bug#45349: 27.1.50; ruby-mode widens buffer when saving

[Eric Hanchrow]

put the following three lines of ruby code into /tmp/wat.rb

#####
def hey_you
  puts "So what"
end
####

start emacs with "emacs -nw"
visit the file:
  C-x C-f /tmp/wat.rb RET
add some spaces to the end of the second line:
  C-n C-e SPC SPC SPC
narrow to that second line:
  C-SPC
  M-m
  C-x n n
save the buffer:
  C-x C-s

You'll see that the buffer is no longer narrowed.

The fix is to simply add a "save-restriction" in the function
`ruby-mode-set-encoding`, like this

    modified   lisp/progmodes/ruby-mode.el
    @@ -794,6 +794,7 @@ ruby--encoding-comment-required-p
     (defun ruby-mode-set-encoding ()
       "Insert a magic comment header with the proper encoding if necessary."
       (save-excursion
    +    (save-restriction
           (widen)
           (goto-char (point-min))
           (when (ruby--encoding-comment-required-p)
    @@ -811,7 +812,7 @@ ruby-mode-set-encoding
                       (t (when ruby-insert-encoding-magic-comment
                            (ruby--insert-coding-comment coding-system))))
                 (when (buffer-modified-p)
    -            (basic-save-buffer-1)))))))
    +              (basic-save-buffer-1))))))))

     (defvar ruby--electric-indent-chars '(?. ?\) ?} ?\]))


In GNU Emacs 27.1.50 (build 2, x86_64-pc-linux-gnu)
 of 2020-12-04 built on ip-10-0-0-79
Repository revision: a4dd03ebe918ebc9cfbbec70d8c8910fae822b42
Repository branch: emacs-27
System Description: Amazon Linux AMI 2018.03

Recent messages:
Saving file /mnt3/git-repos/3rd-party/emacs/lisp/progmodes/ruby-mode.el...
Wrote /mnt3/git-repos/3rd-party/emacs/lisp/progmodes/ruby-mode.el
ruby-mode-set-encoding
Mark set
Saving file /tmp/wat.rb...
Wrote /tmp/wat.rb
Mark set [2 times]
Saving file /tmp/wat.rb...
Wrote /tmp/wat.rb
Mark saved where search started

Configured using:
 'configure --without-x'

Configured features:
SOUND NOTIFY INOTIFY LIBSELINUX GNUTLS LIBXML2 ZLIB XIM MODULES THREADS
PDUMPER GMP

Important settings:
  value of $LC_ALL: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
  bug-reference-prog-mode: t
  magit-auto-revert-mode: t
  global-git-commit-mode: t
  async-bytecomp-package-mode: t
  projectile-mode: t
  savehist-mode: t
  elisp-slime-nav-mode: t
  shell-dirtrack-mode: t
  ws-butler-mode: t
  global-auto-revert-mode: t
  recentf-mode: t
  ido-everywhere: t
  tracking-mode: t
  override-global-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
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Memory information:
((conses 16 2175918 349601)
 (symbols 48 57407 6)
 (strings 32 270955 36472)
 (string-bytes 1 7444009)
 (vectors 16 62351)
 (vector-slots 8 1111470 121082)
 (floats 8 3152 11089)
 (intervals 56 132518 8142)
 (buffers 1000 55)
 (heap 1024 88222 6475))