This is a light revamp of our plan output to make use of Terraform core's
new ability to report both the previous run state and the refreshed state,
allowing us to explicitly report changes made outside of Terraform.
Because whether a plan has "changes" or not is no longer such a
straightforward matter, this now merges views.Operation.Plan with
views.Operation.PlanNoChanges to produce a single function that knows how
to report all of the various permutations. This was also an opportunity
to fill some holes in our previous logic which caused it to produce some
confusing messages, including a new tailored message for when
"terraform destroy" detects that nothing needs to be destroyed.
This also allows users to request the refresh-only planning mode using a
new -refresh-only command line option. In that case, Terraform _only_
performs drift detection, and so applying a refresh-only plan only
involves writing a new state snapshot, without changing any real
infrastructure objects.
This allows a similar effect to pre-tainting an object but does the action
within the context of a normal plan and apply, avoiding the need for an
intermediate state where the old object still exists but is marked as
tainted.
The core functionality for this was already present, so this commit is
just the UI-level changes to make that option available for use and to
explain how it contributed to the resulting plan in Terraform's output.
So far we've only had "normal mode" and "destroy mode", where the latter
is activated either by "terraform plan -destroy" or "terraform destroy".
In preparation for introducing a third mode "refresh only" this
generalizes how we handle modes so we can potentially deal with an
arbitrary number of modes, although for now we only intend to have three.
Mostly this is just a different implementation of the same old behavior,
but there is one small user-visible difference here: the "terraform apply"
command now accepts a -destroy option, mirroring the option of the same
name on "terraform plan", which in turn makes "terraform destroy"
effectively a shorthand for "terraform apply -destroy".
This is intended to make us consistent that "terraform apply" without a
plan file argument accepts all of the same plan-customization options that
"terraform plan" does, which will in turn avoid us having to add a new
alias of "terraform plan" for each new plan mode we might add. The -help
output is changed in that vein here, although we'll wait for subsequent
commit to make a similar change to the website documentation just so we
can deal with the "refresh only mode" docs at the same time.
The auto-approve argument was part of the arguments.Operation type,
which resulted in adding a silent -auto-approve flag to plan and
refresh. This was unintended, and is fixed in this commit by moving the
flag to the arguments.Apply type and updating the downstream callers.
Martin Atkins