Internal error using compile re in inner function

[RonVider]

Running mypy on latest master raises internal error for the following code:

import re


def func(arg: str) -> None:
    if not (match := re_pattern.match(arg)):
        return

    print(arg)


re_pattern = re.compile(r".*")

func("hello")

Traceback attached:

/tmp/tst.py:5: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.rtfd.io/en/latest/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.781
Traceback (most recent call last):
  File "/usr/local/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/usr/local/lib/python3.8/site-packages/mypy/__main__.py", line 8, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "/usr/local/lib/python3.8/site-packages/mypy/main.py", line 89, in main
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/usr/local/lib/python3.8/site-packages/mypy/build.py", line 180, in build
    result = _build(
  File "/usr/local/lib/python3.8/site-packages/mypy/build.py", line 252, in _build
    graph = dispatch(sources, manager, stdout)
  File "/usr/local/lib/python3.8/site-packages/mypy/build.py", line 2626, in dispatch
    process_graph(graph, manager)
  File "/usr/local/lib/python3.8/site-packages/mypy/build.py", line 2949, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/usr/local/lib/python3.8/site-packages/mypy/build.py", line 3047, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/usr/local/lib/python3.8/site-packages/mypy/build.py", line 2107, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 294, in check_first_pass
    self.accept(d)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 401, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.8/site-packages/mypy/nodes.py", line 676, in accept
    return visitor.visit_func_def(self)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 726, in visit_func_def
    self._visit_func_def(defn)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 730, in _visit_func_def
    self.check_func_item(defn, name=defn.name)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 792, in check_func_item
    self.check_func_def(defn, typ, name)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 975, in check_func_def
    self.accept(item.body)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 401, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.8/site-packages/mypy/nodes.py", line 1004, in accept
    return visitor.visit_block(self)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 1973, in visit_block
    self.accept(s)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 401, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.8/site-packages/mypy/nodes.py", line 1195, in accept
    return visitor.visit_if_stmt(self)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 3212, in visit_if_stmt
    if_map, else_map = self.find_isinstance_check(e)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 3928, in find_isinstance_check
    if_map, else_map = self.find_isinstance_check_helper(node)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 4135, in find_isinstance_check_helper
    left, right = self.find_isinstance_check_helper(node.expr)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 4104, in find_isinstance_check_helper
    return self.find_isinstance_check_helper(node.target)
  File "/usr/local/lib/python3.8/site-packages/mypy/checker.py", line 4108, in find_isinstance_check_helper
    vartype = type_map[node]
KeyError: <mypy.nodes.NameExpr object at 0x7f832bd6c0c0>

[ilevkivskyi]

Confirm the crash. Note there is also #8986

[hauntsaninja]

Closing as a dupe of #9054 which now has a little more discussion

[hauntsaninja]

@RonVider thanks for reporting! And thanks to llchan this should be fixed on master :-) I was wondering if the code you're working on is open source? My interest is in adding projects to https://github.com/hauntsaninja/mypy_primer that use newer Python features.