scheme: move the drive letter checking in its own function

This help the readability of the main function as is was taking much more room
than the main logic.

hgext/schemes.py

@@ -119,23 +119,24 b' schemes = {'
 }
 
 
-def extsetup(ui):
-    schemes.update(dict(ui.configitems(b'schemes')))
-    t = templater.engine(templater.parse)
-    for scheme, url in schemes.items():
+def _check_drive_letter(scheme):
+    """check if a scheme conflict with a Windows drive letter"""
         if (
             pycompat.iswindows
             and len(scheme) == 1
             and scheme.isalpha()
             and os.path.exists(b'%s:\\' % scheme)
         ):
-            raise error.Abort(
-                _(
-                    b'custom scheme %s:// conflicts with drive '
-                    b'letter %s:\\\n'
-                )
-                % (scheme, scheme.upper())
-            )
+        msg = _(b'custom scheme %s:// conflicts with drive letter %s:\\\n')
+        msg %= (scheme, scheme.upper())
+        raise error.Abort(msg)
+
+
+def extsetup(ui):
+    schemes.update(dict(ui.configitems(b'schemes')))
+    t = templater.engine(templater.parse)
+    for scheme, url in schemes.items():
+        _check_drive_letter(schemes)
         url_scheme = urlutil.url(url).scheme
         if url_scheme in hg.peer_schemes:
             hg.peer_schemes[scheme] = ShortRepository(url, scheme, t)