1import gc
2import re
3import sys
4import textwrap
5import threading
6import types
7import unittest
8import weakref
9
10from test import support
11from test.support import threading_helper
12from test.support.script_helper import assert_python_ok
13
14
15class ClearTest(unittest.TestCase):
16    """
17    Tests for frame.clear().
18    """
19
20    def inner(self, x=5, **kwargs):
21        1/0
22
23    def outer(self, **kwargs):
24        try:
25            self.inner(**kwargs)
26        except ZeroDivisionError as e:
27            exc = e
28        return exc
29
30    def clear_traceback_frames(self, tb):
31        """
32        Clear all frames in a traceback.
33        """
34        while tb is not None:
35            tb.tb_frame.clear()
36            tb = tb.tb_next
37
38    def test_clear_locals(self):
39        class C:
40            pass
41        c = C()
42        wr = weakref.ref(c)
43        exc = self.outer(c=c)
44        del c
45        support.gc_collect()
46        # A reference to c is held through the frames
47        self.assertIsNot(None, wr())
48        self.clear_traceback_frames(exc.__traceback__)
49        support.gc_collect()
50        # The reference was released by .clear()
51        self.assertIs(None, wr())
52
53    def test_clear_does_not_clear_specials(self):
54        class C:
55            pass
56        c = C()
57        exc = self.outer(c=c)
58        del c
59        f = exc.__traceback__.tb_frame
60        f.clear()
61        self.assertIsNot(f.f_code, None)
62        self.assertIsNot(f.f_locals, None)
63        self.assertIsNot(f.f_builtins, None)
64        self.assertIsNot(f.f_globals, None)
65
66    def test_clear_generator(self):
67        endly = False
68        def g():
69            nonlocal endly
70            try:
71                yield
72                self.inner()
73            finally:
74                endly = True
75        gen = g()
76        next(gen)
77        self.assertFalse(endly)
78        # Clearing the frame closes the generator
79        gen.gi_frame.clear()
80        self.assertTrue(endly)
81
82    def test_clear_executing(self):
83        # Attempting to clear an executing frame is forbidden.
84        try:
85            1/0
86        except ZeroDivisionError as e:
87            f = e.__traceback__.tb_frame
88        with self.assertRaises(RuntimeError):
89            f.clear()
90        with self.assertRaises(RuntimeError):
91            f.f_back.clear()
92
93    def test_clear_executing_generator(self):
94        # Attempting to clear an executing generator frame is forbidden.
95        endly = False
96        def g():
97            nonlocal endly
98            try:
99                1/0
100            except ZeroDivisionError as e:
101                f = e.__traceback__.tb_frame
102                with self.assertRaises(RuntimeError):
103                    f.clear()
104                with self.assertRaises(RuntimeError):
105                    f.f_back.clear()
106                yield f
107            finally:
108                endly = True
109        gen = g()
110        f = next(gen)
111        self.assertFalse(endly)
112        # Clearing the frame closes the generator
113        f.clear()
114        self.assertTrue(endly)
115
116    def test_lineno_with_tracing(self):
117        def record_line():
118            f = sys._getframe(1)
119            lines.append(f.f_lineno-f.f_code.co_firstlineno)
120
121        def test(trace):
122            record_line()
123            if trace:
124                sys._getframe(0).f_trace = True
125            record_line()
126            record_line()
127
128        expected_lines = [1, 4, 5]
129        lines = []
130        test(False)
131        self.assertEqual(lines, expected_lines)
132        lines = []
133        test(True)
134        self.assertEqual(lines, expected_lines)
135
136    @support.cpython_only
137    def test_clear_refcycles(self):
138        # .clear() doesn't leave any refcycle behind
139        with support.disable_gc():
140            class C:
141                pass
142            c = C()
143            wr = weakref.ref(c)
144            exc = self.outer(c=c)
145            del c
146            self.assertIsNot(None, wr())
147            self.clear_traceback_frames(exc.__traceback__)
148            self.assertIs(None, wr())
149
150
151class FrameAttrsTest(unittest.TestCase):
152
153    def make_frames(self):
154        def outer():
155            x = 5
156            y = 6
157            def inner():
158                z = x + 2
159                1/0
160                t = 9
161            return inner()
162        try:
163            outer()
164        except ZeroDivisionError as e:
165            tb = e.__traceback__
166            frames = []
167            while tb:
168                frames.append(tb.tb_frame)
169                tb = tb.tb_next
170        return frames
171
172    def test_locals(self):
173        f, outer, inner = self.make_frames()
174        outer_locals = outer.f_locals
175        self.assertIsInstance(outer_locals.pop('inner'), types.FunctionType)
176        self.assertEqual(outer_locals, {'x': 5, 'y': 6})
177        inner_locals = inner.f_locals
178        self.assertEqual(inner_locals, {'x': 5, 'z': 7})
179
180    def test_clear_locals(self):
181        # Test f_locals after clear() (issue #21897)
182        f, outer, inner = self.make_frames()
183        outer.clear()
184        inner.clear()
185        self.assertEqual(outer.f_locals, {})
186        self.assertEqual(inner.f_locals, {})
187
188    def test_locals_clear_locals(self):
189        # Test f_locals before and after clear() (to exercise caching)
190        f, outer, inner = self.make_frames()
191        outer.f_locals
192        inner.f_locals
193        outer.clear()
194        inner.clear()
195        self.assertEqual(outer.f_locals, {})
196        self.assertEqual(inner.f_locals, {})
197
198    def test_f_lineno_del_segfault(self):
199        f, _, _ = self.make_frames()
200        with self.assertRaises(AttributeError):
201            del f.f_lineno
202
203
204class ReprTest(unittest.TestCase):
205    """
206    Tests for repr(frame).
207    """
208
209    def test_repr(self):
210        def outer():
211            x = 5
212            y = 6
213            def inner():
214                z = x + 2
215                1/0
216                t = 9
217            return inner()
218
219        offset = outer.__code__.co_firstlineno
220        try:
221            outer()
222        except ZeroDivisionError as e:
223            tb = e.__traceback__
224            frames = []
225            while tb:
226                frames.append(tb.tb_frame)
227                tb = tb.tb_next
228        else:
229            self.fail("should have raised")
230
231        f_this, f_outer, f_inner = frames
232        file_repr = re.escape(repr(__file__))
233        self.assertRegex(repr(f_this),
234                         r"^<frame at 0x[0-9a-fA-F]+, file %s, line %d, code test_repr>$"
235                         % (file_repr, offset + 23))
236        self.assertRegex(repr(f_outer),
237                         r"^<frame at 0x[0-9a-fA-F]+, file %s, line %d, code outer>$"
238                         % (file_repr, offset + 7))
239        self.assertRegex(repr(f_inner),
240                         r"^<frame at 0x[0-9a-fA-F]+, file %s, line %d, code inner>$"
241                         % (file_repr, offset + 5))
242
243class TestIncompleteFrameAreInvisible(unittest.TestCase):
244
245    def test_issue95818(self):
246        # See GH-95818 for details
247        code = textwrap.dedent(f"""
248            import gc
249
250            gc.set_threshold(1,1,1)
251            class GCHello:
252                def __del__(self):
253                    print("Destroyed from gc")
254
255            def gen():
256                yield
257
258            fd = open({__file__!r})
259            l = [fd, GCHello()]
260            l.append(l)
261            del fd
262            del l
263            gen()
264        """)
265        assert_python_ok("-c", code)
266
267    @support.cpython_only
268    def test_sneaky_frame_object(self):
269
270        def trace(frame, event, arg):
271            """
272            Don't actually do anything, just force a frame object to be created.
273            """
274
275        def callback(phase, info):
276            """
277            Yo dawg, I heard you like frames, so I'm allocating a frame while
278            you're allocating a frame, so you can have a frame while you have a
279            frame!
280            """
281            nonlocal sneaky_frame_object
282            sneaky_frame_object = sys._getframe().f_back
283            # We're done here:
284            gc.callbacks.remove(callback)
285
286        def f():
287            while True:
288                yield
289
290        old_threshold = gc.get_threshold()
291        old_callbacks = gc.callbacks[:]
292        old_enabled = gc.isenabled()
293        old_trace = sys.gettrace()
294        try:
295            # Stop the GC for a second while we set things up:
296            gc.disable()
297            # Create a paused generator:
298            g = f()
299            next(g)
300            # Move all objects to the oldest generation, and tell the GC to run
301            # on the *very next* allocation:
302            gc.collect()
303            gc.set_threshold(1, 0, 0)
304            # Okay, so here's the nightmare scenario:
305            # - We're tracing the resumption of a generator, which creates a new
306            #   frame object.
307            # - The allocation of this frame object triggers a collection
308            #   *before* the frame object is actually created.
309            # - During the collection, we request the exact same frame object.
310            #   This test does it with a GC callback, but in real code it would
311            #   likely be a trace function, weakref callback, or finalizer.
312            # - The collection finishes, and the original frame object is
313            #   created. We now have two frame objects fighting over ownership
314            #   of the same interpreter frame!
315            sys.settrace(trace)
316            gc.callbacks.append(callback)
317            sneaky_frame_object = None
318            gc.enable()
319            next(g)
320            # g.gi_frame should be the the frame object from the callback (the
321            # one that was *requested* second, but *created* first):
322            self.assertIs(g.gi_frame, sneaky_frame_object)
323        finally:
324            gc.set_threshold(*old_threshold)
325            gc.callbacks[:] = old_callbacks
326            sys.settrace(old_trace)
327            if old_enabled:
328                gc.enable()
329
330    @support.cpython_only
331    @threading_helper.requires_working_threading()
332    def test_sneaky_frame_object_teardown(self):
333
334        class SneakyDel:
335            def __del__(self):
336                """
337                Stash a reference to the entire stack for walking later.
338
339                It may look crazy, but you'd be surprised how common this is
340                when using a test runner (like pytest). The typical recipe is:
341                ResourceWarning + -Werror + a custom sys.unraisablehook.
342                """
343                nonlocal sneaky_frame_object
344                sneaky_frame_object = sys._getframe()
345
346        class SneakyThread(threading.Thread):
347            """
348            A separate thread isn't needed to make this code crash, but it does
349            make crashes more consistent, since it means sneaky_frame_object is
350            backed by freed memory after the thread completes!
351            """
352
353            def run(self):
354                """Run SneakyDel.__del__ as this frame is popped."""
355                ref = SneakyDel()
356
357        sneaky_frame_object = None
358        t = SneakyThread()
359        t.start()
360        t.join()
361        # sneaky_frame_object can be anything, really, but it's crucial that
362        # SneakyThread.run's frame isn't anywhere on the stack while it's being
363        # torn down:
364        self.assertIsNotNone(sneaky_frame_object)
365        while sneaky_frame_object is not None:
366            self.assertIsNot(
367                sneaky_frame_object.f_code, SneakyThread.run.__code__
368            )
369            sneaky_frame_object = sneaky_frame_object.f_back
370
371if __name__ == "__main__":
372    unittest.main()
373