Merge pull request #10228 from hashicorp/jbardin/map-crash

ResourceConfig.get should never return (nil, true)

builtin/providers/test/resource_test.go

@@ -393,6 +393,40 @@ resource "test_resource" "foo" {
 	})
 }
 
+// Reproduces plan-time panic when the wrong type is interpolated in a list of
+// maps.
+// TODO: this should return a type error, rather than silently setting an empty
+//       list
+func TestResource_dataSourceListMapPanic(t *testing.T) {
+	resource.UnitTest(t, resource.TestCase{
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckResourceDestroy,
+		Steps: []resource.TestStep{
+			resource.TestStep{
+				Config: strings.TrimSpace(`
+resource "test_resource" "foo" {
+  required = "val"
+  required_map = {x = "y"}
+  list_of_map = "${var.maplist}"
+}
+
+variable "maplist" {
+  type = "list"
+
+  default = [
+    {a = "b"}
+  ]
+}
+				`),
+				ExpectError: nil,
+				Check: func(s *terraform.State) error {
+					return nil
+				},
+			},
+		},
+	})
+}
+
 func testAccCheckResourceDestroy(s *terraform.State) error {
 	return nil
 }

terraform/resource.go

@@ -316,7 +316,8 @@ func (c *ResourceConfig) get(
 			// prefix so were split as path components above.
 			actualKey := strings.Join(parts[i-1:], ".")
 			if prevMap, ok := previous.(map[string]interface{}); ok {
-				return prevMap[actualKey], true
+				v, ok := prevMap[actualKey]
+				return v, ok
 			}
 
 			return nil, false

terraform/resource_test.go

@@ -160,6 +160,18 @@ func TestResourceConfigGet(t *testing.T) {
 			Key:   "mapname.0.listkey.0.key",
 			Value: 3,
 		},
+
+		// A map assigned to a list via interpolation should Get a non-existent
+		// value. The test code now also checks that Get doesn't return (nil,
+		// true), which it previously did for this configuration.
+		{
+			Config: map[string]interface{}{
+				"maplist": "${var.maplist}",
+			},
+			Key:   "maplist.0",
+			Value: nil,
+		},
+
 		// FIXME: this is ambiguous, and matches the nested map
 		//        leaving here to catch this behaviour if it changes.
 		{
@@ -226,7 +238,11 @@ func TestResourceConfigGet(t *testing.T) {
 
 		// Test getting a key
 		t.Run(fmt.Sprintf("get-%d", i), func(t *testing.T) {
-			v, _ := rc.Get(tc.Key)
+			v, ok := rc.Get(tc.Key)
+			if ok && v == nil {
+				t.Fatal("(nil, true) returned from Get")
+			}
+
 			if !reflect.DeepEqual(v, tc.Value) {
 				t.Fatalf("%d bad: %#v", i, v)
 			}