Make swift-format default True on Mac hosts

Also make swift lint strict to catch every formatting errors.

Bug: 1263872
Change-Id: Ie717c1f03ec1a0257cafceecc2055767d0be2077
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3605589
Reviewed-by: Brian Ryner <bryner@google.com>
Auto-Submit: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Gavin Mak <gavinmak@google.com>

git_cl.py

@@ -5168,7 +5168,7 @@ def _RunSwiftFormat(opts, swift_diff_files, top_dir, upstream_commit):
 
   cmd = [swift_format_tool]
   if opts.dry_run:
-    cmd.append('lint')
+    cmd += ['lint', '-s']
   else:
     cmd += ['format', '-i']
   cmd += swift_diff_files
@@ -5242,7 +5242,7 @@ def CMDformat(parser, args):
       '--swift-format',
       dest='use_swift_format',
       action='store_true',
-      default=False,
+      default=swift_format.IsSwiftFormatSupported(),
       help='Enables formatting of Swift file types using swift-format '
       '(macOS host only).')
   parser.add_option(

swift_format.py

@@ -40,6 +40,8 @@ def FindSwiftFormatToolInChromiumTree():
 
 
 def IsSwiftFormatSupported():
+  if sys.platform != 'darwin':
+    return False
   try:
     FindSwiftFormatToolInChromiumTree()
     return True