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 is a wrapper around State that is able to perform higher-level
manipulations (at the granularity of the entire state) in a
concurrency-safe manner, using the lower-level APIs exposed by State and
all of the types it contains.
The granularity of a SyncState operation roughly matches the granularity
off a state-related EvalNode in the "terraform" package, performing a
sequence of more primitive operations while guaranteeing atomicity of the
entire change.
As a compromise for convenience of usage, it's still possible to access
the individual state data objects via this API, but they are always copied
before returning to ensure that two distinct callers cannot have data
races. Callers should access the most granular object possible for their
operation.
Martin Atkins