patch: highlight the trailing white space in diff view

Summary:
This diffs make the worddiff highlights the trailing white space. Trailing white space is hard to see, highlighting it will make it easier to review the changes.

Another alternative solution is to change the "tokenizer" to make it cannot have two consecutive tokens like `(True, b" "), (False, b"\n")`. This approach is likely faster but less robust than the change proposed in this diff.

Reviewed By: sggutier

Differential Revision: D64603891

fbshipit-source-id: 608939288837ebae4bb522915e44a3b2df6480d5

eden/scm/sapling/patch.py

@@ -2888,16 +2888,19 @@ def diffsinglehunkinline(hunklines):
         (b"+", "diff.inserted", btokens),
     ]:
         isprevnewline = True
-        for changed, token in tokens:
+        length = len(tokens)
+        for i, (changed, token) in enumerate(tokens):
             if isprevnewline:
                 yield (prefix, label)
                 isprevnewline = False
             # special handling line end
+            isnextnewline = i + 1 < length and tokens[i + 1][1] == b"\n"
             isendofline = token.endswith(b"\n")
-            if isendofline:
-                chomp = token[:-1]  # chomp
+            if isendofline or isnextnewline:
+                chomp = token[:-1] if isendofline else token  # chomp
                 token = chomp.rstrip()  # detect spaces at the end
                 endspaces = chomp[len(token) :]
+
             # scan tabs
             for maybetab in tabsplitter.findall(token):
                 if b"\t" == maybetab[0:1]:
@@ -2908,11 +2911,13 @@ def diffsinglehunkinline(hunklines):
                     else:
                         currentlabel = label + ".unchanged"
                 yield (maybetab, currentlabel)
-            if isendofline:
+
+            if isendofline or isnextnewline:
                 if endspaces:
                     yield (endspaces, "diff.trailingwhitespace")
-                yield (b"\n", "")
-                isprevnewline = True
+                if isendofline:
+                    yield (b"\n", "")
+                    isprevnewline = True
 
 
 def difflabel(func, *args, **kw):

eden/scm/tests/test-diff-color.t

@@ -282,12 +282,12 @@ test trailing spaces color diff
   > this is the first line
   > this is the second line 
   > EOF
-tofix: the second line should end with diff.trailingwhitespace
+the second line should end with diff.trailingwhitespace
   $ hg diff --config experimental.worddiff=True --color=debug
   [diff.diffline|diff --git a/file1 b/file1]
   [diff.file_a|--- a/file1]
   [diff.file_b|+++ b/file1]
   [diff.hunk|@@ -1,2 +1,2 @@]
    this is the first line
   [diff.deleted|-][diff.deleted.unchanged|this is the second line]
-  [diff.inserted|+][diff.inserted.unchanged|this is the second line][diff.inserted.changed| ]
+  [diff.inserted|+][diff.inserted.unchanged|this is the second line][diff.trailingwhitespace| ]