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

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):