The verification program entry point (main) is defined in a C source
file, so the C compiler should be used to link when only Fortran and C
are involved. The C++ compiler should still be used when the CXX option
is enabled.
This function builds a simple test project using a combination of
Fortran and C (and optionally C++) to verify that the compilers are
compatible. The idea is to help projects report very early to users
that the compilers specified cannot mix languages.
We split the main detection logic into a Detect.cmake support module and
load it only when detection results are not already available. This
allows results computed by the main project to be used in try-compile
projects without recomputing them. The call to try_compile() need only
to pass FortranCInterface_BINARY_DIR through the CMAKE_FLAGS option.
This is a new FortranCInterface.cmake module to replace the previous
prototype. All module support files lie in a FortranCInterface
directory next to it.
This module uses a new approach to detect Fortran symbol mangling. We
build a single test project which defines symbols in a Fortran library
(one per object-file) and calls them from a Fortran executable. The
executable links to a C library which defines symbols encoding all known
manglings (one per object-file). The C library falls back to the
Fortran library for symbols it cannot provide. Therefore the executable
will always link, but prefers the C-implemented symbols when they match.
These symbols store string literals of the form INFO:symbol[<name>] so
we can parse them out of the executable.
This module also provides a simpler interface. It always detects the
mangling as soon as it is included. A single macro is provided to
generate mangling macros and optionally pre-mangled symbols.
Brad King
Bill Hoffman