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.
Martin Atkins