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.
Until now we've not really cared much about the state snapshot produced
by the previous Terraform operation, except to use it as a jumping-off
point for our refresh step.
However, we'd like to be able to report to an end-user whenever Terraform
detects a change that occurred outside of Terraform, because that's often
helpful context for understanding why a plan contains changes that don't
seem to have corresponding changes in the configuration.
As part of reporting that we'll need to keep track of the state as it
was before we did any refreshing work, so we can then compare that against
the state after refreshing. To retain enough data to achieve that, the
existing Plan field State is now two fields: PrevRunState and PriorState.
This also includes a very shallow change in the core package to make it
populate something somewhat-reasonable into this field so that integration
tests can function reasonably. However, this shallow implementation isn't
really sufficient for real-world use of PrevRunState because we'll
actually need to update PrevRunState as part of planning in order to
incorporate the results of any provider-specific state upgrades to make
the PrevRunState objects compatible with the current provider schema, or
else our diffs won't be valid. This deeper awareness of PrevRunState in
Terraform Core will follow in a subsequent commit, prior to anything else
making use of Plan.PrevRunState.
This is to make it more obvious at all uses of this field that it's not
something to be used for anything other than UI decisions, hopefully
prompting a reader of code elsewhere to refer to the comments to
understand why it has this unusual prefix and thus see what its intended
purpose is.
This only includes the internal mechanisms to make it work, and not any
of the necessary UI changes to "terraform plan" and "terraform apply" to
activate it yet.
The force-replace options are ultimately handled inside the
NodeAbstractResourceInstance.plan method, at the same place we handle the
similar situation of the provider indicating that replacement is needed,
and so the rest of the changes here are just to propagate the settings
through all of the layers in order to reach that point.
This only includes the core mechanisms to make it work. There's not yet
any way to turn this mode on as an end-user, because we have to do some
more work at the UI layer to present this well before we could include it
as an end-user-visible feature in a release.
At the lowest level of abstraction inside the graph nodes themselves, this
effectively mirrors the existing option to disable refreshing with a new
option to disable change-planning, so that either "half" of the process
can be disabled. As far as the nodes are concerned it would be possible
in principle to disable _both_, but the higher-level representation of
these modes prevents that combination from reaching Terraform Core in
practice, because we block using -refresh-only and -refresh=false at the
same time.
Since the refreshed state is now an artifact of the plan process, it
makes sense to add it to the Plan type, rather than adding an additional
return value to the Context.Plan method.
Due to how often the state and plan types are referenced throughout
Terraform, there isn't a great way to switch them out gradually. As a
consequence, this huge commit gets us from the old world to a _compilable_
new world, but still has a large number of known test failures due to
key functionality being stubbed out.
The stubs here are for anything that interacts with providers, since we
now need to do the follow-up work to similarly replace the old
terraform.ResourceProvider interface with its replacement in the new
"providers" package. That work, along with work to fix the remaining
failing tests, will follow in subsequent commits.
The aim here was to replace all references to terraform.State and its
downstream types with states.State, terraform.Plan with plans.Plan,
state.State with statemgr.State, and switch to the new implementations of
the state and plan file formats. However, due to the number of times those
types are used, this also ended up affecting numerous other parts of core
such as terraform.Hook, the backend.Backend interface, and most of the CLI
commands.
Just as with 5861dbf3fc49b19587a31816eb06f511ab861bb4 before, I apologize
in advance to the person who inevitably just found this huge commit while
spelunking through the commit history.
We shouldn't really need these because the plan is already filtered to
include diffs only for targeted resources, but we currently rely on this
to filter out non-resource items from the diff, and so we'll retain it
for now to avoid reworking how the apply-time graph builder works.
On the first pass here we erroneously assumed that this was redundant with
the backend settings embedded in the configuration itself. In practice,
users can override backend configuration when running "terraform init"
and so we need to record the _effective_ backend configuration.
Along with this, we also return the selected workspace name at the time
the plan was created so we'll later be able to produce a specialized error
for the situation of having the wrong workspace selected. This isn't
strictly required because we'll also check the lineage of the state, but
the error message that would result from that failure would be relatively
opaque and thus less helpful to the user.
Since schemas are required to interpret provider, resource, and
provisioner attributes in configs, states, and plans, these helpers intend
to make it easier to gather up the the necessary provider types in order
to preload all of the needed schemas before beginning further processing.
Config.ProviderTypes returns directly the list of provider types, since
at this level further detail is not useful: we've not yet run the
provider allocation algorithm, and so the only thing we can reliably
extract here is provider types themselves.
State.ProviderAddrs and Plan.ProviderAddrs each return a list of
absolute provider addresses, which can then be turned into a list of
provider types using the new helper providers.AddressedTypesAbs.
Since we're already using configs.Config throughout core, this also
updates the terraform.LoadSchemas helper to use Config.ProviderTypes
to find the necessary providers, rather than implementing its own
discovery logic. states.State is not yet plumbed in, so we cannot yet
use State.ProviderAddrs to deal with the state but there's a TODO comment
to remind us to update that in a later commit when we swap out
terraform.State for states.State.
A later commit will probably refactor this further so that we can easily
obtain schema for the providers needed to interpret a plan too, but that
is deferred here because further work is required to make core work with
the new plan types first. At that point, terraform.LoadSchemas may become
providers.LoadSchemas with a different interface that just accepts lists
of provider and provisioner names that have been gathered by the caller
using these new helpers.
The types in this package are intended to replace plan- and diff-related
types from the "terraform" package, although those older types must remain
for now so that they can be used to implement shims for older codepaths.
type "Changes" is approximately equivalent to terraform.Diff, but renamed
since it now describes whole objects before and after rather than an
attribute-level diff as before. The term "diff" is now reserved for the
visual rendition of the changes we'll display to the user, although
rendering of this new Changes model is not yet implemented.
Martin Atkins