Crash with custom plugin and ErrorCode

[cdce8p]

Crash Report
Cross posting it here for better visibility. The original post: #15218 (comment)
The crash / regression (in dev) is caused by the change in #15218.

The example below is with a custom plugin. However this does effect others as well if an error is emitted. I discovered it while testing code with the pydantic mypy plugin.

/CC: @svalentin

Traceback

$ mypy --config-file=custom.ini --show-traceback test.py
test.py:5: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 1.4.0+dev.ce2c918f73fa4e98c9d0398401431fc45b608e29
Traceback (most recent call last):
  File "mypy/checkexpr.py", line 4871, in accept
  File "mypy/checkexpr.py", line 426, in visit_call_expr
  File "mypy/checkexpr.py", line 546, in visit_call_expr_inner
  File "mypy/checkexpr.py", line 1206, in check_call_expr_with_callee_type
  File "mypy/checkexpr.py", line 1289, in check_call
  File "mypy/checkexpr.py", line 1499, in check_callable_call
  File "mypy/checkexpr.py", line 1029, in apply_function_plugin
  File "/.../plugin.py", line 21, in emit_error
    ctx.api.fail("Custom error", ctx.context, code=ERROR)
  File "mypy/checker.py", line 6478, in fail
  File "mypy/messages.py", line 283, in fail
  File "mypy/messages.py", line 258, in report
  File "mypy/errors.py", line 436, in report
  File "mypy/errors.py", line 478, in add_error_info
  File "mypy/errors.py", line 577, in is_ignored_error
  File "mypy/errors.py", line 604, in is_error_code_enabled
AttributeError: attribute 'sub_code_of' of 'ErrorCode' undefined
test.py:9: : note: use --pdb to drop into pdb

To Reproduce

# test.py
def main() -> int:
    return 2

main()

reveal_type(1)

# custom.ini
[mypy]
plugins = plugin.py

# plugin.py
from typing import Callable

from mypy.errorcodes import ErrorCode
from mypy.plugin import FunctionContext, Plugin
from mypy.types import AnyType, Type, TypeOfAny

ERROR = ErrorCode("custom", "", "Custom")


def plugin(version: str) -> type[Plugin]:
    return CustomPlugin


class CustomPlugin(Plugin):
    def get_function_hook(
        self, fullname: str
    ) -> Callable[[FunctionContext], Type] | None:
        if fullname.endswith(".main"):
            return self.emit_error
        return None

    def emit_error(self, ctx: FunctionContext) -> Type:
        ctx.api.fail("Custom error", ctx.context, code=ERROR)
        return AnyType(TypeOfAny.from_error)

Make sure to install the latest compiled version of mypy. E.g. from https://github.com/mypyc/mypy_mypyc-wheels/releases/tag/v1.4.0%2Bdev.ce2c918f73fa4e98c9d0398401431fc45b608e29

mypy --config-file=custom.ini --show-traceback test.py

Your Environment

• Mypy version used: mypy 1.4.0+dev.ce2c918f73fa4e98c9d0398401431fc45b608e29 (compiled: yes)
• Python version used: 3.11