fix: Avoid warnings in 'terraform output -json' (#38512)

[ChrisJr404]

Summary

Closes #38512.

The same backend deprecation warnings that #38487 suppressed for terraform output -raw also pollute stdout when running terraform output -json, breaking terraform output -json | jq … pipelines. As the issue reporter noted, the same fix shape applies.

Change

Apply the ErrorsOnly() filter the raw formatter already uses to the JSON formatter:

func (v *OutputJSON) Diagnostics(diags tfdiags.Diagnostics) {
	// filter out warnings as these wouldn't be expected in JSON mode
	// either: pipelines like `terraform output -json | jq` cannot
	// tolerate non-JSON content on stdout, and warnings typically don't
	// influence the exit code so the user cannot expect them in stdout.
	// Mirrors the same suppression added for `-raw` in #38487.
	errsOnly := diags.ErrorsOnly()
	v.view.Diagnostics(errsOnly)
}

The ErrorsOnly() helper added to tfdiags/diagnostics.go in #38487 is reused as-is — no new helper.

Test

TestOutputJSON_warningsSuppressed mirrors TestOutputRaw_warningsSuppressed introduced in #38487. It:

• reuses the output-backend-with-deprecation fixture
• registers the deprecatedInmemBackend that emits a deprecation warning during PrepareConfig
• runs terraform output -json foo
• asserts exit code 0
• asserts "deprecated" does not appear on stdout (the parseable-JSON gate that Deprecation warning pollutes STDOUT with output -json #38512 was reporting)
• asserts "deprecated" does not appear on stderr in this case (no error to surface)
• asserts the remaining stdout is the parseable JSON value \"bar\"

$ go test ./internal/command -run "TestOutput(Raw|JSON)_warningsSuppressed" -v
=== RUN   TestOutputRaw_warningsSuppressed
--- PASS: TestOutputRaw_warningsSuppressed (0.00s)
=== RUN   TestOutputJSON_warningsSuppressed
--- PASS: TestOutputJSON_warningsSuppressed (0.00s)
PASS

Changelog

Added .changes/v1.16/BUG FIXES-20260504-160000.yaml per the changie flow:

kind: BUG FIXES
body: Avoid warnings on stdout in 'terraform output -json' so the result remains parseable JSON
time: 2026-05-04T16:00:00.000000+00:00
custom:
    Issue: "38512"

Target Release

1.16.x (matches the target-1.16.x shape #38487 used; happy to add a backport label if you'd like this on 1.15.x as well, since the same break exists there).

Rollback Plan

This is a single-method change in views/output.go. Reverting the commit restores the prior behavior without any state migration concerns.

Notes for review

• I deliberately mirrored fix: Avoid warnings in terraform output -raw #38487's exact pattern instead of refactoring the two methods into a shared helper. The two Diagnostics impls are now nearly identical and could be hoisted into a nonHumanDiagnostics helper, but that would be a wider refactor than this bug fix — happy to do it as a follow-up if you'd prefer.
• The new test asserts JSON validity by string-comparing the trimmed stdout to "bar". If you'd prefer a json.Unmarshal round-trip assertion, easy to swap.

[hashicorp-cla-app]

All committers have signed the CLA.

[erpel]

Thanks for taking this on so quickly. A backport to 1.15.x would be greatly appreciated.

[ChrisJr404]

Thanks @erpel! Backports here are usually triggered by a maintainer adding a backport release/... label once the main PR merges. Happy to open the 1.15.x branch PR by hand if the maintainer prefers that route — let me know either way.

[crw]

Hi @ChrisJr404, thanks for this submission. Per https://github.com/hashicorp/terraform/blob/main/.github/CONTRIBUTING.md, is there a missing disclosure with regards to GenAI usage?

I will raise this in triage as the fix seems similar to a previous PR.

[radeksimko]

I'm fine with the solution but the reason behind is different and I think that should be reflected in the comment which I propose updating.

As per @crw's question - Can you also clarify whether AI was used to prepare this PR?

Thanks.

[radeksimko]

Suggested change

	// filter out warnings as these wouldn't be expected in JSON mode
	// either: pipelines like `terraform output -json | jq` cannot
	// tolerate non-JSON content on stdout, and warnings typically don't
	// influence the exit code so the user cannot expect them in stdout.
	// Mirrors the same suppression added for `-raw` in #38487.
	// filter out warnings as we cannot change the current format
	// to introduce them gracefully (without breaking existing usage)

[github-actions]

Changelog Warning

Currently this PR would target a v1.15 release. Please add a changelog entry for in the .changes/v1.15 folder, or discuss which release you'd like to target with your reviewer. If you believe this change does not need a changelog entry, please add the 'no-changelog-needed' label.