[SCons] Use pathlib to write combined License file

Use a dictionary to collect the license file paths and names. This data
structure is more natural for this mapping of packages to files. It also
simplifies the loop to collect the files.

ext/SConscript

@@ -1,11 +1,12 @@
+from pathlib import Path
 from buildutils import *
 
 Import('env', 'build', 'install', 'libraryTargets')
 localenv = env.Clone()
 copyenv = localenv.Clone() # no CPPPATH addition, to avoid circular dependencies
 
-license_files = [('Cantera', '#License.txt'),
-                 ('Libexecstream', 'libexecstream/doc/license.txt')]
+license_files = {"Cantera": File("#License.txt"),
+                 "Libexecstream": File("#ext/libexecstream/doc/license.txt")}
 
 def prep_default(env):
     localenv = env.Clone()
@@ -45,7 +46,7 @@ for subdir, extensions, prepFunction in libs:
 ext_copies = []
 
 if not env['system_fmt']:
-    license_files.append(('fmtlib', 'fmt/LICENSE.rst'))
+    license_files["fmtlib"] = File("#ext/fmt/LICENSE.rst")
     localenv = prep_default(env)
     localenv.Prepend(CPPPATH=Dir('#ext/fmt/include'))
     libraryTargets.extend(
@@ -61,7 +62,7 @@ if env['system_sundials'] == 'n':
     localenv = prep_default(env)
     localenv.Prepend(CPPPATH=[Dir('#include/cantera/ext'),
                               Dir('#ext/sundials/src/sundials')])
-    license_files.append(('Sundials', 'sundials/LICENSE'))
+    license_files["Sundials"] = File("#ext/sundials/LICENSE")
 
     # Generate sundials_config.h
     sundials_configh = {}
@@ -99,7 +100,7 @@ if env['system_sundials'] == 'n':
 if not env['system_yamlcpp']:
     localenv = prep_default(env)
     localenv.Prepend(CPPPATH=Dir('#include/cantera/ext'))
-    license_files.append(('YAML-CPP', 'yaml-cpp/LICENSE'))
+    license_files["YAML-CPP"] = File("#ext/yaml-cpp/LICENSE")
 
     # Copy header files into common include directory
     for subdir in ('', 'contrib', 'node', 'node/detail'):
@@ -119,7 +120,7 @@ if not env['system_yamlcpp']:
 
 
 if not env['system_eigen']:
-    license_files.append(('Eigen', 'eigen/COPYING.MPL2'))
+    license_files["Eigen"] = File("#ext/eigen/COPYING.MPL2")
     h = build(copyenv.Command('#include/cantera/ext/Eigen', '#ext/eigen/Eigen',
                               Copy('$TARGET', '$SOURCE')))
     copyenv.Depends(copyenv['config_h_target'], h)
@@ -136,28 +137,33 @@ if env['googletest'] == 'submodule':
 
 env["ext_include_copies_target"] = build(ext_copies)
 
-# Create license file containing licenses for Cantera and all included packages
+
 def generate_license(target, source, env):
-    stars = '*'*50 + '\n' + '*'*50 + '\n'
-    tpl = stars + 'The following license applies to {}\n' + stars + '\n{}\n'
+    target = Path(target[0].abspath)
+    stars = "*" * 50 + "\n" + "*" * 50 + "\n"
+    tpl = stars + "The following license applies to {}\n" + stars + "\n{}\n"
 
     license = []
-    for (package,_),filename in zip(license_files, source):
-        license.append(tpl.format(package, open(filename.path).read().strip()))
+    for package, license_file in env["license_files"].items():
+        license_file = Path(license_file.abspath)
+        license.append(tpl.format(package, license_file.read_text().strip()))
+    license = "\n".join(license)
+    if target.suffix == ".rtf":
+        license = license.replace("\\", "\\\\").replace("{", "\\{").replace("}", "\\}")
+        license = license.replace("\n", " \\par\n")
+        license = (r"{\rtf1\ansi{\fonttbl\f0\fswiss Arial;}\f0\pard\fs16 "
+                   + license + "}")
 
-    license = '\n'.join(license)
-    if target[0].path.endswith('.rtf'):
-        license = license.replace('\\', '\\\\').replace('{', '\\{').replace('}', '\\}')
-        license = license.replace('\n', ' \\par\n')
-        license = r'{\rtf1\ansi{\fonttbl\f0\fswiss Arial;}\f0\pard\fs16 ' + license + '}'
+    target.write_text(license)
 
-    open(target[0].path, 'w').write(license)
 
-license = build(localenv.Command('LICENSE.txt', [x[1] for x in license_files],
+localenv["license_files"] = license_files
+license = build(localenv.Command("LICENSE.txt", license_files.values(),
                                  generate_license))
+env["license_target"] = license
 install('$inst_docdir', license)
 
 if env['OS'] == 'Windows':
     # RTF version is required for Windows installer
-    build(localenv.Command('LICENSE.rtf', [x[1] for x in license_files],
+    build(localenv.Command("LICENSE.rtf", license_files.values(),
                            generate_license))