bug#30277: 26.0.91; Infinite recursion in python-nav-beginning-of-statement

[Ola Nilsson <ola.nilsson@gmail.com>]

The infinite recursion is triggered when the first line of a
python-mode buffer starts with space and ends with a backslash.

With emacs -Q

* create a new buffer
* M-x python-mode
* Insert SPACE \ ENTER

=> Lisp nesting exceeds ‘max-lisp-eval-depth’

The infinite recursion is also triggered if the first line of a narrowed
region starts with space and ends on a backslash.


I ran into this problem using mmm-mode with python submode regions.
The file format (bitbake from the Yocto Project) uses this style of
python function:

python foo() {
    # Python code here
    ...
}

mmm-mode narrows to the function content for fontification and if the
first line is properly indented Python code that ends with a backslash,
I see a list nesting error.

-- 
Ola

In GNU Emacs 26.0.91 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2018-01-23 built on blue
Repository revision: 1fc98ed073a2d26ad941748ecb13aa6f47dd7b01
Windowing system distributor 'The X.Org Foundation', version 11.0.11902000
System Description:    Debian GNU/Linux 9.3 (stretch)

Recent messages:
Desktop lazily opening font-lock.el.gz (2 remaining)...
uncompressing font-lock.el.gz...done
Desktop lazily opening font-lock.el.gz (2 remaining)...done
Desktop lazily opening mmm-mason.el (1 remaining)...done
Lazy desktop load complete
Sun Jan 28 19:48:27 2018: saving desktop file
Desktop saved in ~/.emacs.d/
Reverting buffer ‘useradd.bbclass’.
GNU Emacs 26.0.91 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
of 2018-01-23
Making completion list...

Configured using:
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