This is the provider-side UpgradeState implementation for a particular
resource. This new function will be called to upgrade a saved state with
an old schema version to the current schema.
UpgradeState also requires a record of the last schema and version that
could have been stored as a flatmapped state. If the stored state is in
the legacy flatmap format, this will allow the provider to properly
decode the flatmapped state into the expected structure for the new json
encoded state. If the stored state's version is below that of the
LegacySchema.Version value, it will first be processed by the legacy
MigrateState function.
The schema package provides a high-level interface for writing resource
providers for Terraform.
If you're writing a resource provider, we recommend you use this package.
The interface exposed by this package is much friendlier than trying to
write to the Terraform API directly. The core Terraform API is low-level
and built for maximum flexibility and control, whereas this library is built
as a framework around that to more easily write common providers.
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