Allow to enable/disable plugin error codes

Fixes python#12987

* Ignore unknown error codes in process_options
* Reload enabled / disabled error codes after loading plugins
* Unknown errors codes no longer a hard failure, they only get logged to
  stderr

mypy/build.py

@@ -46,6 +46,7 @@
 
 import mypy.semanal_main
 from mypy.checker import TypeChecker
+from mypy.errorcodes import error_codes
 from mypy.errors import CompileError, ErrorInfo, Errors, report_internal_error
 from mypy.indirection import TypeIndirectionVisitor
 from mypy.messages import MessageBuilder
@@ -241,6 +242,32 @@ def _build(
     errors = Errors(options, read_source=lambda path: read_py_file(path, cached_read))
     plugin, snapshot = load_plugins(options, errors, stdout, extra_plugins)
 
+    # Plugins might define own error codes, take a look again now
+
+    # Process `--enable-error-code` and `--disable-error-code` flags
+    disabled_codes = set(options.disable_error_code)
+    enabled_codes = set(options.enable_error_code)
+
+    valid_error_codes = set(error_codes.keys())
+    invalid_codes = (enabled_codes | disabled_codes) - valid_error_codes
+    if invalid_codes:
+        print(f"Invalid error code(s): {', '.join(sorted(invalid_codes))}", file=stderr)
+
+    options.disabled_error_codes |= {
+        error_codes[code] for code in disabled_codes if code in error_codes
+    }
+    options.enabled_error_codes |= {
+        error_codes[code] for code in enabled_codes if code in error_codes
+    }
+
+    # Enabling an error code always overrides disabling
+    options.disabled_error_codes -= options.enabled_error_codes
+
+    # Update error codes in Errors object (might use a different
+    # set instance if original was empty)
+    errors.disabled_error_codes = options.disabled_error_codes
+    errors.enabled_error_codes = options.enabled_error_codes
+
     # Add catch-all .gitignore to cache dir if we created it
     cache_dir_existed = os.path.isdir(options.cache_dir)
 

mypy/main.py

@@ -1302,14 +1302,13 @@ def set_strict_flags() -> None:
     disabled_codes = set(options.disable_error_code)
     enabled_codes = set(options.enable_error_code)
 
-    valid_error_codes = set(error_codes.keys())
-
-    invalid_codes = (enabled_codes | disabled_codes) - valid_error_codes
-    if invalid_codes:
-        parser.error(f"Invalid error code(s): {', '.join(sorted(invalid_codes))}")
-
-    options.disabled_error_codes |= {error_codes[code] for code in disabled_codes}
-    options.enabled_error_codes |= {error_codes[code] for code in enabled_codes}
+    # Plugins might define own error codes later, only load those we already know about here
+    options.disabled_error_codes |= {
+        error_codes[code] for code in disabled_codes if code in error_codes
+    }
+    options.enabled_error_codes |= {
+        error_codes[code] for code in enabled_codes if code in error_codes
+    }
 
     # Enabling an error code always overrides disabling
     options.disabled_error_codes -= options.enabled_error_codes