backend: Only show root module output changes

When rendering planned output changes, we need to filter the plan's
output changes to ensure that only root module outputs which have
changed are rendered. Otherwise we will render changes for submodule
outputs, and (with concise diff disabled) render unchanged outputs also.

backend/local/backend_plan.go

@@ -314,8 +314,18 @@ func RenderPlan(plan *plans.Plan, baseState *states.State, schemas *terraform.Sc
 
 	// If there is at least one planned change to the root module outputs
 	// then we'll render a summary of those too.
-	if len(plan.Changes.Outputs) > 0 {
-		ui.Output(colorize.Color("[reset]\n[bold]Changes to Outputs:[reset]" + format.OutputChanges(plan.Changes.Outputs, colorize)))
+	var changedRootModuleOutputs []*plans.OutputChangeSrc
+	for _, output := range plan.Changes.Outputs {
+		if !output.Addr.Module.IsRoot() {
+			continue
+		}
+		if output.ChangeSrc.Action == plans.NoOp {
+			continue
+		}
+		changedRootModuleOutputs = append(changedRootModuleOutputs, output)
+	}
+	if len(changedRootModuleOutputs) > 0 {
+		ui.Output(colorize.Color("[reset]\n[bold]Changes to Outputs:[reset]" + format.OutputChanges(changedRootModuleOutputs, colorize)))
 	}
 }
 

backend/local/testdata/plan-outputs-changed/main.tf

@@ -1,3 +1,7 @@
+module "submodule" {
+  source = "./submodule"
+}
+
 output "changed" {
   value = "after"
 }

backend/local/testdata/plan-outputs-changed/submodule/main.tf

@@ -0,0 +1,3 @@
+output "foo" {
+  value = "bar"
+}