helper/schema: use reflection to set maps

helper/schema/resource_data.go

@@ -394,7 +394,19 @@ func (d *ResourceData) setMapValue(
 		}
 	*/
 
-	vs := value.(map[string]interface{})
+	v := reflect.ValueOf(value)
+	if v.Kind() != reflect.Map {
+		return fmt.Errorf("%s: must be a map", k)
+	}
+	if v.Type().Key().Kind() != reflect.String {
+		return fmt.Errorf("%s: keys must strings", k)
+	}
+	vs := make(map[string]interface{})
+	for _, mk := range v.MapKeys() {
+		mv := v.MapIndex(mk)
+		vs[mk.String()] = mv.Interface()
+	}
+
 	for subKey, v := range vs {
 		err := d.set(fmt.Sprintf("%s.%s", k, subKey), nil, elemSchema, v)
 		if err != nil {

helper/schema/resource_data_test.go

@@ -907,6 +907,45 @@ func TestResourceDataSet(t *testing.T) {
 				},
 			},
 		},
+
+		// Set a list of maps
+		{
+			Schema: map[string]*Schema{
+				"config_vars": &Schema{
+					Type:     TypeList,
+					Optional: true,
+					Computed: true,
+					Elem: &Schema{
+						Type: TypeMap,
+					},
+				},
+			},
+
+			State: nil,
+
+			Diff: nil,
+
+			Key: "config_vars",
+			Value: []interface{}{
+				map[string]string{
+					"foo": "bar",
+				},
+				map[string]string{
+					"bar": "baz",
+				},
+			},
+			Err: false,
+
+			GetKey: "config_vars",
+			GetValue: []interface{}{
+				map[string]interface{}{
+					"foo": "bar",
+				},
+				map[string]interface{}{
+					"bar": "baz",
+				},
+			},
+		},
 	}
 
 	for i, tc := range cases {