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

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Karl Fogel <kfogel <at> red-bean.com>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#21884: closed (25.0.50; Unexpected indentation from
 `open-line' due to new `electric-indent-mode' default.)
Date: Sun, 22 Nov 2015 06:30:05 +0000

[Message part 1 (text/plain, inline)]

Your message dated Sun, 22 Nov 2015 00:29:01 -0600
with message-id <87fuzy35ua.fsf <at> red-bean.com>
and subject line Closing this bug, since we'd discuss before reviving new behavior.
has caused the debbugs.gnu.org bug report #21884,
regarding 25.0.50; Unexpected indentation from `open-line' due to new `electric-indent-mode' default.
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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From: Karl Fogel <kfogel <at> red-bean.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.0.50; Unexpected indentation from `open-line' due to new
 `electric-indent-mode' default.
Date: Thu, 12 Nov 2015 01:57:34 -0600

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.

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From: Karl Fogel <kfogel <at> red-bean.com>
To: 21884-done <at> debbugs.gnu.org
Subject: Closing this bug, since we'd discuss before reviving new behavior.
Date: Sun, 22 Nov 2015 00:29:01 -0600

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.

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