guppylang.error.InternalGuppyError: Unexpected assignment pattern

[aborgna-q]

module = GuppyModule("test")
@guppy(module)
def main() -> None:
    bs = [True]
    bs[0] = bs[0]

Running this errors out with

guppylang/error.py:101: in pretty_errors_wrapped
    return f(*args, **kwargs)
guppylang/module.py:346: in compile
    self.check()
guppylang/module.py:323: in check
    other_defs = self._check_defs(
guppylang/module.py:295: in _check_defs
    defn.check(parsed_globals) if isinstance(defn, CheckableDef) else defn
guppylang/definition/function.py:106: in check
    cfg = check_global_func_def(self.defined_at, self.ty, globals)
guppylang/checker/func_checker.py:80: in check_global_func_def
    return check_cfg(cfg, inputs, ty.output, generic_params, func_def.name, globals)
guppylang/checker/cfg_checker.py:84: in check_cfg
    checked_cfg.entry_bb = check_bb(
guppylang/checker/cfg_checker.py:200: in check_bb
    checked_stmts = StmtChecker(ctx, bb, return_ty).check_stmts(bb.statements)
guppylang/checker/stmt_checker.py:91: in check_stmts
    return [self.visit(s) for s in stmts]
guppylang/ast_util.py:53: in visit
    return visitor(node, *args, **kwargs)
guppylang/checker/stmt_checker.py:279: in visit_Assign
    node.targets = [self._check_assign(target, node.value, ty)]
../../.local/share/uv/python/cpython-3.12.5-macos-aarch64-none/lib/python3.12/functools.py:944: in _method
    return method.__get__(obj, cls)(*args, **kwargs)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <guppylang.checker.stmt_checker.StmtChecker object at 0x1117337d0>
lhs = <ast.Subscript object at 0x1117aec10>
rhs = <guppylang.nodes.PlaceNode object at 0x111710290>
rhs_ty = OpaqueType(args=[], defn=OpaqueTypeDef(id=DefId(id=3, module=None), name='bool', defined_at=None, description='type', params=[], always_linear=False, to_hugr=<function <lambda> at 0x11115dc60>, bound=None))

    @functools.singledispatchmethod
    def _check_assign(self, lhs: ast.expr, rhs: ast.expr, rhs_ty: Type) -> ast.expr:
        """Helper function to check assignments with patterns."""
>       raise InternalGuppyError("Unexpected assignment pattern")
E       guppylang.error.InternalGuppyError: Unexpected assignment pattern

guppylang/checker/stmt_checker.py:104: InternalGuppyError

I'd expect this to emit a nicer error rather than panic internally.