Since these error messages get printed in Terraform's output and we
encourage users to share them as part of bug reports, we should avoid
including sensitive information in them to reduce the risk of accidental
exposure.
Previously we were just asserting that the number of elements didn't grow
between planned and actual. We still can't precisely correlate elements in
sets with unknown values, but here we adapt some logic we added earlier
to config/hcl2shim to ensure that we can find a plausible correlation for
each element in each set to at least one element in the other set, and
thus catch more cases where set elements might vanish or appear between
plan and apply, for improved safety.
This will still generate false negatives in some cases where unknown
values are present due to having to assume correlation is intended
wherever it is possible, but we'll catch situations where the actual value
is obviously contrary to what was planned.
This function's goal is to ensure that the "final" plan value produced
by a provider during the apply step is always consistent with the known
parts of the planned value produced during the plan step.
Any error produced here indicates a bug in the provider.
Martin Atkins