"UnboundLocalError" on an annotation for a nonlocal variable

[shirayu]

This code causes UnboundLocalError with mypy 0.711 and the latest master sources (Version: 0.720+dev.46aa00d8a8d5c870c6ef24b82261b6b257e2ea03).

#!/usr/bin/env python3

import typing


def main():
    bar = []  # type: typing.List[int]

    def foo():
        nonlocal bar
        bar = []  # type: typing.List[int]


if __name__ == '__main__':
    main()

Traceback (most recent call last):
  File "/usr/lib/python3.5/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.5/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/dev/shm/mypy/mypy/__main__.py", line 12, in <module>
    main(None, sys.stdout, sys.stderr)
  File "/dev/shm/mypy/mypy/main.py", line 83, in main
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/dev/shm/mypy/mypy/build.py", line 164, in build
    result = _build(sources, options, alt_lib_path, flush_errors, fscache, stdout, stderr)
  File "/dev/shm/mypy/mypy/build.py", line 224, in _build
    graph = dispatch(sources, manager, stdout)
  File "/dev/shm/mypy/mypy/build.py", line 2567, in dispatch
    process_graph(graph, manager)
  File "/dev/shm/mypy/mypy/build.py", line 2880, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/dev/shm/mypy/mypy/build.py", line 2981, in process_stale_scc
    graph[id].semantic_analysis()
  File "/dev/shm/mypy/mypy/build.py", line 2073, in semantic_analysis
    self.manager.semantic_analyzer.visit_file(self.tree, self.xpath, self.options, patches)
  File "/dev/shm/mypy/mypy/semanal.py", line 321, in visit_file
    self.accept(d)
  File "/dev/shm/mypy/mypy/semanal.py", line 3853, in accept
    node.accept(self)
  File "/dev/shm/mypy/mypy/nodes.py", line 655, in accept
    return visitor.visit_func_def(self)
  File "/dev/shm/mypy/mypy/semanal.py", line 393, in visit_func_def
    self._visit_func_def(defn)
  File "/dev/shm/mypy/mypy/semanal.py", line 484, in _visit_func_def
    self.analyze_function(defn)
  File "/dev/shm/mypy/mypy/semanal.py", line 784, in analyze_function
    postponed.accept(self)
  File "/dev/shm/mypy/mypy/nodes.py", line 655, in accept
    return visitor.visit_func_def(self)
  File "/dev/shm/mypy/mypy/semanal.py", line 393, in visit_func_def
    self._visit_func_def(defn)
  File "/dev/shm/mypy/mypy/semanal.py", line 484, in _visit_func_def
    self.analyze_function(defn)
  File "/dev/shm/mypy/mypy/semanal.py", line 779, in analyze_function
    defn.body.accept(self)
  File "/dev/shm/mypy/mypy/nodes.py", line 978, in accept
    return visitor.visit_block(self)
  File "/dev/shm/mypy/mypy/semanal.py", line 1731, in visit_block
    self.accept(s)
  File "/dev/shm/mypy/mypy/semanal.py", line 3853, in accept
    node.accept(self)
  File "/dev/shm/mypy/mypy/nodes.py", line 1036, in accept
    return visitor.visit_assignment_stmt(self)
  File "/dev/shm/mypy/mypy/semanal.py", line 1792, in visit_assignment_stmt
    self.analyze_lvalues(s)
  File "/dev/shm/mypy/mypy/semanal.py", line 1813, in analyze_lvalues
    is_final=s.is_final_def)
  File "/dev/shm/mypy/mypy/semanal.py", line 2119, in analyze_lvalue
    self.analyze_name_lvalue(lval, add_global, explicit_type, is_final)
  File "/dev/shm/mypy/mypy/semanal.py", line 2198, in analyze_name_lvalue
    self.make_name_lvalue_point_to_existing_def(lval, explicit_type, is_final)
  File "/dev/shm/mypy/mypy/semanal.py", line 2281, in make_name_lvalue_point_to_existing_def
    self.name_already_defined(lval.name, lval, original_def)
  File "/dev/shm/mypy/mypy/semanal.py", line 3817, in name_already_defined
    self.already_defined(name, ctx, original_ctx, noun='Name')
  File "/dev/shm/mypy/mypy/semanal.py", line 3808, in already_defined
    elif node and node.line != -1:
UnboundLocalError: local variable 'node' referenced before assignment

[JelleZijlstra]

Confirmed on master and 0.711. The code passes with --new-semantic-analyzer though.

[JukkaL]

Since this is not a regression (it also happens with 0.670 at least) and fixed in the new semantic analyzer, this doesn't seem urgent to fix. The only action seems to be adding a test case to prevent a future regression.