default optional+computed to prior value

internal/terraform/context_plan_test.go

@@ -4543,6 +4543,11 @@ func TestContext2Plan_ignoreChangesWildcard(t *testing.T) {
 			t.Error("computed id set in plan config")
 		}
 
+		foo := req.Config.GetAttr("foo")
+		if foo.IsNull() {
+			t.Error(`missing "foo" during plan, was set to "bar" in state and config`)
+		}
+
 		return testDiffFn(req)
 	}
 
@@ -4552,7 +4557,7 @@ func TestContext2Plan_ignoreChangesWildcard(t *testing.T) {
 		mustResourceInstanceAddr("aws_instance.foo").Resource,
 		&states.ResourceInstanceObjectSrc{
 			Status:    states.ObjectReady,
-			AttrsJSON: []byte(`{"id":"bar","ami":"ami-abcd1234","instance":"t2.micro","type":"aws_instance"}`),
+			AttrsJSON: []byte(`{"id":"bar","ami":"ami-abcd1234","instance":"t2.micro","type":"aws_instance","foo":"bar"}`),
 		},
 		mustProviderConfig(`provider["registry.terraform.io/hashicorp/aws"]`),
 	)

internal/terraform/node_resource_abstract_instance.go

@@ -1165,7 +1165,7 @@ func (n *NodeAbstractResource) processIgnoreChanges(prior, config cty.Value, sch
 		// to the provider as if they were included in the configuration.
 		ret, _ := cty.Transform(prior, func(path cty.Path, v cty.Value) (cty.Value, error) {
 			attr := schema.AttributeByPath(path)
-			if attr != nil && attr.Computed {
+			if attr != nil && attr.Computed && !attr.Optional {
 				return cty.NullVal(v.Type()), nil
 			}
 

internal/terraform/testdata/plan-ignore-changes-wildcard/main.tf

@@ -5,6 +5,7 @@ variable "bar" {}
 resource "aws_instance" "foo" {
   ami      = "${var.foo}"
   instance = "${var.bar}"
+  foo = "bar"
 
   lifecycle {
     ignore_changes = all