fix: Assume divergence until established otherwise

[aggrand]

what

This modifies the divergence checking behavior to assume divergence unless proven otherwise. On any errors it will say that there is a divergence.

why

The documentation on the merge checkout strategy describe the issue where a failure to use the updated main branch can delete resources that are configured on the main branch. Depending on the resource in question, this could be an unforseeable change that could have disastrous consequences. The existing behavior seemed to assume safety unless proven unsafe. It would be incredibly bad for a series of poorly-timed transient network failures on fetches to result in an apply that destroys resources. Our usage prioritizes safety and we would prefer that the plan/apply bail if it cannot establish safety.

I realize that this is an opinionated change, but I suspect that most people who go out of their way to enable the merge strategy and undiverged requirement are expecting to make their processes as safe as possible. I was surprised by the behavior. If preferred, I could also lock this behavior behind an option. I'm not sure to what extent this would be a breaking change.

tests

references

[lukemassa]

This makes sense to me, could you include a note to the docs that this is the expected behavior?

[aggrand]

@lukemassa thank you; I have updated the PR to include a note in the docs!