RequiresReplace does not consider SemanticEquals

[oscarhermoso]

Currently, the RequiresReplace planmodifier doesn't respect StringSemanticEquals.

...this may not be a bug, it may be working as intended. If so, would be nice to have a new plan modifier - something like stringplanmodifier.RequiresReplaceIfSemanticallyDifferent()

Thankyou!

Module version

github.com/hashicorp/terraform-plugin-framework v1.15.0

Relevant provider source code

I have defined a custom value TrimmedStringValue which is essentially identical to StringValue, but it ignores leading/trailing whitespace when semantic equality is checked.

// trimmed_string_custom_type.go

var _ basetypes.StringValuable = TrimmedStringValue{}
var _ basetypes.StringValuableWithSemanticEquals = TrimmedStringValue{}

type TrimmedStringValue struct {
	basetypes.StringValue
}

// ... 

func (v TrimmedStringValue) StringSemanticEquals(ctx context.Context, newValuable basetypes.StringValuable) (bool, diag.Diagnostics) {
	var diags diag.Diagnostics

	// The framework should always pass the correct value type, but always check
	newValue, ok := newValuable.(TrimmedStringValue)
	if !ok {
		diags.AddError("Semantic Equality Check Error", "...")
		return false, diags
	}

	// ignore leading/training whitespace
	priorString := strings.TrimSpace(v.StringValue.ValueString())
	newString := strings.TrimSpace(newValue.ValueString())

	// If the strings are equivalent, keep the prior value
	return priorString == newString, diags
}

I then implement in in my schema with CustomType: TrimmedStringType{} and plan modifier stringplanmodifier.RequiresReplace().

// ssh_key_resource.go

func (r *sshKeyResource) Schema(ctx context.Context, req resource.SchemaRequest, resp *resource.SchemaResponse) {
	resp.Schema = resources.SshKeyResourceSchema(ctx)

	// ...

	publicKeyDescription := "The public key in OpenSSH \"authorized_keys\" format. This should be a valid public key, " +
		"such as one generated by `ssh-keygen`."
	resp.Schema.Attributes["public_key"] = schema.StringAttribute{
		Required:            true,
		Description:         publicKeyDescription,
		MarkdownDescription: publicKeyDescription,
		PlanModifiers:       []planmodifier.String{stringplanmodifier.RequiresReplace()},
		CustomType:          TrimmedStringType{}, // Ignore leading/trailing whitespace
	}
}

Terraform Configuration Files

I then test this in my unit tests

First test step:

resource "binarylane_ssh_key" "test" {
  name       = "tf-test-key-resource-test"
  public_key = "` + publicKey + `"
}

Second test step:

resource "binarylane_ssh_key" "test" {
  name  = "tf-test-key-resource-test"
	# Test public key with a newline to ensure it does not get recreated
  public_key = <<EOT
` + publicKey + `
EOT
}`

I am expecting an empty plan, with

	ConfigPlanChecks: resource.ConfigPlanChecks{
		PreApply: []plancheck.PlanCheck{
			plancheck.ExpectEmptyPlan(),
		},
	},

Debug Output

Not a full debug output, but should sufficient explain the issue:

=== NAME  TestSshKeyResource
    ssh_key_resource_test.go:22: Step 4/4 error: Pre-apply plan check(s) failed:
        expected empty plan, but binarylane_ssh_key.test has planned action(s): [delete create]

Expected Behavior

Plan is empty due to semantic equality.

Actual Behavior

Plan wants to delete & create resource.

Steps to Reproduce

1. Implement custom type and value with StringSemanticEquals
2. Define schema with plan modifier RequiresReplace
3. Modify string while maintaining semantic equality

References

• 🐝 Trim wrapping whitespace on ssh key oscarhermoso/terraform-provider-binarylane#76
• oscarhermoso/terraform-provider-binarylane@6d559de