From 1eb68125786974bf1f4f89e8a675fad408ced730 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Tue, 28 Apr 2020 17:07:25 +0200
Subject: [PATCH] bpo-40421: Add PyFrame_GetLastInstr() function

New PyFrame_GetLastInstr() function: get the index of last attempted
instruction in bytecode of a frame.

Replace frame->f_lasti with PyFrame_GetLastInstr(frame).
---
 Doc/c-api/reflection.rst                              | 11 +++++++++++
 Doc/whatsnew/3.9.rst                                  |  2 ++
 Include/cpython/frameobject.h                         |  2 ++
 .../C API/2020-04-28-19-25-20.bpo-40421.iHT9OE.rst    |  2 ++
 Objects/frameobject.c                                 |  8 ++++++++
 Python/traceback.c                                    |  6 +++---
 6 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/C API/2020-04-28-19-25-20.bpo-40421.iHT9OE.rst

diff --git a/Doc/c-api/reflection.rst b/Doc/c-api/reflection.rst
index b313ea302598e6c..976d5f641a71c7f 100644
--- a/Doc/c-api/reflection.rst
+++ b/Doc/c-api/reflection.rst
@@ -40,6 +40,17 @@ Reflection
    .. versionadded:: 3.9
 
 
+.. c:function:: int PyFrame_GetLastInstr(PyFrameObject *frame)
+
+   Get the index of last attempted instruction in bytecode of *frame*.
+
+   Return ``-1`` for new frame (not run yet).
+
+   *frame* must not be ``NULL``.
+
+   .. versionadded:: 3.9
+
+
 .. c:function:: int PyFrame_GetLineNumber(PyFrameObject *frame)
 
    Return the line number that *frame* is currently executing.
diff --git a/Doc/whatsnew/3.9.rst b/Doc/whatsnew/3.9.rst
index e3751fa1680117b..696714a8c647ff1 100644
--- a/Doc/whatsnew/3.9.rst
+++ b/Doc/whatsnew/3.9.rst
@@ -539,6 +539,8 @@ Build and C API Changes
 
 * New :c:func:`PyFrame_GetCode` function: return a borrowed reference to the
   frame code.
+  New :c:func:`PyFrame_GetLastInstr` function: get the index of last attempted
+  instruction in bytecode of a frame.
   (Contributed by Victor Stinner in :issue:`40421`.)
 
 * Add :c:func:`PyFrame_GetLineNumber` to the limited C API.
diff --git a/Include/cpython/frameobject.h b/Include/cpython/frameobject.h
index e819cefd13cbeb1..536b7e7159f35f2 100644
--- a/Include/cpython/frameobject.h
+++ b/Include/cpython/frameobject.h
@@ -79,6 +79,8 @@ PyAPI_FUNC(int) PyFrame_ClearFreeList(void);
 
 PyAPI_FUNC(void) _PyFrame_DebugMallocStats(FILE *out);
 
+PyAPI_FUNC(int) PyFrame_GetLastInstr(PyFrameObject *frame);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/Misc/NEWS.d/next/C API/2020-04-28-19-25-20.bpo-40421.iHT9OE.rst b/Misc/NEWS.d/next/C API/2020-04-28-19-25-20.bpo-40421.iHT9OE.rst
new file mode 100644
index 000000000000000..e28c8ac455a1a83
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2020-04-28-19-25-20.bpo-40421.iHT9OE.rst	
@@ -0,0 +1,2 @@
+New :c:func:`PyFrame_GetLastInstr` function: get the index of last attempted
+instruction in bytecode of a frame.
diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index 92206c5f521086d..74d42e7db255062 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -1229,3 +1229,11 @@ PyFrame_GetCode(PyFrameObject *frame)
     assert(frame != NULL);
     return frame->f_code;
 }
+
+
+int
+PyFrame_GetLastInstr(PyFrameObject *frame)
+{
+    assert(frame != NULL);
+    return frame->f_lasti;
+}
diff --git a/Python/traceback.c b/Python/traceback.c
index 1ea6cbada964f53..476dc3e6e475564 100644
--- a/Python/traceback.c
+++ b/Python/traceback.c
@@ -233,7 +233,8 @@ _PyTraceBack_FromFrame(PyObject *tb_next, PyFrameObject *frame)
     assert(tb_next == NULL || PyTraceBack_Check(tb_next));
     assert(frame != NULL);
 
-    return tb_create_raw((PyTracebackObject *)tb_next, frame, frame->f_lasti,
+    return tb_create_raw((PyTracebackObject *)tb_next, frame,
+                         PyFrame_GetLastInstr(frame),
                          PyFrame_GetLineNumber(frame));
 }
 
@@ -767,8 +768,7 @@ dump_frame(int fd, PyFrameObject *frame)
         PUTS(fd, "???");
     }
 
-    /* PyFrame_GetLineNumber() was introduced in Python 2.7.0 and 3.2.0 */
-    lineno = PyCode_Addr2Line(code, frame->f_lasti);
+    lineno = PyCode_Addr2Line(code, PyFrame_GetLastInstr(frame));
     PUTS(fd, ", line ");
     if (lineno >= 0) {
         _Py_DumpDecimal(fd, (unsigned long)lineno);