Crash on code mixing instances and type typed variables

[guillonb]

Crash Report

INTERNAL ERROR

Traceback

mwe-mypy2.py:19: 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: 1.20.0+dev.56c33f251cb6b3791297fdaa57453d4afaa8c4dc
Traceback (most recent call last):
 File "/home/.../.venv/bin/mypy", line 8, in <module>
 sys.exit(console_entry())
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/__main__.py", line 15, in console_entry
 main()
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/main.py", line 135, in main
 res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/main.py", line 219, in run_build
 res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/build.py", line 320, in build
 result = build_inner(
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/build.py", line 417, in build_inner
 graph = dispatch(sources, manager, stdout)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/build.py", line 3178, in dispatch
 process_graph(graph, manager)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/build.py", line 3588, in process_graph
 done, still_working, results = manager.wait_for_done(graph)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/build.py", line 1070, in wait_for_done
 process_stale_scc(graph, next_scc, self)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/build.py", line 3752, in process_stale_scc
 graph[id].type_check_first_pass()
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/build.py", line 2543, in type_check_first_pass
 self.type_checker().check_first_pass()
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 530, in check_first_pass
 self.accept(d)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 641, in accept
 stmt.accept(self)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/nodes.py", line 1004, in accept
 return visitor.visit_func_def(self)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 1198, in visit_func_def
 self._visit_func_def(defn)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 1202, in _visit_func_def
 self.check_func_item(defn, name=defn.name)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 1237, in check_func_item
 self.check_func_def(defn, typ, name, allow_empty)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 1510, in check_func_def
 self.accept(item.body)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 641, in accept
 stmt.accept(self)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/nodes.py", line 1582, in accept
 return visitor.visit_block(self)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 3159, in visit_block
 self.accept(s)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 641, in accept
 stmt.accept(self)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/nodes.py", line 1669, in accept
 return visitor.visit_assignment_stmt(self)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 3212, in visit_assignment_stmt
 self.check_assignment(s.lvalues[-1], s.rvalue, s.type is None, s.new_syntax)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 3387, in check_assignment
 rvalue_type, lvalue_type = self.check_simple_assignment(
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checker.py", line 4668, in check_simple_assignment
 rvalue_type = self.expr_checker.accept(
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 6081, in accept
 typ = self.accept_maybe_cache(node, type_context=type_context)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 6116, in accept_maybe_cache
 typ = node.accept(self)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/nodes.py", line 2298, in accept
 return visitor.visit_call_expr(self)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 508, in visit_call_expr
 return self.visit_call_expr_inner(e, allow_none_return=allow_none_return)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 645, in visit_call_expr_inner
 ret_type = self.check_call_expr_with_callee_type(
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 1495, in check_call_expr_with_callee_type
 ret_type, callee_type = self.check_call(
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 1588, in check_call
 return self.check_callable_call(
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 1799, in check_callable_call
 arg_types = self.infer_arg_types_in_context(callee, args, arg_kinds, formal_to_actual)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 1973, in infer_arg_types_in_context
 res[ai] = self.accept(args[ai], arg_type)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 6083, in accept
 typ = node.accept(self) # r-value type, when interpreted as a value expression
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/nodes.py", line 2198, in accept
 return visitor.visit_name_expr(self)
 ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 357, in visit_name_expr
 narrowed = self.narrow_type_from_binder(e, result)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/checkexpr.py", line 6394, in narrow_type_from_binder
 narrowed = narrow_declared_type(known_type, restriction)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/meet.py", line 141, in narrow_declared_type
 narrow_declared_type(d, n)
 ~~~~~~~~~~~~~~~~~~~~^^^^^^
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/meet.py", line 222, in narrow_declared_type
 return meet_types(original_declared, original_narrowed)
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/meet.py", line 113, in meet_types
 return t.accept(TypeMeetVisitor(s))
 ~~~~~~~~^^^^^^^^^^^^^^^^^^^^
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/types.py", line 2846, in accept
 return visitor.visit_tuple_type(self)
 ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/meet.py", line 1079, in visit_tuple_type
 return t.copy_modified(items=[meet_types(it, self.s.args[0]) for it in t.items])
 ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^mwe-mypy2.py:19: : note: use --pdb to drop into pdb

 File "/home/.../.venv/lib/python3.13/site-packages/mypy/meet.py", line 113, in meet_types
 return t.accept(TypeMeetVisitor(s))
 ~~~~~~~~^^^^^^^^^^^^^^^^^^^^
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/types.py", line 3416, in accept
 return visitor.visit_union_type(self)
 ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/meet.py", line 793, in visit_union_type
 meets = [meet_types(x, self.s) for x in t.items]
 ~~~~~~~~~~^^^^^^^^^^^
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/meet.py", line 113, in meet_types
 return t.accept(TypeMeetVisitor(s))
 ~~~~~~~~^^^^^^^^^^^^^^^^^^^^
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/types.py", line 1250, in accept
 return visitor.visit_unpack_type(self)
 ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
 File "/home/.../.venv/lib/python3.13/site-packages/mypy/meet.py", line 845, in visit_unpack_type
 raise NotImplementedError
NotImplementedError: 

To Reproduce

from typing import Hashable, cast

type Key[K: Hashable] = K | type[K]
type TP[K: Hashable] = tuple[Key[K], ...]
type Value[V] = V | type[V] | None
type T[K: Hashable, V] = tuple[*TP[K], Value[V]]

def f[K, V](one: TP[K] | T[K, V], other: TP[K] | T[K, V]) -> TP[K] | T[K, V] | None:
 if len(one) < len(other):
 return None
 if one[:len(other)] != other:
 return None
 return cast(TP[K] | T[K, V], one[len(other):])

def g[K, V](one: TP[K] | T[K, V], other: TP[K] | T[K, V]) -> int | None:
 d: TP[K] | T[K, V] | None = f(one, other)
 if d is None:
 return None
 n: int = len(d)
 return n

and then run mypy on it.

Your Environment

• Mypy version used: mypy 1.20.0+dev.56c33f251cb6b3791297fdaa57453d4afaa8c4dc (compiled: no)
• Mypy command-line flags: --show-traceback
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: Python 3.13.5
• Operating system and version: 6.12.57+deb13-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.57-1 (2025-11-05) x86_64 GNU/Linux

[A5rocks]

Minimized:

type Prefix[K] = tuple[K | type[K], ...]
type Added[K, V] = tuple[*Prefix[K], V]

def g[K, V](_a: K, _b: V) -> int | None:
 d: Prefix[K] | Added[K, V] | None = None
 assert d is not None
 return len(d)

[A5rocks]

Slightly more minimized:

type Prefix[K] = tuple[K | list[int], ...]

def g[K](_a: K) -> None:
 d: Prefix[K] | tuple[*Prefix[int], int] | None = None
 assert d is not None
 reveal_type(d)