Better default behavior for building the Matlab toolbox with SCons

If Matlab is found on the path, build the toolbox by default,
otherwise skip it. If the toolbox is required and Matlab can't be
found, exit with an error.

SConstruct

@@ -33,7 +33,7 @@ opts.AddVariables(
                  '', PathVariable.PathAccept),
     PathVariable('cantera_python_home', 'where to install the python package',
                  '', PathVariable.PathAccept),
-    EnumVariable('matlab_toolbox', '', 'n', ('y', 'n', 'default')),
+    EnumVariable('matlab_toolbox', '', 'default', ('y', 'n', 'default')),
     PathVariable('matlab_cmd', 'Path to the matlab executable',
                  'matlab', PathVariable.PathAccept),
     BoolVariable('f90_interface', 'Build Fortran90 interface?', False),
@@ -154,6 +154,19 @@ if env['python_package'] in ('full','default'):
             warnNoPython = True
             env['python_package'] = 'minimal'
 
+
+if env['matlab_toolbox'] == 'y' and which(env['matlab_cmd']) is None:
+    print """ERROR: Unable to find the Matlab executable '%s'""" % env['matlab_cmd']
+    sys.exit(1)
+elif env['matlab_toolbox'] == 'default':
+    cmd = which(env['matlab_cmd'])
+    if cmd is not None:
+        env['matlab_toolbox'] = 'y'
+        print """INFO: Building the Matlab toolbox using '%s'""" % cmd
+    else:
+        print """INFO: Skipping compilation of the Matlab toolbox. """
+
+
 # **************************************
 # *** Set options needed in config.h ***
 # **************************************
@@ -337,10 +350,18 @@ inst = env.Install('$ct_bindir', pjoin('bin', 'exp3to2.sh'))
 installTargets.extend(inst)
 
 ### Meta-targets ###
-build_cantera = Alias('build', buildTargets)
 build_demos = Alias('demos', demoTargets)
 
-Default(build_cantera)
+def postBuildMessage(target, source, env):
+    print "**************************************************************"
+    print "Compiliation complete. Type '[sudo] scons install' to install."
+    print "**************************************************************"
+
+finish_build = env.Command('finish_build', [], postBuildMessage)
+env.Depends(finish_build, buildTargets)
+build_cantera = Alias('build', finish_build)
+
+Default('build')
 
 def postInstallMessage(target, source, env):
     v = sys.version_info

buildutils.py

@@ -102,6 +102,25 @@ def psplit(s):
     return path
 
 
+def which(program):
+    """ Replicates the functionality of the 'which' shell command """
+    import os
+    def is_exe(fpath):
+        return os.path.exists(fpath) and os.access(fpath, os.X_OK)
+
+    fpath, fname = os.path.split(program)
+    if fpath:
+        if is_exe(program):
+            return program
+    else:
+        for path in os.environ["PATH"].split(os.pathsep):
+            exe_file = os.path.join(path, program)
+            if is_exe(exe_file):
+                return exe_file
+
+    return None
+
+
 # This tool adds the builder:
 #
 #   env.RecursiveInstall(target, path)