The upgrade guide had its last major upgrade while we were preparing for
the alpha releases. Now that the upgrade tool is more complete we can
describe the required changes in terms of that tool, and also add
additional information about provider upgrades.
We will revise this at least one more time before v0.12.0 final, but this
is an interim copy of the upgrade guide intended to help those who are
testing the beta releases.
This mirrors the change made for providers, so that default values can
be inserted into the config by the backend implementation. This is only
the interface and method name changes, it does not yet add any default
values.
We brought forward a new implementation of "terraform validate" that was
originally scheduled for a later release after finding that it would be
simpler than reworking the old implementation for new v0.12 assumptions,
but we didn't yet implement "terraform plan -validate-only" in spite of
it being mentioned in the updated docs for "terraform validate".
For now then, the documentation will make the weaker suggestion of running
"terraform plan" to validate a particular _run_ rather than a particular
_module_, which is the closest thing we have for now. At some point after
v0.12.0 we will evaluate whether a validate-only mode for "terraform plan"
(which could then run without configuring the providers at all) is needed.
Previously we checked can-update in order to determine if a user had the
required permissions to apply a run, but that wasn't sufficient. So we
added a new permission, can-queue-apply, that we now use instead.
A common new-user mistake is to place variable _declarations_ into .tfvars
files instead of variable _values_. To guide towards the correct approach
here, we add a specialized error message for that situation that includes
guidance on the distinction between declaring and setting values for
variables, and an example of what setting a value should look like.
Terraform 0.11 and prior had an odd special case where a resource
attribute access for "count" would be resolved as the count for the
whole resource, rather than as an attribute of an individual instance as
for all other attributes.
Because Terraform 0.12 makes test_instance.foo appear as a list when count
is set (so it can be used in other expressions), it's no longer possible
to have an attribute in that position: lists don't have attributes.
Fortunately we don't really need that special case anymore since it
doesn't do anything we can't now do with the length(...) function.
This upgrade rule, then, detects references like test_instance.foo.count
and rewrites to length(test_instance.foo). As a special case, if
test_instance.foo doesn't have "count" set then it just rewrites as the
constant 1, which mimics what would've happened in that case in Terraform
0.11.
Mars Hall