Integrate pytest-faulthandler into the core

* Add pytest-faulthandler files unchanged
* Adapt imports and tests
* Add code to skip registration of the external `pytest_faulthandler`
  to avoid conflicts

Fix pytest-dev#5440

changelog/5440.feature.rst

@@ -0,0 +1,4 @@
+The `faulthandler <https://docs.python.org/3/library/faulthandler.html>`__ standard library
+module is now enabled by default to help users diagnose crashes in C modules.
+
+For more information see the docs: https://docs.pytest.org/en/latest/usage.html#fault-handler

doc/en/usage.rst

@@ -408,7 +408,6 @@ Pytest supports the use of ``breakpoint()`` with the following behaviours:
 Profiling test execution duration
 -------------------------------------
 
-.. versionadded: 2.2
 
 To get a list of the slowest 10 test durations:
 
@@ -418,6 +417,24 @@ To get a list of the slowest 10 test durations:
 
 By default, pytest will not show test durations that are too small (<0.01s) unless ``-vv`` is passed on the command-line.
 
+
+.. _faulthandler:
+
+Fault Handler
+-------------
+
+.. versionadded:: 5.0
+
+The `faulthandler <https://docs.python.org/3/library/faulthandler.html>`__ standard module
+can be used to dump Python tracebacks on a segfault or after a timeout.
+
+The module is automatically enabled for pytest runs, unless the ``--no-faulthandler`` is given
+on the command-line.
+
+Also the ``--faulthandler-timeout=X`` can be used to dump the traceback of all threads if a test
+takes longer than ``X`` seconds to finish (not available on Windows).
+
+
 Creating JUnitXML format files
 ----------------------------------------------------
 

src/_pytest/config/__init__.py

@@ -141,6 +141,7 @@ def directory_arg(path, optname):
     "warnings",
     "logging",
     "reports",
+    "faulthandler",
 )
 
 builtin_plugins = set(default_plugins)
@@ -299,7 +300,7 @@ def parse_hookspec_opts(self, module_or_class, name):
         return opts
 
     def register(self, plugin, name=None):
-        if name in ["pytest_catchlog", "pytest_capturelog"]:
+        if name in _pytest.deprecated.DEPRECATED_EXTERNAL_PLUGINS:
             warnings.warn(
                 PytestConfigWarning(
                     "{} plugin has been merged into the core, "

src/_pytest/deprecated.py

@@ -14,6 +14,14 @@
 
 YIELD_TESTS = "yield tests were removed in pytest 4.0 - {name} will be ignored"
 
+# set of plugins which have been integrated into the core; we use this list to ignore
+# them during registration to avoid conflicts
+DEPRECATED_EXTERNAL_PLUGINS = {
+    "pytest_catchlog",
+    "pytest_capturelog",
+    "pytest_faulthandler",
+}
+
 
 FIXTURE_FUNCTION_CALL = (
     'Fixture "{name}" called directly. Fixtures are not meant to be called directly,\n'

src/_pytest/faulthandler.py

@@ -0,0 +1,81 @@
+import io
+import os
+import sys
+
+import pytest
+
+
+def pytest_addoption(parser):
+    group = parser.getgroup("terminal reporting")
+    group.addoption(
+        "--no-faulthandler",
+        action="store_false",
+        dest="fault_handler",
+        default=True,
+        help="Disable faulthandler module.",
+    )
+
+    group.addoption(
+        "--faulthandler-timeout",
+        type=int,
+        dest="fault_handler_timeout",
+        metavar="TIMEOUT",
+        default=0,
+        help="Dump the traceback of all threads if a test takes "
+        "more than TIMEOUT seconds to finish.\n"
+        "Not available on Windows.",
+    )
+
+
+def pytest_configure(config):
+    if config.getoption("fault_handler"):
+        import faulthandler
+
+        try:
+            stderr_fileno = sys.stderr.fileno()
+        except (AttributeError, io.UnsupportedOperation):
+            # python-xdist monkeypatches sys.stderr with an object that is not an actual file.
+            # https://docs.python.org/3/library/faulthandler.html#issue-with-file-descriptors
+            # This is potentially dangerous, but the best we can do.
+            stderr_fileno = sys.__stderr__.fileno()
+        stderr_fd_copy = os.dup(stderr_fileno)
+        config.fault_handler_stderr = os.fdopen(stderr_fd_copy, "w")
+        faulthandler.enable(config.fault_handler_stderr)
+        # we never disable faulthandler after it was enabled
+        # see pytest-dev/pytest-faulthandler#3
+
+
+@pytest.hookimpl(hookwrapper=True)
+def pytest_runtest_protocol(item):
+    enabled = item.config.getoption("fault_handler")
+    timeout = item.config.getoption("fault_handler_timeout")
+    if enabled and timeout > 0:
+        import faulthandler
+
+        stderr = item.config.fault_handler_stderr
+        faulthandler.dump_traceback_later(timeout, file=stderr)
+        try:
+            yield
+        finally:
+            faulthandler.cancel_dump_traceback_later()
+    else:
+        yield
+
+
+@pytest.hookimpl(tryfirst=True)
+def pytest_enter_pdb():
+    """Cancel any traceback dumping due to timeout before entering pdb.
+    """
+    import faulthandler
+
+    faulthandler.cancel_dump_traceback_later()
+
+
+@pytest.hookimpl(tryfirst=True)
+def pytest_exception_interact():
+    """Cancel any traceback dumping due to an interactive exception being
+    raised.
+    """
+    import faulthandler
+
+    faulthandler.cancel_dump_traceback_later()

testing/deprecated_test.py

@@ -69,9 +69,9 @@ def test_terminal_reporter_writer_attr(pytestconfig):
     assert terminal_reporter.writer is terminal_reporter._tw
 
 
-@pytest.mark.parametrize("plugin", ["catchlog", "capturelog"])
+@pytest.mark.parametrize("plugin", ["catchlog", "capturelog", "faulthandler"])
 @pytest.mark.filterwarnings("default")
-def test_pytest_catchlog_deprecated(testdir, plugin):
+def test_external_plugins_integrated(testdir, plugin):
     testdir.makepyfile(
         """
         def test_func(pytestconfig):
@@ -83,7 +83,10 @@ def test_func(pytestconfig):
     res = testdir.runpytest()
     assert res.ret == 0
     res.stdout.fnmatch_lines(
-        ["*pytest-*log plugin has been merged into the core*", "*1 passed, 1 warnings*"]
+        [
+            "*pytest-{} plugin has been merged into the core*".format(plugin),
+            "*1 passed, 1 warnings*",
+        ]
     )
 
 

testing/test_faulthandler.py

@@ -0,0 +1,99 @@
+import sys
+
+import pytest
+
+
+def test_enabled(testdir):
+    """Test single crashing test displays a traceback."""
+    testdir.makepyfile(
+        """
+    import faulthandler
+    def test_crash():
+        faulthandler._sigabrt()
+    """
+    )
+    result = testdir.runpytest_subprocess()
+    result.stderr.fnmatch_lines(["*Fatal Python error*"])
+    assert result.ret != 0
+
+
+def test_crash_near_exit(testdir):
+    """Test that fault handler displays crashes that happen even after
+    pytest is exiting (for example, when the interpreter is shutting down).
+    """
+    testdir.makepyfile(
+        """
+    import faulthandler
+    import atexit
+    def test_ok():
+        atexit.register(faulthandler._sigabrt)
+    """
+    )
+    result = testdir.runpytest_subprocess()
+    result.stderr.fnmatch_lines(["*Fatal Python error*"])
+    assert result.ret != 0
+
+
+def test_disabled(testdir):
+    """Test option to disable fault handler in the command line.
+    """
+    testdir.makepyfile(
+        """
+    import faulthandler
+    def test_disabled():
+        assert not faulthandler.is_enabled()
+    """
+    )
+    result = testdir.runpytest_subprocess("--no-faulthandler")
+    result.stdout.fnmatch_lines(["*1 passed*"])
+    assert result.ret == 0
+
+
+@pytest.mark.parametrize("enabled", [True, False])
+def test_timeout(testdir, enabled):
+    """Test option to dump tracebacks after a certain timeout.
+    If faulthandler is disabled, no traceback will be dumped.
+    """
+    testdir.makepyfile(
+        """
+    import time
+    def test_timeout():
+        time.sleep(2.0)
+    """
+    )
+    args = ["--faulthandler-timeout=1"]
+    if not enabled:
+        args.append("--no-faulthandler")
+
+    result = testdir.runpytest_subprocess(*args)
+    tb_output = "most recent call first"
+    if sys.version_info[:2] == (3, 3):
+        tb_output = "Thread"
+    if enabled:
+        result.stderr.fnmatch_lines(["*%s*" % tb_output])
+    else:
+        assert tb_output not in result.stderr.str()
+    result.stdout.fnmatch_lines(["*1 passed*"])
+    assert result.ret == 0
+
+
+@pytest.mark.parametrize("hook_name", ["pytest_enter_pdb", "pytest_exception_interact"])
+def test_cancel_timeout_on_hook(monkeypatch, pytestconfig, hook_name):
+    """Make sure that we are cancelling any scheduled traceback dumping due
+    to timeout before entering pdb (pytest-dev/pytest-faulthandler#12) or any other interactive
+    exception (pytest-dev/pytest-faulthandler#14).
+    """
+    import faulthandler
+    from _pytest import faulthandler as plugin_module
+
+    called = []
+
+    monkeypatch.setattr(
+        faulthandler, "cancel_dump_traceback_later", lambda: called.append(1)
+    )
+
+    # call our hook explicitly, we can trust that pytest will call the hook
+    # for us at the appropriate moment
+    hook_func = getattr(plugin_module, hook_name)
+    hook_func()
+    assert called == [1]