terraform: Use real version in UA header

[radeksimko]

The existing implementation leverages Terraform's version package as Terraform currently provides the SDK for interacting with core and is therefore imported by the provider, including the version package.

The side effect of this is that provider reports version of vendored Terraform (i.e. plugin SDK), not the version which actually talks to the provider's gRPC server and parses the configuration.

This PR is leveraging recent changes introduced in 0.12 to fix that and report accurate version.

---

This also changes the header from the following

Terraform/X.Y.Z (+https://www.terraform.io)

to

HashiCorp Terraform/X.Y.Z (+https://www.terraform.io)

to align UA string with hashicorp/terraform#22272

---

This also requires bumping github.com/hashicorp/terraform to the latest revision from master - I'm not sure how to do that in the context of this project though.

Release Note for Downstream PRs (will be copied)

[modular-magician]

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[abombss]

Will this change force people to use TF 0.12 or will it be backward compatible with 0.11? What is the strategy for the Google Terraform provider to maintain backward compatibility and are their any tests to verify that?

[radeksimko]

Generally speaking we don't have extensive testing CI in place for this specific scenario, but the protocol changes are additive and we intend to keep it backwards compatible (certainly protocol-wise) until we start versioning the plugin SDK separately - which will be communicated appropriately and this is the first step towards that direction.

The future extracted plugin SDK (not published yet) will not offer version package anymore (which httpclient.UserAgentString() basically exposes, so that will go away too), so if providers want to get the Terraform version in the future, getting it through the protocol will be the only way.
At that point (on go module level) we will be versioning that standalone SDK which providers depend on and that will define the compatibility layer per plugin protocol and the protocol versioning along with plugin SDK versioning will communicate breaking changes through semver.

This specific change will not force people to use any particular Terraform version - it will just report accurate version (sent by Terraform binary over gRPC to the provider binary) if people use 0.12+, rather than reporting 0.12 "statically" for latest version of the provider, just because the provider vendors Terraform 0.12 at it depends on Terraform plugin SDK which is part of the same repo now.

[paddycarver]

This looks reasonable enough to me.

[paddycarver]

I think when the downstreams are merged we can go ahead and generate the PRs from this and get them merged.

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
This PR seems not to have generated downstream PRs before, as of 1fd42c2.

Pull request statuses

No diff detected in Inspec.

New Pull Requests

I built this PR into one or more new PRs on other repositories, and when those are closed, this PR will also be merged and closed.
depends: hashicorp/terraform-provider-google-beta#1107
depends: GoogleCloudPlatform/terraform-google-conversion#186
depends: hashicorp/terraform-provider-google#4374
depends: modular-magician/ansible#379

[modular-magician]

Hi! I'm the modular magician, I work on Magic Modules.
I see that this PR has already had some downstream PRs generated. Any open downstreams are already updated to your most recent commit, 1fd42c2.

Pull request statuses

terraform-provider-google-beta already has an open PR.
terraform-google-conversion already has an open PR.
terraform-provider-google already has an open PR.
No diff detected in Ansible.
No diff detected in Inspec.

New Pull Requests

I didn't open any new pull requests because of this PR.