Buildstream should identify if an element moves from `build-depend` to `depend`, and not recompile.

[BuildStream-Migration-Bot]

See original issue on GitLab
In GitLab by [Gitlab user @tcanabrava] on Oct 13, 2020, 15:22

when we have a library that is incorrectly configured, and we need to move an element from build-depend to depend there is no need to recompile.
If this library is down on the stack, it get's worse as everything that depends on it will also be recompiled, but the result library is the same.

[BuildStream-Migration-Bot]

In GitLab by [Gitlab user @tristanvb] on Oct 13, 2020, 15:36

Seems like this should produce the same cache key for the element itself, but not for any reverse dependencies which have a build dependency on the element which changed.

• When you move a dependency from build-depends to depends, you are making a statement that this dependency is required at runtime.
• A reverse dependency which build depends on this element, requires this element to run at the time the reverse dependency builds, thus, the new runtime dependency is necessarily a new build time dependency for any reverse build dependencies.

Is this essentially the behavior you are observing ? Or is the element itself also rebuilt as a result of this, not only its reverse dependencies ?

[BuildStream-Migration-Bot]

In GitLab by [Gitlab user @tcanabrava] on Oct 13, 2020, 18:46

you are completely right, I misunderstood the issue.