fix: display project_vpc_id computed on plan

CHANGELOG.md

@@ -14,7 +14,8 @@ nav_order: 1
 - Add `alloydbomni` BETA resource and datasource
 - Add `aiven_alloydbomni_user` BETA resource and datasource
 - Add `aiven_alloydbomni_database` BETA resource and datasource
-- Fix `terraform plan`: new resources don't display zero values for user configuration options
+- Fix `terraform plan` doesn't display automatically assigned `project_vpc_id`
+- Fix `terraform plan` doesn't display fields with zero values in service user config
 - Add `aiven_service_integration` resource and datasource field `destination_service_project`: Destination service project name
 - Add `aiven_service_integration` resource and datasource field `source_service_project`: Source service project name
 - Change `aiven_account_team_project` resource and datasource field `team_type` (enum): remove

internal/schemautil/custom_diff.go

@@ -21,6 +21,7 @@ import (
 func CustomizeDiffGenericService(serviceType string) schema.CustomizeDiffFunc {
 	return customdiff.Sequence(
 		SetServiceTypeIfEmpty(serviceType),
+		CustomizeDiffProjectVPCID,
 		CustomizeDiffDisallowMultipleManyToOneKeys,
 		customdiff.IfValueChange("tag",
 			ShouldNotBeEmpty,
@@ -320,3 +321,60 @@ func CustomizeDiffAdditionalDiskSpace(ctx context.Context, diff *schema.Resource
 	// which otherwise will be suppressed by TF
 	return diff.SetNew(k, "0B")
 }
+
+// CustomizeDiffProjectVPCID
+// 1. Validates project_vpc_id when set
+// 2. Sets project_vpc_id when there is only one VPC in the cloud (that's how it works on the backend)
+func CustomizeDiffProjectVPCID(ctx context.Context, d *schema.ResourceDiff, _ any) error {
+	client, err := common.GenClient()
+	if err != nil {
+		return err
+	}
+
+	if v, ok := d.GetOk("project_vpc_id"); ok {
+		return validateProjectVPCID(ctx, client, v.(string))
+	}
+
+	project := d.Get("project").(string)
+	list, err := client.VpcList(ctx, project)
+	if err != nil {
+		return err
+	}
+
+	vpcIDs := make([]string, 0)
+	cloudName := d.Get("cloud_name").(string)
+	for _, v := range list {
+		if v.CloudName == cloudName {
+			vpcIDs = append(vpcIDs, v.ProjectVpcId)
+		}
+	}
+
+	switch len(vpcIDs) {
+	case 0:
+		// It would be nice to set the project_vpc_id to an empty string here,
+		// but it just won't work because TF takes "" and nil as nothing set.
+		// That would still result in project_vpc_id marked "known after apply" in the plan,
+		// even though we know it's going to be empty.
+		return nil
+	case 1:
+		return d.SetNew("project_vpc_id", BuildResourceID(project, vpcIDs[0]))
+	}
+
+	return fmt.Errorf(
+		"project %q has multiple active VPCs in cloud %q. Please specify the project_vpc_id: %s",
+		project, cloudName, strings.Join(vpcIDs, ", "),
+	)
+}
+
+func validateProjectVPCID(ctx context.Context, client avngen.Client, projectVPCID string) error {
+	project, vpcID, err := SplitResourceID2(projectVPCID)
+	if err != nil {
+		return err
+	}
+
+	_, err = client.VpcGet(ctx, project, vpcID)
+	if avngen.IsNotFound(err) {
+		return fmt.Errorf("VPC ID %q not found in project %q", vpcID, project)
+	}
+	return err
+}

internal/schemautil/schemautil.go

@@ -12,6 +12,8 @@ import (
 	"github.com/aiven/aiven-go-client/v2"
 	"github.com/aiven/go-client-codegen/handler/service"
 	"github.com/docker/go-units"
+	"github.com/hashicorp/go-cty/cty"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/diag"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
 )
 
@@ -195,6 +197,29 @@ func ValidateEmailAddress(v any, k string) (ws []string, errors []error) {
 	return
 }
 
+// ValidateIDN validates that the given string is a valid resource ID with n parts
+func ValidateIDN(n int, expected ...string) schema.SchemaValidateDiagFunc {
+	if n != len(expected) {
+		panic(fmt.Sprintf("expected %d parts, got %d", n, len(expected)))
+	}
+
+	return func(i any, _ cty.Path) diag.Diagnostics {
+		_, err := SplitResourceID(i.(string), n)
+		if err == nil {
+			return nil
+		}
+
+		return diag.Errorf(
+			"invalid resource id, should have the following format %q",
+			strings.Join(expected, "/"),
+		)
+	}
+}
+
+func ValidateIDWithProject(expected string) schema.SchemaValidateDiagFunc {
+	return ValidateIDN(2, "project_name", expected)
+}
+
 func BuildResourceID(parts ...string) string {
 	finalParts := make([]string, len(parts))
 	for idx, part := range parts {

internal/schemautil/service.go

@@ -136,10 +136,11 @@ func ServiceCommonSchema() map[string]*schema.Schema {
 			Description: "Aiven internal service type code",
 		},
 		"project_vpc_id": {
-			Type:        schema.TypeString,
-			Optional:    true,
-			Computed:    true,
-			Description: "Specifies the VPC the service should run in. If the value is not set the service is not run inside a VPC. When set, the value should be given as a reference to set up dependencies correctly and the VPC must be in the same cloud and region as the service itself. Project can be freely moved to and from VPC after creation but doing so triggers migration to new servers so the operation can take significant amount of time to complete if the service has a lot of data.",
+			Type:             schema.TypeString,
+			Optional:         true,
+			Computed:         true,
+			Description:      "Specifies the VPC the service should run in. If the value is not set the service is not run inside a VPC. When set, the value should be given as a reference to set up dependencies correctly and the VPC must be in the same cloud and region as the service itself. Project can be freely moved to and from VPC after creation but doing so triggers migration to new servers so the operation can take significant amount of time to complete if the service has a lot of data.",
+			ValidateDiagFunc: ValidateIDWithProject("project_vpc_id"),
 		},
 		"maintenance_window_dow": {
 			Type:        schema.TypeString,