Return 1 if --diff changed the code.

This is how GNU diff acts.

CHANGELOG

@@ -5,6 +5,7 @@
 ## [0.16.4] Unreleased
 ### Changed
 - Adjust blank lines on formatting boundaries when using the `--lines` option.
+- Return 1 if a diff changed the code. This is in line with how GNU diff acts.
 
 ## [0.16.3] 2017-07-13
 ### Changed

yapf/__init__.py

@@ -177,7 +177,7 @@ def main(argv):
   if not files:
     raise errors.YapfError('Input filenames did not match any python files')
 
-  FormatFiles(
+  changed = FormatFiles(
       files,
       lines,
       style_config=args.style,
@@ -186,7 +186,7 @@ def main(argv):
       print_diff=args.diff,
       verify=args.verify,
       parallel=args.parallel)
-  return 0
+  return 1 if changed and args.diff else 0
 
 
 def FormatFiles(filenames,

yapf/yapflib/reformatter.py

@@ -68,8 +68,8 @@ def Reformat(uwlines, verify=False, lines=None):
       if prev_uwline and prev_uwline.disable:
         # Keep the vertical spacing between a disabled and enabled formatting
         # region.
-        _RetainRequiredVerticalSpacingBetweenTokens(
-            uwline.first, prev_uwline.last, lines)
+        _RetainRequiredVerticalSpacingBetweenTokens(uwline.first,
+                                                    prev_uwline.last, lines)
       if any(tok.is_comment for tok in uwline.tokens):
         _RetainVerticalSpacingBeforeComments(uwline)
 
@@ -134,7 +134,7 @@ def _RetainRequiredVerticalSpacingBetweenTokens(cur_tok, prev_tok, lines):
     cur_lineno = cur_tok.lineno
 
   if prev_tok.value.endswith('\\'):
-    prev_lineno = prev_lineno + prev_tok.value.count('\n')
+    prev_lineno += prev_tok.value.count('\n')
 
   required_newlines = cur_lineno - prev_lineno
 

yapf/yapflib/unwrapped_line.py

@@ -331,9 +331,9 @@ def _SpaceRequiredBetween(left, right):
 
 def _MustBreakBefore(prev_token, cur_token):
   """Return True if a line break is required before the current token."""
-  if prev_token.is_comment or (
-      prev_token.previous_token and prev_token.is_pseudo_paren and
-      prev_token.previous_token.is_comment):
+  if prev_token.is_comment or (prev_token.previous_token and
+                               prev_token.is_pseudo_paren and
+                               prev_token.previous_token.is_comment):
     # Must break if the previous token was a comment.
     return True
   if (cur_token.is_string and prev_token.is_string and

yapf/yapflib/yapf_api.py

@@ -152,7 +152,7 @@ def FormatCode(unformatted_source,
       unformatted_source, reformatted_source, filename=filename)
 
   if print_diff:
-    return code_diff, code_diff != ''
+    return code_diff, code_diff
 
   return reformatted_source, True
 

yapftests/yapf_test.py

@@ -492,7 +492,10 @@ def f():
         suffix='.py', dirname=self.test_tmpdir) as (out, _):
       with utils.TempFileContents(
           self.test_tmpdir, unformatted_code, suffix='.py') as filepath:
-        subprocess.check_call(YAPF_BINARY + ['--diff', filepath], stdout=out)
+        try:
+          subprocess.check_call(YAPF_BINARY + ['--diff', filepath], stdout=out)
+        except subprocess.CalledProcessError as e:
+          self.assertEqual(e.returncode, 1)  # Indicates the text changed.
 
   def testReformattingSpecificLines(self):
     unformatted_code = textwrap.dedent("""\