Previously the logic for inferring a provider type from a resource name
was buried a utility function in the 'terraform' package. Instead here we
lift it up into the 'config' package where we can make broader use of it
and where it's easier to discover.
duplicate entries could end up in "depends_on" in the state, which could
possible lead to erroneous state comparisons. Remove them when walking
the graph, and remove existing duplicates when pruning the state.
* "external" provider for gluing in external logic
This provider will become a bit of glue to help people interface external
programs with Terraform without writing a full Terraform provider.
It will be nowhere near as capable as a first-class provider, but is
intended as a light-touch way to integrate some pre-existing or custom
system into Terraform.
* Unit test for the "resourceProvider" utility function
This small function determines the dependable name of a provider for
a given resource name and optional provider alias. It's simple but it's
a key part of how resource nodes get connected to provider nodes so
worth specifying the intended behavior in the form of a test.
* Allow a provider to export a resource with the provider's name
If a provider only implements one resource of each type (managed vs. data)
then it can be reasonable for the resource names to exactly match the
provider name, if the provider name is descriptive enough for the
purpose of the each resource to be obvious.
* provider/external: data source
A data source that executes a child process, expecting it to support a
particular gateway protocol, and exports its result. This can be used as
a straightforward way to retrieve data from sources that Terraform
doesn't natively support..
* website: documentation for the "external" provider
Adds an "alias" field to the provider which allows creating multiple instances
of a provider under different names. This provides support for configurations
such as multiple AWS providers for different regions. In each resource, the
provider can be set with the "provider" field.
(thanks to Cisco Cloud for their support)
