How are changed packages detected in a monorepo?

[jonathantredway]

I'm trying to understand if package changes are detected based on last release, or if the PR labels contribute to this detection. I'll give my example set up to illustrate:

Let's say I have a monorepo setup with 2 independently versioned packages (package A and package B) and have onlyGraduateWithReleaseLabel set to true in my auto config

• I make internal changes to both packages and don't want auto shipit to trigger a release, so I don't add the release label to the PR
• I merge to main and no release is created (as expected)
• I then make breaking changes to package A and want to release a major version update, so I add the release label.
• When I merge to develop, does only package A get the major version release?

Both packages will have changed since the last release, but only package A shows up in the diff against main when the release label was applied.

I realize this might be somewhat of a lerna behavior question, but fits at the intersection of auto and lerna since auto is the one with knowledge of labels and is responsible for determining what the since should be when telling lerna to find changed packages.