Internal error checking xarray with `--check-untyped-defs`

[tlambert03]

Crash Report

Not sure whether this is a mypy issue, or an xarray issue... but I'm getting RuntimeError: TypeGuard should not appear here when running mypy on a file that imports xarray when using the --check-untyped-defs flag. Minimal env on mypy master:

To Reproduce

conda create -n test -c conda-forge python
conda activate test
pip install xarray
pip install git+https://github.com/python/mypy.git
echo "import xarray" > m.py
mypy --check-untyped-defs --show-traceback m.py

Traceback

❯ mypy --check-untyped-defs --show-traceback m.py
/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/xarray/core/common.py:1659: 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: 0.920+dev.7576f659d42ee271c78e69d7481b9d49517a49f6
Traceback (most recent call last):
  File "/Users/talley/miniconda3/envs/test/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/__main__.py", line 11, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/main.py", line 87, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/main.py", line 165, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/build.py", line 179, in build
    result = _build(
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/build.py", line 254, in _build
    graph = dispatch(sources, manager, stdout)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/build.py", line 2707, in dispatch
    process_graph(graph, manager)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/build.py", line 3031, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/build.py", line 3129, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/build.py", line 2175, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 295, in check_first_pass
    self.accept(d)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 402, in accept
    stmt.accept(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/nodes.py", line 530, in accept
    return visitor.visit_overloaded_func_def(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 435, in visit_overloaded_func_def
    self._visit_overloaded_func_def(defn)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 457, in _visit_overloaded_func_def
    defn.impl.accept(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/nodes.py", line 696, in accept
    return visitor.visit_func_def(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 734, in visit_func_def
    self._visit_func_def(defn)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 738, in _visit_func_def
    self.check_func_item(defn, name=defn.name)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 800, in check_func_item
    self.check_func_def(defn, typ, name)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 983, in check_func_def
    self.accept(item.body)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 402, in accept
    stmt.accept(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/nodes.py", line 1024, in accept
    return visitor.visit_block(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 1996, in visit_block
    self.accept(s)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 402, in accept
    stmt.accept(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/nodes.py", line 1216, in accept
    return visitor.visit_if_stmt(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 3313, in visit_if_stmt
    self.accept(b)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 402, in accept
    stmt.accept(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/nodes.py", line 1024, in accept
    return visitor.visit_block(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 1996, in visit_block
    self.accept(s)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 402, in accept
    stmt.accept(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/nodes.py", line 1216, in accept
    return visitor.visit_if_stmt(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checker.py", line 3303, in visit_if_stmt
    t = get_proper_type(self.expr_checker.accept(e))
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checkexpr.py", line 3910, in accept
    typ = node.accept(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/nodes.py", line 1663, in accept
    return visitor.visit_unary_expr(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checkexpr.py", line 2873, in visit_unary_expr
    operand_type = self.accept(e.expr)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checkexpr.py", line 3910, in accept
    typ = node.accept(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/nodes.py", line 1600, in accept
    return visitor.visit_call_expr(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checkexpr.py", line 277, in visit_call_expr
    return self.visit_call_expr_inner(e, allow_none_return=allow_none_return)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checkexpr.py", line 366, in visit_call_expr_inner
    ret_type = self.check_call_expr_with_callee_type(callee_type, e, fullname,
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checkexpr.py", line 873, in check_call_expr_with_callee_type
    return self.check_call(callee_type, e.args, e.arg_kinds, e,
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checkexpr.py", line 933, in check_call
    return self.check_callable_call(callee, args, arg_kinds, context, arg_names,
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checkexpr.py", line 1030, in check_callable_call
    self.check_argument_types(arg_types, arg_kinds, args, callee, formal_to_actual, context,
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checkexpr.py", line 1493, in check_argument_types
    check_arg(expanded_actual, actual_type, arg_kinds[actual],
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/checkexpr.py", line 1523, in check_arg
    elif not is_subtype(caller_type, callee_type):
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/subtypes.py", line 93, in is_subtype
    return _is_subtype(left, right,
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/subtypes.py", line 147, in _is_subtype
    return left.accept(SubtypeVisitor(orig_right,
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/types.py", line 1747, in accept
    return visitor.visit_union_type(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/subtypes.py", line 476, in visit_union_type
    return all(self._is_subtype(item, self.orig_right) for item in left.items)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/subtypes.py", line 476, in <genexpr>
    return all(self._is_subtype(item, self.orig_right) for item in left.items)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/subtypes.py", line 205, in _is_subtype
    return is_subtype(left, right,
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/subtypes.py", line 93, in is_subtype
    return _is_subtype(left, right,
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/subtypes.py", line 147, in _is_subtype
    return left.accept(SubtypeVisitor(orig_right,
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/types.py", line 296, in accept
    return visitor.visit_type_guard_type(self)
  File "/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/mypy/subtypes.py", line 479, in visit_type_guard_type
    raise RuntimeError("TypeGuard should not appear here")
RuntimeError: TypeGuard should not appear here
/Users/talley/miniconda3/envs/test/lib/python3.9/site-packages/xarray/core/common.py:1659: : note: use --pdb to drop into pdb

Your Environment

• Mypy version used: 0.920+dev.7576f659d42ee271c78e69d7481b9d49517a49f6
• Mypy command-line flags: --check-untyped-defs
• Mypy configuration options from mypy.ini (and other config files): no config files
• Python version used: 3.9.6
• Operating system and version: macos 10.15.7

❯ pip list
Package           Version
----------------- --------------------------------------------------
mypy              0.920+dev.7576f659d42ee271c78e69d7481b9d49517a49f6
mypy-extensions   0.4.3
numpy             1.21.2
pandas            1.3.2
pip               21.2.4
python-dateutil   2.8.2
pytz              2021.1
setuptools        57.4.0
six               1.16.0
tomli             1.1.0
typing-extensions 3.10.0.0
wheel             0.37.0
xarray            0.19.0

[JelleZijlstra]

This is surely a bug in mypy, thanks for the report!

I don't know what version of xarray you're running exactly, but looking at master right now, there is a call to is_scalar at line 1646 (https://github.com/pydata/xarray/blob/main/xarray/core/common.py#L1646). Mypy's TypeGuard support is a little buggy in general, so we probably just need to add a case somewhere.

[hauntsaninja]

Probably the same as #10647

Also not the first time we've had an issue stemming from xarray's typing (#9437), could be good to ensure mypy_primer coverage...

[hauntsaninja]

( @tlambert03 if your project using xarray + mypy is open source, let me know, and I can add it to mypy_primer. It looks like I already have xarray in there, but clearly that wasn't enough)

edit: found https://github.com/arviz-devs/arviz.git which reproduces the crash

[JelleZijlstra]

The repro case here apparently is just importing xarray, so it's not clear why mypy-primer wouldn't catch that.

[hauntsaninja]

My guess would be because xarray's mypy.ini doesn't have check untyped defs

[tlambert03]

here's the most relevant thing I could find about the way xarray uses mypy internally:

https://github.com/pydata/xarray/blob/808b2e9eec1ec48d43cf9311dee27cd5550b8fd2/setup.cfg#L242-L245

[mypy]
exclude = properties|asv_bench|doc
files = xarray/**/*.py
show_error_codes = True

# version spanning code is hard to type annotate (and most of this module will
# be going away soon anyways)
[mypy-xarray.core.pycompat]
ignore_errors = True

[tlambert03]

but I'm not an xarray developer, I work on a project (napari) which had an xarray import which broke my ability to test our own package. The minimal reproducible example above is just a fresh environment with a couple installs, a single import xarray statement with --check-untyped-defs