detect scaled in resources when evaluating *s

terraform/context_apply_test.go

@@ -9541,3 +9541,62 @@ func TestContext2Apply_plannedInterpolatedCount(t *testing.T) {
 		t.Fatalf("apply failed: %s", err)
 	}
 }
+
+func TestContext2Apply_scaleInMultivarRef(t *testing.T) {
+	m := testModule(t, "apply-resource-scale-in")
+
+	p := testProvider("aws")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+
+	providerResolver := ResourceProviderResolverFixed(
+		map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+	)
+
+	s := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.one": {
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "foo",
+						},
+						Provider: "provider.aws",
+					},
+					"aws_instance.two": {
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "foo",
+							Attributes: map[string]string{
+								"val": "foo",
+							},
+						},
+						Provider: "provider.aws",
+					},
+				},
+			},
+		},
+	}
+
+	ctx := testContext2(t, &ContextOpts{
+		Module:           m,
+		ProviderResolver: providerResolver,
+		State:            s,
+		Variables:        map[string]interface{}{"count": "0"},
+	})
+
+	_, err := ctx.Plan()
+	if err != nil {
+		t.Fatalf("plan failed: %s", err)
+	}
+
+	// Applying the plan should now succeed
+	_, err = ctx.Apply()
+	if err != nil {
+		t.Fatalf("apply failed: %s", err)
+	}
+}

terraform/interpolate.go

@@ -820,7 +820,13 @@ func (i *Interpolater) resourceCountMax(
 	// use "cr.Count()" but that doesn't work if the count is interpolated
 	// and we can't guarantee that so we instead depend on the state.
 	max := -1
-	for k, _ := range ms.Resources {
+	for k, s := range ms.Resources {
+		// This resource may have been just removed, in which case the Primary
+		// may be nil, or just empty.
+		if s == nil || s.Primary == nil || len(s.Primary.Attributes) == 0 {
+			continue
+		}
+
 		// Get the index number for this resource
 		index := ""
 		if k == id {

terraform/test-fixtures/apply-resource-scale-in/main.tf

@@ -0,0 +1,13 @@
+variable "count" {}
+
+resource "aws_instance" "one" {
+  count = "${var.count}"
+}
+
+locals {
+  "one_id" = "${element(concat(aws_instance.one.*.id, list("")), 0)}"
+}
+
+resource "aws_instance" "two" {
+  val = "${local.one_id}"
+}