bug#57260: 29.0.50; Python font-lock support is limited to single line

[kobarity]

Hi,

Current font-lock support for Python is limited to a single line.  For
example, function names and variable names in the following code are
not font-locked.

#+begin_src python
def \
        func():
    [
        a,
        b
    ] = (
        1,
        2
    )
#+end_src

Attached is a patch to enable font-lock of such multiline constructs.
To support multiline font-lock, a function to be set as
`font-lock-extend-after-change-region-function' is added.  This
function expands the region to be fontified to statement boundaries so
that multiline constructs can be identified.

Please note that this patch does not support newlines in type hints
such as following.

#+begin_src python
d: Mapping[int,
           str] = {1: 'bar', 2: 'baz'}
#+end_src

Best Regards,

--

In GNU Emacs 29.0.50 (build 10, x86_64-pc-linux-gnu)
 of 2022-08-15 built on ubuntu
System Description: Ubuntu 22.04.1 LTS

Configured using:
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Configured features:
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Important settings:
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Major mode: Python

Minor modes in effect:
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  global-font-lock-mode: t
  font-lock-mode: t
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Memory information:
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font-lock-multiline.patch
Description: Binary data