By observing the sorts of questions people ask in the community, and the
ways they ask them, we've inferred that various different people have been
confused by Terraform reporting that a value won't be known until apply
or that a value is sensitive as part of an error message when that message
doesn't actually relate to the known-ness and sensitivity of any value.
Quite reasonably, someone who sees Terraform discussing an unfamiliar
concept like unknown values can assume that it must be somehow relevant to
the problem being discussed, and so in that sense Terraform's current
error messages are giving "too much information": information that isn't
actually helpful in understanding the problem being described, and in the
worst case is a distraction from understanding the problem being described.
With that in mind then, here we introduce an explicit annotation on
diagnostic objects that are directly talking about unknown values or
sensitive values, and then the diagnostic renderer will react to that to
avoid using the terminology "known only after apply" or "sensitive" in the
generated diagnostic annotations unless we're rendering a message that is
explicitly related to one of those topics.
This ends up being a bit of a cross-cutting concern because the code that
generates these diagnostics and the code that renders them are in separate
packages and are not directly aware of each other. With that in mind, the
logic for actually deciding for a particular diagnostic whether it's
flagged in one of these special ways lives inside the tfdiags package as
an intermediation point, which both the diagnostic generator (in the core
package) and the diagnostic renderer can both depend on.
Our original messaging here was largely just lifted from the equivalent
message for unknown values in "count", and it didn't really include any
specific advice on how to update a configuration to make for_each valid,
instead focusing only on the workaround of using the -target planning
option.
It's tough to pack in a fully-actionable suggestion here since unknown
values in for_each keys tends to be a gnarly architectural problem rather
than a local quirk -- when data flows between modules it can sometimes be
unclear whether it'll end up being used in a context which allows unknown
values.
I did my best to summarize the advice we've been giving in community forum
though, in the hope that more people will be able to address this for
themselves without asking for help, until we're one day able to smooth
this out better with a mechanism such as "partial apply".
This is part of a general effort to move all of Terraform's non-library
package surface under internal in order to reinforce that these are for
internal use within Terraform only.
If you were previously importing packages under this prefix into an
external codebase, you could pin to an earlier release tag as an interim
solution until you've make a plan to achieve the same functionality some
other way.
