git-rev-list: fix "--dense" flag

Right now --dense will _always_ show the root commit. I didn't do the
logic that does the diff against an empty tree. I was lazy.

This patch does that.  The first round was incorrect but
this patch is even slightly tested, and might do a better job.

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

diff --git a/rev-list.c b/rev-list.c
index 5f125fd..edf3b37 100644 (file)
--- a/rev-list.c
+++ b/rev-list.c
@@ -81,23 +81,28 @@ static void show_commit(struct commit *commit)
        fflush(stdout);
 }
 
-static void rewrite_one(struct commit **pp)
+static int rewrite_one(struct commit **pp)
 {
        for (;;) {
                struct commit *p = *pp;
                if (p->object.flags & (TREECHANGE | UNINTERESTING))
-                       return;
-               /* Only single-parent commits don't have TREECHANGE */
+                       return 0;
+               if (!p->parents)
+                       return -1;
                *pp = p->parents->item;
        }
 }
 
 static void rewrite_parents(struct commit *commit)
 {
-       struct commit_list *parent = commit->parents;
-       while (parent) {
-               rewrite_one(&parent->item);
-               parent = parent->next;
+       struct commit_list **pp = &commit->parents;
+       while (*pp) {
+               struct commit_list *parent = *pp;
+               if (rewrite_one(&parent->item) < 0) {
+                       *pp = parent->next;
+                       continue;
+               }
+               pp = &parent->next;
        }
 }
 
@@ -439,6 +444,30 @@ static int same_tree(struct tree *t1, struct tree *t2)
        return !is_different;
 }
 
+static int same_tree_as_empty(struct tree *t1)
+{
+       int retval;
+       void *tree;
+       struct tree_desc empty, real;
+
+       if (!t1)
+               return 0;
+
+       tree = read_object_with_reference(t1->object.sha1, "tree", &real.size, NULL);
+       if (!tree)
+               return 0;
+       real.buf = tree;
+
+       empty.buf = "";
+       empty.size = 0;
+
+       is_different = 0;
+       retval = diff_tree(&empty, &real, "", &diff_opt);
+       free(tree);
+
+       return retval >= 0 && !is_different;
+}
+
 static struct commit *try_to_simplify_merge(struct commit *commit, struct commit_list *parent)
 {
        if (!commit->tree)
@@ -523,11 +552,17 @@ static void compress_list(struct commit_list *list)
                struct commit_list *parent = commit->parents;
                list = list->next;
 
+               if (!parent) {
+                       if (!same_tree_as_empty(commit->tree))
+                               commit->object.flags |= TREECHANGE;
+                       continue;
+               }
+
                /*
                 * Exactly one parent? Check if it leaves the tree
                 * unchanged
                 */
-               if (parent && !parent->next) {
+               if (!parent->next) {
                        struct tree *t1 = commit->tree;
                        struct tree *t2 = parent->item->tree;
                        if (!t1 || !t2 || same_tree(t1, t2))