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[antecrescent]

mypy-1.8.0 added a third parameter to the flush_error signature (python/mypy@8c57df0). 97aff1e updated flush_error in pytest_mypy_plugins/item.py to match it, but failed taking into account that <mypy-1.8.0 still expects the two-parameter signature to flush errors after a file is processed.

As a consequence, pytest test cases fail if mypy's process_stale_scc function calls our three-parameter flush_error with two arguments.
I'm not familiar with the innards of mypy but this happens every time pytest runs with the --mypy-same-process option.

Reproducible setup:

$ pip install mypy==1.7.1
$ pip install -r requirements.txt
$ pytest --mypy-same-process

Output

============================= test session starts ==============================
platform linux -- Python 3.12.2, pytest-8.0.2, pluggy-1.4.0
rootdir: /root/pytest-mypy-plugins
configfile: pyproject.toml
plugins: mypy-plugins-3.0.0
collected 60 items

pytest_mypy_plugins/tests/test-extension.yml F
pytest_mypy_plugins/tests/test-mypy-config.yml F
pytest_mypy_plugins/tests/test-parametrized.yml FFFFFFFFFF
pytest_mypy_plugins/tests/test-paths-from-env.yml F
pytest_mypy_plugins/tests/test-regex_assertions.yml FFFFFFFF
pytest_mypy_plugins/tests/test-simple-cases.yml FFFFFFFFF
pytest_mypy_plugins/tests/test_configs/test_join_toml_configs.py ......
pytest_mypy_plugins/tests/test_explicit_configs.py ......
pytest_mypy_plugins/tests/test_input_schema.py .......
pytest_mypy_plugins/tests/test_utils.py ...........

=================================== FAILURES ===================================
_______________________ reveal_type_extension_is_loaded ________________________
Traceback (most recent call last):
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/runner.py", line 342, in from_call
    result: Optional[TResult] = func()
                                ^^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/runner.py", line 263, in <lambda>
    lambda: ihook(item=item, **kwds), when=when, reraise=reraise
            ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/pluggy/_hooks.py", line 501, in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/pluggy/_manager.py", line 119, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/pluggy/_callers.py", line 138, in _multicall
    raise exception.with_traceback(exception.__traceback__)
  File "/tmp/venv/lib/python3.12/site-packages/pluggy/_callers.py", line 121, in _multicall
    teardown.throw(exception)  # type: ignore[union-attr]
    ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/threadexception.py", line 87, in pytest_runtest_call
    yield from thread_exception_runtest_hook()
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/threadexception.py", line 63, in thread_exception_runtest_hook
    yield
  File "/tmp/venv/lib/python3.12/site-packages/pluggy/_callers.py", line 121, in _multicall
    teardown.throw(exception)  # type: ignore[union-attr]
    ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/unraisableexception.py", line 90, in pytest_runtest_call
    yield from unraisable_exception_runtest_hook()
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/unraisableexception.py", line 65, in unraisable_exception_runtest_hook
    yield
  File "/tmp/venv/lib/python3.12/site-packages/pluggy/_callers.py", line 121, in _multicall
    teardown.throw(exception)  # type: ignore[union-attr]
    ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/logging.py", line 839, in pytest_runtest_call
    yield from self._runtest_for(item, "call")
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/logging.py", line 822, in _runtest_for
    yield
  File "/tmp/venv/lib/python3.12/site-packages/pluggy/_callers.py", line 121, in _multicall
    teardown.throw(exception)  # type: ignore[union-attr]
    ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/capture.py", line 882, in pytest_runtest_call
    return (yield)
            ^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/pluggy/_callers.py", line 121, in _multicall
    teardown.throw(exception)  # type: ignore[union-attr]
    ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/skipping.py", line 256, in pytest_runtest_call
    return (yield)
            ^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/pluggy/_callers.py", line 102, in _multicall
    res = hook_impl.function(*args)
          ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/runner.py", line 178, in pytest_runtest_call
    raise e
  File "/tmp/venv/lib/python3.12/site-packages/_pytest/runner.py", line 170, in pytest_runtest_call
    item.runtest()
  File "/root/pytest-mypy-plugins/pytest_mypy_plugins/item.py", line 273, in runtest
    returncode, (stdout, stderr) = self.typecheck_in_same_process(execution_path, mypy_cmd_options)
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/pytest-mypy-plugins/pytest_mypy_plugins/item.py", line 231, in typecheck_in_same_process
    return_code = run_mypy_typechecking(mypy_cmd_options, stdout=stdout, stderr=stderr)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/pytest-mypy-plugins/pytest_mypy_plugins/item.py", line 99, in run_mypy_typechecking
    build.build(sources, options, flush_errors=flush_errors, fscache=fscache, stdout=stdout, stderr=stderr)
  File "mypy/build.py", line 189, in build
  File "mypy/build.py", line 263, in _build
  File "mypy/build.py", line 2941, in dispatch
  File "mypy/build.py", line 3339, in process_graph
  File "mypy/build.py", line 3461, in process_stale_scc
TypeError: run_mypy_typechecking.<locals>.flush_errors() missing 1 required positional argument: 'serious'

[error repeats for all test cases that don't run mypy in a sub-process]

=========================== short test summary info ============================
FAILED pytest_mypy_plugins/tests/test-extension.yml::reveal_type_extension_is_loaded
FAILED pytest_mypy_plugins/tests/test-mypy-config.yml::custom_mypy_config_disallow_any_explicit_set
FAILED pytest_mypy_plugins/tests/test-parametrized.yml::only_main[a=1,revealed_type=builtins.int]
FAILED pytest_mypy_plugins/tests/test-parametrized.yml::only_main[a=1.0,revealed_type=builtins.float]
FAILED pytest_mypy_plugins/tests/test-parametrized.yml::with_extra[a=2,b=None,rt=Any]
FAILED pytest_mypy_plugins/tests/test-parametrized.yml::with_extra[a=3,b=3,rt=Any]
FAILED pytest_mypy_plugins/tests/test-parametrized.yml::with_out[what=cat,rt=builtins.str]
FAILED pytest_mypy_plugins/tests/test-parametrized.yml::with_out[what=dog,rt=builtins.str]
FAILED pytest_mypy_plugins/tests/test-parametrized.yml::parametrized_can_skip_mypy_config_section[val=False]
FAILED pytest_mypy_plugins/tests/test-parametrized.yml::parametrized_can_skip_mypy_config_section[val=True]
FAILED pytest_mypy_plugins/tests/test-parametrized.yml::with_mypy_config[allow_any=true]
FAILED pytest_mypy_plugins/tests/test-parametrized.yml::with_mypy_config[allow_any=false]
FAILED pytest_mypy_plugins/tests/test-paths-from-env.yml::add_mypypath_env_var_to_package_search
FAILED pytest_mypy_plugins/tests/test-regex_assertions.yml::expected_message_regex
FAILED pytest_mypy_plugins/tests/test-regex_assertions.yml::expected_message_regex_with_out
FAILED pytest_mypy_plugins/tests/test-regex_assertions.yml::regex_with_out_does_not_hang
FAILED pytest_mypy_plugins/tests/test-regex_assertions.yml::regex_with_comment_does_not_hang
FAILED pytest_mypy_plugins/tests/test-regex_assertions.yml::expected_single_message_regex
FAILED pytest_mypy_plugins/tests/test-regex_assertions.yml::rexex_but_not_turned_on
FAILED pytest_mypy_plugins/tests/test-regex_assertions.yml::rexex_but_turned_off
FAILED pytest_mypy_plugins/tests/test-regex_assertions.yml::regex_does_not_match
FAILED pytest_mypy_plugins/tests/test-simple-cases.yml::simplest_case - TypeE...
FAILED pytest_mypy_plugins/tests/test-simple-cases.yml::revealed_type_with_environment
FAILED pytest_mypy_plugins/tests/test-simple-cases.yml::revealed_type_with_disabled_cache
FAILED pytest_mypy_plugins/tests/test-simple-cases.yml::external_output_lines
FAILED pytest_mypy_plugins/tests/test-simple-cases.yml::create_files - TypeEr...
FAILED pytest_mypy_plugins/tests/test-simple-cases.yml::error_case - TypeErro...
FAILED pytest_mypy_plugins/tests/test-simple-cases.yml::skip_if_false - TypeE...
FAILED pytest_mypy_plugins/tests/test-simple-cases.yml::fail_if_message_does_not_match
FAILED pytest_mypy_plugins/tests/test-simple-cases.yml::fail_if_message_from_outdoes_not_match
======================== 30 failed, 30 passed in 48.83s ========================

Issue pip install mypy==1.8.0 and the same test run succeeds.

[sobolevn]

@antecrescent I suggest making a *args function here to support older versions instead.
There are projects that use matrix checks with different mypy versions. Let's change #138

[antecrescent]

I've tried two possible approaches but 'm not sure how to proceed and I'd be happy to hear your thoughts.

*args approach

It does not work, because mypy does not call flush_errors with keyword arguments.
Also the static type-checking fails because mypy complains about our flush_errors signature not matching its own:

diff --git a/pytest_mypy_plugins/item.py b/pytest_mypy_plugins/item.py
index 2094eed..937d9f0 100644
--- a/pytest_mypy_plugins/item.py
+++ b/pytest_mypy_plugins/item.py
@@ -85,7 +85,7 @@ def run_mypy_typechecking(cmd_options: List[str], stdout: TextIO, stderr: TextIO
     # discard filename parameter '_'. Mypy uses it to generate
     # one junit-xml test entry per file with failures (--junit-format per_file)
     # and we don't support mypy's --junit-xml option in the first place.
-    def flush_errors(_: str | None, new_messages: List[str], serious: bool) -> None:
+    def flush_errors(*_: str | None, new_messages: List[str], serious: bool) -> None:
         error_messages.extend(new_messages)
         f = stderr if serious else stdout
         try:

pytest_mypy_plugins/item.py:99: error: Argument "flush_errors" to "build" has incompatible type "Callable[[VarArg(str | None), NamedArg(list[str], 'new_messages'), NamedArg(bool, 'serious')], None]"; expected "Callable[[str | None, list[str], bool], None] | None"  [arg-type]

Branch conditional on mypy version

This works fine but type-checking fails.

diff --git a/pytest_mypy_plugins/item.py b/pytest_mypy_plugins/item.py
index 2094eed..466cdac 100644
--- a/pytest_mypy_plugins/item.py
+++ b/pytest_mypy_plugins/item.py
@@ -7,6 +7,7 @@ import tempfile
 from pathlib import Path
 from typing import TYPE_CHECKING, Any, Dict, List, Optional, TextIO, Tuple, Union
 
+from packaging.version import Version
 import py
 import pytest
 from _pytest._code import ExceptionInfo
@@ -16,6 +17,7 @@ from _pytest.config import Config
 from mypy import build
 from mypy.fscache import FileSystemCache
 from mypy.main import process_options
+from mypy.version import __version__ as mypy_version
 
 if TYPE_CHECKING:
     from _pytest._code.code import _TracebackStyle
@@ -82,10 +84,7 @@ def run_mypy_typechecking(cmd_options: List[str], stdout: TextIO, stderr: TextIO
 
     error_messages = []
 
-    # discard filename parameter '_'. Mypy uses it to generate
-    # one junit-xml test entry per file with failures (--junit-format per_file)
-    # and we don't support mypy's --junit-xml option in the first place.
-    def flush_errors(_: str | None, new_messages: List[str], serious: bool) -> None:
+    def flush_errors(new_messages: List[str], serious: bool) -> None:
         error_messages.extend(new_messages)
         f = stderr if serious else stdout
         try:
@@ -96,7 +95,19 @@ def run_mypy_typechecking(cmd_options: List[str], stdout: TextIO, stderr: TextIO
             sys.exit(ReturnCodes.FATAL_ERROR)
 
     try:
-        build.build(sources, options, flush_errors=flush_errors, fscache=fscache, stdout=stdout, stderr=stderr)
+        if Version(mypy_version) <  Version("1.8.0"):
+            def short_args_wrapper(new_messages: List[str], serious: bool) -> None:
+                flush_errors(new_messages, serious)
+
+            build.build(sources, options, flush_errors=short_args_wrapper, fscache=fscache, stdout=stdout, stderr=stderr)
+        else:
+            # discard filename parameter '_'. Mypy >= 1.8.0 uses it to generate
+            # one junit-xml test entry per file with failures (--junit-format per_file)
+            # and we don't support mypy's --junit-xml option in the first place.
+            def long_args_wrapper(_: str | None, new_messages: List[str], serious: bool) -> None:
+                flush_errors(new_messages, serious)
+
+            build.build(sources, options, flush_errors=long_args_wrapper, fscache=fscache, stdout=stdout, stderr=stderr)
 
     except SystemExit as sysexit:
         return sysexit.code

The problem is that mypy type-checks both branches against its own signature, which obviously fails since only one branch has the correct signature for either <mypy-1.8.0 or >=mypy-1.8.0.
With mypy 1.7.1

# mypy .
pytest_mypy_plugins/item.py:110: error: Argument "flush_errors" to "build" has incompatible type "Callable[[str | None, list[str], bool], None]"; expected "Callable[[list[str], bool], None] | None"  [arg-type]
Found 1 error in 1 file (checked 11 source files)

With mypy 1.8.0

# mypy .
pytest_mypy_plugins/item.py:102: error: Argument "flush_errors" to "build" has incompatible type "Callable[[list[str], bool], None]"; expected "Callable[[str | None, list[str], bool], None] | None"  [arg-type]
Found 1 error in 1 file (checked 11 source files)

Workaround:
Patch the second approach as follows and run mypy with --no-warn-unused-ignores. The reason for --no-warn-unused-ignores is the same as above. One branch passes the type-checking despite its type: ignore comment:

diff --git a/pytest_mypy_plugins/item.py b/pytest_mypy_plugins/item.py
index 466cdac..83fffb2 100644
--- a/pytest_mypy_plugins/item.py
+++ b/pytest_mypy_plugins/item.py
@@ -99,7 +99,7 @@ def run_mypy_typechecking(cmd_options: List[str], stdout: TextIO, stderr: TextIO
             def short_args_wrapper(new_messages: List[str], serious: bool) -> None:
                 flush_errors(new_messages, serious)
 
-            build.build(sources, options, flush_errors=short_args_wrapper, fscache=fscache, stdout=stdout, stderr=stderr)
+            build.build(sources, options, flush_errors=short_args_wrapper, fscache=fscache, stdout=stdout, stderr=stderr) # type: ignore
         else:
             # discard filename parameter '_'. Mypy >= 1.8.0 uses it to generate
             # one junit-xml test entry per file with failures (--junit-format per_file)
@@ -107,7 +107,7 @@ def run_mypy_typechecking(cmd_options: List[str], stdout: TextIO, stderr: TextIO
             def long_args_wrapper(_: str | None, new_messages: List[str], serious: bool) -> None:
                 flush_errors(new_messages, serious)
 
-            build.build(sources, options, flush_errors=long_args_wrapper, fscache=fscache, stdout=stdout, stderr=stderr)
+            build.build(sources, options, flush_errors=long_args_wrapper, fscache=fscache, stdout=stdout, stderr=stderr) # type: ignore
 
     except SystemExit as sysexit:
         return sysexit.code

[sobolevn]

*args: Any?

[antecrescent]

I may not understand your suggestion correctly...
def flush_errors(*_: Any, new_messages: List[str], serious: bool) -> None fails the type-checking with:
pytest_mypy_plugins/item.py:99: error: Argument "flush_errors" to "build" has incompatible type "Callable[[VarArg(Any), NamedArg(list[str], 'new_messages'), NamedArg(bool, 'serious')], None]"; expected "Callable[[str | None, list[str], bool], None] | None" [arg-type]

This also fails at runtime for the same reason listed in the first approach:
TypeError: run_mypy_typechecking.<locals>.flush_errors() missing 2 required keyword-only arguments: 'new_messages' and 'ser...

[sobolevn]

@antecrescent please, take a look at my suggestion :)

[antecrescent]

Ah yes, makes sense! I'm not very versed in Python but this seems to be a more sensible approach. I'll rebase this to get rid my erroneous commit and fix a typo in your comment.

[sobolevn]

Thanks!

[antecrescent]

Thank you for helping me fix this and teaching me a bit of Python :P