Avoid traceback formatting for xfail(run=False)

changelog/9436.improvement.rst

@@ -0,0 +1 @@
+Avoid formatting tracebacks for tests marked with ``xfail(run=False)``.

src/_pytest/reports.py

@@ -435,7 +435,10 @@ def from_item_and_call(cls, item: Item, call: CallInfo[None]) -> TestReport:
                 longrepr = _format_exception_group_all_skipped_longrepr(item, excinfo)
             else:
                 outcome = "failed"
-                longrepr = _format_failed_longrepr(item, call, excinfo)
+                if getattr(excinfo.value, "_pytest_xfail_not_run", False):
+                    longrepr = str(excinfo.value)
+                else:
+                    longrepr = _format_failed_longrepr(item, call, excinfo)
         for rwhen, key, content in item._report_sections:
             sections.append((f"Captured {key} {rwhen}", content))
         return cls(

src/_pytest/skipping.py

@@ -10,6 +10,7 @@
 import platform
 import sys
 import traceback
+from typing import NoReturn
 
 from _pytest.config import Config
 from _pytest.config import hookimpl
@@ -244,6 +245,12 @@ def evaluate_xfail_marks(item: Item) -> Xfail | None:
 xfailed_key = StashKey[Xfail | None]()
 
 
+def _xfail_not_run(reason: str) -> NoReturn:
+    exc = xfail.Exception("[NOTRUN] " + reason)
+    exc._pytest_xfail_not_run = True  # type: ignore[attr-defined]
+    raise exc
+
+
 @hookimpl(tryfirst=True)
 def pytest_runtest_setup(item: Item) -> None:
     skipped = evaluate_skip_marks(item)
@@ -252,7 +259,7 @@ def pytest_runtest_setup(item: Item) -> None:
 
     item.stash[xfailed_key] = xfailed = evaluate_xfail_marks(item)
     if xfailed and not item.config.option.runxfail and not xfailed.run:
-        xfail("[NOTRUN] " + xfailed.reason)
+        _xfail_not_run(xfailed.reason)
 
 
 @hookimpl(wrapper=True)
@@ -262,7 +269,7 @@ def pytest_runtest_call(item: Item) -> Generator[None]:
         item.stash[xfailed_key] = xfailed = evaluate_xfail_marks(item)
 
     if xfailed and not item.config.option.runxfail and not xfailed.run:
-        xfail("[NOTRUN] " + xfailed.reason)
+        _xfail_not_run(xfailed.reason)
 
     try:
         return (yield)

testing/test_skipping.py

@@ -453,6 +453,63 @@ def test_this_false():
             ]
         )
 
+    def test_xfail_not_run_does_not_format_traceback(self, pytester: Pytester) -> None:
+        item = pytester.getitem(
+            """
+            import pytest
+            @pytest.mark.xfail(run=False, reason="noway")
+            def test_func():
+                assert 0
+        """
+        )
+
+        def repr_failure(*args, **kwargs):
+            raise AssertionError(  # pragma: no cover
+                "xfail(run=False) should not format a traceback"
+            )
+
+        item.repr_failure = repr_failure  # type: ignore[method-assign]
+        item._repr_failure_py = repr_failure  # type: ignore[method-assign]
+
+        reports = runtestprotocol(item, log=False)
+
+        assert reports[0].skipped
+        assert reports[0].wasxfail == "[NOTRUN] noway"
+        assert reports[0].longrepr == "[NOTRUN] noway"
+
+    def test_regular_failure_still_formats_traceback(self, pytester: Pytester) -> None:
+        item = pytester.getitem(
+            """
+            def test_func():
+                raise ValueError("boom")
+        """
+        )
+
+        reports = runtestprotocol(item, log=False)
+
+        assert reports[1].failed
+        assert "ValueError: boom" in reports[1].longreprtext
+
+    def test_xfail_not_run_call_phase_marks_exception(self, pytester: Pytester) -> None:
+        from _pytest.skipping import pytest_runtest_call
+
+        item = pytester.getitem(
+            """
+            import pytest
+            @pytest.mark.xfail(run=False, reason="call phase")
+            def test_func():
+                assert 0
+        """
+        )
+
+        runtest_call = pytest_runtest_call(item)
+
+        with pytest.raises(pytest.xfail.Exception) as excinfo:
+            next(runtest_call)
+
+        assert excinfo.value.msg == "[NOTRUN] call phase"
+        assert excinfo.value._pytest_xfail_not_run is True  # type: ignore[attr-defined]
+
     def test_xfail_not_run_no_setup_run(self, pytester: Pytester) -> None:
         p = pytester.makepyfile(
             test_one="""