On 17 Aug 2015, at 08:21, Roland Haas <rhaas@aei.mpg.de> wrote:

Hello all,

This happens a lot.  It would be good to be able to put something
into the optionlist which told the MPI thorn that it should use an
auto-detected library, rather than building the library.

Most thorns support a XXX_DIR=NO_BUILD option which then (depends on the
thorn) may require you to actually specify the location of the libraries
or may still allow searching for it. Basically all auto-detection (with
the exception of MPI which also seems to fail here) should fail on
modern Debian/Ubuntu systems that support "multi-arch" installations
since the libraries are no longer in /usr/lib but in /usr/lib/x86-amd64
or so. Bruno was working on fixing this before the last release but the
results were too fragile to be included in the current release branch.

I know about the NO_BUILD option, but was under the impression that it doesn't do or mean what it appears to mean.   I can't find any evidence of this at the moment, but I thought there were at least some thorns which would attempt to build anyway, even if you had set NO_BUILD.  This would be the case if the thorn didn't know about the NO_BUILD option (external library handling is very nonuniform, with each library having to implement the same logic), but I thought it also happened for some thorns which did know about the option.  I might be misremembering though.