hashicorp/terraform · error

Failed to marshal get attr step name %#v

Error message

Failed to marshal get attr step name %#v: %s

What it means

Thrown by jsonplan.encodePath for a cty.GetAttrStep: the attribute name (a Go string) is passed to encoding/json.Marshal and that call failed. Because s.Name is an ordinary string, this branch is virtually unreachable under normal operation; hitting it implies memory corruption, an extremely unusual rune set, or a json encoder whose Encode method was replaced/misconfigured.

Solutions

1. Upgrade Terraform to rule out a transient/tooling issue.
2. Inspect whether any linked code overrides encoding/json behavior.
3. Report upstream with the %#v of the name from the message.

if _, err := jsonplan.Marshal(plans); err != nil {
    // This branch is effectively unreachable; if hit, suspect a swapped json encoder.
    log.Printf("attr-step marshal failed unexpectedly: %v", err)
    return err
}

When it happens

Trigger: A GetAttrStep.Name value that the json encoder cannot serialize; a customized/monkey-patched json.Marshal in the process; an empty struct masquerading as a string due to unsafe casts.

Common situations: Effectively only seen in test harnesses or build-time instrumentation that swaps the json encoder; not a realistic end-user failure.

Related errors

• Failed to marshal index step key %#v
• Unsupported path step %#v (%t)
• cannot decode tfvars from a null value
• could not decode output
• could not interpret output

AI-assisted analysis of hashicorp/terraform@d32a084675 (2026-08-11). Data as JSON: /api/errors/9cc1a54b733992b3. Report an issue: GitHub.

Appendix: source

Thrown at internal/command/jsonplan/plan.go:1078

	}

	return json.Marshal(jsonPaths)
}

func encodePath(path cty.Path) (json.RawMessage, error) {
	steps := make([]json.RawMessage, 0, len(path))
	for _, step := range path {
		switch s := step.(type) {
		case cty.IndexStep:
			key, err := ctyjson.Marshal(s.Key, s.Key.Type())
			if err != nil {
				return nil, fmt.Errorf("Failed to marshal index step key %#v: %s", s.Key, err)
			}
			steps = append(steps, key)
		case cty.GetAttrStep:
			name, err := json.Marshal(s.Name)
			if err != nil {
				return nil, fmt.Errorf("Failed to marshal get attr step name %#v: %s", s.Name, err)
			}
			steps = append(steps, name)
		default:
			return nil, fmt.Errorf("Unsupported path step %#v (%t)", step, step)
		}
	}
	return json.Marshal(steps)
}

View on GitHub (pinned to d32a084675)