fix: fix tab-space mix with tab indenation and continuation_align_style=SPACE

CHANGELOG

@@ -13,6 +13,8 @@
   method definitions inside a class are surrounded by a single blank line as
   prescribed by PEP8.
 - Fixed the '...' token to be spaced after a colon.
+- With `USE_TABS=True` and `continuation_align_style=SPACE` no space tab mix
+  is produced anymore.
 
 ## [0.31.0] 2021-03-14
 ### Added

yapf/yapflib/format_token.py

@@ -77,7 +77,9 @@ def _TabbedContinuationAlignPadding(spaces, align_style, tab_width):
     if spaces > 0:
       return '\t' * int((spaces + tab_width - 1) / tab_width)
     return ''
-  return ' ' * spaces
+  if tab_width > 1 and spaces % tab_width == 0:
+    return '\t' * (spaces // tab_width)
+  return ' ' * spaces  # TODO: add a comment why we indent with spaces in a tab area?
 
 
 class FormatToken(object):

yapftests/format_token_test.py

@@ -30,7 +30,7 @@ def testSpace(self):
     self.assertEqual(pad, '')
 
     pad = format_token._TabbedContinuationAlignPadding(2, align_style, 2)
-    self.assertEqual(pad, ' ' * 2)
+    self.assertEqual(pad, '\t')
 
     pad = format_token._TabbedContinuationAlignPadding(5, align_style, 2)
     self.assertEqual(pad, ' ' * 5)