setup: add support for sassc sass compiler (#13515)

setup.py

@@ -10,6 +10,8 @@ import tempfile
 import xml.etree.ElementTree as ET
 
 from distutils.cmd import Command
+from distutils.errors import CompileError
+from distutils.spawn import find_executable
 from setuptools.command.install_lib import install_lib as _install_lib
 from distutils.command.build import build as _build
 from distutils.command.sdist import sdist
@@ -87,6 +89,14 @@ class compile_scss(Command):
         pass
 
     def run(self):
+        sass_bin = None
+        for program in ('sass', 'sassc'):
+            sass_bin = find_executable(program)
+            if sass_bin:
+                break
+        if not sass_bin:
+            raise CompileError('A sass compiler is required but none was found.  See sass-lang.com for choices.')
+
         for package in self.distribution.packages:
             for package_path in __import__(package).__path__:
                 for path, dirnames, filenames in os.walk(package_path):
@@ -95,8 +105,8 @@ class compile_scss(Command):
                             continue
                         if filename.startswith('_'):
                             continue
-                        subprocess.check_call(['sass', '%s/%s:%s/%s' % (
-                            path, filename, path, filename.replace('.scss', '.css'))])
+                        subprocess.check_call([sass_bin, '%s/%s' % (path, filename),
+                            '%s/%s' % (path, filename.replace('.scss', '.css'))])
 
 
 class build_icons(Command):