Incorrect code collapse while prompting where the error is.

Bug report

Bug description:

Read the following code:

# incorrect_collapse.py
def fib(number: int) -> int:
    assert number > 0
    if number == 1:
        return 1

    return fib(number - 1) + fib(number - 2)  # Notice here


print(fib(2))

There is a mistake in the code above, so if you try to run it, you will get the following traceback:

PC-Killer@ArchLinuxPC ~/p/bugs> python incorrect_collapse.py
Traceback (most recent call last):
  File "/home/PC-Killer/python_work/bugs/incorrect_collapse.py", line 9, in <module>
    print(fib(2))
          ~~~^^^
  File "/home/PC-Killer/python_work/bugs/incorrect_collapse.py", line 6, in fib
    return fib(number - 1) + fib(number - 2)  # Notice here
                             ~~~^^^^^^^^^^^^
  File "/home/PC-Killer/python_work/bugs/incorrect_collapse.py", line 2, in fib
    assert number > 0
           ^^^^^^^^^^
AssertionError

Notice that the error happened while running the code fib(number - 2).
However, if the number is 5, the duplicate code will be automatically collapsed:

# incorrect_collapse.py
def fib(number: int) -> int:
    assert number > 0
    if number == 1:
        return 1

    return fib(number - 1) + fib(number - 2)  # Notice here


print(fib(5))

PC-Killer@ArchLinuxPC ~/p/bugs [1]> python incorrect_collapse.py
Traceback (most recent call last):
  File "/home/PC-Killer/python_work/bugs/incorrect_collapse.py", line 9, in <module>
    print(fib(5))
          ~~~^^^
  File "/home/PC-Killer/python_work/bugs/incorrect_collapse.py", line 6, in fib
    return fib(number - 1) + fib(number - 2)  # Notice here
           ~~~^^^^^^^^^^^^
  File "/home/PC-Killer/python_work/bugs/incorrect_collapse.py", line 6, in fib
    return fib(number - 1) + fib(number - 2)  # Notice here
           ~~~^^^^^^^^^^^^
  File "/home/PC-Killer/python_work/bugs/incorrect_collapse.py", line 6, in fib
    return fib(number - 1) + fib(number - 2)  # Notice here
           ~~~^^^^^^^^^^^^
  [Previous line repeated 1 more time]
  File "/home/PC-Killer/python_work/bugs/incorrect_collapse.py", line 2, in fib
    assert number > 0
           ^^^^^^^^^^
AssertionError

The error happened in fib(number - 2). However, in the traceback above, I can only suppose the error happened while running fib(number - 1), which increases the time to find where the real bug is.

CPython versions tested on:

3.13, 3.14

Operating systems tested on:

Linux

Linked PRs

• gh-129973

まず、CPython 3.13 または 3.14 で、issue にある 2 つの Fibonacci の例を使って traceback-collapse の動作を再現し、次に traceback のフォーマット処理とフレームの折りたたみ処理のエントリポイントを調べます。折りたたんだ出力を、切り詰めていない traceback およびリンク先の PR gh-129973 と比較します。繰り返されたフレームを折りたたんだ後も失敗する式を区別できれば完了です。