Packaging:Fortran

This is a draft document

This document is loosely based on the Fortran library draft and the Fortran modules directory guideline. It is supposed to replace both of them, due to the bug in the Fortran modules directory guidelines.

Introduction

FORTRAN [1] (short for FORmula TRANslator) was the first programming language ever, invented in 1957 and standardized in 1966. The Fortran 77 standard introduced improved support for structured programming such as if clauses.

Fortran natively handles matrices and is rather easy to program and for these reasons it was widely adopted in the scientific community. Due to the large amount of legacy code, Fortran is still widely used in computational science. Some modernization has taken place, though.

Fortran 90 presented a modernization of the language to support among others dynamic memory allocation, free-form source input and an argument passing mechanism to support compile time interface checking. Fortran 95 introduced many useful features such as vectorization constructs for high performance computing.

The Fortran 2003 standard added e.g. access to command line arguments and environment variables. The current standard under development is Fortran 2008.

Modules and include files

The fortran modules files, ending in .mod are files describing a fortran 90 (and above) module API and ABI. These are not like C header files describing an API, they are compiler dependent and arch dependent, and not easily readable by a human being. They are nevertheless searched for in the includes directories by gfortran (in directories specified with -I).

Due to the ABI specificity, the module directory used must be architecture specific. In addition each gfortran release (e.g. from 4.4 to 4.5) may lead to an incompatible change in the .mod files, therefore mass rebuilds of Fortran packages must take place when gfortran is updated.

Fortran can also use include files, similar to C headers. Common used filename suffixes are '.inc' and '.h', although '.fh' has been used for files that are designed to function as public headers.

Packaging of Fortran programs

Fortran programs in Fedora MUST be compiled, if possible, using the default Fortran compiler in Fedora, 'gfortran'. As usual, standard Fedora optimization flags %{optflags} MUST be used in the compilation.

Fortran include files MUST be placed in the standard include directory: either directly in %{_includedir}, or if headers have general names or upstream recommends having an own directory, in e.g. %{_includedir}/%{name}.

As Fortran modules are architecture and GCC version specific, they MUST be placed into %{_fmoddir} (or its package-specific subfolder in case the modules have generic names), which is owned by 'gcc-gfortran'. For directory ownership any packages containing Fortran modules MUST Requires: gcc-gfortran%{_isa}.

To use the modules in the Fortran module directory, one needs to add -I%{_fmoddir} to the compiler flags (this is already included in FFLAGS used by %configure).

Required changes

Packages that contain modules in the wrong place must be found and fixed (e.g. find all packages that BR: gcc-gfortran and contain '.mod' files).

The module files depend on the used compiler version and the architecture. The versioning should not matter, as mass rebuilds are done anyway whenever GCC is updated to a newer version. It is important, however, if there are multiple Fortran compilers present on the system.

• If it is decided to keep using an unversioned, multilib compatible %{_fmoddir}, the gcc-gfortran package must be changed to own %{_fmoddir} and all package containing modules must Requires: gcc-gfortran.
• If it is decided to use a GCC-versioned %{_fmoddir}, the preexisting %{_fmoddir} macro in redhat-rpm-macros must be changed from %{_libdir}/gfortran/modules to /usr/lib/gcc/<target>/<version>/finclude which is already used and owned by gfortran. After that a mass rebuild of all packages containing Fortran modules must be performed.