bug#63959: python-mode does not keep indentation in square brackets []

[kobarity]

I wrote:
> Eli Zaretskii wrote:
> > > From: Konstantin Kharlamov <hi-angel@yandex.ru>
> > > Date: Thu, 08 Jun 2023 12:39:23 +0300
> > > 
> > > Usually in programming modes, when previous indentation is kind of 
> > > "special",
> > > the new lines should keep the indentation from the previous line. 
> > > However, it
> > > doesn't work in this case.
> > > 
> > > 
> > > # Steps to reproduce
> > > 
> > > 1. Create file `test.py` with following content:
> > > 
> > >     for infix in [ # some description
> > >                   "_cdata", "_cmeta", "_corig", "_cpool", "_cvol", 
> > > "_wcorig",
> > >                   "indentation is broken here", "bar"]:
> > >         print(infix)
> > > 
> > > 2. Open it as `emacs -Q test.py`
> > > 3. Put a caret on the 3rd line (which says "indentation is broken"
> > > 4. Press TAB
> > > 
> > > 
> > > ## Expected
> > > 
> > > Indentation won't change
> > > 
> > > ## Actual
> > > 
> > > The line goes back by 4 spaces or so
> > > 
> > > # Additional information
> > > 
> > > emacs version: compiled from latest git a week ago, commit 5cace109d2b
> > 
> > kobarity, any comments?
> 
> I think the current Python mode tries to indent based on parens,
> regardless of the indentation of the previous line.  However, it would
> also be reasonable to maintain the indentation of the previous line.
> I will see if I can implement it.

Attached is a patch to implement it.  I introduced a new indent
context `:inside-paren-continuation-line' for the continuation lines
within paren.  The indent context respects the indentation of the
previous line.

However, it may happen that the previous line is indented for the
inner paren as in the ERT `python-indent-inside-paren-2':

data = {'key': {
    'objlist': [
        {'pk': 1,
         'name': 'first'},
        {'pk': 2,
         'name': 'second'}
    ]
}}

The line "{'pk': 2," is considered as the continuation line, but it
should not respect the indentation of the PREVIOUS line "'name':
'first'},".  So skipping such lines with inner parens were needed.
It searches backward for the line which starts with the item of the
same opening paren as the target line.

In the case of the above example, if the target line is "{'pk': 2,",
its opening paren is "[" in the line "'objlist': [".  It first checks
the previous line "'name': 'first'},", but its opening paren is "{" in
"{'pk': 1,".  So this line is skipped.  Next, it checks the line
"{'pk': 1," and its opening paren is "[" in the line "'objlist': [",
which is same as the target line.  So the target line's indentation
will be as same as the line "{'pk': 1,".

It would be helpful if you could try this patch.

Does anyone think we should have a customize variable that switches
between the traditional behavior of ignoring the indentation of the
previous line and this new behavior?

0001-Fix-Python-indentation-of-continuation-lines-within-.patch
Description: Binary data