We will need access to this information in order to render interactive
input prompts, and it will also be useful in returning schema information
to external tools such as text editors that have autocomplete-like
functionality.
In order to parse provider, resource and data source configuration from
HCL2 config files, we need to know the relevant configuration schema.
This new method allows Terraform Core to request these from a provider.
This is a breaking change to this interface, so all of its implementers
in this package are updated too. This includes concrete implementations
of the new method in helper/schema that use the schema conversion code
added in an earlier commit to produce a configschema.Block automatically.
Plugins compiled against prior versions of helper/schema will not have
support for this method, and so calls to them will fail. Callers of
this new method will therefore need to sniff for support using the
SchemaAvailable field added to both ResourceType and DataSource.
This careful handling will need to persist until next time we increment
the plugin protocol version, at which point we can make the breaking
change of requiring this information to be available.
We don't currently have any need for this information, but we're
propagating it out of helper/schema here pre-emptively so that once we
later have a use for it we will not need to rebuild the providers to gain
access to it.
The long-term expected use-case for this is to have Terraform Core use
static analysis techniques to trace the path of sensitive data through
interpolations so that intermediate results can be flagged as sensitive
too, but we have a lot more work to do before such a thing would actually
be possible.
As part of moving to the next-generation HCL implementation,
Terraform Core is getting its own representation of configuration schema
that is tailored for configuration-processing use-cases. The capabilities
of this are a subset of the helper/schema model primarily concerned with
the configuration structure and value types, leaving detailed validation
and defaults for helper/schema to still solve.
These new methods allow mechanical creation of a schema in the new Core
schema model from a schema expressed in the helper/schema model. This is
not yet used as of this commit, but will be used later to implement some
new ResourceProvider methods that will allow core to obtain the schema
for provider, resource and data source configuration while remaining
source-compatible with existing provider implementations.
Martin Atkins