bpo-24746: Avoid stripping trailing whitespace in doctest fancy diff (python#10639)

Author: CuriousLearner

Lib/doctest.py

@@ -1690,8 +1690,6 @@ def output_difference(self, example, got, optionflags):
  kind = 'ndiff with -expected +actual'
  else:
  assert 0, 'Bad diff option'
- # Remove trailing whitespace on diff output.
- diff = [line.rstrip() + '\n' for line in diff]
  return 'Differences (%s):\n' % kind + _indent(''.join(diff))
 
  # If we're not using diff, then simply list the expected

Lib/test/test_doctest.py

@@ -2451,6 +2451,11 @@ def test_unittest_reportflags():
  Then the default eporting options are ignored:
 
  >>> result = suite.run(unittest.TestResult())
+ """
+ """
+ *NOTE*: These doctest are intentionally not placed in raw string to depict
+ the trailing whitespace using `\x20` in the diff below.
+
  >>> print(result.failures[0][1]) # doctest: +ELLIPSIS
  Traceback ...
  Failed example:
@@ -2464,7 +2469,7 @@ def test_unittest_reportflags():
  Differences (ndiff with -expected +actual):
  a
  - <BLANKLINE>
- +
+ +\x20
  b
  <BLANKLINE>
  <BLANKLINE>
@@ -2953,6 +2958,47 @@ def test_CLI(): r"""
 
 """
 
+def test_no_trailing_whitespace_stripping():
+ r"""
+ The fancy reports had a bug for a long time where any trailing whitespace on
+ the reported diff lines was stripped, making it impossible to see the
+ differences in line reported as different that differed only in the amount of
+ trailing whitespace. The whitespace still isn't particularly visible unless
+ you use NDIFF, but at least it is now there to be found.
+
+ *NOTE*: This snippet was intentionally put inside a raw string to get rid of
+ leading whitespace error in executing the example below
+
+ >>> def f(x):
+ ... r'''
+ ... >>> print('\n'.join(['a ', 'b']))
+ ... a
+ ... b
+ ... '''
+ """
+ """
+ *NOTE*: These doctest are not placed in raw string to depict the trailing whitespace
+ using `\x20`
+
+ >>> test = doctest.DocTestFinder().find(f)[0]
+ >>> flags = doctest.REPORT_NDIFF
+ >>> doctest.DocTestRunner(verbose=False, optionflags=flags).run(test)
+ ... # doctest: +ELLIPSIS
+ **********************************************************************
+ File ..., line 3, in f
+ Failed example:
+ print('\n'.join(['a ', 'b']))
+ Differences (ndiff with -expected +actual):
+ - a
+ + a
+ b
+ TestResults(failed=1, attempted=1)
+
+ *NOTE*: `\x20` is for checking the trailing whitespace on the +a line above.
+ We cannot use actual spaces there, as a commit hook prevents from committing
+ patches that contain trailing whitespace. More info on Issue 24746.
+ """
+
 ######################################################################
 ## Main
 ######################################################################

Misc/NEWS.d/next/Library/2018-11-22-15-22-56.bpo-24746.eSLKBE.rst

@@ -0,0 +1,2 @@
+Avoid stripping trailing whitespace in doctest fancy diff. Orignial patch by
+R. David Murray & Jairo Trad. Enhanced by Sanyam Khurana.