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 #5440

7 files changed, 245 insertions, 17 deletions

diff --git a/changelog/5440.feature.rst b/changelog/5440.feature.rst
new file mode 100644
index 000000000..d3bb95f58
--- /dev/null
+++ b/changelog/5440.feature.rst
@@ -0,0 +1,8 @@
+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.
+
+This functionality was provided by integrating the external
+`pytest-faulthandler <https://github.com/pytest-dev/pytest-faulthandler>`__ plugin into the core,
+so users should remove that plugin from their requirements if used.
+
+For more information see the docs: https://docs.pytest.org/en/latest/usage.html#fault-handler
diff --git a/doc/en/usage.rst b/doc/en/usage.rst
index acf736f21..c1332706f 100644
--- a/doc/en/usage.rst
+++ b/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
 ----------------------------------------------------
 
diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index 1f6ae98f9..74ee4a2bc 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -141,6 +141,7 @@ default_plugins = essential_plugins + (
     "warnings",
     "logging",
     "reports",
+    "faulthandler",
 )
 
 builtin_plugins = set(default_plugins)
@@ -299,7 +300,7 @@ class PytestPluginManager(PluginManager):
         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, "
diff --git a/src/_pytest/deprecated.py b/src/_pytest/deprecated.py
index 3feae8b43..1c544fd36 100644
--- a/src/_pytest/deprecated.py
+++ b/src/_pytest/deprecated.py
@@ -14,6 +14,14 @@ from _pytest.warning_types import UnformattedWarning
 
 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'
diff --git a/src/_pytest/faulthandler.py b/src/_pytest/faulthandler.py
new file mode 100644
index 000000000..48fe0f218
--- /dev/null
+++ b/src/_pytest/faulthandler.py
@@ -0,0 +1,102 @@
+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=float,
+        dest="fault_handler_timeout",
+        metavar="TIMEOUT",
+        default=0.0,
+        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
+
+        # avoid trying to dup sys.stderr if faulthandler is already enabled
+        if faulthandler.is_enabled():
+            return
+
+        stderr_fd_copy = os.dup(_get_stderr_fileno())
+        config.fault_handler_stderr = os.fdopen(stderr_fd_copy, "w")
+        faulthandler.enable(file=config.fault_handler_stderr)
+
+
+def _get_stderr_fileno():
+    try:
+        return 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.
+        return sys.__stderr__.fileno()
+
+
+def pytest_unconfigure(config):
+    if config.getoption("fault_handler"):
+        import faulthandler
+
+        faulthandler.disable()
+        # close our dup file installed during pytest_configure
+        f = getattr(config, "fault_handler_stderr", None)
+        if f is not None:
+            # re-enable the faulthandler, attaching it to the default sys.stderr
+            # so we can see crashes after pytest has finished, usually during
+            # garbage collection during interpreter shutdown
+            config.fault_handler_stderr.close()
+            del config.fault_handler_stderr
+            faulthandler.enable(file=_get_stderr_fileno())
+
+
+@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()
diff --git a/testing/deprecated_test.py b/testing/deprecated_test.py
index 177594c4a..5cbb694b1 100644
--- a/testing/deprecated_test.py
+++ b/testing/deprecated_test.py
@@ -1,6 +1,7 @@
 import os
 
 import pytest
+from _pytest import deprecated
 from _pytest.warning_types import PytestDeprecationWarning
 from _pytest.warnings import SHOW_PYTEST_WARNINGS_ARG
 
@@ -69,22 +70,14 @@ 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", deprecated.DEPRECATED_EXTERNAL_PLUGINS)
 @pytest.mark.filterwarnings("default")
-def test_pytest_catchlog_deprecated(testdir, plugin):
-    testdir.makepyfile(
-        """
-        def test_func(pytestconfig):
-            pytestconfig.pluginmanager.register(None, 'pytest_{}')
-    """.format(
-            plugin
-        )
-    )
-    res = testdir.runpytest()
-    assert res.ret == 0
-    res.stdout.fnmatch_lines(
-        ["*pytest-*log plugin has been merged into the core*", "*1 passed, 1 warnings*"]
-    )
+def test_external_plugins_integrated(testdir, plugin):
+    testdir.syspathinsert()
+    testdir.makepyfile(**{plugin: ""})
+
+    with pytest.warns(pytest.PytestConfigWarning):
+        testdir.parseconfig("-p", plugin)
 
 
 def test_raises_message_argument_deprecated():
diff --git a/testing/test_faulthandler.py b/testing/test_faulthandler.py
new file mode 100644
index 000000000..d1f2e8b9a
--- /dev/null
+++ b/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]