refactor: Make NewPluggable return a Pluggable concrete type, instead of an instance of the backend.Backend interface.

Author: SarahFrench

internal/backend/pluggable/pluggable.go

@@ -28,7 +28,7 @@ import (
 //
 // By wrapping a configured provider in a Pluggable we allow calling code
 // to use the provider's gRPC methods when interacting with state.
-func NewPluggable(p providers.Interface, typeName string) (backend.Backend, error) {
+func NewPluggable(p providers.Interface, typeName string) (*Pluggable, error) {
 	if p == nil {
 		return nil, errors.New("Attempted to initialize pluggable state with a nil provider interface. This is a bug in Terraform and should be reported")
 	}

internal/backend/pluggable/pluggable_test.go

@@ -417,12 +417,7 @@ func TestPluggable_ProviderSchema(t *testing.T) {
 			t.Fatalf("unexpected error: %s", err)
 		}
 
-		// Calling code will need to case to Pluggable after using NewPluggable,
-		// so we do something similar in this test
-		var providerSchema *configschema.Block
-		if pluggable, ok := p.(*Pluggable); ok {
-			providerSchema = pluggable.ProviderSchema()
-		}
+		providerSchema := p.ProviderSchema()
 
 		if !mock.GetProviderSchemaCalled {
 			t.Fatal("expected ProviderSchema to call the GetProviderSchema RPC")
@@ -450,12 +445,7 @@ func TestPluggable_ProviderSchema(t *testing.T) {
 			t.Fatalf("unexpected error: %s", err)
 		}
 
-		// Calling code will need to case to Pluggable after using NewPluggable,
-		// so we do something similar in this test
-		var providerSchema *configschema.Block
-		if pluggable, ok := p.(*Pluggable); ok {
-			providerSchema = pluggable.ProviderSchema()
-		}
+		providerSchema := p.ProviderSchema()
 
 		if !mock.GetProviderSchemaCalled {
 			t.Fatal("expected ProviderSchema to call the GetProviderSchema RPC")

internal/command/meta_backend.go

@@ -1946,7 +1946,6 @@ func (m *Meta) savedStateStore(sMgr *clistate.LocalState, factory providers.Fact
 	// The provider and state store will be configured using the backend state file.
 
 	var diags tfdiags.Diagnostics
-	var b backend.Backend
 
 	if factory == nil {
 		diags = diags.Append(&hcl.Diagnostic{
@@ -2099,7 +2098,7 @@ func (m *Meta) savedStateStore(sMgr *clistate.LocalState, factory providers.Fact
 
 	// Now we have a fully configured state store, ready to be used.
 	// To make it usable we need to return it in a backend.Backend interface.
-	b, err = backendPluggable.NewPluggable(provider, s.StateStore.Type)
+	b, err := backendPluggable.NewPluggable(provider, s.StateStore.Type)
 	if err != nil {
 		diags = diags.Append(err)
 	}