scons: Replace the extname property with os.path.splitext().

This is almost exactly the same, except it leaves the "." on the
extension, and returns an empty string instead of None if there is no
extension.

Change-Id: Idb540771007f9f7ca8aafdb09512eb1219010237
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48122
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>

src/SConscript

@@ -43,6 +43,7 @@ import distutils.spawn
 import functools
 import imp
 import os
+import os.path
 import re
 import sys
 import zlib
@@ -281,15 +282,6 @@ class SourceFile(object, metaclass=SourceMeta):
     def basename(self):
         return basename(self.filename)
 
-    @property
-    def extname(self):
-        index = self.basename.rfind('.')
-        if index <= 0:
-            # dot files aren't extensions
-            return self.basename, None
-
-        return self.basename[:index], self.basename[index+1:]
-
     def __lt__(self, other): return self.filename < other.filename
     def __le__(self, other): return self.filename <= other.filename
     def __gt__(self, other): return self.filename > other.filename
@@ -386,8 +378,8 @@ class PySource(SourceFile):
         '''specify the python package, the source file, and any tags'''
         super(PySource, self).__init__(source, tags, add_tags)
 
-        modname,ext = self.extname
-        assert ext == 'py'
+        modname, ext = os.path.splitext(self.basename)
+        assert ext == '.py'
 
         if package:
             path = package.split('.')
@@ -472,8 +464,8 @@ class ProtoBuf(SourceFile):
             error('Got protobuf to build, but lacks support!')
 
         # Get the file name and the extension
-        modname,ext = self.extname
-        assert ext == 'proto'
+        modname, ext = os.path.splitext(self.basename)
+        assert ext == '.proto'
 
         self.cc_file, self.hh_file = env.ProtoBufCC(source=source)