, it should also have the option to ignore specific warnings from being treated as such (so that package updates can still happen while CI keeps getting the warning). The warning itself shouldn't be ignored.