Update build.py

Author: ilevkivskyi

mypy/build.py

@@ -144,6 +144,10 @@ def __init__(self, manager: BuildManager, graph: Graph) -> None:
         self.errors: list[str] = []  # Filled in by build if desired
 
 
+def build_error(msg: str) -> NoReturn:
+    raise CompileError([f"mypy: error: {msg}"])
+
+
 def build(
     sources: list[BuildSource],
     options: Options,
@@ -239,6 +243,9 @@ def _build(
     errors = Errors(options, read_source=lambda path: read_py_file(path, cached_read))
     plugin, snapshot = load_plugins(options, errors, stdout, extra_plugins)
 
+    # Validate error codes after plugins are loaded.
+    options.process_error_codes(error_callback=build_error)
+
     # Add catch-all .gitignore to cache dir if we created it
     cache_dir_existed = os.path.isdir(options.cache_dir)
 
@@ -504,9 +511,6 @@ def load_plugins(
     """
     custom_plugins, snapshot = load_plugins_from_config(options, errors, stdout)
 
-    if options._on_plugins_loaded is not None:
-        options._on_plugins_loaded()
-
     custom_plugins += extra_plugins
 
     default_plugin: Plugin = DefaultPlugin(options)