Testing SCons + Fortran

This repo contains some basic examples which test if SCons is working properly for Fortran compilation.

Prerequisites

A fortran compiler. You would need GNU Fortran or Intel Fortran installed on your system.

A virtual environment with SCons. With your preferred Python interpreter do this: Linux or MacOS

python -m venv venv
. ./venv/bin/activate
pip install scons

Windows

python -m venv venv
.\venv\Scripts\activate
pip install scons

Fortran Code

The source code is divided into three modules:

• main_prog.f The main program in a fixed form file. Depends on module_one and module_two.
• module_one.f90 A Fortran module containing two public functions, in free form, depends on module_two.
• module_two.f90 A Fortran module continaing a public function, in free form

Identical source code is in the TestFlat and TestSConscript directories.

TestFlat

Here the Fortran files are all in one directory and can be compiled using different SConstruct files:

• SConstruct Uses the DefaultEnvironment to build the Program
• SConstruct_gfortran2 Defines an Environment, passing the tools, to build the Program
• SConstruct_gfortran3 Uses the DefaultEnvironment but reverses the order of the source files.

TestSConscript

Here the content from the SConstruct files from the TestFlat directory are moved into SConscript files. The code in this area can be built in two different ways:

1. Individual SConstruct files that process the corresponding SConscript file.
2. A single SConstruct file that uses variant_dir for each.

Issues

I tried everything here with the scons repo checked out locally and ran pip install -e . into the virtual environment:

dnwillia@comp scons % which python
/Users/dnwillia/Developer/SConsTests/venvmain/bin/python
dnwillia@comp scons % ls    
CHANGES.txt             README-SF.rst*          SCons/                  lgtm.yml                runtest.py*             src/
CONTRIBUTING.rst        README-local            SConstruct              packaging/              scripts/                template/
LICENSE                 README-package.rst*     bench/                  pyproject.toml          setup.cfg               test/
LICENSE-local           README.rst*             bin/                    requirements-dev.txt    setup.py                testing/
MANIFEST.in             RELEASE.txt             bootstrap.py*           requirements-pkg.txt    shippable.yml           timings/
NEWS.d/                 ReleaseConfig*          doc/                    requirements.txt        site_scons/
dnwillia@comp scons % pip install -e .
Obtaining file:///Users/dnwillia/Developer/scons
  Installing build dependencies ... done
  Checking if build backend supports build_editable ... done
  Getting requirements to build editable ... done
  Installing backend dependencies ... done
  Preparing editable metadata (pyproject.toml) ... done
Requirement already satisfied: setuptools in /Users/dnwillia/Developer/SConsTests/venvmain/lib/python3.11/site-packages (from SCons==4.5.2) (65.5.0)
Building wheels for collected packages: SCons
  Building editable for SCons (pyproject.toml) ... done
  Created wheel for SCons: filename=SCons-4.5.2-0.editable-py3-none-any.whl size=6702 sha256=c976e86bd3f9adc8c8033b7e8aac87eb12c5708635a3e1205445aa51fd7e8448
  Stored in directory: /private/var/folders/v_/6ksn5x2x6lzf3chrr8c9qrq80000gp/T/pip-ephem-wheel-cache-p1w1z26u/wheels/64/d0/41/73382133e4e90272845a07e0405b5aff6a4e818d1e0a48c056
Successfully built SCons
Installing collected packages: SCons
Successfully installed SCons-4.5.2
dnwillia@comp scons % which scons
/Users/dnwillia/Developer/SConsTests/venvmain/bin/scons
dnwillia@comp scons % scons --version
SCons by Steven Knight et al.:
        SCons: v4.5.2.b3744e8862927899e3d0ebcb41297f9b4c142c63, Sun, 04 Jun 2023 15:36:48 -0700, by bdbaddog on M1Dog2021
        SCons path: ['/Users/dnwillia/Developer/scons/SCons']
Copyright (c) 2001 - 2023 The SCons Foundation

• None of this code builds out of the box at all on Windows. The ifort tool does not configure properly even if you have it pre-configured in the environment.

• For gfortran + MacOS/Linux a modified gfortran.py tool is required. Specific issues are highlighted below.

• On MacOS the aliases for f77, f90, f95, etc... are not provided. This seems to cause an issue with the FORTRAN construction variable which ends up defaulting to f77 and that does not exist on MacOS. The modified gfortran.py module in the site_tools area forces FORTRAN=gfortran to get it working. None of the code will build on MacOS and without the modifiations to the tool this is the error:

dnwillia@comp TestFlat % scons -f SConstruct_gfortran1
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
f77 -o main_prog.o -c main_prog.f
sh: f77: command not found
scons: *** [main_prog.o] Error 127
scons: building terminated because of errors.
dnwillia@comp TestFlat % 

• Building code with fortran modules does not work right with variant_dir. You need to set the location where fortran modules (.mod) get generated otherwise they get stored into the same directory as the SConstruct. Setting the module output location to be the same as the object file target at this line of code ensures the .mod files are produced into the variant_dir. Passing --warn=all shows the issue:

dnwillia@comp SConsTests % scons -f SConstructVariant --warn=all
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
gfortran -o TestSConscript/builds1/darwin/module_two.o -c TestSConscript/builds1/darwin/module_two.f90

scons: warning: Cannot find target TestSConscript/builds1/darwin/module_two.mod after building
File "/Users/dnwillia/Developer/SConsTests/venv/bin/scons", line 8, in <module>
gfortran -o TestSConscript/builds1/darwin/module_one.o -c TestSConscript/builds1/darwin/module_one.f90

The warning is generated because the .mod file is generated into the cwd where scons is called.

• Building code with fortran modules does not seem to work properly when using variant_dir and duplicate=False. See SConscriptVariant2. You get the build error below, note the warning reporting that no dependency information is generated for module_two.

dnwillia@comp SConsTests % scons -f SConstructVariant --warn=all
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
gfortran -o TestSConscript/builds1/darwin/module_two.o -c -JTestSConscript/builds1/darwin TestSConscript/builds1/darwin/module_two.f90
gfortran -o TestSConscript/builds1/darwin/module_one.o -c -JTestSConscript/builds1/darwin TestSConscript/builds1/darwin/module_one.f90
gfortran -o TestSConscript/builds1/darwin/main_prog.o -c -JTestSConscript/builds1/darwin TestSConscript/builds1/darwin/main_prog.f
gfortran -o TestSConscript/builds1/darwin/main_prog.exe TestSConscript/builds1/darwin/module_one.o TestSConscript/builds1/darwin/module_two.o TestSConscript/builds1/darwin/main_prog.o

scons: warning: No dependency generated for file: module_two.mod (referenced by: TestSConscript/module_one.f90) -- file not found
File "/Users/dnwillia/Developer/SConsTests/venv/bin/scons", line 8, in <module>
gfortran -o TestSConscript/builds2/darwin/module_one.o -c -JTestSConscript/builds2/darwin TestSConscript/module_one.f90
TestSConscript/module_one.f90:2:7:

    2 |   use module_two
      |       1
Fatal Error: Cannot open module file 'module_two.mod' for reading at (1): No such file or directory
compilation terminated.
scons: *** [TestSConscript/builds2/darwin/module_one.o] Error 1
scons: building terminated because of errors.