Extending ecm_generate_headers to create cross-forwarding headers?

[David Faure]

On Sunday 12 January 2014 23:04:03 Friedrich W. H. Kossebau wrote:
> Hi,
> 
> ecm_generate_headers currently only supports forwarding includes for classes
> which are declared in a matching class.h header. Just, in KF5 there are a
> few classes which are declared in non-matching classes. E.g. in KParts, if
> you grep for KPARTS_EXPORT, you will find some like that.
> 
> Worse, there were cross-forwarding (proper wording?) headers in
> kdelibs4/kde4support, so with just KF5::Parts some code will stop compiling,
> e.g. if it has
> #include <KParts/ReadOnlyPart>
> because KParts::ReadOnlyPart is declared in parts.h
> 
> Looking at Qt5 I still cross-forwarding headers, e.g.
> $ cat qt5/qtbase/include/QtWidgets/QVBoxLayout
> #include "qboxlayout.h"
> 
> I guess everyone agrees that just having to write
> #include <Class>
> or
> #include <Namespace/Class>
> without having to look in which header a class is really defined is very
> comfortable to have, right? So we would have to fix things.

Yes.

> Solutions:
> A) move any class declarations into proper class.h files
> For backward compatibility any moved class declarations would be substituted
> with a #include "class.h" at the old place, guarded by some #ifdef
> KDE4Support

Yes, this is what I did in a few places when converting everything to 
ecm_generate_headers.
(e.g. karchive, but also some others).
Seems I missed KParts.
Ah - I know why - that's one of the *two* frameworks out of 57 that I didn't 
port myself ;)

I think this solution is the easiest and the best one.
* easiest because no need to make ecm_generate_headers more complex
(honestly "cross forwarding" would mean nothing to me, without reading this 
entire email)
* best because it makes the source code clean. You look for a class in order 
to hack on it -> it's in <lowerclassname>.h

Qt doesn't do that in qboxlayout.h for old historical reasons, but does so in 
any newer code AFAIK.

-- 
David Faure, faure at kde.org, http://www.davidfaure.fr
Working on KDE, in particular KDE Frameworks 5