combine-diff: do not send NULL to printf

When we run combined diff from working tree (diff-files --cc),
we sent NULL to printf that is returned by find_unique_abbrev().

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

diff --git a/combine-diff.c b/combine-diff.c
index 250de1c..50db39b 100644 (file)
--- a/combine-diff.c
+++ b/combine-diff.c
@@ -623,6 +623,7 @@ int show_combined_diff(struct combine_diff_path *elem, int num_parent,
                write_to_temp_file(ourtmp, result, size);
        }
        else {
+               /* Used by diff-tree to read from the working tree */
                struct stat st;
                int fd;
                ourtmp = elem->path;
@@ -701,6 +702,11 @@ int show_combined_diff(struct combine_diff_path *elem, int num_parent,
        show_hunks = make_hunks(sline, cnt, num_parent, dense);
 
        if (show_hunks) {
+               const char *abb;
+               char null_abb[DEFAULT_ABBREV + 1];
+
+               memset(null_abb, '0', DEFAULT_ABBREV);
+               null_abb[DEFAULT_ABBREV] = 0;
                if (header) {
                        shown_header++;
                        puts(header);
@@ -713,13 +719,18 @@ int show_combined_diff(struct combine_diff_path *elem, int num_parent,
                putchar('\n');
                printf("index ");
                for (i = 0; i < num_parent; i++) {
-                       printf("%s%s",
-                              i ? "," : "",
-                              find_unique_abbrev(elem->parent_sha1[i],
-                                                 DEFAULT_ABBREV));
+                       if (memcmp(elem->parent_sha1[i], null_sha1, 20))
+                               abb = find_unique_abbrev(elem->parent_sha1[i],
+                                                        DEFAULT_ABBREV);
+                       else
+                               abb = null_abb;
+                       printf("%s%s", i ? "," : "", abb);
                }
-               printf("..%s\n",
-                      find_unique_abbrev(elem->sha1, DEFAULT_ABBREV));
+               if (memcmp(elem->sha1, null_sha1, 20))
+                       abb = find_unique_abbrev(elem->sha1, DEFAULT_ABBREV);
+               else
+                       abb = null_abb;
+               printf("..%s\n", abb);
                dump_sline(sline, cnt, num_parent);
        }
        if (ourtmp == ourtmp_buf)