bug#21884: 25.0.50; Unexpected indentation from `open-line' due to new `electric-indent-mode' default.

bug#21884: 25.0.50; Unexpected indentation from `open-line' due to new `electric-indent-mode' default.

[Karl Fogel]

Note that this bug report summarizes a discussion on the Emacs Devel mailing list -- please check there for updates:

  "Questioning the new behavior of `open-line'."
  https://lists.gnu.org/archive/html/emacs-devel/2015-11/threads.html#01100

The problem:

Since Artur Malabarba's commits of 2015-10-24 in simple.el, `open-line' has a new indentation behavior, because those commits made `open-line' sensitive to `electric-indent-mode', which in turn is now on by default.

For example, suppose you have the following text in a buffer, in just about any mode (i.e., not necessarily a programming language mode), and 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 get removed:

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

Thus 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.

Solutions:

One solution would be to revert `open-line' to being entirely insensitive to `electric-indent-mode'.  But Artur points out (in https://lists.gnu.org/archive/html/emacs-devel/2015-11/msg01100.html) that when point is in the middle of a line, one might want electric-indent behavior from `open-line'.  For instance, in the above example, put point at the first ‘h’ and do C-o.  If `open-line' just ignores electric-indent, then this would be the result:

  A lovely
haiku
  An example for this bug
  For Emacs Devel

Whereas with Artur's changes, the result would be this (which at least some people, including Artur, would desire):

  A lovely
  haiku
  An example for this bug
  For Emacs Devel

John Wiegley has proposed that `open-line' just be aware of when point is in column 0 and not do the electric-indent behavior then.  This preserves the common use case of C-a C-o, but also preserves Artur's "fix" (for those who agree it is a fix) for when C-o is invoked in the middle of a line.

Discussion is ongoing as of this writing.

bug#21884: Behavior reverted on emacs-25 branch.

[Karl Fogel]

As per Artur's recent message, the indentation-sensitive behavior is
reverted on the 'emacs-25' branch while we continue to discuss.  See
http://git.savannah.gnu.org/cgit/emacs.git/commit/?h=emacs-25&id=c593538968a6d6c3d03da9ef6f489da6210e70e1
for details.

bug#21884: Cleanup commit on emacs-25 branch finishes reversion.

[Karl Fogel]

A followup change was needed to complete the reversion:

    commit 8726de6663608b74e81ff88e530b4ddc6165700f
    Author: Karl Fogel <kfogel@red-bean.com>
    Date:   Sat Nov 21 22:50:05 2015 -0600

bug#21884: Closing this bug, since we'd discuss before reviving new behavior.

[Karl Fogel]

Closing this bug as the electric-indent behavior is reverted in the 'emacs-25' branch now and the reversion will eventually be automatically ported to 'master'.  If the electric indentation behavior is revived, it would be through a discussion anyway.  We can re-open this ticket then if we want, but there might be no need: the continued mailing list discussion would probably be enough.