combine-diff: add safety check to --cc.

The earlier change implemented "only two version" check but
without checking if the change rewrites from all the parents.
This implements a check to make sure that a change introduced
by the merge from all the parents is caught to be interesting.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/combine-diff.c b/combine-diff.c
index 44931b2..8f295c8 100644 (file)
--- a/combine-diff.c
+++ b/combine-diff.c
@@ -397,7 +397,23 @@ static int make_hunks(struct sline *sline, unsigned long cnt,
                hunk_end = j;
 
                /* [i..hunk_end) are interesting.  Now is it really
-                * interesting?
+                * interesting?  We check if there are only two versions
+                * and the result matches one of them.  That is, we look
+                * at:
+                *   (+) line, which records lines added to which parents;
+                *       this line appears in the result.
+                *   (-) line, which records from what parents the line
+                *       was removed; this line does not appear in the result.
+                * then check the set of parents the result has difference
+                * from, from all lines.  If there are lines that has
+                * different set of parents that the result has differences
+                * from, that means we have more than two versions.
+                *
+                * Even when we have only two versions, if the result does
+                * not match any of the parents, the it should be considered
+                * interesting.  In such a case, we would have all '+' line.
+                * After passing the above "two versions" test, that would
+                * appear as "the same set of parents" to be "all parents".
                 */
                same_diff = 0;
                has_interesting = 0;
@@ -429,7 +445,7 @@ static int make_hunks(struct sline *sline, unsigned long cnt,
                        }
                }
 
-               if (!has_interesting) {
+               if (!has_interesting && same_diff != all_mask) {
                        /* This hunk is not that interesting after all */
                        for (j = hunk_begin; j < hunk_end; j++)
                                sline[j].flag &= ~mark;