stop_here: always stop where set_trace was used from

This is relevant for when `skip` is used.

Ref: https://bugs.python.org/issue38806
Ref: python/cpython#17159

NOTE: pypy2: needs the extra check for frame, which makes sense in general
      (via test_sigint_in_interaction_without_new_cmdloop).

Author: blueyed

src/pdbpp.py

@@ -1767,6 +1767,15 @@ def set_step(self):
             del self._set_trace_use_next
             self.set_next(self._via_set_trace_frame)
 
+    def stop_here(self, frame):
+        # Always stop at starting frame (https://bugs.python.org/issue38806).
+        if self.stopframe is None:
+            if getattr(self, "_via_set_trace_frame", None) == frame:
+                if not self._stopped_for_set_trace:
+                    self._stopped_for_set_trace = True
+                    return True
+        return super(Pdb, self).stop_here(frame)
+
     def set_trace(self, frame=None):
         """Remember starting frame.
 
@@ -1782,6 +1791,7 @@ def set_trace(self, frame=None):
         if frame is None:
             frame = sys._getframe().f_back
         self._via_set_trace_frame = frame
+        self._stopped_for_set_trace = False
 
         self.start_filename = frame.f_code.co_filename
         self.start_lineno = frame.f_lineno

testing/test_pdb.py

@@ -5084,3 +5084,44 @@ def cm():
         ]
     else:
         assert pos[0] == contextlib.__file__.rstrip("c")
+
+
+def test_set_trace_in_skipped_module(testdir):
+    def fn():
+        class SkippingPdbTest(PdbTest):
+            def __init__(self, *args, **kwargs):
+                kwargs["skip"] = ["testing.test_pdb"]
+                super(SkippingPdbTest, self).__init__(*args, **kwargs)
+
+                self.calls = []
+
+            def is_skipped_module(self, module_name):
+                self.calls.append(module_name)
+                if len(self.calls) == 1:
+                    print("is_skipped_module?", module_name)
+                    ret = super(SkippingPdbTest, self).is_skipped_module(module_name)
+                    assert module_name == "testing.test_pdb"
+                    assert ret is True
+                    return True
+                return False
+
+        set_trace(Pdb=SkippingPdbTest)  # 1
+        set_trace(Pdb=SkippingPdbTest, cleanup=False)  # 2
+        set_trace(Pdb=SkippingPdbTest, cleanup=False)  # 3
+
+    check(fn, r"""
+[NUM] > .*fn()
+-> set_trace(Pdb=SkippingPdbTest, cleanup=False)  # 2
+   5 frames hidden (try 'help hidden_frames')
+# n
+is_skipped_module\? testing.test_pdb
+[NUM] > .*fn()
+-> set_trace(Pdb=SkippingPdbTest, cleanup=False)  # 3
+   5 frames hidden (try 'help hidden_frames')
+# c
+--Return--
+[NUM] > .*fn()
+-> set_trace(Pdb=SkippingPdbTest, cleanup=False)  # 3
+   5 frames hidden (try 'help hidden_frames')
+# c
+""")