fix: bytecode cache invalidation for moved test files (#14552)

changelog/14552.bugfix.rst

@@ -0,0 +1 @@
+Fixed stale ``co_filename`` values after a test module or directory is moved. Assertion-rewrite caches are reused when the source hash still matches, and in-memory code objects are pointed at the current path.

src/_pytest/assertion/rewrite.py

@@ -56,6 +56,14 @@
     from _pytest.assertion import AssertionState
 
 
+try:
+    from _imp import (  # type: ignore[attr-defined]
+        _fix_co_filename as _imp_fix_co_filename,
+    )
+except ImportError:  # pragma: no cover
+    _imp_fix_co_filename = None
+
+
 assertstate_key = StashKey["AssertionState"]()
 
 # pytest caches rewritten pycs in pycache dirs
@@ -379,7 +387,37 @@ def _read_pyc(
         if not isinstance(co, types.CodeType):
             trace(f"_read_pyc({source}): not a code object")
             return None
+        # A cached pyc can be moved together with the source file (for example
+        # by renaming a package or test directory). In that case the marshaled
+        # code object's ``co_filename`` still points to the old source path.
+        # Fix it in memory the same way importlib does for ordinary pycs: the
+        # cache stays valid, only the in-memory location is corrected.
+        return _fix_code_filename(co, str(source))
+
+
+def _replace_code_filenames(co: types.CodeType, filename: str) -> types.CodeType:
+    """Pure-Python fallback: rebuild the code object tree with *filename*."""
+    return co.replace(
+        co_filename=filename,
+        co_consts=tuple(
+            _replace_code_filenames(c, filename) if isinstance(c, types.CodeType) else c
+            for c in co.co_consts
+        ),
+    )
+
+
+def _fix_code_filename(co: types.CodeType, filename: str) -> types.CodeType:
+    """Point *co* and its nested code objects at *filename*.
+
+    Mirrors what importlib does for every pyc it loads: the cache stays valid,
+    only the in-memory location is corrected.
+    """
+    if co.co_filename == filename:
+        return co
+    if _imp_fix_co_filename is not None:
+        _imp_fix_co_filename(co, filename)  # in place, recursive, C
         return co
+    return _replace_code_filenames(co, filename)
 
 
 def rewrite_asserts(

testing/test_assertrewrite.py

@@ -1161,6 +1161,66 @@ def test_foo():
             glob.glob("__pycache__/*.pyc")
         )
 
+    @pytest.mark.parametrize("implementation", ["import-lib", "pure-python"])
+    def test_moved_test_file_updates_code_filename(
+        self,
+        pytester: Pytester,
+        monkeypatch: pytest.MonkeyPatch,
+        implementation: str,
+    ) -> None:
+        """Moving a test module must keep ``co_filename`` synchronized with ``__file__``.
+
+        The rewritten pyc is reused: filenames are corrected in memory, not by
+        rewriting the cache.
+        """
+        from _pytest.assertion.rewrite import (  # type: ignore[attr-defined]
+            _imp_fix_co_filename,
+        )
+
+        monkeypatch.delenv("PYTHONDONTWRITEBYTECODE", raising=False)
+        monkeypatch.delenv("PYTHONPYCACHEPREFIX", raising=False)
+
+        if implementation == "import-lib":
+            if _imp_fix_co_filename is None:
+                pytest.skip("_imp._fix_co_filename is not available")
+        else:
+            # The inner pytest runs in a subprocess, so patch there.
+            pytester.makeconftest(
+                """
+                import _pytest.assertion.rewrite as rewrite
+                rewrite._imp_fix_co_filename = None
+                """
+            )
+
+        source = pytester.makepyfile(
+            **{
+                "test1/test_a.py": """
+                from inspect import currentframe
+
+                def test_a():
+                    assert currentframe().f_code.co_filename == __file__
+                """
+            }
+        )
+
+        first = pytester.runpytest_subprocess("-s", "test1/test_a.py")
+        first.assert_outcomes(passed=1)
+
+        pyc = get_cache_dir(source) / ("test_a" + PYC_TAIL)
+        assert pyc.is_file()
+
+        pyc_mtime = pyc.stat().st_mtime_ns
+
+        pytester.path.joinpath("test1").rename(pytester.path.joinpath("test2"))
+
+        moved_source = pytester.path / "test2" / "test_a.py"
+        moved_pyc = get_cache_dir(moved_source) / ("test_a" + PYC_TAIL)
+        assert moved_pyc.is_file()
+
+        second = pytester.runpytest_subprocess("-s", "test2/test_a.py")
+        second.assert_outcomes(passed=1)
+        assert moved_pyc.stat().st_mtime_ns == pyc_mtime
+
     @pytest.mark.skipif('"__pypy__" in sys.modules')
     def test_pyc_vs_pyo(
         self,