Fix difflib `?` hint in diff output when dealing with tabs (GH-15201)
(cherry picked from commit e1c638da6a065af6803028ced1afcc679e63f59d)
Co-authored-by: Anthony Sottile <asottile@umich.edu>
diff --git a/Lib/difflib.py b/Lib/difflib.py
index 887c3c2..3de1b3d 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -733,20 +733,15 @@
# Strip scores for the best n matches
return [x for score, x in result]
-def _count_leading(line, ch):
- """
- Return number of `ch` characters at the start of `line`.
- Example:
+def _keep_original_ws(s, tag_s):
+ """Replace whitespace with the original whitespace characters in `s`"""
+ return ''.join(
+ c if tag_c == " " and c.isspace() else tag_c
+ for c, tag_c in zip(s, tag_s)
+ )
- >>> _count_leading(' abc', ' ')
- 3
- """
- i, n = 0, len(line)
- while i < n and line[i] == ch:
- i += 1
- return i
class Differ:
r"""
@@ -1033,7 +1028,7 @@
def _qformat(self, aline, bline, atags, btags):
r"""
- Format "?" output and deal with leading tabs.
+ Format "?" output and deal with tabs.
Example:
@@ -1047,22 +1042,16 @@
'+ \tabcdefGhijkl\n'
'? \t ^ ^ ^\n'
"""
-
- # Can hurt, but will probably help most of the time.
- common = min(_count_leading(aline, "\t"),
- _count_leading(bline, "\t"))
- common = min(common, _count_leading(atags[:common], " "))
- common = min(common, _count_leading(btags[:common], " "))
- atags = atags[common:].rstrip()
- btags = btags[common:].rstrip()
+ atags = _keep_original_ws(aline, atags).rstrip()
+ btags = _keep_original_ws(bline, btags).rstrip()
yield "- " + aline
if atags:
- yield "? %s%s\n" % ("\t" * common, atags)
+ yield f"? {atags}\n"
yield "+ " + bline
if btags:
- yield "? %s%s\n" % ("\t" * common, btags)
+ yield f"? {btags}\n"
# With respect to junk, an earlier version of ndiff simply refused to
# *start* a match with a junk element. The result was cases like this: