New Feature - preflight initial implementation and POC (#32260)

Co-authored-by: Catriona <catriona@hashicorp.com>
Co-authored-by: Catriona <86247157+catriona-m@users.noreply.github.com>

Author: jackofallops

internal/clients/client.go

@@ -7,6 +7,8 @@ import (
 	"context"
 	"fmt"
 
+	preflight "github.com/hashicorp/terraform-provider-azurerm/internal/preflight/client"
+
 	"github.com/Azure/go-autorest/autorest"
 	"github.com/Azure/go-autorest/autorest/validation"
 	aadb2c_v2021_04_01_preview "github.com/hashicorp/go-azure-sdk/resource-manager/aadb2c/2021-04-01-preview"
@@ -160,6 +162,8 @@ type Client struct {
 	Account  *ResourceManagerAccount
 	Features features.UserFeatures
 
+	Preflight *preflight.Client
+
 	AadB2c                            *aadb2c_v2021_04_01_preview.Client
 	Advisor                           *advisor.Client
 	AnalysisServices                  *analysisservices_v2017_08_01.Client
@@ -304,6 +308,10 @@ func (client *Client) Build(ctx context.Context, o *common.ClientOptions) error
 
 	var err error
 
+	if client.Preflight, err = preflight.NewClient(o); err != nil {
+		return fmt.Errorf("building client for preflight validator: %+v", err)
+	}
+
 	if client.AadB2c, err = aadb2c.NewClient(o); err != nil {
 		return fmt.Errorf("building clients for AadB2c: %+v", err)
 	}

internal/features/defaults.go

@@ -13,6 +13,8 @@ func Default() UserFeatures {
 		EnhancedValidation: EnhancedValidationFeatures{
 			Locations:         !FivePointOh(),
 			ResourceProviders: !FivePointOh(),
+			PreflightEnabled:  false,
+			LocationFallback:  nil,
 		},
 		AppConfiguration: AppConfigurationFeatures{
 			PurgeSoftDeleteOnDestroy: true,

internal/features/enhanced_validation.go

@@ -106,3 +106,28 @@ func ValidateEnhancedValidationEnvVars() error {
 
 	return nil
 }
+
+// EnhancedValidationPreflightEnabled returns whether Azure Preflight Validation is enabled.
+//
+// Preflight validation is always opt-in and defaults to false in all provider versions.
+// Set ARM_PROVIDER_ENHANCED_VALIDATION_PREFLIGHT_ENABLED=true to enable it without
+// requiring an explicit config block.
+func EnhancedValidationPreflightEnabled() bool {
+	if !FivePointOh() {
+		return false
+	}
+
+	return strings.EqualFold(os.Getenv("ARM_PROVIDER_ENHANCED_VALIDATION_PREFLIGHT_ENABLED"), "true")
+}
+
+// EnhancedValidationLocationFallback returns the location fallback string for Azure Preflight Validation.
+//
+// This checks the `ARM_PROVIDER_ENHANCED_VALIDATION_LOCATION_FALLBACK` environment variable,
+// which can be used to set a default location for resources that don't have a specific location.
+func EnhancedValidationLocationFallback() *string {
+	value := os.Getenv("ARM_PROVIDER_ENHANCED_VALIDATION_LOCATION_FALLBACK")
+	if value != "" {
+		return &value
+	}
+	return nil
+}

internal/features/user_flags.go

@@ -11,22 +11,22 @@ type UserFeatures struct {
 	AppConfiguration         AppConfigurationFeatures
 	ApplicationInsights      ApplicationInsightFeatures
 	CognitiveAccount         CognitiveAccountFeatures
+	DatabricksWorkspace      DatabricksWorkspaceFeatures
 	EnhancedValidation       EnhancedValidationFeatures
-	VirtualMachine           VirtualMachineFeatures
-	VirtualMachineScaleSet   VirtualMachineScaleSetFeatures
 	KeyVault                 KeyVaultFeatures
-	TemplateDeployment       TemplateDeploymentFeatures
 	LogAnalyticsWorkspace    LogAnalyticsWorkspaceFeatures
-	ResourceGroup            ResourceGroupFeatures
-	RecoveryServicesVault    RecoveryServicesVault
+	MachineLearning          MachineLearningFeatures
 	ManagedDisk              ManagedDiskFeatures
-	Storage                  StorageFeatures
-	Subscription             SubscriptionFeatures
+	NetApp                   NetAppFeatures
 	PostgresqlFlexibleServer PostgresqlFlexibleServerFeatures
-	MachineLearning          MachineLearningFeatures
 	RecoveryService          RecoveryServiceFeatures
-	NetApp                   NetAppFeatures
-	DatabricksWorkspace      DatabricksWorkspaceFeatures
+	RecoveryServicesVault    RecoveryServicesVault
+	ResourceGroup            ResourceGroupFeatures
+	Storage                  StorageFeatures
+	Subscription             SubscriptionFeatures
+	TemplateDeployment       TemplateDeploymentFeatures
+	VirtualMachine           VirtualMachineFeatures
+	VirtualMachineScaleSet   VirtualMachineScaleSetFeatures
 }
 
 type CognitiveAccountFeatures struct {
@@ -36,6 +36,8 @@ type CognitiveAccountFeatures struct {
 type EnhancedValidationFeatures struct {
 	Locations         bool
 	ResourceProviders bool
+	PreflightEnabled  bool
+	LocationFallback  *string
 }
 
 type VirtualMachineFeatures struct {