bug#19029: Cut down on useless "really edit the buffer?" prompts

bug#19029: Cut down on useless "really edit the buffer?" prompts

[Paul Pogonyshev]

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When switching between different branches in a VCS system, file
modification date may change even though its contents isn't. For example,
when switching from trunk to a branch X where the file is modified, then
switching back.

As a result, if the file was opened in Emacs before the switches, and I
attempt to edit it afterwards, Emacs prompts me with "... changed on disk;
really edit the buffer?" even though the only thing that "changed" about it
is the modification time. (To make it worse, Emacs requires _three_
confirmation to edit and save...)

Request: if Emacs detects timestamp change, let it read the file and
compare it with the buffer; if they are byte-to-byte identical, just ignore
the timestamp.

To reproduce: open any existing file, say 'x.txt'. Now type:

    M-! touch x.txt

and try to edit the buffer.

Paul

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bug#19029: Cut down on useless "really edit the buffer?" prompts

[npostavs]

tags 19029 fixed
close 19029 26.1
quit

Paul Pogonyshev <pogonyshev@gmail.com> writes:

> Request: if Emacs detects timestamp change, let it read the file and compare it with the buffer; if they are byte-to-byte identical, just ignore the timestamp.
>
> To reproduce: open any existing file, say 'x.txt'. Now type:
>
> M-! touch x.txt
>
> and try to edit the buffer.
>
> Paul

This is implemented in master [1: 5a4bffb661].

etc/NEWS:

    ** No more prompt about changed file when the file's content is unchanged.
    Instead of only checking the modification time, Emacs now also checks
    the file's actual content before prompting the user.

1: 2016-09-02 11:44:13 -0400 5a4bffb6617a274ca19bc7f5c1b1ceb6345651ab
  Check actual contents before promting about changed file