Support upgrading resource state #42
Description
Module version
N/A
Use-cases
Sometimes resource schemas change over time and need massaging to be converted to the new format. This isn't usually needed; a refresh should update everything nicely. But if some values can't be populated by refresh, or refresh can't run without some values, and those values need to be migrate to a new data type or format, then provider-assisted state upgrades are necessary.
We should offer an optional method on resource types to support this callback.
Attempted Solutions
N/A
Proposal
Add an optional method on the Resource interface that lets providers modify the state when Terraform calls UpgradeResourceState.