Re: [PATCH v2] configure: add support for pseudo-"in source tree" builds

[Daniel P . Berrangé]

On Thu, Aug 20, 2020 at 04:15:59PM -0500, Eric Blake wrote:
> On 8/20/20 12:31 PM, Daniel P. Berrangé wrote:
> > Meson requires the build dir to be separate from the source tree. Many
> > people are used to just running "./configure && make" though and the
> > meson conversion breaks that.
> > 
> > This introduces some backcompat support to make it appear as if an
> > "in source tree" build is being done, but with the the results in the
> > "build/" directory. This allows "./configure && make" to work as it
> > did historically, albeit with the output binaries staying under build/.
> 
> An observation:
> 
> If you already had out-of-tree builds, this does not change anything. You
> can do an incremental build, where a tree that builds pre-merge should
> continue to build incrementally with 'make -C dir' post-merge.
> 
> If you are used to in-tree builds, and do a fresh checkout, this lets you
> maintain the illusion of an in-tree build although binaries may be located
> differently than you are used to.
> 
> But if you do an incremental update to an in-tree build, this will cause
> some odd behaviors, starting with the git update:

snip.

> So I'm not sure why the first build gets as far as it does, but does NOT
> complete things and yet does not fail make, but my advice is that you should
> NOT try to an incremental build on in-tree build when crossing the meson
> epoch.  If you are a fan of in-tree convenience, you need a ONE-TIME
> distclean when pulling in these changes (the fact that you HAVE to clean up
> trace.h files to merge in the meson stuff should be a hint for that).  After
> that has been done, you can go back to pretending meson supports in-tree.

Yeah, I think that's something we'll have to live with. The amount of
extra complexity that would be required to try to make the incremental
build work across the meson introduction would be quite large. A more
efficient use of time is to just clean the dir manually, rather than
debugging some makefile rules that will only be needed once.

Regards,
Daniel
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