[CMake] choosing specific version of a library with find_package (i.e. choosing macports in /opt/local over system default in /usr)

[Andreas Mohr]

Hi,

On Tue, Jun 05, 2012 at 11:11:44AM -0400, cmake-request at cmake.org wrote:
> Date: Mon, 4 Jun 2012 17:01:34 -0700
> From: Natalie Tasman <natalie.tasman at insilicos.com>
> I'm writing a CMakeLists.txt file, and I'm having problems getting
> find_package to choose libraries under /opt/local rather than
> /usr/local.  Specifically, I've installed libarchive using macports
> and CMake cannot find it.  When CMake configuration finds the the
> library in /usr/lib (/usr/lib/libarchive.dylib) but no corresponding
> header, it fails, and I would like to find a way to tell CMake to fall
> back to /opt/local, where a version of the library as well as the
> archive.h header is installed.

I believe that this is covered by the (now very lengthy)
description of find_package() in man cmakecommands
(or, to mention the main one-stop docs solution,
"cmake --help-command find_package").
You possibly need to set (well, probably _extend_)
CMAKE_PREFIX_PATH or CMAKE_FRAMEWORK_PATH, probably in outer shell environment
(or perhaps only on CMake script side, should work fine, too).

[[background explanation:
I believe the deeper intention behind these global-switch mechanisms
is to let the user manually specify which specific architecture
a build should be done for, i.e. you could have a full toolchain/library set
for a specific embedded architecture (ARM, MIPS, ..., i.e. NOT
compatible with the usually activated x86 libraries on your CMake setup),
and by properly predefining these settings (which for special platforms
should probably be cleanly carried out in user-custom CMake Platform setup
files?), CMake knows which library paths to reference (i.e. below which
PREFIX[es]).]]

I've actually successfully done the same thing on my Mac setup
(where things provided by e.g. macports/Fink/... need to be referenced additionally),
and I've simply extended configuration in the script file that
holds all my main config settings of the project (sorry,
cannot provide code at the moment).
(ok, well, in fact I think it's indeed preferable to extend these things
on script side rather than shell side, since many users would fail
to *manually* set up shell side config correctly, and after all
the project config itself knows best what it needs on certain platforms).

> Solutions tried I've so far: Based on other related posts, I've tried
> things like declaring INCLUDE_DIRECTORIES(/opt/local/include) and

BTW CMake >= 2.8.8 (AFAIR) now finally has a target-specific (i.e.
non-directory scope) INCLUDE_DIRECTORIES property for specifying these
things. 

HTH,

Andreas Mohr