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.
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.
Our previous state models in the "terraform" package had a few limitations
that are addressed here:
- Instance attributes were stored as map[string]string with dot-separated
keys representing traversals through a data structure. Now that we have
a full type system, it's preferable to store it as a real data
structure.
- The existing state structures skipped over the "resource" concept and
went straight to resource instance, requiring heuristics to decide
whether a particular resource should appear as a single object or as
a list of objects when used in configuration expressions.
- Related to the previous point, the state models also used incorrect
terminology where "ResourceState" was really a resource instance state
and "InstanceState" was really the state of a particular remote object
associated with an instance. These new models use the correct names for
each of these, introducing the idea of a "ResourceInstanceObject" as
the local record of a remote object associated with an instance.
This is a first pass at fleshing out a new model for state. Undoubtedly
there will be further iterations of this as we work on integrating these
new models into the "terraform" package.
These new model types no longer serve double-duty as a description of the
JSON state file format, since they are for in-memory use only. A
subsequent commit will introduce a separate package that deals with
persisting state to files and reloading those files later.
