pythongh-93883: elide traceback indicators when possible (python#93994)

* pythongh-93883: elide traceback indicators when possible

Elide traceback column indicators when the entire line of the
frame is implicated.  This reduces traceback length and draws
even more attention to the remaining (very relevant) indicators.

Example:
```
Traceback (most recent call last):
  File "query.py", line 99, in <module>
    bar()
  File "query.py", line 66, in bar
    foo()
  File "query.py", line 37, in foo
    magic_arithmetic('foo')
  File "query.py", line 18, in magic_arithmetic
    return add_counts(x) / 25
           ^^^^^^^^^^^^^
  File "query.py", line 24, in add_counts
    return 25 + query_user(user1) + query_user(user2)
                ^^^^^^^^^^^^^^^^^
  File "query.py", line 32, in query_user
    return 1 + query_count(db, response['a']['b']['c']['user'], retry=True)
                               ~~~~~~~~~~~~~~~~~~^^^^^
TypeError: 'NoneType' object is not subscriptable
```

Rather than going out of our way to provide indicator coverage
in every traceback test suite, the indicator test suite should
be responible for sufficient coverage (e.g. by adding a basic
exception group test to ensure that margin strings are covered).

Doc/library/traceback.rst

@@ -464,41 +464,36 @@ The output for the example would look similar to this:
    *** print_tb:
      File "<doctest...>", line 10, in <module>
        lumberjack()
-       ^^^^^^^^^^^^
    *** print_exception:
    Traceback (most recent call last):
      File "<doctest...>", line 10, in <module>
        lumberjack()
-       ^^^^^^^^^^^^
      File "<doctest...>", line 4, in lumberjack
        bright_side_of_death()
-       ^^^^^^^^^^^^^^^^^^^^^^
    IndexError: tuple index out of range
    *** print_exc:
    Traceback (most recent call last):
      File "<doctest...>", line 10, in <module>
        lumberjack()
-       ^^^^^^^^^^^^
      File "<doctest...>", line 4, in lumberjack
        bright_side_of_death()
-       ^^^^^^^^^^^^^^^^^^^^^^
    IndexError: tuple index out of range
    *** format_exc, first and last line:
    Traceback (most recent call last):
    IndexError: tuple index out of range
    *** format_exception:
    ['Traceback (most recent call last):\n',
-    '  File "<doctest default[0]>", line 10, in <module>\n    lumberjack()\n    ^^^^^^^^^^^^\n',
-    '  File "<doctest default[0]>", line 4, in lumberjack\n    bright_side_of_death()\n    ^^^^^^^^^^^^^^^^^^^^^^\n',
+    '  File "<doctest default[0]>", line 10, in <module>\n    lumberjack()\n',
+    '  File "<doctest default[0]>", line 4, in lumberjack\n    bright_side_of_death()\n',
     '  File "<doctest default[0]>", line 7, in bright_side_of_death\n    return tuple()[0]\n           ~~~~~~~^^^\n',
     'IndexError: tuple index out of range\n']
    *** extract_tb:
    [<FrameSummary file <doctest...>, line 10 in <module>>,
     <FrameSummary file <doctest...>, line 4 in lumberjack>,
     <FrameSummary file <doctest...>, line 7 in bright_side_of_death>]
    *** format_tb:
-   ['  File "<doctest default[0]>", line 10, in <module>\n    lumberjack()\n    ^^^^^^^^^^^^\n',
-    '  File "<doctest default[0]>", line 4, in lumberjack\n    bright_side_of_death()\n    ^^^^^^^^^^^^^^^^^^^^^^\n',
+   ['  File "<doctest default[0]>", line 10, in <module>\n    lumberjack()\n',
+    '  File "<doctest default[0]>", line 4, in lumberjack\n    bright_side_of_death()\n',
     '  File "<doctest default[0]>", line 7, in bright_side_of_death\n    return tuple()[0]\n           ~~~~~~~^^^\n']
    *** tb_lineno: 10
 

Doc/whatsnew/3.11.rst

@@ -117,7 +117,6 @@ when dealing with deeply nested dictionary objects and multiple function calls,
     Traceback (most recent call last):
       File "query.py", line 37, in <module>
         magic_arithmetic('foo')
-        ^^^^^^^^^^^^^^^^^^^^^^^
       File "query.py", line 18, in magic_arithmetic
         return add_counts(x) / 25
                ^^^^^^^^^^^^^

Lib/idlelib/idle_test/test_run.py

@@ -3,7 +3,7 @@
 from idlelib import run
 import io
 import sys
-from test.support import captured_output, captured_stderr, has_no_debug_ranges
+from test.support import captured_output, captured_stderr
 import unittest
 from unittest import mock
 import idlelib
@@ -33,14 +33,9 @@ def __eq__(self, other):
                         run.print_exception()
 
         tb = output.getvalue().strip().splitlines()
-        if has_no_debug_ranges():
-            self.assertEqual(11, len(tb))
-            self.assertIn('UnhashableException: ex2', tb[3])
-            self.assertIn('UnhashableException: ex1', tb[10])
-        else:
-            self.assertEqual(13, len(tb))
-            self.assertIn('UnhashableException: ex2', tb[4])
-            self.assertIn('UnhashableException: ex1', tb[12])
+        self.assertEqual(11, len(tb))
+        self.assertIn('UnhashableException: ex2', tb[3])
+        self.assertIn('UnhashableException: ex1', tb[10])
 
     data = (('1/0', ZeroDivisionError, "division by zero\n"),
             ('abc', NameError, "name 'abc' is not defined. "

Lib/test/test_cmd_line_script.py

@@ -549,10 +549,10 @@ def test_pep_409_verbiage(self):
             script_name = _make_test_script(script_dir, 'script', script)
             exitcode, stdout, stderr = assert_python_failure(script_name)
             text = stderr.decode('ascii').split('\n')
-            self.assertEqual(len(text), 6)
+            self.assertEqual(len(text), 5)
             self.assertTrue(text[0].startswith('Traceback'))
             self.assertTrue(text[1].startswith('  File '))
-            self.assertTrue(text[4].startswith('NameError'))
+            self.assertTrue(text[3].startswith('NameError'))
 
     def test_non_ascii(self):
         # Mac OS X denies the creation of a file with an invalid UTF-8 name.

Lib/test/test_doctest.py

@@ -2854,7 +2854,7 @@ def test_testmod(): r"""
     # Skip the test: the filesystem encoding is unable to encode the filename
     supports_unicode = False
 
-if supports_unicode and not support.has_no_debug_ranges():
+if supports_unicode:
     def test_unicode(): """
 Check doctest with a non-ascii filename:
 
@@ -2876,10 +2876,8 @@ def test_unicode(): """
         Traceback (most recent call last):
           File ...
             exec(compile(example.source, filename, "single",
-            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
           File "<doctest foo-bär@baz[0]>", line 1, in <module>
             raise Exception('clé')
-            ^^^^^^^^^^^^^^^^^^^^^^
         Exception: clé
     TestResults(failed=1, attempted=1)
     """