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Re: [libtool] make install fails after an incremental build after a pref

From: Kees-Jan Dijkzeul
Subject: Re: [libtool] make install fails after an incremental build after a prefix change?
Date: Wed, 30 Dec 2015 09:51:19 +0100

On Tue, Dec 29, 2015 at 9:14 PM, Gavin Smith <address@hidden> wrote:
> You want not to rebuild files that don't need to be rebuilt.

Although I tend to agree, we may differ on opinion on the importance
of this. I'd argue that it is much more important to not forget
rebuilding files that actually needed to be rebuilt. The only good
thing I can say about the current behaviour is that, at least, it is
not failing silently.

> Depending
> on config.h doesn't achieve this: any source files including it will
> have to be compiled again. If most of the source files do include
> config.h, they'll all be rebuilt and it won't be much quicker to avoid
> running "make clean" first.

I'm not suggesting to solve this particular problem using config.h. I
was merely pointing it out as a precedent where the autotools do their
best to manage dependencies. It is also an example of where autotools
err on the side of safety. If only one setting changes in config.h,
all files that depend on it are rebuilt, regardless of whether they
depend on that particular setting. It defaults to doing too much, and
this is a good thing.

> Running configure changes the Makefile, and I believe that this is a
> difficult problem to solve to know what has to be rebuilt in this
> case.

Then I'd propose to err on the side of safety again, and rebuild everything :-)

Note, though, that in my particular case, rebuilding everything is not
required. It seems sufficient to just re-link everything. Normally,
compling takes much longer than linking, so relinking everything when
the Makefile changes should be much faster than doing a clean build.



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