If the package suite was given (e.g. DUNE_ROOT=/blum), then the code
set up the root for each individual package automatically (e.g.
DUNE_COMMON_ROOT=/blum/dune-common), but the path which was then
activated did not get the local build sub-directory (e.g. if we are
building opm-autodiff in /frub/opm-autodiff/build, then the local
build directory is "build/"), and thus this was not appended to the
library search path. The result was that the source was found (because
the root pointed to a valid source tree), but the library was not
(because it is "hidden" in the subdirectory).
Some packages are split up in several library files, where each of them
doesn't have their own CMake find-module. So we cannot put this list in
the prerequisites. Unlike the headers, where we just add the directory,
all the libraries must be explicitly named on the link line. Thus, we
should allow to specify more than one name in the lib parameter.
The first name specified is designated as the "primary" library and is
assigned to the _LIBRARY variable; the others occur in _LIBRARIES as if
they were prerequisites.
Note that the build system cannot replicate this setup itself; it always
assumes that we are building (at most) one library from the source
files.
Header and library directory may be specified separately by using the
variables e.g. OPM_CORE_INCLUDE_DIR and OPM_CORE_LIB_DIR. These override
even the OPM_CORE_ROOT. This allows us to use a backported version which
uses versioned directory names.
v2: incorporate Roland's nitpicks (I hope)
v3: It was decided that it's better to change the default behavior
v4: make sure the CMake syntax is correct even if the value of the
variable contains spaces (if it contains double quotes it's a
different matter, but that's pretty much a corner case, IMHO)
v5: properly escape backslash and double quote characters in the cmake
syntax
Boost does not set the BOOST_FOUND variable to indicate that the
package is found (as it would if it had used the usual routine
find_package_handle_standard_args), but rather Boost_FOUND. This
patch tests for that condition, and print some more helpful debug
messages if a prerequisite is missing.
If an optional package require further packages, those packages should
not be marked as REQUIRED because CMake will then terminate the
configuration if it is not found (although it is transitively optional).
Conversely, we should be able to specify REQUIRED prerequisites for
REQUIRED packages and have a failure cascade up to termination.
This changeset allows us to specify REQUIRED or not in the list of
prerequisites, and have OpmPackage sort of whether it should be honored
or not.
