INTERNAL ERROR on match-case statement

Bug Report

The following causes an INTERNAL ERROR. The issue seems to be related to the usage of match-case. https://mypy-play.net/?mypy=master&python=3.12&flags=show-traceback&gist=7ccec270743b3e26d66d211839e82e64

To Reproduce

from typing import Self, Protocol, overload
from collections.abc import Sequence

class Encoder(Protocol):
    def __call__(self, u, /): ...

    def simplify(self) -> "Encoder":
        return self

class Chain(Encoder, Sequence[Encoder]):

    encoders: list[Encoder]

    def __init__(self, *encoders: Encoder):
        self.encoders = list(encoders)

    def __len__(self) -> int:
        return len(self.encoders)

    @overload
    def __getitem__(self, index: int) -> Encoder: ...
    @overload
    def __getitem__(self, index: slice) -> Self: ...
    def __getitem__(self, index,  /):
        return self.encoders[index]

    def __call__(self, x):
        for encoder in self.encoders:
            x = encoder(x)
        return x

    def simplify(self) -> Encoder | Self:
        match self:
            case [encoder]:
                return encoder.simplify()
            case _:
                cls = type(self)
                return cls(*(e.simplify() for e in self.encoders))

        # The equivalent code below works...
        # if len(self)==1:
        #     return self.encoders[0].simplify()
        # cls = type(self)
        # return cls(*(e.simplify() for e in self.encoders))

Actual Behavior

main.py:33: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
If this issue continues with mypy master, please report a bug at https://github.com/python/mypy/issues
version: 1.11.0+dev.0570f71f000489c94021d956662ab3373f7296bc
main.py:33: : note: please use --show-traceback to print a traceback when reporting a bug

Full Traceback

``` Traceback (most recent call last): File "", line 198, in _run_module_as_main File "", line 88, in _run_code File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/__main__.py", line 37, in console_entry() File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/__main__.py", line 15, in console_entry main() File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/main.py", line 100, in main res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/main.py", line 182, in run_build res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 192, in build result = _build( File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 266, in _build graph = dispatch(sources, manager, stdout) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 2942, in dispatch process_graph(graph, manager) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 3340, in process_graph process_stale_scc(graph, scc, manager) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 3441, in process_stale_scc graph[id].type_check_first_pass() File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 2310, in type_check_first_pass self.type_checker().check_first_pass() File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 481, in check_first_pass self.accept(d) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 589, in accept stmt.accept(self) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/nodes.py", line 1142, in accept return visitor.visit_class_def(self) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 2340, in visit_class_def self.accept(defn.defs) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 589, in accept stmt.accept(self) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/nodes.py", line 1223, in accept return visitor.visit_block(self) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 2802, in visit_block self.accept(s) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 589, in accept stmt.accept(self) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/nodes.py", line 787, in accept return visitor.visit_func_def(self) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 1000, in visit_func_def self._visit_func_def(defn) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 1004, in _visit_func_def self.check_func_item(defn, name=defn.name) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 1077, in check_func_item self.check_func_def(defn, typ, name, allow_empty) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 1309, in check_func_def self.accept(item.body) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 589, in accept stmt.accept(self) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/nodes.py", line 1223, in accept return visitor.visit_block(self) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 2802, in visit_block self.accept(s) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 589, in accept stmt.accept(self) File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/nodes.py", line 1607, in accept return visitor.visit_match_stmt(self) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 5107, in visit_match_stmt pattern_types = [self.pattern_checker.accept(p, subject_type) for p in s.patterns] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkpattern.py", line 129, in accept result = o.accept(self) ^^^^^^^^^^^^^^ File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/patterns.py", line 93, in accept return visitor.visit_sequence_pattern(self) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkpattern.py", line 335, in visit_sequence_pattern new_type = self.construct_sequence_child(current_type, new_inner_type) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkpattern.py", line 756, in construct_sequence_child assert isinstance(proper_type, Instance) AssertionError: main.py:33: 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: 1.11.0+dev.0570f71f000489c94021d956662ab3373f7296bc main.py:33: : note: use --pdb to drop into pdb ```

Your Environment

https://mypy-play.net/?mypy=master&python=3.12&flags=show-traceback&gist=7ccec270743b3e26d66d211839e82e64

python / mypy

INTERNAL ERROR on match-case statement #17134