The template resources don't actually need to retain any state, so they
are good candidates to be data sources.
This includes a few tweaks to the acceptance tests -- now configured to
run as unit tests -- since it seems that they have been slightly broken
for a while now. In particular, the "update" cases are no longer tested
because updating is not a meaningful operation for a data source.
I noticed we had two mechanisms for unit test override. One that dropped
a sentinel into the env var, and another with a struct member on
TestCase. This consolidates the two, using the cleaner struct member
internal mechanism and the nicer `resource.UnitTest()` entry point.
The work integrated in hashicorp/terraform#6322 silently broke the
ability to use remote state correctly. This commit adds a fix for that,
making use of the work integrated in hashicorp/terraform#7124.
In order to deal with outputs which are complex structures, we use a
forked version of the flatmap package - the difference in the version
this commit vs the github.com/hashicorp/terraform/flatmap package is
that we add in an additional key for map counts which state requires.
Because we bypass the normal helper/schema mechanism, this is not set
for us.
Because of the HIL type checking of maps, values must be of a homogenous
type. This is unfortunate, as it means we can no longer refer to outputs
as:
${terraform_remote_state.foo.output.outputname}
Instead we had to bring them to the top level namespace:
${terraform_remote_state.foo.outputname}
This actually does lead to better overall usability - and the BC
breakage is made better by the fact that indexing would have broken the
original syntax anyway.
We also add a real-world test and assert against specific values. Tests
which were previously acceptance tests are now run as unit tests, so
regression should be identified at a much earlier stage.
As a first example of a real-world data source, the pre-existing
terraform_remote_state resource is adapted to be a data source. The
original resource is shimmed to wrap the data source for backward
compatibility.
