feat(zero_trust_device_posture_rule): improve v4 to v5 migration

[tamas-jozsa]

Summary

Implements migration support for the name field in zero_trust_device_posture_rule resource when upgrading from provider v4 to v5. The name field was optional in v4 but became required in v5, requiring special handling during migration.

Problem

In v4, the name field was optional for device posture rules. When users didn't provide a name, the API stored an empty string. In v5, the name field is required, causing migration failures for resources that were created without names.

Solution

Implements a three-tier fallback strategy to automatically populate missing names during migration:

1. State lookup: Check v4 state for existing name
2. API fallback: Query Cloudflare API for the actual resource name if state is empty
3. Resource name fallback: Use Terraform resource name as last resort

This ensures all v4 configurations migrate successfully to v5 without requiring manual intervention.

Implementation Details

Core Changes

v4_to_v5.go:

• Added name field detection and population logic in TransformConfig()
• Implemented fetchNameFromAPI() to retrieve resource names from Cloudflare API
• Direct parsing of ctx.StateJSON using gjson for state lookups
• Fallback chain ensures valid config generation in all scenarios

main.go:

• Added user-visible logging for state file operations:
  • ✓ Loaded state file for config cross-referencing
  • ⚠ Failed to read state file
  • ℹ No state file specified

Test Coverage

v4_to_v5_test.go:

• Test: Name field populated from state when missing in config
• Test: Name field not overwritten when present in config
• Test: Graceful fallback to resource name when state is nil
• Simplified test structure to use standard TransformConfig() method

Testing

All unit tests pass:
✓ TestConfigTransformation (11 subtests)
✓ TestConfigTransformationWithState (3 subtests)
✓ TestStateTransformation (12 subtests)

Acceptance test passes with real API:
✓ TestMigrateDevicePostureRuleWithoutName - Verifies v4 resources without names successfully migrate to v5

Migration Behavior

Before:

# v4 config (name optional, not specified)
resource "cloudflare_device_posture_rule" "example" {
  account_id = "abc123"
  type       = "os_version"
  # name not specified
}

After Migration:
# v5 config (name required, auto-generated)
resource "cloudflare_zero_trust_device_posture_rule" "example" {
  account_id = "abc123"
  type       = "os_version"
  name       = "example"  # ← Automatically added using resource name
}

The migration tool now handles this transformation automatically, preventing migration failures.