[oe] [OE-core] [RFC][PATCH] cmake: respect ${S} and ${B}

[Martin Jansa]

On Thu, Dec 05, 2013 at 10:10:02AM +0000, Richard Purdie wrote:
> On Thu, 2013-12-05 at 00:38 +0000, Ross Burton wrote:
> > Hi,
> > 
> > This is a Request For Comments because it changes behaviour of the cmake class
> > and I'm not entirely knowledgeable in cmake.
> > 
> > For some reason, cmake.bbclass doesn't use ${S} and ${B}, but instead has it's
> > own variables OECMAKE_SOURCEPATH ("." by default) and OECMAKE_BUILDPATH ("" by
> > default).  Those defaults meant that the build happened in the source directory,
> > which conveniently was ${S}.  Unless ${B} was also set, in which case it all
> > broke.
> > 
> > I don't see a good reason for cmake.bbclass having it's own special versions of
> > ${S} and ${B}, so this patch drops them and replicates some of the logic in
> > autotools.bbclass: specifically the part where if ${S} and ${B} are different,
> > delete ${B} before building.  This ensures that switching machine doesn't re-use
> > the same build directory, which was the cause of me going back to look at this
> > (libproxy trying to use the nuc sysroot when I'm building for qemux86-64).
> > 
> > Some open questions:
> > 
> > 1) As I understand it cmake has more reliable support for out-of-tree builds
> > than autotools.  If this is the case should cmake.bbclass set B ?=
> > "${WORKDIR}/build", or leave setting of B to separatebuilddir.inc?  Are there
> > known recipes using cmake that fail with out-of-tree builds?
> 
> separatebuilddir.inc was really a stopgap solution to see how widespread
> potential issues were. Ideally I'd like to get to the point where
> recipes flag themselves are broken with out of tree builds rather than
> having a list of ones which are compatible.
> 
> Doing this for OE-Core is straightforward now but what about meta-oe?
> 
> Would there be interest in trying to change that default or is it going
> to be too painful?

It would be nice to change it in smaller steps, e.g. by bbclasses.

I'm already using separate B by default in meta-qt5 and it works good.

Adding it in cmake, qmake4, then autotools.bbclass, then ... would allow
to fix meta-oe recipes in smaller chunks instead of trying to fix them
all at once. And if we change it only for few .bbclasses then it would
still be improvement.

> This means I'm in favour of changing the cmake default if we can, it
> looks like a simpler problem space than autotools.bbclass

-- 
Martin 'JaMa' Jansa     jabber: Martin.Jansa at gmail.com
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