Re: [Qemu-devel] [RFC PATCH] Add qemu .clang-format

[Wang, Lei]

On 8/31/2022 6:39 PM, Daniel P. Berrangé wrote:
> On Wed, Aug 31, 2022 at 05:18:34PM +0800, Wang, Lei wrote:
> > On 8/31/2022 4:49 PM, Daniel P. Berrangé wrote:
> > > On Wed, Aug 31, 2022 at 02:23:51PM +0800, Wang, Lei wrote:
> > > > On 10/2/2015 1:30 AM, marcandre.lureau@redhat.com wrote:
> > > > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > > >
> > > > > clang-format is awesome to reflow your code according to qemu coding
> > > > > style in an editor (in the region you modify).
> > > > >
> > > > > (note: clang-tidy should be able to add missing braces around
> > > > > statements, but I haven't tried it, it's quite recent)
> > > > >
> > > > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > > > ---
> > > > >     .clang-format | 6 ++++++
> > > > >     1 file changed, 6 insertions(+)
> > > > >     create mode 100644 .clang-format
> > > > >
> > > > > diff --git a/.clang-format b/.clang-format
> > > > > new file mode 100644
> > > > > index 0000000..6422547
> > > > > --- /dev/null
> > > > > +++ b/.clang-format
> > > > > @@ -0,0 +1,6 @@
> > > > > +BasedOnStyle: LLVM
> > > > > +IndentWidth: 4
> > > > > +UseTab: Never
> > > > > +BreakBeforeBraces: Linux
> > > > > +AllowShortIfStatementsOnASingleLine: false
> > > > > +IndentCaseLabels: false
> > > >
> > > > Hi, any progress on this? I also found a gist on GitHub which can be a
> > > > reference: https://gist.github.com/elmarco/aa5e0b23567f46fb7f0e73cde586a0c1
> > >
> > > clang-format is a great tool and I'd highly recommend its use on
> > > any newly started projects, and even retrospectively on existing
> > > projects which are small scale. Adding it to large existing projects
> > > is problematic though.
> > >
> > > None of the QEMU code complies with it today and indeed there is
> > > quite a bit of style variance across different parts of QEMU. If
> > > we add this config file, and someone makes a 1 line change in a
> > > file, clang-format will reformat the entire file contents.
> > >
> > > The only practical way to introduce use of clang-format would be
> > > to do a bulk reformat of the entire codebase. That is something
> > > that is quite disruptive to both people with patches they're
> > > working on but not submitted yet, as well as people wanting to
> > > cherry-pick new commits back to old code branches.
> > >
> > > With regards,
> > > Daniel
> >
> > I think the benefits of introducing clang-format mainly for its ability to
> > format a code range, which means for any future contributions, we could
> > encourage a range format before the patch is generated. This can extensively
> > simplify my workflow, especially because I use the Neovim + LSP combination,
> > which supports a built-in function "lua vim.lsp.buf.range_formatting()".
>
> IMHO partial format conversions are even worse than full conversions,
> because they would make code inconsistent within the scope of a file.

So you mean when we're adding new code in an old file, the coding style 
should also be the old one? That sounds a bit unreasonable. I thought we 
are shifting the coding style in an on-demand way, so we can finally 
achieve to the new style mildly, if each time we're using the old coding 
style, that could be impossible.

> > I have no interest in reformatting the existing code and also think using it
> > to reformat an entire file shouldn't be encouraged, but, we can leverage
> > this tool to give future contributions a better experience. It's also
> > important to note that the kernel already has a ".clang-format" file, so I
> > think we can give it a try:)
>
> The mere action of introducing a .clang-format file in the root of the
> repository will cause some contributors' editors to automatically
> reformat files every time they are saved. IOW even if you don't want
> intend to do reformatting, that will be a net result.
>
> With regards,
> Daniel

I think that depends on developer's configuration, as far as I know, 
format on save is a feature which can be easily disabled on most of the 
IDE's, such as VSCode.