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

---
 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 9755d61dd26..81bba8a130f 100644
--- a/Lib/bdb.py
+++ b/Lib/bdb.py
@@ -461,6 +461,14 @@ class Bdb:
             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 456effc0109..8136c591a33 100644
--- a/Lib/test/test_pdb.py
+++ b/Lib/test/test_pdb.py
@@ -3396,6 +3396,36 @@ def bœr():
         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 00000000000..a882a632fdd
--- /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.