Allow use of backend block to set initial state for a state key

internal/backend/local/test.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/zclconf/go-cty/cty"
 
+	"github.com/hashicorp/terraform/internal/backend"
 	"github.com/hashicorp/terraform/internal/backend/backendrun"
 	"github.com/hashicorp/terraform/internal/command/junit"
 	"github.com/hashicorp/terraform/internal/command/views"
@@ -29,6 +30,15 @@ import (
 type TestSuiteRunner struct {
 	Config *configs.Config
 
+	// BackendFactory is used to enable initialising multiple backend types,
+	// depending on which backends are used in a test suite.
+	//
+	// Note: This is currently necessary because the source of the init functions,
+	// the backend/init package, experiences import cycles if used in other test-related
+	// packages. We set this field on a TestSuiteRunner when making runners in the
+	// command package, which is the main place where backend/init has previously been used.
+	BackendFactory func(string) backend.InitFn
+
 	TestingDirectory string
 
 	// Global variables comes from the main configuration directory,
@@ -270,9 +280,10 @@ func (runner *TestFileRunner) Test(file *moduletest.File) {
 
 	// Build the graph for the file.
 	b := graph.TestGraphBuilder{
-		File:        file,
-		GlobalVars:  runner.EvalContext.VariableCaches.GlobalVariables,
-		ContextOpts: runner.Suite.Opts,
+		File:           file,
+		GlobalVars:     runner.EvalContext.VariableCaches.GlobalVariables,
+		ContextOpts:    runner.Suite.Opts,
+		BackendFactory: runner.Suite.BackendFactory,
 	}
 	g, diags := b.Build()
 	file.Diagnostics = file.Diagnostics.Append(diags)

internal/command/test.go

@@ -260,7 +260,8 @@ func (c *TestCommand) Run(rawArgs []string) int {
 		}
 	} else {
 		localRunner := &local.TestSuiteRunner{
-			Config: config,
+			BackendFactory: backendInit.Backend,
+			Config:         config,
 			// The GlobalVariables are loaded from the
 			// main configuration directory
 			// The GlobalTestVariables are loaded from the

internal/moduletest/graph/test_graph_builder.go

@@ -7,6 +7,7 @@ import (
 	"log"
 
 	"github.com/hashicorp/terraform/internal/addrs"
+	"github.com/hashicorp/terraform/internal/backend"
 	"github.com/hashicorp/terraform/internal/backend/backendrun"
 	"github.com/hashicorp/terraform/internal/dag"
 	"github.com/hashicorp/terraform/internal/moduletest"
@@ -18,9 +19,10 @@ import (
 // a terraform test file. The file may contain multiple runs, and each run may have
 // dependencies on other runs.
 type TestGraphBuilder struct {
-	File        *moduletest.File
-	GlobalVars  map[string]backendrun.UnparsedVariableValue
-	ContextOpts *terraform.ContextOpts
+	File           *moduletest.File
+	GlobalVars     map[string]backendrun.UnparsedVariableValue
+	ContextOpts    *terraform.ContextOpts
+	BackendFactory func(string) backend.InitFn
 }
 
 type graphOptions struct {
@@ -47,7 +49,9 @@ func (b *TestGraphBuilder) Steps() []terraform.GraphTransformer {
 	}
 	steps := []terraform.GraphTransformer{
 		&TestRunTransformer{opts},
-		&TestStateTransformer{File: b.File},
+		// Could setting initial state based on backends be better-implemented as
+		// another transformer?
+		&TestStateTransformer{File: b.File, BackendFactory: b.BackendFactory},
 		&TestStateCleanupTransformer{opts},
 		terraform.DynamicTransformer(validateRunConfigs),
 		&TestProvidersTransformer{},

internal/moduletest/graph/transform_state.go

@@ -5,9 +5,12 @@ package graph
 
 import (
 	"fmt"
+	"log"
 	"maps"
 
 	"github.com/hashicorp/hcl/v2"
+	"github.com/hashicorp/hcl/v2/hcldec"
+	"github.com/hashicorp/terraform/internal/backend"
 	"github.com/hashicorp/terraform/internal/configs"
 	"github.com/hashicorp/terraform/internal/dag"
 	"github.com/hashicorp/terraform/internal/moduletest"
@@ -32,7 +35,8 @@ type TestFileState struct {
 // TestStateTransformer is a GraphTransformer that initializes the context with
 // all the states produced by the test file.
 type TestStateTransformer struct {
-	File *moduletest.File
+	File           *moduletest.File
+	BackendFactory func(string) backend.InitFn
 }
 
 func (t *TestStateTransformer) Transform(g *terraform.Graph) error {
@@ -48,11 +52,44 @@ func (t *TestStateTransformer) Transform(g *terraform.Graph) error {
 	for node := range dag.SelectSeq(g.VerticesSeq(), runFilter) {
 		key := node.run.Config.StateKey
 		if _, exists := statesMap[key]; !exists {
-			state := &TestFileState{
-				File:  t.File,
-				Run:   nil,
-				State: states.NewState(),
+
+			var state *TestFileState
+
+			if bc, exists := t.File.Config.BackendConfigs[key]; exists {
+				// If the state for that state key should come from a backend,
+				// obtain and use that
+				if t.BackendFactory == nil {
+					return fmt.Errorf("error retrieving state for state key %q from backend: nil BackendFactory. This is a bug in Terraform and should be reported.", key)
+				}
+
+				f := t.BackendFactory(bc.Backend.Type)
+				if f == nil {
+					return fmt.Errorf("error retrieving state for state key %q from backend: No init function found for backend type %q. This is a bug in Terraform and should be reported.", key, bc.Backend.Type)
+				}
+				be, err := getBackendInstance(key, bc.Backend, f)
+				if err != nil {
+					return err
+				}
+
+				stmgr, err := be.StateMgr(backend.DefaultStateName) // We only allow use of the default workspace
+				if err != nil {
+					return fmt.Errorf("error retrieving state for state key %q from backend: error retrieving state manager: %w", key, err)
+				}
+
+				log.Printf("[TRACE] TestConfigTransformer.Transform: set initial state for state key %q using backend of type %T declared at %s", key, be, bc.Backend.DeclRange)
+				state = &TestFileState{
+					Run:   nil,
+					State: stmgr.State(),
+				}
+			} else {
+				// Else, set an empty in-memory state for the state key
+				log.Printf("[TRACE] TestConfigTransformer.Transform: set initial state for state key %q as empty state", key)
+				state = &TestFileState{
+					Run:   nil,
+					State: states.NewState(),
+				}
 			}
+
 			statesMap[key] = state
 		}
 
@@ -64,7 +101,39 @@ func (t *TestStateTransformer) Transform(g *terraform.Graph) error {
 	return nil
 }
 
-func (t *TestStateTransformer) addRootConfigNode(g *terraform.Graph, statesMap map[string]*TestFileState) *dynamicNode {
+// getBackendInstance uses the config for a given run block's backend block to create and return a configured
+// instance of that backend type.
+func getBackendInstance(stateKey string, config *configs.Backend, f backend.InitFn) (backend.Backend, error) {
+	b := f()
+	log.Printf("[TRACE] TestConfigTransformer.Transform: instantiated backend of type %T", b)
+
+	schema := b.ConfigSchema()
+	decSpec := schema.NoneRequired().DecoderSpec()
+	configVal, hclDiags := hcldec.Decode(config.Config, decSpec, nil)
+	if hclDiags.HasErrors() {
+		return nil, fmt.Errorf("error decoding backend configuration for state key %s : %v", stateKey, hclDiags.Errs())
+	}
+
+	if !configVal.IsWhollyKnown() {
+		return nil, fmt.Errorf("unknown values within backend definition for state key %s", stateKey)
+	}
+
+	newVal, validateDiags := b.PrepareConfig(configVal)
+	validateDiags = validateDiags.InConfigBody(config.Config, "")
+	if validateDiags.HasErrors() {
+		return nil, validateDiags.Err()
+	}
+
+	configureDiags := b.Configure(newVal)
+	configureDiags = configureDiags.InConfigBody(config.Config, "")
+	if validateDiags.HasErrors() {
+		return nil, configureDiags.Err()
+	}
+
+	return b, nil
+}
+
+func (t *TestConfigTransformer) addRootConfigNode(g *terraform.Graph, statesMap map[string]*TestFileState) *dynamicNode {
 	rootConfigNode := &dynamicNode{
 		eval: func(ctx *EvalContext) tfdiags.Diagnostics {
 			var diags tfdiags.Diagnostics