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bug#23824: 25.0.95; Prevent compare one buffer with itself

From: Tino Calancha
Subject: bug#23824: 25.0.95; Prevent compare one buffer with itself
Date: Fri, 24 Jun 2016 14:07:29 +0900 (JST)
User-agent: Alpine 2.20 (DEB 67 2015-01-07)

On Thu, 23 Jun 2016, Eli Zaretskii wrote:
But then what is that "also" word doing in the doc string?
Nothing special:
It states that the person whom wrote this func took in account both cases:
*) When buf-a is not visiting file-b (let's call it 'default' case).
*) When buf-a is visiting file-b ('special' case).
Something like: "Dear doc readers, i let you know that i have _also_
considered the case when buf-a is visiting file-b".

I think there's more here than meets the eye.  Did you ask yourself
why the user is asked twice whether to save the same buffer to the
same file in your scenario?  Why does it do that?  What does it have
in mind?

I guess is just a bug in the logic.  The author of this code
overlooked that
(get-file-buffer file-b)
may return the very same buffer that buf-a (when buf-a is visiting file-b).
Then, calling
(highlight-markup-buffers BUF-A FILE-B BUF-A FILE-B)
will prompt you twice to save BUF-A when BUF-A is modified.
It prompts you to save buf-a again even if you saved buf-a after
the first prompt: this is because `highlight-markup-buffers'
save the bit on the modification status of BUF-A and BUF-B at the
top of the function.

In my patch, for this case (buf-a visiting file-b), i explicitely create a temporary buffer whose content equals file-b content.
Then, I call
(set-buffer-modified-p nil)
to prevent being prompted to save this temporary buffer.

Oh, it matters a lot.  insert-file-contents-literally will bypass any
decoding and leave the CR-LF EOLs untranslated, something that you
don't want to affect the comparison.

I see.  Another example that reviewing a patch before applying it
is a good thing.
Then, my patch need to be modified:

insert-file-contents-literally -> insert-file-contents

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