Initial fix for issue 14112-pytest crashing with ptest-xdist

Author: evanwilson2123

src/_pytest/assertion/rewrite.py

@@ -371,42 +371,46 @@ def _read_pyc(
         fp = open(pyc, "rb")
     except OSError:
         return None
-    with fp:
-        try:
-            stat_result = os.stat(source)
-            mtime = int(stat_result.st_mtime)
-            size = stat_result.st_size
-            data = fp.read(16)
-        except OSError as e:
-            trace(f"_read_pyc({source}): OSError {e}")
-            return None
-        # Check for invalid or out of date pyc file.
-        if len(data) != (16):
-            trace(f"_read_pyc({source}): invalid pyc (too short)")
-            return None
-        if data[:4] != importlib.util.MAGIC_NUMBER:
-            trace(f"_read_pyc({source}): invalid pyc (bad magic number)")
-            return None
-        if data[4:8] != b"\x00\x00\x00\x00":
-            trace(f"_read_pyc({source}): invalid pyc (unsupported flags)")
-            return None
-        mtime_data = data[8:12]
-        if int.from_bytes(mtime_data, "little") != mtime & 0xFFFFFFFF:
-            trace(f"_read_pyc({source}): out of date")
-            return None
-        size_data = data[12:16]
-        if int.from_bytes(size_data, "little") != size & 0xFFFFFFFF:
-            trace(f"_read_pyc({source}): invalid pyc (incorrect size)")
-            return None
-        try:
-            co = marshal.load(fp)
-        except Exception as e:
-            trace(f"_read_pyc({source}): marshal.load error {e}")
-            return None
-        if not isinstance(co, types.CodeType):
-            trace(f"_read_pyc({source}): not a code object")
-            return None
-        return co
+    try:
+        with fp:
+            try:
+                stat_result = os.stat(source)
+                mtime = int(stat_result.st_mtime)
+                size = stat_result.st_size
+                data = fp.read(16)
+            except OSError as e:
+                trace(f"_read_pyc({source}): OSError {e}")
+                return None
+            # Check for invalid or out of date pyc file.
+            if len(data) != (16):
+                trace(f"_read_pyc({source}): invalid pyc (too short)")
+                return None
+            if data[:4] != importlib.util.MAGIC_NUMBER:
+                trace(f"_read_pyc({source}): invalid pyc (bad magic number)")
+                return None
+            if data[4:8] != b"\x00\x00\x00\x00":
+                trace(f"_read_pyc({source}): invalid pyc (unsupported flags)")
+                return None
+            mtime_data = data[8:12]
+            if int.from_bytes(mtime_data, "little") != mtime & 0xFFFFFFFF:
+                trace(f"_read_pyc({source}): out of date")
+                return None
+            size_data = data[12:16]
+            if int.from_bytes(size_data, "little") != size & 0xFFFFFFFF:
+                trace(f"_read_pyc({source}): invalid pyc (incorrect size)")
+                return None
+            try:
+                co = marshal.load(fp)
+            except Exception as e:
+                trace(f"_read_pyc({source}): marshal.load error {e}")
+                return None
+            if not isinstance(co, types.CodeType):
+                trace(f"_read_pyc({source}): not a code object")
+                return None
+            return co
+    except OSError as e:
+        trace(f"_read_pyc({source}): OSError {e}")
+        return None
 
 
 def rewrite_asserts(

testing/test_assertrewrite.py

@@ -1362,6 +1362,39 @@ def test_read_pyc(self, tmp_path: Path) -> None:
 
         assert _read_pyc(source, pyc) is None  # no error
 
+    def test_read_pyc_handles_context_manager_oserror(self, tmp_path: Path) -> None:
+        from _pytest.assertion.rewrite import _read_pyc
+
+        source = tmp_path / "source.py"
+        pyc = Path(str(source) + "c")
+        source.write_text("def test(): pass", encoding="utf-8")
+        py_compile.compile(str(source), str(pyc))
+
+        real_open = open
+
+        class FailingContextManager:
+            def __init__(self, fp) -> None:
+                self.fp = fp
+
+            def __enter__(self):
+                return self.fp
+
+            def __exit__(self, exc_type, exc, tb) -> None:
+                self.fp.close()
+                raise OSError(errno.EIO, "Input/output error")
+
+            def __getattr__(self, name):
+                return getattr(self.fp, name)
+
+        def mock_open(file, mode="r", *args, **kwargs):
+            fp = real_open(file, mode, *args, **kwargs)
+            if Path(file) == pyc and mode == "rb":
+                return FailingContextManager(fp)
+            return fp
+
+        with mock.patch("builtins.open", mock_open):
+            assert _read_pyc(source, pyc) is None
+
     def test_read_pyc_success(self, tmp_path: Path, pytester: Pytester) -> None:
         """
         Ensure that the _rewrite_test() -> _write_pyc() produces a pyc file