Fix terraform_remote_state backend version check

[alisdair]

The change recently introduced to ensure that remote backend users do not accidentally upgrade their state file (#26947) needs to be disabled for all read-only uses, including the builtin terraform_remote_state data source. Without doing this, the remote state data source fails to read state from remote backend sources which do not have an exactly matching Terraform version.

I don't see any reasonable way to add automated tests for this change. Here is an example of the manual verification I'm doing:

data "terraform_remote_state" "sfv" {
  backend = "remote"

  config = {
    workspaces = {
      name = "sfv"
    }
    organization = "alisdair-v2"
  }
}

output "foobar" {
  value = data.terraform_remote_state.sfv.outputs.foobar
}

If approved, I intend to backport this change to 0.14, 0.13, and 0.12.

Fixes #27200

[codecov]

Codecov Report

Merging #27197 (107dc0c) into master (93c36e6) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

Impacted Files	Coverage Δ
builtin/providers/terraform/data_source_state.go	87.42% <0.00%> (-1.12%)	⬇️
internal/providercache/dir.go	67.34% <0.00%> (-6.13%)	⬇️
terraform/node_resource_plan.go	96.11% <0.00%> (-1.95%)	⬇️
dag/marshal.go	61.90% <0.00%> (-1.59%)	⬇️
terraform/evaluate.go	52.89% <0.00%> (-0.42%)	⬇️

[apparentlymart]

I'm not really sure I understand why "is the enhanced remote backend" is the right condition here, but the testing procedure you showed in the writeup makes sense to me and this seems to be an urgent-type fix so I'm approving this with the goal of understanding why this is the right answer later, after we've got the release done. 😀

[alisdair]

I'm not really sure I understand why "is the enhanced remote backend" is the right condition here

If I understand what you mean here, this is because the change in #26947 was only implemented as a method on the remote backend type—other backends used for remote state don't have an equivalent method.

[ghost]

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