[Foxy backport] Improve error message for malformed YAML files

rcl/src/rcl/arguments.c

@@ -372,11 +372,10 @@ rcl_parse_arguments(
         if (i + 1 < argc) {
           // Attempt to parse next argument as parameter file rule
           args_impl->parameter_files[args_impl->num_param_files_args] = NULL;
-          if (
-            RCL_RET_OK == _rcl_parse_param_file(
-              argv[i + 1], allocator, args_impl->parameter_overrides,
-              &args_impl->parameter_files[args_impl->num_param_files_args]))
-          {
+          ret = _rcl_parse_param_file(
+            argv[i + 1], allocator, args_impl->parameter_overrides,
+            &args_impl->parameter_files[args_impl->num_param_files_args]);
+          if (RCL_RET_OK == ret) {
             ++(args_impl->num_param_files_args);
             RCUTILS_LOG_DEBUG_NAMED(
               ROS_PACKAGE_NAME,
@@ -386,6 +385,19 @@ rcl_parse_arguments(
             ++i;  // Skip flag here, for loop will skip rule.
             continue;
           }
+          if (RCL_RET_ERROR == ret) {
+            // If _rcl_parse_param_file() returned
+            // RCL_RET_ERROR then the argument contained the
+            // '__params:=' prefix, but parsing the parameter
+            // file failed without any notice.
+            rcl_error_string_t prev_error_string = rcl_get_error_string();
+            rcl_reset_error();
+            RCL_SET_ERROR_MSG_WITH_FORMAT_STRING(
+              "Couldn't parse params file: '%s'. Error: %s",
+              args_impl->parameter_files[args_impl->num_param_files_args],
+              prev_error_string.str);
+            goto fail;
+          }
           rcl_error_string_t prev_error_string = rcl_get_error_string();
           rcl_reset_error();
           RCL_SET_ERROR_MSG_WITH_FORMAT_STRING(
@@ -606,7 +618,7 @@ rcl_parse_arguments(
   }
 
   // Drop parameter overrides if none was found.
-  if (0U == args_impl->parameter_overrides->num_nodes) {
+  if (NULL != args_impl->parameter_overrides && 0U == args_impl->parameter_overrides->num_nodes) {
     rcl_yaml_node_struct_fini(args_impl->parameter_overrides);
     args_impl->parameter_overrides = NULL;
   }

rcl/test/rcl/test_arguments.cpp

@@ -935,3 +935,21 @@ TEST_F(CLASSNAME(TestArgumentsFixture, RMW_IMPLEMENTATION), test_param_overrides
   ASSERT_TRUE(NULL != param_value->string_value);
   EXPECT_STREQ("foo", param_value->string_value);
 }
+
+// Regression test for https://github.com/ros2/rcl/issues/815
+// Testing behaviour that was broken in Foxy
+TEST_F(CLASSNAME(TestArgumentsFixture, RMW_IMPLEMENTATION), test_malformed_param_file) {
+  const std::string parameters_filepath = (test_path / "test_malformed_parameters.1.yaml").string();
+  const std::string parameter_rule = "__params:=" + parameters_filepath;
+  const char * argv[] = {
+    "process_name", "--ros-args", "--params-file", parameter_rule.c_str()
+  };
+  int argc = sizeof(argv) / sizeof(const char *);
+  rcl_ret_t ret;
+
+  rcl_allocator_t alloc = rcl_get_default_allocator();
+  rcl_arguments_t parsed_args = rcl_get_zero_initialized_arguments();
+
+  ret = rcl_parse_arguments(argc, argv, alloc, &parsed_args);
+  ASSERT_EQ(RCL_RET_ERROR, ret) << rcl_get_error_string().str;
+}

rcl/test/resources/test_arguments/test_malformed_parameters.1.yaml

@@ -0,0 +1,5 @@
+some_node:
+  ros_parameters: # must have double _
+    int_param: 1
+    param_group:
+      string_param: foo