Re: [Qemu-trivial] [Qemu-devel] [PATCH v2] Add .dir-locals.el file to configure emacs coding style

[Markus Armbruster]

"Daniel P. Berrange" <address@hidden> writes:

> On Tue, Sep 15, 2015 at 09:31:08AM -0600, Eric Blake wrote:
>> ping
>> 
>> On 08/24/2015 06:15 PM, John Snow wrote:
>> > 
>> > 
>> > On 06/18/2015 10:05 AM, Markus Armbruster wrote:
>> >> Peter Maydell <address@hidden> writes:
>> >>
>> >>> On 18 June 2015 at 10:28, Markus Armbruster <address@hidden> wrote:
>> >>>> However, I can't see how I could define a new C style there without
>> >>>> pushing the "local variables" feature well beyond its intended use, and
>> >>>> triggering the confirmation prompts.
>> >>>
>> >>> We wouldn't want to define a new C style, but in general the items
>> >>> I have in my config over the Stroustrup defaults are going to be there
>> >>> because I've noticed something where Stroustrup doesn't indent right...
>> >>
>> >> As far as I can see, the difference bwteen stroustrup style and yours is
>> >> a few tweaks to c-offsets-alist and c-hanging-braces-alist.  I'm not
>> >> sure how to do that from .dir-locals.el.
>> >>
>> >>>> If we take Dan's patch, every Emacs user who hasn't already configured a
>> >>>> suitable style profits.  Users who have may have to adjust their
>> >>>> configuration to work with or around Dan's patch.
>> >>>
>> >>> Is there some way to tell whether your emacs has picked up the local
>> >>> style info rather than the one you have in your .emacs ?
>> >>
>> >> The obvious way is to check the buffer-local variables.  Buffer-local
>> >> variable c-indentation-style is the name of the style in use.  Without
>> >> anything in .emacs or local variables, it's "gnu".  With your
>> >> (c-add-style "qemu" qemu-c-style) in .emacs, it should be "qemu".  With
>> >> Dan's .dir-locals.el, it should be "stroustrup".
>> >>
>> >> When you can't or don't want to create or modify a .dir-locals.el, you
>> >> can do something like this instead:
>> >>
>> >>     (dir-locals-set-class-variables 'qemu '((c-mode
>> >> . ((c-file-style . "qemu")))))
>> >>     (dir-locals-set-directory-class "~/work/qemu" 'qemu)
>> >>
>> >> This *overrides* .dir-locals.el in my testing.
>> >>
>> > 
>> > ping -- any love for this for 2.5?
>
> So just to re-cap.....
>
> My original proposed .dir-locals.el was pretty short:
>
>   ((c-mode . ((c-file-style . "stroustrup")
>              (indent-tabs-mode . nil))))
>
> IIUC, the quote above says it is possible to override this with more
> developer custom styles if desired, so it shouldn't cause any obvious
> disadvantage / problem to contributors to have this set by default.
>
> I have tried an alternative .dir-locals.el that contains all of
> Peter's rules (from http://wiki.linaro.org/PeterMaydell/QemuEmacsStyle)
> which looks like this:
>
>
>   ;; Based on https://wiki.linaro.org/PeterMaydell/QemuEmacsStyle
>   ;; which aims to apply CODING_STYLE guidelines
>   ((c-mode . (
>       (c-file-style . "stroustrup")
>       (indent-tabs-mode . nil)
>       (tab-width . 8)
>       (c-comment-only-line-offset . 1)
>       (c-hanging-braces-alist . ((substatement-open before after)))
>       (c-offsets-alist . (
>           (statement-block-intro . +)
>           (substatement-open . 0)
>           (label . 0)
>           (statement-cont . +)
>           (innamespace . 0)
>           (inline-open . 0)
>       ))
>       (c-hanging-braces-alist . (
>           (brace-list-open)
>           (brace-list-intro)
>           (brace-list-entry)
>           (brace-list-close)
>           (brace-entry-open)
>           (block-close . c-snug-do-while)
>           ;; structs have hanging braces on open
>           (class-open . (after))
>           ;; ditto if statements
>           (substatement-open . (after))
>           ;; and no auto newline at the end
>           (class-close)
>       ))
>   )))
>
> The main downside/problem I found with having this more comprehensive
> .dir-locals.el file, is that emacs will raise a warning at launch time:
>
> "The local variables list in /home/berrange/src/virt/qemu
>  contains vlaues that may not be safe (*).
>
>  Do you want to apply it? You can type
>   y -- to apply the local variables list.
>   n -- to ignore the local variables list.
>   ! -- to apply the local variables list and permanently
>        mark these values (*) as safe (in the future, they
>        will be set automatically)"
>
> It will ask this every time it launches unless you say "!"
> whereupon it modifies your $HOME/.emacs to disable the warning
>
> Personally I be fine with both the minimal approach or the more
> comprehensive approach of Peter's, but I'd probably tend towards
> the minimal approach to avoid the warnings problem.

Seconded.

The "minimal approach" has been on the list since June, and it has my
R-by.  It's clearly better than nothing.  Let's commit it now.  We can
always improve on it later.