gh-133349: Enable auto-indent for pdb's multi-line mode

[gaogaotiantian]

• Issue: Auto-indent for pdb's multi-line mode #133349

[gaogaotiantian]

Sorry for trying to squeeze this in 3.14 before beta freeze :) I think this should be pretty straightforward to review and it could help user experiences.

[gaogaotiantian]

Hey @iritkatriel , do you think we still have a chance to merge this before beta freeze?

[iritkatriel]

Is indent always 4?

[gaogaotiantian]

We kind of dictated there, it is consistent with how we auto-fill the space when we hit <tab>. However, we can be smart and search for the history for the last indent. I have the time to do it and it should not be rocket science. Do you want me to do that?

[iritkatriel]

Up to you. This is fine.

[gaogaotiantian]

Let's land this today and if people are complaining, we can treat that as a bug and fix it later :)

[vstinner]

test_pdb.test_multiline_auto_indent() fails on FreeBSD:

FAIL: test_multiline_auto_indent (test.test_pdb.PdbTestReadline.test_multiline_auto_indent)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/home/vstinner/python/main/Lib/test/test_pdb.py", line 4870, in test_multiline_auto_indent
    self.assertIn(b'42', output)
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^
AssertionError: b'42' not found in bytearray(b"def f(x):\r\nif x > 0:\r\nx += 1\r\nreturn x\r\nelse:\r\nreturn -x\r\n\r\nf(-21-21)\r\nc\r\n> <string>(2)<module>()\r\n(Pdb) def f(x):\r\n...       if x > 0:\r\n...           x += 1\r\n...           return x\r\n...           else:\r\n*** SyntaxError: invalid syntax\r\n(Pdb) return -x\r\n*** Invalid argument: -x\r\n      Usage: r(eturn)\r\n(Pdb) \r\n*** Invalid argument: -x\r\n      Usage: r(eturn)\r\n(Pdb) f(-21-21)\r\n*** NameError: name \'f\' is not defined\r\n(Pdb) c\r\n")

Reformatted output (the bytearray):

"def f(x):\r\n
if x > 0:\r\n
x += 1\r\n
return x\r\n
else:\r\n
return -x\r\n
\r\n
f(-21-21)\r\n
c\r\n
> <string>(2)<module>()\r\n
(Pdb) def f(x):\r\n
...       if x > 0:\r\n
...           x += 1\r\n
...           return x\r\n
...           else:\r\n
*** SyntaxError: invalid syntax\r\n
(Pdb) return -x\r\n
*** Invalid argument: -x\r\n
      Usage: r(eturn)\r\n
(Pdb) \r\n
*** Invalid argument: -x\r\n
      Usage: r(eturn)\r\n
(Pdb) f(-21-21)\r\n
*** NameError: name \'f\' is not defined\r\n
(Pdb) c\r\n
"

And then test_multiline_indent_completion() hangs.

[gaogaotiantian]

I think the easy way is just to skip these tests on freebsd. This is a test issue, where freebsd does not consider \x08 a backspace. We might be able to find a character that actually works on freebsd, but I don't have a machine to test it out. It's a tier3 support so maybe we just let it go?

[vstinner]

I have a FreeBSD machine, I can try some changes if you want. But if I have no clue why \x08 is not treated as backspace.

I would also be fine with skipping the test on FreeBSD.

[gaogaotiantian]

Could you try \x7f and see if that works?

[vstinner]

Could you try \x7f and see if that works?

test_multiline_auto_indent() still fails if I replace \x08 with \x7f.

[vstinner]

I wrote #133566 to skip the two tests on FreeBSD.

[tanloong]

freebsd does not consider \x08 a backspace

Just a remark, I tried and found that FreeBSD does interpret \x08 as backspace. The problem is that the auto-indented whitespaces are undeletable for some reason.

""" test-pdb-auto-indent.py """
import textwrap
from test.support.pty_helper import run_pty

script = textwrap.dedent("""
    import pdb; pdb.Pdb().set_trace()
""")

input = b"def g\x08f(x):                # g is successfully deleted and replaced by f:\n"
input += b"if x > 0:\n"
input += b"x += 1\n"
input += b"return x\n"
input += b"\x08\x08\x08\x08else:           # fails to delete the auto-indented whitespaces:\n"
input += b"return -x\n"
input += b"\n"
input += b"f(-21-21)\n"
input += b"c\n"

output = run_pty(script, input)
print(output)

$ ./python ./test-pdb-auto-indent.py | sed -E 's/\\r\\n/\n/g'
bytearray(b"def g\x08 \x08f(x):                # g is successfully deleted and replaced by f:
if x > 0:
x += 1
return x
else:           # fails to delete the auto-indented whitespaces:
return -x

f(-21-21)
c
> <string>(2)<module>()
(Pdb) def f(x):                # g is successfully deleted and replaced by f:
...       if x > 0:
...           x += 1
...           return x
...           else:           # fails to delete the auto-indented whitespaces:
*** SyntaxError: invalid syntax
(Pdb) return -x
*** Invalid argument: -x
      Usage: r(eturn)
(Pdb) 
*** Invalid argument: -x
      Usage: r(eturn)
(Pdb) f(-21-21)
*** NameError: name \'f\' is not defined
(Pdb) c
")

The weird thing is that it happens only in the pseudo-terminal opened by run_pty(). In a normal terminal (kitty+bash) it can't be reproduced, the auto-indented whitespaces are deletable by pressing backspaces.

simplescreenrecorder-2025-05-08_19.03.22.mp4