[QBS] RFC pkgconfig support

[Oswald Buddenhagen]

On Thu, Feb 23, 2012 at 10:19:08PM +0600, ext Ruslan Nigmatullin wrote:
> 23.02.2012, 21:38, "Joerg Bornemann" <joerg.bornemann at nokia.com>:
> > Allright. The user writes Depends { name: "foo" } into his project.

> > The module "foo" cannot be found in any search path.
>
no, just trigger the factories. see below.

> > What about rules that can be part of a module?
>
that's sort of irrelevant. remember that this about locating 3rd party
modules we know nothing about.

> May be we should use more declarative way? So the rules won't be a problem anyway
> 
good idea.

> ---pkg-config-module-factory.qbs---
> ModuleFactory {
> 	name: 'pkgconfig'
> 	property var binary: 'pkg-config'
> 
> 	Component {
>
better name that ModuleTemplate.

> 		name: "pkgconfigModule"
>
that's pointless.
but give it an id so you can refer to it.

> 		Module {
> 			property string packageName
> 			Depends { name: "cpp" }
> 			function packageProperty (property) {
> 				var p = new Process();
> 				p.start(binary, [ '--cflags', packageName ]
> 				return p.readAll();
> 			}
> 			cpp.cflags: packageProperty("--cflags");
> 			cpp.libs: packageProperty("--libs");
>
i wouldn't put any code here. you need to inject some properties anyway,
so you can inject all of them just as well.

> 		}
> 	}
> 
> 	createModule: {
> 		// Script that gets a module name.
> 		// The script creates module object on success,
> 		// returns undefined otherwise.
> 
nope. return true/false only. the module itself already comes from
instantiating the ModuleTemplate. then you also don't need to invoke magic
function to construct it.

> 		var p = new Process();
> 		var packageName = convertToPackage(moduleName);
> 		if (p.start(binary, ['--exists', packageName]) != 0)
> 		return undefined;
> 
> 		return pkgconfigModule.create({ "name": moduleName, "packageName": packageName });
>
theid.name = ...
...

> 	}
> }
> 
> > What happens if more than one module factory can generate a module
> > "foo"? Who wins? Do we add dependencies between module factories or
> > priorities?
> 
> Because all factories should provide similar module's data (If we want
> to build with system library usually there exists only one system
> library), simple priorities should be enough.
>
yes. see https://bugreports.qt-project.org/browse/QBS-61

> More interesting is the situation when interested library is not found
> at all. Would be there any way to write workarounds around it if user
> wants to make application still be possible to build?
> 
of course. i wouldn't call different configurations workarounds, even.

> Depends { name: "gstreamer"; relaxed: true }
>
the plan says that there should be Recommends and Suggests in addition
to Depends, so "relaxed" is not necessary.

> Group {
> 	condition: gstreamer.found
> 	files: [ "gstreamerbasedimpl.h", "gstreamerbasedimpl.cpp" ]
> 	cpp.defines: [ "HAVE_GSTREAMER" ]
> }
> 
something like that.