Previously we used a single plan action "Replace" to represent both the
destroy-before-create and the create-before-destroy variants of replacing.
However, this forces the apply graph builder to jump through a lot of
hoops to figure out which nodes need it forced on and rebuild parts of
the graph to represent that.
If we instead decide between these two cases at plan time, the actual
determination of it is more straightforward because each resource is
represented by only one node in the plan graph, and then we can ensure
we put the right nodes in the graph during DiffTransformer and thus avoid
the logic for dealing with deposed instances being spread across various
different transformers and node types.
As a nice side-effect, this also allows us to show the difference between
destroy-then-create and create-then-destroy in the rendered diff in the
CLI, although this change doesn't fully implement that yet.
During the plan operation we need to retain _somewhere_ the planned
changes for all outputs so we can refer to them during expression
evaluation. For consistency with how we handle resource instance changes,
we'll keep them in the plan so we can properly retain unknown values,
which cannot be written to state.
As with output values in the state, only root output plans are retained
in a round-trip through the on-disk plan file format, but that's okay
because we can trivially re-calculate all of these during apply. We
include the _root_ outputs in the plan file only because they are
externally-visible side effects that ought to be included in any rendering
of the plan made from the plan file for user inspection.
Since we do our deletes using a separate graph node from all of the other
actions, and a "Replace" change implies both a delete _and_ a create, we
need to pretend at apply time that a single replace change was actually
two separate changes.
This will also early-exit eval if a destroy node finds a non-Delete change
or if an apply node finds a Delete change. These should not happen in
practice because we leave these nodes out of the graph when they are not
needed for the given action, but we do this here for robustness so as not
to have an invisible dependency between the graph builder and the eval
phase.
We were previously tracking this as a []cty.Path, but having it turned
into a pathset on creation makes downstream use of it more convenient and
ensures that it'll obey expected invariants like not containing the same
path twice.
This allows a provider to retain arbitrary extra data in the plan and
make use of it during apply. The contents are not used by Terraform and
never shown to the user.
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.
The types here were originally written to allow us to defer decoding of
object values until schemas are available, but it turns out that this was
forcing us to defer decoding longer than necessary and potentially decode
the same value multiple times.
To avoid this, we create pairs of types to represent the encoded and
decoded versions and methods for moving between them. These types are
identical to one another apart from how the dynamic values are
represented.
This allows us to record the resource-to-provider associations we made
during the plan phase and ensure that we use the same config during
apply.
This isn't technically necessary, since we can in principle just repeat
the same matching algorithm against the config, but that algorithm is
relatively complicated and so if we execute it just once during plan we
remove the risk of bugs causing different decisions to be made during
the apply phase.
This also includes updates to the plan file format to include the provider
addresses. Since we've not actually shipped any version of Terraform
using our protobuf schema yet, we renumber here all of the fields after
the new one to keep them incrementing consecutively. This example should
not be followed after we have a released version of Terraform using this,
as a courtesy to anyone trying to parse these files (even though we're
not yet guaranteeing compatibility between releases).
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