Re: [Xen-devel] [Qemu-ppc] [PATCH] qemu: include generated files with <> and not ""

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

On Wed, Mar 21, 2018 at 01:29:53PM +0000, Daniel P. Berrangé wrote:
> On Wed, Mar 21, 2018 at 03:08:36PM +0200, Michael S. Tsirkin wrote:
> > On Wed, Mar 21, 2018 at 08:16:00AM +0100, Thomas Huth wrote:
> > > On 20.03.2018 13:05, Michael S. Tsirkin wrote:
> > > > On Tue, Mar 20, 2018 at 09:58:23AM +0100, Laurent Vivier wrote:
> > > >> Le 20/03/2018 à 02:54, Michael S. Tsirkin a écrit :
> > > >>> QEMU coding style at the moment asks for all non-system
> > > >>> include files to be used with #include "foo.h".
> > > >>> However this rule actually does not make sense and
> > > >>> creates issues for when the included file is generated.
> > > >>
> > > >> If you change that, we can have issue when a system include has the 
> > > >> same
> > > >> name as our local include. With "<FILE>", system header are taken 
> > > >> first.
> > > > 
> > > > Are you sure? I just tested and that is not the case with
> > > > either gcc or clang.
> > > > 
> > > >>> In C, include "file" means look in current directory,
> > > >>> then on include search path. Current directory here
> > > >>> means the source file directory.
> > > >>> By comparison include <file> means look on include search path.
> > > >>
> > > >> Not exactly, there is the notion of "system header" too.
> > > >>
> > > >> https://gcc.gnu.org/onlinedocs/cpp/Include-Syntax.html
> > > >>
> > > >> #include <file>
> > > >> This variant is used for system header files. It searches for a file
> > > >> named file in a standard list of system directories. You can prepend
> > > >> directories to this list with the -I option (see Invocation).
> > > > 
> > > > This is exactly what we do.
> > > > 
> > > >> #include "file"
> > > >> This variant is used for header files of your own program. It searches
> > > >> for a file named file first in the directory containing the current
> > > >> file, then in the quote directories and then the same directories used
> > > >> for <file>. You can prepend directories to the list of quote 
> > > >> directories
> > > >> with the -iquote option.
> > > > 
> > > > Since we do not use -iquote, "" just adds the current directory.
> > > 
> > > So why don't we simply switch to use -iquote instead of -I for adding
> > > search paths for our own headers? We then would get a clean separation
> > > of QEMU headers from system headers.
> > > 
> > >  Thomas
> > 
> > It still leaves us with a host of problems e.g. the problem of stale
> > headers in the source directory.
> 
> We have a patch on list which effectively solves the problem of stale
> generated files in source directory, so that's largely a non-issue at
> this point IMHO.
> 
> Regards,
> Daniel

That was just one, and the solution is just to fail build.
I think we can strive to address at least some of the following:
- make sure that an incorrect use of a header fails to build
- make it easier for new developers to understand the codebase
- build correctly rather than fail in as many configurations as possible
- actually support a mix of in and out of tree builds

I think my patch under discussion does not address all issues here.
I'll post a new proposal now.

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