From acfd3d570ebb7c82797d1b3447865a090d7d041f Mon Sep 17 00:00:00 2001
From: Tian Gao <gaogaotiantian@hotmail.com>
Date: Tue, 15 Oct 2024 12:56:33 -0700
Subject: [PATCH 1/3] gh-58956: Set f_trace on frames with breakpoints after
 setting a new breakpoint (GH-124454) (cherry picked from commit
 12eaadc0ad33411bb02945d700b6ed7e758bb188)

Co-authored-by: Tian Gao <gaogaotiantian@hotmail.com>
---
 Lib/bdb.py                                    |  8 +++++
 Lib/test/test_pdb.py                          | 30 +++++++++++++++++++
 ...4-09-24-18-16-59.gh-issue-58956.0wFrBR.rst |  1 +
 3 files changed, 39 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2024-09-24-18-16-59.gh-issue-58956.0wFrBR.rst

diff --git a/Lib/bdb.py b/Lib/bdb.py
index 3486deacd86a7c..3f6cfc4d4979d9 100644
--- a/Lib/bdb.py
+++ b/Lib/bdb.py
@@ -396,6 +396,14 @@ def set_break(self, filename, lineno, temporary=False, cond=None,
             return 'Line %s:%d does not exist' % (filename, lineno)
         self._add_to_breaks(filename, lineno)
         bp = Breakpoint(filename, lineno, temporary, cond, funcname)
+        # After we set a new breakpoint, we need to search through all frames
+        # and set f_trace to trace_dispatch if there could be a breakpoint in
+        # that frame.
+        frame = self.enterframe
+        while frame:
+            if self.break_anywhere(frame):
+                frame.f_trace = self.trace_dispatch
+            frame = frame.f_back
         return None
 
     def _load_breaks(self):
diff --git a/Lib/test/test_pdb.py b/Lib/test/test_pdb.py
index 778aa03a63ab63..7a921a36b997f9 100644
--- a/Lib/test/test_pdb.py
+++ b/Lib/test/test_pdb.py
@@ -2371,6 +2371,36 @@ def test_issue26053(self):
         self.assertRegex(res, "Restarting .* with arguments:\na b c")
         self.assertRegex(res, "Restarting .* with arguments:\nd e f")
 
+    def test_issue58956(self):
+        # Set a breakpoint in a function that already exists on the call stack
+        # should enable the trace function for the frame.
+        script = """
+            import bar
+            def foo():
+                ret = bar.bar()
+                pass
+            foo()
+        """
+        commands = """
+            b bar.bar
+            c
+            b main.py:5
+            c
+            p ret
+            quit
+        """
+        bar = """
+            def bar():
+                return 42
+        """
+        with open('bar.py', 'w') as f:
+            f.write(textwrap.dedent(bar))
+        self.addCleanup(os_helper.unlink, 'bar.py')
+        stdout, stderr = self.run_pdb_script(script, commands)
+        lines = stdout.splitlines()
+        self.assertIn('-> pass', lines)
+        self.assertIn('(Pdb) 42', lines)
+
     def test_step_into_botframe(self):
         # gh-125422
         # pdb should not be able to step into the botframe (bdb.py)
diff --git a/Misc/NEWS.d/next/Library/2024-09-24-18-16-59.gh-issue-58956.0wFrBR.rst b/Misc/NEWS.d/next/Library/2024-09-24-18-16-59.gh-issue-58956.0wFrBR.rst
new file mode 100644
index 00000000000000..a882a632fddf1b
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-09-24-18-16-59.gh-issue-58956.0wFrBR.rst
@@ -0,0 +1 @@
+Fixed a bug in :mod:`pdb` where sometimes the breakpoint won't trigger if it was set on a function which is already in the call stack.

From ea13885617710e2233de88e6c23308757c2d46f7 Mon Sep 17 00:00:00 2001
From: Tian Gao <gaogaotiantian@hotmail.com>
Date: Tue, 15 Oct 2024 18:05:29 -0400
Subject: [PATCH 2/3] Add enterframe to bdb

---
 Lib/bdb.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Lib/bdb.py b/Lib/bdb.py
index 3f6cfc4d4979d9..43463acf90801e 100644
--- a/Lib/bdb.py
+++ b/Lib/bdb.py
@@ -33,6 +33,7 @@ def __init__(self, skip=None):
         self.breaks = {}
         self.fncache = {}
         self.frame_returning = None
+        self.enterframe = None
 
         self._load_breaks()
 
@@ -84,6 +85,9 @@ def trace_dispatch(self, frame, event, arg):
 
         The arg parameter depends on the previous event.
         """
+
+        self.enterframe = frame
+
         if self.quitting:
             return # None
         if event == 'line':
@@ -335,6 +339,7 @@ def set_trace(self, frame=None):
         if frame is None:
             frame = sys._getframe().f_back
         self.reset()
+        self.enterframe = frame
         while frame:
             frame.f_trace = self.trace_dispatch
             self.botframe = frame

From 4f9d5dd128ed290c36be23e77cb71c210c3cefae Mon Sep 17 00:00:00 2001
From: Tian Gao <gaogaotiantian@hotmail.com>
Date: Fri, 17 Jan 2025 15:27:12 -0500
Subject: [PATCH 3/3] Clear trace when enter set_trace

---
 Lib/bdb.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Lib/bdb.py b/Lib/bdb.py
index 43463acf90801e..4c6ea316df5551 100644
--- a/Lib/bdb.py
+++ b/Lib/bdb.py
@@ -336,6 +336,7 @@ def set_trace(self, frame=None):
 
         If frame is not specified, debugging starts from caller's frame.
         """
+        sys.settrace(None)
         if frame is None:
             frame = sys._getframe().f_back
         self.reset()