bpo-43950: support some multi-line expressions for PEP 657 (GH-27339)

This is basically something that I noticed up while fixing test runs for another issue. It is really common to have multiline calls, and when they fail the display is kind of weird since we omit the annotations. E.g;

```
 $ ./python t.py
Traceback (most recent call last):
  File "/home/isidentical/cpython/cpython/t.py", line 11, in <module>
    frame_1()
    ^^^^^^^^^
  File "/home/isidentical/cpython/cpython/t.py", line 5, in frame_1
    frame_2(              
  File "/home/isidentical/cpython/cpython/t.py", line 2, in frame_2
    return a / 0 / b / c
           ~~^~~
ZeroDivisionError: division by zero
```

This patch basically adds support for annotating the rest of the line, if the instruction covers multiple lines (start_line != end_line).

Automerge-Triggered-By: GH:isidentical

1 files changed, 10 insertions, 8 deletions

diff --git a/Lib/traceback.py b/Lib/traceback.py
index 15bdb3c8c2e..4ad8c9a17b3 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -4,6 +4,7 @@ import collections
 import itertools
 import linecache
 import sys
+from contextlib import suppress
 
 __all__ = ['extract_stack', 'extract_tb', 'format_exception',
            'format_exception_only', 'format_list', 'format_stack',
@@ -463,19 +464,20 @@ class StackSummary(list):
 
             stripped_characters = len(frame._original_line) - len(frame.line.lstrip())
             if (
-                frame.end_lineno == frame.lineno
-                and frame.colno is not None
+                frame.colno is not None
                 and frame.end_colno is not None
             ):
                 colno = _byte_offset_to_character_offset(frame._original_line, frame.colno)
                 end_colno = _byte_offset_to_character_offset(frame._original_line, frame.end_colno)
 
-                try:
-                    anchors = _extract_caret_anchors_from_line_segment(
-                        frame._original_line[colno - 1:end_colno - 1]
-                    )
-                except Exception:
-                    anchors = None
+                anchors = None
+                if frame.lineno == frame.end_lineno:
+                    with suppress(Exception):
+                        anchors = _extract_caret_anchors_from_line_segment(
+                            frame._original_line[colno - 1:end_colno - 1]
+                        )
+                else:
+                    end_colno = stripped_characters + len(frame.line.strip())
 
                 row.append('    ')
                 row.append(' ' * (colno - stripped_characters))