AssertionError assert file not in self.flushed_files on master and release-1.15

[clambert-jt]

Crash Report

Using dmpy on mypy release 1.15 and on master, adjusting a specific line that changes the return type to not match the annotated one results in an internal error. This is not an issue on mypy 1.10.

Traceback

<file>:<line1>: 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: 1.16.0+dev.66dde1497fae172988d577ef1a41ee0d89a47b56.dirty
<file>:<line2>: 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: 1.16.0+dev.66dde1497fae172988d577ef1a41ee0d89a47b56.dirty
<file>:<line3>: 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: 1.16.0+dev.66dde1497fae172988d577ef1a41ee0d89a47b56.dirty
Daemon crashed!
Traceback (most recent call last):
  File ".../mypy/dmypy_server.py", line 237, in serve
    resp = self.run_command(command, data)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/dmypy_server.py", line 286, in run_command
    ret = method(self, **data)
          ^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/dmypy_server.py", line 354, in cmd_run
    return self.check(sources, export_types, is_tty, terminal_width)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/dmypy_server.py", line 433, in check
    messages = self.fine_grained_increment_follow_imports(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/dmypy_server.py", line 701, in fine_grained_increment_follow_imports
    messages = fine_grained_manager.update([], to_delete)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/server/update.py", line 286, in update
    changed_modules = propagate_changes_using_dependencies(
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/server/update.py", line 882, in propagate_changes_using_dependencies
    triggered |= reprocess_nodes(manager, graph, id, nodes, deps, processed_targets)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/server/update.py", line 1026, in reprocess_nodes
    more = checker.check_second_pass(nodes)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/checker.py", line 522, in check_second_pass
    self.check_partial(node)
  File ".../mypy/checker.py", line 531, in check_partial
    self.accept(node)
  File ".../mypy/checker.py", line 578, in accept
    report_internal_error(err, self.errors.file, stmt.line, self.errors, self.options)
  File ".../mypy/errors.py", line 1276, in report_internal_error
    raise err
  File ".../mypy/checker.py", line 576, in accept
    stmt.accept(self)
  File ".../mypy/nodes.py", line 813, in accept
    return visitor.visit_func_def(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/checker.py", line 1079, in visit_func_def
    self._visit_func_def(defn)
  File ".../mypy/checker.py", line 1083, in _visit_func_def
    self.check_func_item(defn, name=defn.name)
  File ".../mypy/checker.py", line 1117, in check_func_item
    self.check_func_def(defn, typ, name, allow_empty)
  File ".../mypy/checker.py", line 1393, in check_func_def
    self.accept(item.body)
  File ".../mypy/checker.py", line 578, in accept
    report_internal_error(err, self.errors.file, stmt.line, self.errors, self.options)
  File ".../mypy/errors.py", line 1276, in report_internal_error
    raise err
  File ".../mypy/checker.py", line 576, in accept
    stmt.accept(self)
  File ".../mypy/nodes.py", line 1280, in accept
    return visitor.visit_block(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/checker.py", line 3062, in visit_block
    self.accept(s)
  File ".../mypy/checker.py", line 578, in accept
    report_internal_error(err, self.errors.file, stmt.line, self.errors, self.options)
  File ".../mypy/errors.py", line 1276, in report_internal_error
    raise err
  File ".../mypy/checker.py", line 576, in accept
    stmt.accept(self)
  File ".../mypy/nodes.py", line 1476, in accept
    return visitor.visit_return_stmt(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../mypy/checker.py", line 4770, in visit_return_stmt
    self.check_return_stmt(s)
  File ".../mypy/checker.py", line 4851, in check_return_stmt
    self.check_subtype(
  File ".../mypy/checker.py", line 7196, in check_subtype
    self.fail(msg, context)
  File ".../mypy/checker.py", line 7539, in fail
    self.msg.fail(msg.value, context, code=msg.code)
  File ".../mypy/messages.py", line 295, in fail
    self.report(
  File ".../mypy/messages.py", line 270, in report
    self.errors.report(
  File ".../mypy/errors.py", line 466, in report
    self.add_error_info(info)
  File ".../mypy/errors.py", line 532, in add_error_info
    self._add_error_info(file, info)
  File ".../mypy/errors.py", line 469, in _add_error_info
    assert file not in self.flushed_files
AssertionError

To Reproduce

I was unable to reproduce this error in an isolated environment after trying, though I could try more with multi-file setups if needed. For context, the section of code that when modified causes this crash looks like.

class Foo:
    ...
    class Bar(enum.Enum):
        A = 0
        B = 1
    ...
    bar: Bar
    @classmethod
    def baz(cls, old: Foo, new: Foo) -> Mapping[str, str]:
        ret = {
            "a": some_str_function(),
            "b": str(new.bar.value), # <<< modify this removing and adding the str call
            "c": f'[{some_str_function2()}]',
        }
	...
        return ret

Your Environment

• Mypy version used: master 66dde14
• Mypy command-line flags: dmypy run -- <directory> -v
• Mypy configuration options from mypy.ini (and other config files):

[mypy]
warn_unused_configs = True
show_error_code_links = True
warn_redundant_casts = True

[mypy-<module>.*]
disallow_untyped_defs = True
disallow_any_generics = True
strict_equality = True
no_implicit_reexport = True
local_partial_types = True
warn_unused_ignores = True
enable_error_code = possibly-undefined, truthy-iterable, truthy-bool

• Python version used: 3.12.2
• Operating system and version: Linux AMD64