8000 gh-133363: Fix Cmd completion for lines beginning with `! ` by godlygeek · Pull Request #133364 · python/cpython · GitHub
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gh-133363: Fix Cmd completion for lines beginning with ! #133364

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Merged
merged 4 commits into from
May 4, 2025
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gh-133363: Fix Cmd completion for lines beginning with ! #133364

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12e2495
Fix Cmd completion for lines beginning with `! `
godlygeek May 4, 2025
973bef6
Check falsiness instead
godlygeek May 4, 2025
1c6248e
Make news entry less descriptive
godlygeek May 4, 2025
c259bef
Test with and without a space after !
godlygeek May 4, 2025
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Fix Cmd completion for lines beginning with ! 
When a line begins with `!` and there's no `do_shell` method defined,
`parsecmd` returns `None` as the `cmd`, which incorrectly leads to
`None` being concatenated to `complete_` and triggering a `TypeError`.

Instead, recognize `None` as a sentinel that means we should call
`completedefault`, as an empty string already is.
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godlygeek committed May 4, 2025
commit 12e2495c3b84a94f50f61312ba708163f972eeda
2 changes: 1 addition & 1 deletion Lib/cmd.py
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Expand Up @@ -273,7 +273,7 @@ def complete(self, text, state):
endidx = readline.get_endidx() - stripped
if begidx>0:
cmd, args, foo = self.parseline(line)
if cmd == '':
if cmd in ('', None):
compfunc = self.completedefault
else:
try:
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25 changes: 25 additions & 0 deletions Lib/test/test_cmd.py
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Expand Up @@ -289,6 +289,31 @@ def do_tab_completion_test(self, args):
self.assertIn(b'ab_completion_test', output)
self.assertIn(b'tab completion success', output)

def test_bang_completion_without_do_shell(self):
script = textwrap.dedent("""
import cmd
class simplecmd(cmd.Cmd):
def completedefault(self, text, line, begidx, endidx):
return ["hello"]

def default(self, line):
if line == "! hello":
print('tab completion success')
else:
print('tab completion failure')
return True

simplecmd().cmdloop()
""")

# '! h' and complete 'ello' to '! hello'
input = b"! h\t\n"
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We should do add check here for !h\t\n (without space) as well. No need for another method, just another input.

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That does need to be another method, because the assertions are:

        self.assertIn(b'hello', output)
        self.assertIn(b'tab completion success', output)

and those would pass if either of the two inputs succeeded, not only if both of them did.

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Or maybe we could use a subtest for this? I know how to avoid duplication with pytest, but I'm not really familiar with unittest. Does this work?

        # '! h' or '!h' and complete 'ello' to 'hello'
        for input in [b"! h\t\n", b"!h\t\n"]:
            with self.subTest(input=input):
                output = run_pty(script, input)
                self.assertIn(b'hello', output)
                self.assertIn(b'tab completion success', output)

Seems to...

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I mean just use the same script and do two run_pty - I don't think you even need a subtest. It's a very small case.


output = run_pty(script, input)

self.assertIn(b'ello', output)
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ello because that's what is completed? hello is not part of the output?

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Oh, because that's what is used in the previous test.

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@godlygeek godlygeek May 4, 2025 •
edited
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ello because that's what's completed, yes. hello is part of the output, but I'm just matching the test above that I copy-pasted from, which only checks for ab_completion_test, heh

The tests do both pass if I adjust them to check for hello and tab_completion_test respectively.

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I just realized I co-authored that test. Ha.

self.assertIn(b'tab completion success', output)

def load_tests(loader, tests, pattern):
tests.addTest(doctest.DocTestSuite())
return tests
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5 changes: 5 additions & 0 deletions Misc/NEWS.d/next/Library/2025-05-03-21-55-33.gh-issue-133363.PTLnRP.rst
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@@ -0,0 +1,5 @@
The :class:`cmd.Cmd` class has been fixed to call the ``completedefault``
method whenever the ``do_shell`` method is not defined and tab completion is
requested for a line beginning with ``!``. Previously ``completedefault``
was called only if there were no spaces between the ``!`` and the cursor
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@gaogaotiantian gaogaotiantian May 4, 2025 •
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Previously completedefault was called only if there were no spaces between the ! and the cursor position where tab completion was attempted.

Is that even true? I thought the completion never works:

        elif line[0] == '!':
            if hasattr(self, 'do_shell'):
                line = 'shell ' + line[1:]
            else:
                return None, None, line

Anyway, normally in the news we only need to say what is fixed, we don't need to do a complete description of what's the previous behavior. News entry should be a concise sentence.

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@godlygeek godlygeek May 4, 2025 •
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Is that even true? I thought the completion never works:

Yes, because parsecmd is only called if begidx > 0, so in the !foo<Tab> case (begidx=0 endidx=3) we don't hit this buggy codepath.

Anyway, normally in the news we only need to say what is fixed, we don't need to do a complete description of what's the previous behavior. News entry should be a concise sentence.

OK, I've shortened it and just say that it's fixed to reliably call the method, since previously it was inconsistent.

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Okay but it's still not good, because that's not really a name. It still won't give us the correct completion.

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Let's not worry about that, we can do that in pdb I believe. I don't want to change cmd so close to beta freeze. I'll loop back to this after beta freeze.

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@godlygeek godlygeek May 4, 2025 •
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Okay but it's still not good, because that's not really a name. It still won't give us the correct completion.

True, though that seems to need a bigger change if you want to fix that... Do you want to special case ! at the start of the line, and do:

            if begidx>0:
                ...
            elif line.startswith("!"):
                compfunc = self.completedefault
            else:
                compfunc = self.completenames

Even that's not enough to make PDB's completion work without the space, though, because that'll give a text="!h" and PDB will say that none of the object names it knows of start with "!". Which means that making that work requires changes in the PDB module, too.

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I was wrong. ! was by default a delimiter and that's why your current code passes. cmd is handling this correctly because begidx will >0 when you complete !h<tab>. pdb somehow removed ! from delimiters and I did not figure out why. However, we can deal with in pdb only, this is not a cmd issue.

position where tab completion was attempted.
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