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

[Daniel P . Berrangé]

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.

> > 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).
> 
> #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.
> 
> > As generated files are not in the search directory (unless the build
> > directory happens to match the source directory), it does not make sense
> > to include them with "" - doing so is merely more work for preprocessor
> > and a source or errors if a stale file happens to exist in the source
> > directory.
> 
> I agree there is a problem with stale files. But linux, for instance,
> asks for a "make mrproper" to avoid this.

We can follow what autoconf does, and add a check to configure to see if
there are generated files left in the source dir, when configuring with
builddir != srcdir, and exit with error, telling user to clean their
src dir first.

> > This changes include directives for all generated files, across the
> > tree. The idea is to avoid sending a huge amount of email.  But when
> > merging, the changes will be split with one commit per file, e.g. for
> > ease of bisect in case of build failures, and to ease merging.
> > 
> > Note that should some generated files be missed by this tree-wide
> > refactoring, it isn't a big deal - this merely maintains the status quo,
> > and this can be addressed by a separate patch on top.
> > 
> > Signed-off-by: Michael S. Tsirkin <address@hidden>
> 
> I think your idea conflicts with what Markus has started to do:

Yes, I don't think we should revert what Markus started.   Both ways of
referencing QEMU headers have downsides, but I think "..." has fewer
downsides that "<....">.

The problem Michael is tackling should be pretty rare, because moist
developers aren't frequently switching between srcdir==builddir and
srcdir!=biulddir setups - they have their preference for which to use
and stick with it. As long as we get ./configure to warn about the
dirty srcdir it should be good enough

Regards,
Daniel
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