fix: Instance image diff during Instance import (#2238)

* Populate disk image from instance during Read to avoid import diffs

* Address CoPilot feedback

* Addressed PR comments

* Address more PR comments

Author: ezilber-akamai

linode/instancedisk/framework_model.go

@@ -1,11 +1,13 @@
 package instancedisk
 
 import (
+	"context"
 	"strconv"
 
 	"github.com/hashicorp/terraform-plugin-framework-timeouts/resource/timeouts"
 	"github.com/hashicorp/terraform-plugin-framework-timetypes/timetypes"
 	"github.com/hashicorp/terraform-plugin-framework/types"
+	"github.com/hashicorp/terraform-plugin-log/tflog"
 	"github.com/linode/linodego"
 	"github.com/linode/terraform-provider-linode/v3/linode/helper"
 )
@@ -72,3 +74,26 @@ func (data *ResourceModel) CopyFrom(other ResourceModel, preserveKnown bool) {
 	data.Status = helper.KeepOrUpdateValue(data.Status, other.Status, preserveKnown)
 	data.DiskEncryption = helper.KeepOrUpdateValue(data.DiskEncryption, other.DiskEncryption, preserveKnown)
 }
+
+func (data *ResourceModel) PopulateImageFromParentInstance(
+	ctx context.Context,
+	client *linodego.Client,
+	linodeID int,
+) {
+	if !data.Image.IsNull() {
+		return
+	}
+
+	instance, err := client.GetInstance(ctx, linodeID)
+	if err != nil {
+		tflog.Debug(ctx, "Failed to fetch parent instance for disk image fallback", map[string]any{
+			"linode_id": linodeID,
+			"error":     err.Error(),
+		})
+		return
+	}
+
+	if instance.Image != "" {
+		data.Image = types.StringValue(instance.Image)
+	}
+}

linode/instancedisk/framework_resource.go

@@ -55,6 +55,10 @@ func (r *Resource) Create(
 		return
 	}
 
+	if plan.Image.IsUnknown() {
+		plan.Image = types.StringNull()
+	}
+
 	helper.SetLogFieldBulk(ctx, map[string]any{"linode_id": plan.LinodeID})
 	createTimeout, diags := plan.Timeouts.Create(ctx, DefaultVolumeCreateTimeout)
 	resp.Diagnostics.Append(diags...)
@@ -207,7 +211,10 @@ func (r *Resource) Read(
 		return
 	}
 
+	state.PopulateImageFromParentInstance(ctx, client, linodeID)
+
 	state.FlattenDisk(disk, false)
+
 	resp.Diagnostics.Append(resp.State.Set(ctx, &state)...)
 }
 
@@ -223,6 +230,10 @@ func (r *Resource) Update(
 	resp.Diagnostics.Append(req.State.Get(ctx, &state)...)
 	resp.Diagnostics.Append(req.Plan.Get(ctx, &plan)...)
 
+	if plan.Image.IsUnknown() {
+		plan.Image = types.StringNull()
+	}
+
 	ctx = populateLogAttributes(ctx, state)
 
 	updateTimeout, diags := plan.Timeouts.Update(ctx, DefaultVolumeUpdateTimeout)

linode/instancedisk/framework_resource_schema.go

@@ -83,8 +83,10 @@ var frameworkResourceSchema = schema.Schema{
 		"image": schema.StringAttribute{
 			Description: "An Image ID to deploy the Linode Disk from.",
 			Optional:    true,
+			Computed:    true,
 			PlanModifiers: []planmodifier.String{
 				stringplanmodifier.RequiresReplace(),
+				stringplanmodifier.UseStateForUnknown(),
 			},
 		},
 		"root_pass": schema.StringAttribute{