Prior to v0.12 Terraform was liberal about these and allowed them to
mismatch, but now it's important to get this right so that resources
and resource instances can be used directly as object values, and so
we'll fix up any sloppy existing references so things keep working as
expected.
This is particularly important for the pattern of using count to create
conditional resources, since previously the "true" case would create one
instance and Terraform would accept an unindexed reference to that.
The reference syntax is not significantly changed, but there are some
minor additional restrictions on identifiers in HCL2 and as a special case
we need to rewrite references to data.terraform_remote_state .
Along with those mandatory upgrades, we will also switch references to
using normal index syntax where it's safe to do so, as part of
de-emphasizing the old strange integer attribute syntax (like foo.0.bar).
Martin Atkins