core: Update working state for resource instances in refresh-only mode

Previously in refresh-only mode we were skipping making any updates to the
working state at all. That's not correct, though: if the state upgrade or
refresh steps detected changes then we need to at least commit _those_ to
the working state, because those can then be detected by downstream
objects like output values.

terraform/context_plan2_test.go

@@ -740,6 +740,10 @@ func TestContext2Plan_refreshOnlyMode(t *testing.T) {
 			resource "test_object" "a" {
 				arg = "after"
 			}
+
+			output "out" {
+				value = test_object.a.arg
+			}
 		`,
 	})
 	state := states.BuildState(func(s *states.SyncState) {
@@ -838,6 +842,23 @@ func TestContext2Plan_refreshOnlyMode(t *testing.T) {
 			t.Errorf("%s has wrong previous run state after plan\ngot:\n%s\n\nwant substring: %s", addr, got, want)
 		}
 	}
+
+	// The output value should also have updated. If not, it's likely that we
+	// skipped updating the working state to match the refreshed state when we
+	// were evaluating the resource.
+	if outChangeSrc := plan.Changes.OutputValue(addrs.RootModuleInstance.OutputValue("out")); outChangeSrc == nil {
+		t.Errorf("no change planned for output value 'out'")
+	} else {
+		outChange, err := outChangeSrc.Decode()
+		if err != nil {
+			t.Fatalf("failed to decode output value 'out': %s", err)
+		}
+		got := outChange.After
+		want := cty.StringVal("current")
+		if !want.RawEquals(got) {
+			t.Errorf("wrong value for output value 'out'\ngot:  %#v\nwant: %#v", got, want)
+		}
+	}
 }
 
 func TestContext2Plan_invalidSensitiveModuleOutput(t *testing.T) {

terraform/node_resource_plan_instance.go

@@ -226,6 +226,16 @@ func (n *NodePlannableResourceInstance) managedResourceExecute(ctx EvalContext)
 		}
 
 		diags = diags.Append(n.writeChange(ctx, change, ""))
+	} else {
+		// Even if we don't plan changes, we do still need to at least update
+		// the working state to reflect the refresh result. If not, then e.g.
+		// any output values refering to this will not react to the drift.
+		// (Even if we didn't actually refresh above, this will still save
+		// the result of any schema upgrading we did in readResourceInstanceState.)
+		diags = diags.Append(n.writeResourceInstanceState(ctx, instanceRefreshState, workingState))
+		if diags.HasErrors() {
+			return diags
+		}
 	}
 
 	return diags