diff: Help "less" hide ^M from the output

When the tracked contents have CRLF line endings, colored diff output
shows "^M" at the end of output lines, which is distracting, even though
the pager we use by default ("less") knows to hide them.

The problem is that "less" hides a carriage-return only at the end of the
line, immediately before a line feed.  The colored diff output does not
take this into account, and emits four element sequence for each line:

   - force this color;
   - the line up to but not including the terminating line feed;
   - reset color
   - line feed.

By including the carriage return at the end of the line in the second
item, we are breaking the smart our pager has in order not to show "^M".
This can be fixed by changing the sequence to:

   - force this color;
   - the line up to but not including the terminating end-of-line;
   - reset color
   - end-of-line.

where end-of-line is either a single linefeed or a CRLF pair.  When the
output is not colored, "force this color" and "reset color" sequences are
both empty, so we won't have this problem with or without this patch.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/t/t4019-diff-wserror.sh b/t/t4019-diff-wserror.sh
index 7eae1f4500..84a1fe3115 100755
--- a/t/t4019-diff-wserror.sh
+++ b/t/t4019-diff-wserror.sh
@@ -178,4 +178,16 @@ test_expect_success 'trailing empty lines (2)' '
 
 '
 
+test_expect_success 'do not color trailing cr in context' '
+	git config --unset core.whitespace
+	rm -f .gitattributes &&
+	echo AAAQ | tr Q "\015" >G &&
+	git add G &&
+	echo BBBQ | tr Q "\015" >>G
+	git diff --color G | tr "\015" Q >output &&
+	grep "BBB.*${blue_grep}Q" output &&
+	grep "AAA.*\[mQ" output
+
+'
+
 test_done