Add YANG validation for config reload if file is given (sonic-net#3576)

What I did
Add constraint for YANG when config reload, which is already enabled in load_minigraph

How I did it
Check YANG vaidation for the config

How to verify it
Unit test

config/main.py

@@ -1372,6 +1372,19 @@ def multiasic_write_to_db(filename, load_sysinfo):
         migrate_db_to_lastest(ns)
 
 
+def config_file_yang_validation(filename):
+    config_to_check = read_json_file(filename)
+    sy = sonic_yang.SonicYang(YANG_DIR)
+    sy.loadYangModel()
+    try:
+        sy.loadData(configdbJson=config_to_check)
+        sy.validate_data_tree()
+    except sonic_yang.SonicYangException as e:
+        click.secho("{} fails YANG validation! Error: {}".format(filename, str(e)),
+                    fg='magenta')
+        raise click.Abort()
+
+
 # This is our main entrypoint - the main 'config' command
 @click.group(cls=clicommon.AbbreviationGroup, context_settings=CONTEXT_SETTINGS)
 @click.pass_context
@@ -1810,6 +1823,13 @@ def reload(db, filename, yes, load_sysinfo, no_service_restart, force, file_form
             click.echo("Input {} config file(s) separated by comma for multiple files ".format(num_cfg_file))
             return
 
+    if filename is not None:
+        if multi_asic.is_multi_asic():
+            # Multiasic has not 100% fully validated. Thus pass here.
+            pass
+        else:
+            config_file_yang_validation(filename)
+
     #Stop services before config push
     if not no_service_restart:
         log.log_notice("'reload' stopping services...")
@@ -2000,15 +2020,7 @@ def load_minigraph(db, no_service_restart, traffic_shift_away, override_config,
             # Multiasic has not 100% fully validated. Thus pass here.
             pass
         else:
-            sy = sonic_yang.SonicYang(YANG_DIR)
-            sy.loadYangModel()
-            try:
-                sy.loadData(configdbJson=config_to_check)
-                sy.validate_data_tree()
-            except sonic_yang.SonicYangException as e:
-                click.secho("{} fails YANG validation! Error: {}".format(golden_config_path, str(e)),
-                            fg='magenta')
-                raise click.Abort()
+            config_file_yang_validation(golden_config_path)
 
         # Dependency check golden config json
         if multi_asic.is_multi_asic():

tests/config_test.py

@@ -1384,6 +1384,34 @@ def test_reload_yang_config(self, get_cmd_module,
             assert "\n".join([l.rstrip() for l in result.output.split('\n')]) \
                 == RELOAD_YANG_CFG_OUTPUT.format(config.SYSTEM_RELOAD_LOCK)
 
+    def test_reload_config_fails_yang_validation(self, get_cmd_module, setup_single_broadcom_asic):
+        with open(self.dummy_cfg_file, 'w') as f:
+            device_metadata = {
+                "DEVICE_METADATA": {
+                    "localhost": {
+                        "invalid_hwsku": "some_hwsku"
+                    }
+                }
+            }
+            f.write(json.dumps(device_metadata))
+
+        with mock.patch(
+                "utilities_common.cli.run_command",
+                mock.MagicMock(side_effect=mock_run_command_side_effect)
+        ):
+            (config, _) = get_cmd_module
+            runner = CliRunner()
+
+            result = runner.invoke(
+                config.config.commands["reload"],
+                [self.dummy_cfg_file, '-y', '-f'])
+
+            print(result.exit_code)
+            print(result.output)
+            traceback.print_tb(result.exc_info[2])
+            assert result.exit_code != 0
+            assert "fails YANG validation! Error" in result.output
+
     @classmethod
     def teardown_class(cls):
         os.environ['UTILITIES_UNIT_TESTING'] = "0"