bug#28875: 25.3.50; set-default-file-modes ignores execution bits

[Tino Calancha <tino.calancha@gmail.com>]

On Tue, 17 Oct 2017, Andreas Schwab wrote:

> On Okt 17 2017, Tino Calancha <tino.calancha@gmail.com> wrote:
>
>> emacs -Q:
>> (let ((foo (make-temp-file "foo")) mode)
>>   (with-file-modes #o755 (write-region "" nil foo nil 0))
>>   ;; (set-file-modes foo #o755)
>>   (setq mode (nth 8 (file-attributes foo)))
>>   (delete-file foo) mode)
>> => "-rw-------"
>>
>> To set foo file permissions to "-rwxr-xr-x" I need uncomment
>> (set-file-modes foo #o755) above.
>> Why? Is for security reasons?
>
> make-temp-file already creates the file (with restrictive modes), so
> with-file-modes has no effect (write-region does not change the mode of
> existing files).  But write-region also never sets the x bits in the
> first place, it uses #o666 as the base mode.
>
Thank you for th enice explanation.  I understand now.
I think I was fooled by the docstring of `set-default-file-modes':
"Set the file permission bits for newly created files..."

I thought that setting will be used by the functions in my snippet.