Questioning the new behavior of `open-line'.

[Karl Fogel]

Recently, `open-line' has started behaving in a new way due to Arthur 
Malabarba's recent commits [1].  Here is how `open-line' behaves before and 
after the changes.

Suppose you have this text in a buffer, in just about any mode (i.e., not 
necessarily a programming language mode), and it is indented by two spaces as 
below:

  A lovely haiku
  An example for this bug
  For Emacs Devel

Now place point where the imaginary "X" is below and do C-o (`open-line'):

X A lovely haiku
  An example for this bug
  For Emacs Devel

Formerly, that would literally insert a newline, but not remove the the two 
spaces of indendation that come *after* the new newline (the two spaces right 
before "A lovely haiku").  So this would be the result:

[...this is the new line; imagine it's blank...]
  A lovely haiku
  An example for this bug
  For Emacs Devel

But after the recent commits, those two spaces are removed:

[...this is the new line; imagine it's blank...]
A lovely haiku
  An example for this bug
  For Emacs Devel

So now one can no longer just put point in column 0 and type C-o to open a line 
right before a block of indented text while preserving the block's indentation.

This is just a result of `electric-indent-mode' being on by default and 
`open-line' now being sensitive to `electric-indent-mode', I think.  But one of 
the things I always thought was good about `open-line' was that it *wasn't* 
sensitive that way -- that you could just put point in a column of your choice 
and insert a newline, and everything to the right of that column would be 
preserved after the newline.

Arthur was well aware of this change, and even asked about it in his first post 
in the thread "A few questions about open-line" [2]:

> 3. I think, when electric-indent-mode is on, open-line should indent
> the line that was created below if it isn't empty. May I go ahead?

Had I seen that question at the time, I would have answered "Oh, please don't" 
:-).  But maybe mine is a minority opinion?  I encounter the new behavior 
several times a day, and don't like it; turning off `electric-indent-mode' 
seems like a drastic solution.  But if people generally like this new behavior, 
I'll certainly live with being in the minority and figure out the appropritae 
local customization.

So do we think this new behavior is the right one?

(If it stays, then I'll add an item to NEWS about it.)

Best regards,
-Karl

[1] These two commits (note you have to take them together, as the earlier one 
accidentally leaves open-line in a syntactically invalid state, and the later 
one corrects that):

  commit bd4f04f86cea893e3369decdda074a4898491518
  Author: Artur Malabarba <address@hidden>
  Date:   Sat Oct 24 22:26:27 2015 +0100
  
      * lisp/simple.el (open-line): Integrate with electric-indent-mode
      
      Also run `post-self-insert-hook' when called interactively.
  
  M     lisp/simple.el
  
  commit 6939896e2ffe2e742954c14bba6129af456f0857
  Author: Artur Malabarba <address@hidden>
  Date:   Sat Oct 24 22:24:09 2015 +0100
  
      * lisp/simple.el (open-line): Fix docstring
      
      Also explain apparently redundant line.
  
  M     lisp/simple.el

[2] https://lists.gnu.org/archive/html/emacs-devel/2015-10/threads.html#02107