Disable reruns with a warning instead of erroring under --pdb (#374)

* Disable reruns with a warning instead of erroring under --pdb

Combining --pdb with --reruns/--force-reruns/a flaky marker previously
raised a UsageError. Someone reaching for the debugger almost never wants
reruns, so warn and run each test once instead.

Closes #248.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* Do not let -W error escalate the --pdb reruns warning

Escalated PytestWarning instances (from -W error or
filterwarnings = error) are caught and re-emitted under an
"always" filter so the run continues with reruns disabled
instead of aborting with an INTERNALERROR, and the warning is
still recorded for the warnings summary. Also bump the
issue_config_time_warning stacklevel to 3 so the warning points
at check_options() rather than the helper's internals.

Co-Authored-By: Louis Deconinck <louis.dck@gmail.com>

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Michael Howitz <icemac@gmx.net>

Author: 3 people

README.rst

@@ -357,7 +357,8 @@ Compatibility
   `pytest-forked <https://pypi.org/project/pytest-forked/>`_: both plugins
   override ``pytest_runtest_protocol``, and whichever runs first prevents
   the other from working, so tests are not re-run.
-* This plugin is *not* compatible with the core --pdb flag.
+* When the core --pdb flag is used, reruns are disabled (a warning is
+  emitted and tests are run once, as if ``--reruns 0`` was passed).
 * This plugin is *not* compatible with the plugin
   `flaky <https://pypi.org/project/flaky/>`_, you can only have
   ``pytest-rerunfailures`` or ``flaky`` but not both.

changes/248.feature.rst

@@ -0,0 +1,3 @@
+Emit a warning and disable reruns instead of raising a ``UsageError`` when
+``--pdb`` is combined with ``--reruns``, ``--force-reruns`` or the ``flaky``
+marker.

src/pytest_rerunfailures.py

@@ -229,7 +229,7 @@ def check_options(config):
     reruns = config.getoption("force_reruns") or _get_global_reruns(config)
     if not config.getoption("collectonly") and reruns:
         if config.option.usepdb:  # a core option
-            raise pytest.UsageError("--reruns incompatible with --pdb")
+            _warn_pdb_disables_reruns(config)
 
     for name in ("only_rerun", "rerun_except"):
         for pattern in getattr(config.option, name) or config.getini(name):
@@ -245,9 +245,46 @@ def _get_marker(item):
     return item.get_closest_marker("flaky")
 
 
+def _warn_pdb_disables_reruns(config, item=None):
+    """Warn once that --pdb disables reruns.
+
+    Called at config time for command-line/ini reruns and per item for
+    marker-requested reruns, so emit through the channel that pytest records
+    in each case. ``-W error`` / ``filterwarnings = error`` must not escalate
+    the warning into an INTERNALERROR, so an escalated warning is re-emitted
+    under an "always" filter and recorded through pytest's warning hook.
+    """
+    if getattr(config, "_pdb_reruns_warning_issued", False):
+        return
+    config._pdb_reruns_warning_issued = True
+    warning = pytest.PytestWarning(
+        "--reruns incompatible with --pdb: reruns are disabled"
+    )
+    try:
+        if item is not None:
+            item.warn(warning)
+        else:
+            config.issue_config_time_warning(warning, stacklevel=3)
+    except Warning:
+        with warnings.catch_warnings(record=True) as records:
+            warnings.simplefilter("always", type(warning))
+            warnings.warn(warning, stacklevel=3)
+        for record in records:
+            config.hook.pytest_warning_recorded.call_historic(
+                kwargs=dict(
+                    warning_message=record,
+                    when="config" if item is None else "runtest",
+                    nodeid="" if item is None else item.nodeid,
+                    location=None,
+                )
+            )
+
+
 def get_reruns_count(item):
     reruns = item.session.config.getoption("force_reruns")
     if reruns is not None:
+        if item.session.config.option.usepdb:
+            return 0
         return reruns
 
     rerun_marker = _get_marker(item)
@@ -265,10 +302,18 @@ def get_reruns_count(item):
         if item.session.config.getoption("reruns_mode") == "append":
             global_reruns = _get_global_reruns(item.session.config)
             if global_reruns is not None:
-                return marker_reruns + global_reruns
-        return marker_reruns
+                marker_reruns += global_reruns
+        reruns = marker_reruns
+    else:
+        reruns = _get_global_reruns(item.session.config)
 
-    return _get_global_reruns(item.session.config)
+    if reruns and item.session.config.option.usepdb:
+        # --pdb disables reruns; the global/force-reruns case already warned
+        # in check_options(), this catches marker-requested reruns.
+        _warn_pdb_disables_reruns(item.session.config, item=item)
+        return 0
+
+    return reruns
 
 
 def get_reruns_delay(item):
@@ -1241,12 +1286,6 @@ def pytest_runtest_protocol(item, nextitem):
         # flaky
         return
 
-    if reruns and item.session.config.option.usepdb:
-        # the global options are already rejected in check_options(); this
-        # catches reruns requested via the flaky marker, which are only
-        # known once the item is available
-        raise pytest.UsageError("--reruns incompatible with --pdb")
-
     delay = get_reruns_delay(item)
     delay_backoff_factor = get_reruns_delay_backoff_factor(item)
     parallel = not is_master(item.config)

tests/test_pytest_rerunfailures.py

@@ -91,10 +91,33 @@ def assert_outcomes(
     check_outcome_field(outcomes, "rerun", rerun)
 
 
-def test_error_when_run_with_pdb(testdir):
-    testdir.makepyfile("def test_pass(): pass")
-    result = testdir.runpytest("--reruns", "1", "--pdb")
-    result.stderr.fnmatch_lines_random("ERROR: --reruns incompatible with --pdb")
+def make_dummy_pdb(testdir):
+    """Create a pdb class that does not enter an interactive session."""
+    testdir.makepyfile(
+        nopdb="""
+        class DummyPdb:
+            quitting = False
+
+            def __init__(self, *args, **kwargs):
+                pass
+
+            def reset(self):
+                pass
+
+            def interaction(self, *args, **kwargs):
+                pass
+        """
+    )
+
+
+def test_pdb_disables_reruns(testdir):
+    make_dummy_pdb(testdir)
+    testdir.makepyfile("def test_fail(): assert False")
+    result = testdir.runpytest("--reruns", "1", "--pdb", "--pdbcls=nopdb:DummyPdb")
+    assert_outcomes(result, passed=0, failed=1, rerun=0)
+    result.stdout.fnmatch_lines_random(
+        "*--reruns incompatible with --pdb: reruns are disabled"
+    )
 
 
 def test_no_error_when_run_with_pdb_without_reruns(testdir):
@@ -109,30 +132,76 @@ def test_no_error_when_run_with_pdb_and_zero_reruns(testdir):
     assert_outcomes(result)
 
 
-def test_error_when_run_with_pdb_and_reruns_ini(testdir):
-    testdir.makepyfile("def test_pass(): pass")
+def test_pdb_disables_reruns_ini(testdir):
+    make_dummy_pdb(testdir)
+    testdir.makepyfile("def test_fail(): assert False")
     testdir.makeini("[pytest]\nreruns = 1\n")
-    result = testdir.runpytest("--pdb")
-    result.stderr.fnmatch_lines_random("ERROR: --reruns incompatible with --pdb")
+    result = testdir.runpytest("--pdb", "--pdbcls=nopdb:DummyPdb")
+    assert_outcomes(result, passed=0, failed=1, rerun=0)
+    result.stdout.fnmatch_lines_random(
+        "*--reruns incompatible with --pdb: reruns are disabled"
+    )
 
 
-def test_error_when_run_with_pdb_and_force_reruns(testdir):
-    testdir.makepyfile("def test_pass(): pass")
-    result = testdir.runpytest("--force-reruns", "1", "--pdb")
-    result.stderr.fnmatch_lines_random("ERROR: --reruns incompatible with --pdb")
+def test_pdb_disables_force_reruns(testdir):
+    make_dummy_pdb(testdir)
+    testdir.makepyfile("def test_fail(): assert False")
+    result = testdir.runpytest(
+        "--force-reruns", "1", "--pdb", "--pdbcls=nopdb:DummyPdb"
+    )
+    assert_outcomes(result, passed=0, failed=1, rerun=0)
+    result.stdout.fnmatch_lines_random(
+        "*--reruns incompatible with --pdb: reruns are disabled"
+    )
 
 
-def test_error_when_run_with_pdb_and_flaky_marker(testdir):
+def test_pdb_disables_reruns_with_flaky_marker(testdir):
     testdir.makepyfile(
         """
         import pytest
 
         @pytest.mark.flaky(reruns=1)
-        def test_pass(): pass
+        def test_fail(): assert False
         """
     )
-    result = testdir.runpytest("--pdb")
-    result.stderr.fnmatch_lines_random("*--reruns incompatible with --pdb")
+    make_dummy_pdb(testdir)
+    result = testdir.runpytest("--pdb", "--pdbcls=nopdb:DummyPdb")
+    assert_outcomes(result, passed=0, failed=1, rerun=0)
+    result.stdout.fnmatch_lines_random(
+        "*--reruns incompatible with --pdb: reruns are disabled"
+    )
+
+
+def test_pdb_disables_reruns_with_warnings_as_errors(testdir):
+    """`-W error` must not escalate the warning into an INTERNALERROR."""
+    make_dummy_pdb(testdir)
+    testdir.makepyfile("def test_fail(): assert False")
+    result = testdir.runpytest(
+        "-W", "error", "--reruns", "1", "--pdb", "--pdbcls=nopdb:DummyPdb"
+    )
+    assert_outcomes(result, passed=0, failed=1, rerun=0)
+    result.stdout.no_fnmatch_line("INTERNALERROR*")
+    result.stdout.fnmatch_lines_random(
+        "*--reruns incompatible with --pdb: reruns are disabled"
+    )
+
+
+def test_pdb_disables_reruns_marker_with_warnings_as_errors(testdir):
+    make_dummy_pdb(testdir)
+    testdir.makepyfile(
+        """
+        import pytest
+
+        @pytest.mark.flaky(reruns=1)
+        def test_fail(): assert False
+        """
+    )
+    result = testdir.runpytest("-W", "error", "--pdb", "--pdbcls=nopdb:DummyPdb")
+    assert_outcomes(result, passed=0, failed=1, rerun=0)
+    result.stdout.no_fnmatch_line("INTERNALERROR*")
+    result.stdout.fnmatch_lines_random(
+        "*--reruns incompatible with --pdb: reruns are disabled"
+    )
 
 
 def test_no_rerun_on_pass(testdir):