core: Fix destroy when module vars used in provider config

terraform/context_apply_test.go

@@ -443,6 +443,45 @@ func TestContext2Apply_destroySkipsCBD(t *testing.T) {
 	}
 }
 
+func TestContext2Apply_destroyModuleVarProviderConfig(t *testing.T) {
+	m := testModule(t, "apply-destroy-mod-var-provider-config")
+	p := testProvider("aws")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: []string{"root", "child"},
+				Resources: map[string]*ResourceState{
+					"aws_instance.foo": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "foo",
+						},
+					},
+				},
+			},
+		},
+	}
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+		State:   state,
+		Destroy: true,
+	})
+
+	if _, err := ctx.Plan(); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	_, err := ctx.Apply()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+}
+
 // https://github.com/hashicorp/terraform/issues/2892
 func TestContext2Apply_destroyCrossProviders(t *testing.T) {
 	m := testModule(t, "apply-destroy-cross-providers")

terraform/graph_config_node_variable.go

@@ -234,3 +234,24 @@ func (n *GraphNodeConfigVariableFlat) Path() []string {
 
 	return nil
 }
+
+func (n *GraphNodeConfigVariableFlat) Noop(opts *NoopOpts) bool {
+	// First look for provider nodes that depend on this variable downstream
+	modDiff := opts.Diff.ModuleByPath(n.ModulePath)
+	if modDiff != nil && modDiff.Destroy {
+		ds, err := opts.Graph.Descendents(n)
+		if err != nil {
+			log.Printf("[ERROR] Error looking up descendents of %s: %s", n.Name(), err)
+		} else {
+			for _, d := range ds.List() {
+				if _, ok := d.(GraphNodeProvider); ok {
+					log.Printf("[DEBUG] This variable is depended on by a provider, can't be a noop.")
+					return false
+				}
+			}
+		}
+	}
+
+	// Then fall back to existing impl
+	return n.GraphNodeConfigVariable.Noop(opts)
+}

terraform/test-fixtures/apply-destroy-mod-var-provider-config/child/child.tf

@@ -0,0 +1,7 @@
+variable "input" {}
+
+provider "aws" {
+  region = "us-east-${var.input}"
+}
+
+resource "aws_instance" "foo" { }

terraform/test-fixtures/apply-destroy-mod-var-provider-config/main.tf

@@ -0,0 +1,4 @@
+module "child" {
+  source = "./child"
+  input = "1"
+}