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.
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.
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 new format is radically different in than the old in physical
structure, but still has the same logical parts: the plan itself, a
snapshot of the input configuration, and a snapshot of the state as it
existed when the plan was created.
Rather than creating plan-specific serializations of state and config, the
new format instead leans on the existing file formats implemented
elsewhere, wrapping the result up in a zip archive with some internal file
naming conventions.
The plan portion of the file is serialized with protobuf, consistent with
our general strategy of replacing all use of encoding/gob with protobuf
moving forward.
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