set compat version for specific package for whole environment

[SimeonEhrig]

I have the following problem. I develop package A, which changes it's version from 1.0.0 to 2.0.0 because a breaking changes. Now I want to test package A with package B. Package B has as dependency to package A and the compat requires package A==1.0.0. If I add package B, I get the following error:

ERROR: Unsatisfiable requirements detected for package B [...]

A the moment, the solution is to clone the repository of package B, modify the compat section int the Project.toml and add package B as development package. Is there a easy or common solution of my problem?

Also this is only the minimum use case of my problem. For example, we have also a package C, which has package B as dependency and therefore package A is a implicit dependency. Or we have week circular dependencies, because Package A uses Package B in test extra section.

Therefore it would pretty helpful to tell the dependency resolver, that it should use version 2.0.0 of package A, if it finds as dependency of any package, which should be added to the environment.

[aplavin]

Very useful indeed! There even were attempts to add this functionality to Pkg before:
#2285
#1607