bug#3348: 23.0.92.1; Ediff: Creating a multi-file patch

[Mauro Aranda]

Noam Postavsky <npostavs@users.sourceforge.net> writes:

> tag 3348 + confirmed
> severity 3348 minor
> found 3348 25.0.94
> quit
>
> Confirmed this is still an issue. Here is an elisp script for easier
> reproduction (run as emacs -Q -l bug-3348.el):
>
> (defconst bug-3348-test-dir
>   (expand-file-name "bug-3348-testdir" temporary-file-directory))
> (make-directory bug-3348-test-dir t)
> (cd bug-3348-test-dir)
>
> (make-directory "dir-a" t)
> (make-directory "dir-b" t)
>
> (with-temp-file "dir-a/file"
>   (insert "aaa"))
> (with-temp-file "dir-b/file"
>   (insert "bbb"))
>
> (ediff-directories "dir-a" "dir-b" nil)
> (switch-to-buffer "*Ediff Session Group Panel*")
>
> (ediff-next-meta-item 1)
> (ediff-mark-for-operation-at-pos nil)
> (ediff-collect-custom-diffs)
>
> (with-current-buffer "*Ediff Multifile Diffs*"
>   (write-file "foo.patch"))
>
> (with-temp-file "dir-b/file"
>   (insert "BBB"))
>
> (ediff-collect-custom-diffs)
>
> (switch-to-buffer "foo.patch")
> (diff-buffer-with-file)
> (message (concat "Observe foo.patch buffer is different from its file,\n"
>                  "but is marked read-only, not modified"))

This still happens, but I'm not really sure if this should be called a
bug.  ediff-collect-custom-diffs explicitly marks this buffer as not
modified with (set-buffer-modified-p nil).  I can't find the reasons for
that, but that doesn't mean there isn't a good one.  And it is
consistent about doing that.

The first call to ediff-collect-custom-diffs creates the buffer
*Ediff Multifile Diffs* and also marks it as unmodified, even though it
is.  So, why is that not a problem? Why is the second time a problem?

Using write-file again is possible, so what are the expectations of the
second time of typing `P' (or calling ediff-collect-custom-diffs) and
why do they differ from the expectations for the 1st call?