Literal of type string not accepted as keyword name

[twoertwein]

To Reproduce

from typing import Literal

def fun(**kwargs) -> None:
    ...

class A:
    def __init__(self):
        self.a: Literal["a"] = "a"

    def test(self) -> None:
        return fun(**{self.a: "a"})  #  error: Keywords must be strings  [misc]

Your Environment

• Mypy version used: 0.971

[randolf-scholz]

Also happens for dataclasses:

from dataclasses import dataclass
from typing import Literal, Mapping

@dataclass
class Foo:
    a: int
    b: int

x: Mapping[Literal["a", "b"], int] = {"a":1, "b": 2}
y: Foo = Foo(**x)  # error: Keywords must be strings  [misc]

https://mypy-play.net/?mypy=latest&python=3.11&gist=3450797f9c8ca85bb6b04240c8dadb88

[randolf-scholz]

This seems to be the relevant code:

mypy/mypyc/lib-rt/getargs.c

Lines 390 to 396 in b901d21

	while (PyDict_Next(kwargs, &j, &key, &value)) {
	int match = 0;
	if (unlikely(!PyUnicode_Check(key))) {
	PyErr_SetString(PyExc_TypeError,
	"keywords must be strings");
	goto latefail;
	}

at other places _PyDict_GetItemStringWithError is used which wraps keyword argument in PyUnicode_FromString

mypy/mypyc/lib-rt/pythonsupport.h

Lines 358 to 369 in b901d21

	static PyObject *
	_PyDict_GetItemStringWithError(PyObject *v, const char *key)
	{
	PyObject *kv, *rv;
	kv = PyUnicode_FromString(key);
	if (kv == NULL) {
	return NULL;
	}
	rv = PyDict_GetItemWithError(v, kv);
	Py_DECREF(kv);
	return rv;
	}

[JelleZijlstra]

That is not the relevant code, as it is mypyc runtime code. This issue is about mypy, not mypyc. The error appears to be raised here:

mypy/messages.py:            self.fail("Keywords must be strings", context)

I haven't looked further.