When diff encounters a line that consists of a single dot, it emits two
dots instead, stops the current command and emits a substitute command
to replace the double dot with a single one. Then it restarts the
(original) command if necessary and inserts further lines. This is done
because a single dot on a line does have special meaning in ed. (It
stops text insertion.)
However, there are multiple issues with the current implementation,
resulting in mangled output:
- The line number for the substitute command should be the number of the
most recently inserted line. diff instead uses the number of the first
inserted line of the current hunk. The first character of that line is
removed when applying the diff, while the superfluous dot is not.
- The line number of the restarted command is not adjusted for the
number of lines already inserted, resulting in the reordering of lines..
- When there is a bare dot in the replacement text of a change command,
too many lines are deleted, because a second change command is emitted.
An append command should be emitted instead, because the target lines
have already been removed by the first change command.
The following patch fixes all those issues.
Index: diffreg.c
===================================================================
RCS file: /cvs/src/usr.bin/diff/diffreg.c,v
retrieving revision 1.90
diff -u -p -r1.90 diffreg.c
--- diffreg.c 26 Oct 2015 12:52:27 -0000 1.90
+++ diffreg.c 13 Feb 2016 16:35:08 -0000
@@ -1075,8 +1075,12 @@ proceed:
* back and restart where we left off.
*/
diff_output(".\n");
- diff_output("%ds/.//\n", a);
+ diff_output("%ds/.//\n", a + i - 1);
a += i;
+ if (a > b)
+ b += i;
+ else
+ b = a - 1;
c += i;
goto restart;
}
natano
