ll-merge: use a longer conflict marker for internal merge

The primary use of conflict markers is to help the user who resolves
the final (outer) merge by hand to show which part came from which
branch by separating the blocks of lines apart.  When the conflicted
parts from a "virtual ancestor" merge created by merge-recursive
remains in the common ancestor part in the final result, however,
the conflict markers that are the same size as the final merge
become harder to see.

Increase the conflict marker size slightly for these inner merges so
that the markers from the final merge and cruft from internal merge
can be distinguished more easily.

This would help reduce the common issue that prevents "rerere" from
being used on a really complex conflict.

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

ll-merge.c

@@ -376,8 +376,12 @@ int ll_merge(mmbuffer_t *result_buf,
 		}
 	}
 	driver = find_ll_merge_driver(ll_driver_name);
-	if (opts->virtual_ancestor && driver->recursive)
-		driver = find_ll_merge_driver(driver->recursive);
+
+	if (opts->virtual_ancestor) {
+		if (driver->recursive)
+			driver = find_ll_merge_driver(driver->recursive);
+		marker_size += 2;
+	}
 	return driver->fn(driver, result_buf, path, ancestor, ancestor_label,
 			  ours, our_label, theirs, their_label,
 			  opts, marker_size);

t/t6024-recursive-merge.sh

@@ -76,7 +76,7 @@ test_expect_success "result contains a conflict" "test_cmp expect a1"
 
 git ls-files --stage > out
 cat > expect << EOF
-100644 439cc46de773d8a83c77799b7cc9191c128bfcff 1	a1
+100644 ec3fe2a791706733f2d8fa7ad45d9a9672031f5e 1	a1
 100644 cf84443e49e1b366fac938711ddf4be2d4d1d9e9 2	a1
 100644 fd7923529855d0b274795ae3349c5e0438333979 3	a1
 EOF

t/t6036-recursive-corner-cases.sh

@@ -217,7 +217,8 @@ test_expect_success 'git detects differently handled merges conflict' '
 		-L "" \
 		-L "Temporary merge branch 1" \
 		merged empty merge-me &&
-	test $(git rev-parse :1:new_a) = $(git hash-object merged)
+	sed -e "s/^\([<=>]\)/\1\1\1/" merged >merged-internal &&
+	test $(git rev-parse :1:new_a) = $(git hash-object merged-internal)
 '
 
 #