Using the commit-graph file to walk commit history removes the large
cost of parsing commits during the walk. This exposes a performance
issue: lookup_tree() takes a large portion of the computation time,
even when Git never uses those trees.

In anticipation of lazy-loading these trees, rename the 'tree' member
of struct commit to 'maybe_tree'. This serves two purposes: it hints
at the future role of possibly being NULL even if the commit has a
valid tree, and it allows for unambiguous transformation from simple
member access (i.e. commit->maybe_tree) to method access.

Signed-off-by: Derrick Stolee <dsto...@microsoft.com>
---
 blame.c               | 18 +++++++++---------
 builtin/checkout.c    | 12 ++++++------
 builtin/diff.c        |  2 +-
 builtin/fast-export.c |  6 +++---
 builtin/log.c         |  4 ++--
 builtin/reflog.c      |  2 +-
 commit-graph.c        |  4 ++--
 commit.c              |  2 +-
 commit.h              |  2 +-
 fsck.c                |  6 +++---
 http-push.c           |  2 +-
 line-log.c            |  4 ++--
 list-objects.c        | 10 +++++-----
 log-tree.c            |  6 +++---
 merge-recursive.c     |  5 +++--
 notes-merge.c         |  8 ++++----
 packfile.c            |  2 +-
 pretty.c              |  4 ++--
 ref-filter.c          |  2 +-
 revision.c            |  8 ++++----
 sequencer.c           | 12 ++++++------
 sha1_name.c           |  2 +-
 tree.c                |  4 ++--
 walker.c              |  2 +-
 24 files changed, 65 insertions(+), 64 deletions(-)

diff --git a/blame.c b/blame.c
index 200e0ad9a2..b78e649cac 100644
--- a/blame.c
+++ b/blame.c
@@ -553,10 +553,10 @@ static struct blame_origin *find_origin(struct commit 
*parent,
        diff_setup_done(&diff_opts);
 
        if (is_null_oid(&origin->commit->object.oid))
-               do_diff_cache(&parent->tree->object.oid, &diff_opts);
+               do_diff_cache(&parent->maybe_tree->object.oid, &diff_opts);
        else
-               diff_tree_oid(&parent->tree->object.oid,
-                             &origin->commit->tree->object.oid,
+               diff_tree_oid(&parent->maybe_tree->object.oid,
+                             &origin->commit->maybe_tree->object.oid,
                              "", &diff_opts);
        diffcore_std(&diff_opts);
 
@@ -622,10 +622,10 @@ static struct blame_origin *find_rename(struct commit 
*parent,
        diff_setup_done(&diff_opts);
 
        if (is_null_oid(&origin->commit->object.oid))
-               do_diff_cache(&parent->tree->object.oid, &diff_opts);
+               do_diff_cache(&parent->maybe_tree->object.oid, &diff_opts);
        else
-               diff_tree_oid(&parent->tree->object.oid,
-                             &origin->commit->tree->object.oid,
+               diff_tree_oid(&parent->maybe_tree->object.oid,
+                             &origin->commit->maybe_tree->object.oid,
                              "", &diff_opts);
        diffcore_std(&diff_opts);
 
@@ -1257,10 +1257,10 @@ static void find_copy_in_parent(struct blame_scoreboard 
*sb,
                diff_opts.flags.find_copies_harder = 1;
 
        if (is_null_oid(&target->commit->object.oid))
-               do_diff_cache(&parent->tree->object.oid, &diff_opts);
+               do_diff_cache(&parent->maybe_tree->object.oid, &diff_opts);
        else
-               diff_tree_oid(&parent->tree->object.oid,
-                             &target->commit->tree->object.oid,
+               diff_tree_oid(&parent->maybe_tree->object.oid,
+                             &target->commit->maybe_tree->object.oid,
                              "", &diff_opts);
 
        if (!diff_opts.flags.find_copies_harder)
diff --git a/builtin/checkout.c b/builtin/checkout.c
index d76e13c852..b15fed5d85 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -484,7 +484,7 @@ static int merge_working_tree(const struct checkout_opts 
*opts,
 
        resolve_undo_clear();
        if (opts->force) {
-               ret = reset_tree(new_branch_info->commit->tree, opts, 1, 
writeout_error);
+               ret = reset_tree(new_branch_info->commit->maybe_tree, opts, 1, 
writeout_error);
                if (ret)
                        return ret;
        } else {
@@ -570,18 +570,18 @@ static int merge_working_tree(const struct checkout_opts 
*opts,
                        o.verbosity = 0;
                        work = write_tree_from_memory(&o);
 
-                       ret = reset_tree(new_branch_info->commit->tree, opts, 1,
+                       ret = reset_tree(new_branch_info->commit->maybe_tree, 
opts, 1,
                                         writeout_error);
                        if (ret)
                                return ret;
                        o.ancestor = old_branch_info->name;
                        o.branch1 = new_branch_info->name;
                        o.branch2 = "local";
-                       ret = merge_trees(&o, new_branch_info->commit->tree, 
work,
-                               old_branch_info->commit->tree, &result);
+                       ret = merge_trees(&o, 
new_branch_info->commit->maybe_tree, work,
+                               old_branch_info->commit->maybe_tree, &result);
                        if (ret < 0)
                                exit(128);
-                       ret = reset_tree(new_branch_info->commit->tree, opts, 0,
+                       ret = reset_tree(new_branch_info->commit->maybe_tree, 
opts, 0,
                                         writeout_error);
                        strbuf_release(&o.obuf);
                        if (ret)
@@ -1002,7 +1002,7 @@ static int parse_branchname_arg(int argc, const char 
**argv,
                *source_tree = parse_tree_indirect(rev);
        } else {
                parse_commit_or_die(new_branch_info->commit);
-               *source_tree = new_branch_info->commit->tree;
+               *source_tree = new_branch_info->commit->maybe_tree;
        }
 
        if (!*source_tree)                   /* case (1): want a tree */
diff --git a/builtin/diff.c b/builtin/diff.c
index 16bfb22f73..34f18a5f3f 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -398,7 +398,7 @@ int cmd_diff(int argc, const char **argv, const char 
*prefix)
                if (!obj)
                        die(_("invalid object '%s' given."), name);
                if (obj->type == OBJ_COMMIT)
-                       obj = &((struct commit *)obj)->tree->object;
+                       obj = &((struct commit *)obj)->maybe_tree->object;
 
                if (obj->type == OBJ_TREE) {
                        obj->flags |= flags;
diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index 27b2cc138e..91e526b30d 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -578,11 +578,11 @@ static void handle_commit(struct commit *commit, struct 
rev_info *rev,
            get_object_mark(&commit->parents->item->object) != 0 &&
            !full_tree) {
                parse_commit_or_die(commit->parents->item);
-               diff_tree_oid(&commit->parents->item->tree->object.oid,
-                             &commit->tree->object.oid, "", &rev->diffopt);
+               diff_tree_oid(&commit->parents->item->maybe_tree->object.oid,
+                             &commit->maybe_tree->object.oid, "", 
&rev->diffopt);
        }
        else
-               diff_root_tree_oid(&commit->tree->object.oid,
+               diff_root_tree_oid(&commit->maybe_tree->object.oid,
                                   "", &rev->diffopt);
 
        /* Export the referenced blobs, and remember the marks. */
diff --git a/builtin/log.c b/builtin/log.c
index 94ee177d56..f603b53318 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1067,8 +1067,8 @@ static void make_cover_letter(struct rev_info *rev, int 
use_stdout,
 
        diff_setup_done(&opts);
 
-       diff_tree_oid(&origin->tree->object.oid,
-                     &head->tree->object.oid,
+       diff_tree_oid(&origin->maybe_tree->object.oid,
+                     &head->maybe_tree->object.oid,
                      "", &opts);
        diffcore_std(&opts);
        diff_flush(&opts);
diff --git a/builtin/reflog.c b/builtin/reflog.c
index 4719a5354c..b17eabc009 100644
--- a/builtin/reflog.c
+++ b/builtin/reflog.c
@@ -154,7 +154,7 @@ static int commit_is_complete(struct commit *commit)
                for (i = 0; i < found.nr; i++) {
                        struct commit *c =
                                (struct commit *)found.objects[i].item;
-                       if (!tree_is_complete(&c->tree->object.oid)) {
+                       if (!tree_is_complete(&c->maybe_tree->object.oid)) {
                                is_incomplete = 1;
                                c->object.flags |= INCOMPLETE;
                        }
diff --git a/commit-graph.c b/commit-graph.c
index 1fc63d541b..005b4a753e 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -258,7 +258,7 @@ static int fill_commit_in_graph(struct commit *item, struct 
commit_graph *g, uin
        item->graph_pos = pos;
 
        hashcpy(oid.hash, commit_data);
-       item->tree = lookup_tree(&oid);
+       item->maybe_tree = lookup_tree(&oid);
 
        date_high = get_be32(commit_data + g->hash_len + 8) & 0x3;
        date_low = get_be32(commit_data + g->hash_len + 12);
@@ -369,7 +369,7 @@ static void write_graph_chunk_data(struct hashfile *f, int 
hash_len,
                uint32_t packedDate[2];
 
                parse_commit(*list);
-               hashwrite(f, (*list)->tree->object.oid.hash, hash_len);
+               hashwrite(f, (*list)->maybe_tree->object.oid.hash, hash_len);
 
                parent = (*list)->parents;
 
diff --git a/commit.c b/commit.c
index 3e39c86abf..fbc092808c 100644
--- a/commit.c
+++ b/commit.c
@@ -335,7 +335,7 @@ int parse_commit_buffer(struct commit *item, const void 
*buffer, unsigned long s
        if (get_sha1_hex(bufptr + 5, parent.hash) < 0)
                return error("bad tree pointer in commit %s",
                             oid_to_hex(&item->object.oid));
-       item->tree = lookup_tree(&parent);
+       item->maybe_tree = lookup_tree(&parent);
        bufptr += tree_entry_len + 1; /* "tree " + "hex sha1" + "\n" */
        pptr = &item->parents;
 
diff --git a/commit.h b/commit.h
index e57ae4b583..c4d6e6e064 100644
--- a/commit.h
+++ b/commit.h
@@ -22,7 +22,7 @@ struct commit {
        unsigned int index;
        timestamp_t date;
        struct commit_list *parents;
-       struct tree *tree;
+       struct tree *maybe_tree;
        uint32_t graph_pos;
 };
 
diff --git a/fsck.c b/fsck.c
index 5c8c12dde3..3228ca5bee 100644
--- a/fsck.c
+++ b/fsck.c
@@ -396,9 +396,9 @@ static int fsck_walk_commit(struct commit *commit, void 
*data, struct fsck_optio
 
        name = get_object_name(options, &commit->object);
        if (name)
-               put_object_name(options, &commit->tree->object, "%s:", name);
+               put_object_name(options, &commit->maybe_tree->object, "%s:", 
name);
 
-       result = options->walk((struct object *)commit->tree, OBJ_TREE, data, 
options);
+       result = options->walk((struct object *)commit->maybe_tree, OBJ_TREE, 
data, options);
        if (result < 0)
                return result;
        res = result;
@@ -772,7 +772,7 @@ static int fsck_commit_buffer(struct commit *commit, const 
char *buffer,
        err = fsck_ident(&buffer, &commit->object, options);
        if (err)
                return err;
-       if (!commit->tree) {
+       if (!commit->maybe_tree) {
                err = report(options, &commit->object, FSCK_MSG_BAD_TREE, 
"could not load commit's tree %s", sha1_to_hex(tree_sha1));
                if (err)
                        return err;
diff --git a/http-push.c b/http-push.c
index 7dcd9daf62..d83479f32f 100644
--- a/http-push.c
+++ b/http-push.c
@@ -1330,7 +1330,7 @@ static int get_delta(struct rev_info *revs, struct 
remote_lock *lock)
        int count = 0;
 
        while ((commit = get_revision(revs)) != NULL) {
-               p = process_tree(commit->tree, p);
+               p = process_tree(commit->maybe_tree, p);
                commit->object.flags |= LOCAL;
                if (!(commit->object.flags & UNINTERESTING))
                        count += add_send_request(&commit->object, lock);
diff --git a/line-log.c b/line-log.c
index cdc2257db5..e714969ca2 100644
--- a/line-log.c
+++ b/line-log.c
@@ -817,8 +817,8 @@ static void queue_diffs(struct line_log_data *range,
        assert(commit);
 
        DIFF_QUEUE_CLEAR(&diff_queued_diff);
-       diff_tree_oid(parent ? &parent->tree->object.oid : NULL,
-                     &commit->tree->object.oid, "", opt);
+       diff_tree_oid(parent ? &parent->maybe_tree->object.oid : NULL,
+                     &commit->maybe_tree->object.oid, "", opt);
        if (opt->detect_rename) {
                filter_diffs_for_paths(range, 1);
                if (diff_might_be_rename())
diff --git a/list-objects.c b/list-objects.c
index 168bef688a..bfd09f545c 100644
--- a/list-objects.c
+++ b/list-objects.c
@@ -195,7 +195,7 @@ static void mark_edge_parents_uninteresting(struct commit 
*commit,
                struct commit *parent = parents->item;
                if (!(parent->object.flags & UNINTERESTING))
                        continue;
-               mark_tree_uninteresting(parent->tree);
+               mark_tree_uninteresting(parent->maybe_tree);
                if (revs->edge_hint && !(parent->object.flags & SHOWN)) {
                        parent->object.flags |= SHOWN;
                        show_edge(parent);
@@ -212,7 +212,7 @@ void mark_edges_uninteresting(struct rev_info *revs, 
show_edge_fn show_edge)
                struct commit *commit = list->item;
 
                if (commit->object.flags & UNINTERESTING) {
-                       mark_tree_uninteresting(commit->tree);
+                       mark_tree_uninteresting(commit->maybe_tree);
                        if (revs->edge_hint_aggressive && 
!(commit->object.flags & SHOWN)) {
                                commit->object.flags |= SHOWN;
                                show_edge(commit);
@@ -227,7 +227,7 @@ void mark_edges_uninteresting(struct rev_info *revs, 
show_edge_fn show_edge)
                        struct commit *commit = (struct commit *)obj;
                        if (obj->type != OBJ_COMMIT || !(obj->flags & 
UNINTERESTING))
                                continue;
-                       mark_tree_uninteresting(commit->tree);
+                       mark_tree_uninteresting(commit->maybe_tree);
                        if (!(obj->flags & SHOWN)) {
                                obj->flags |= SHOWN;
                                show_edge(commit);
@@ -300,8 +300,8 @@ static void do_traverse(struct rev_info *revs,
                 * an uninteresting boundary commit may not have its tree
                 * parsed yet, but we are not going to show them anyway
                 */
-               if (commit->tree)
-                       add_pending_tree(revs, commit->tree);
+               if (commit->maybe_tree)
+                       add_pending_tree(revs, commit->maybe_tree);
                show_commit(commit, show_data);
 
                if (revs->tree_blobs_in_commit_order)
diff --git a/log-tree.c b/log-tree.c
index bdf23c5f7b..99499af57c 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -806,7 +806,7 @@ static int log_tree_diff(struct rev_info *opt, struct 
commit *commit, struct log
                return 0;
 
        parse_commit_or_die(commit);
-       oid = &commit->tree->object.oid;
+       oid = &commit->maybe_tree->object.oid;
 
        /* Root commit? */
        parents = get_saved_parents(opt, commit);
@@ -831,7 +831,7 @@ static int log_tree_diff(struct rev_info *opt, struct 
commit *commit, struct log
                         * we merged _in_.
                         */
                        parse_commit_or_die(parents->item);
-                       diff_tree_oid(&parents->item->tree->object.oid,
+                       diff_tree_oid(&parents->item->maybe_tree->object.oid,
                                      oid, "", &opt->diffopt);
                        log_tree_diff_flush(opt);
                        return !opt->loginfo;
@@ -846,7 +846,7 @@ static int log_tree_diff(struct rev_info *opt, struct 
commit *commit, struct log
                struct commit *parent = parents->item;
 
                parse_commit_or_die(parent);
-               diff_tree_oid(&parent->tree->object.oid,
+               diff_tree_oid(&parent->maybe_tree->object.oid,
                              oid, "", &opt->diffopt);
                log_tree_diff_flush(opt);
 
diff --git a/merge-recursive.c b/merge-recursive.c
index 869092f7b9..67886a4ff8 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -101,7 +101,7 @@ static struct commit *make_virtual_commit(struct tree 
*tree, const char *comment
        struct commit *commit = alloc_commit_node();
 
        set_merge_remote_desc(commit, comment, (struct object *)commit);
-       commit->tree = tree;
+       commit->maybe_tree = tree;
        commit->object.parsed = 1;
        return commit;
 }
@@ -2154,7 +2154,8 @@ int merge_recursive(struct merge_options *o,
                read_cache();
 
        o->ancestor = "merged common ancestors";
-       clean = merge_trees(o, h1->tree, h2->tree, 
merged_common_ancestors->tree,
+       clean = merge_trees(o, h1->maybe_tree, h2->maybe_tree,
+                           merged_common_ancestors->maybe_tree,
                            &mrtree);
        if (clean < 0) {
                flush_output(o);
diff --git a/notes-merge.c b/notes-merge.c
index c09c5e0e47..1d3edc8942 100644
--- a/notes-merge.c
+++ b/notes-merge.c
@@ -600,14 +600,14 @@ int notes_merge(struct notes_merge_options *o,
                        printf("No merge base found; doing history-less 
merge\n");
        } else if (!bases->next) {
                base_oid = &bases->item->object.oid;
-               base_tree_oid = &bases->item->tree->object.oid;
+               base_tree_oid = &bases->item->maybe_tree->object.oid;
                if (o->verbosity >= 4)
                        printf("One merge base found (%.7s)\n",
                               oid_to_hex(base_oid));
        } else {
                /* TODO: How to handle multiple merge-bases? */
                base_oid = &bases->item->object.oid;
-               base_tree_oid = &bases->item->tree->object.oid;
+               base_tree_oid = &bases->item->maybe_tree->object.oid;
                if (o->verbosity >= 3)
                        printf("Multiple merge bases found. Using the first "
                                "(%.7s)\n", oid_to_hex(base_oid));
@@ -634,8 +634,8 @@ int notes_merge(struct notes_merge_options *o,
                goto found_result;
        }
 
-       result = merge_from_diffs(o, base_tree_oid, &local->tree->object.oid,
-                                 &remote->tree->object.oid, local_tree);
+       result = merge_from_diffs(o, base_tree_oid, 
&local->maybe_tree->object.oid,
+                                 &remote->maybe_tree->object.oid, local_tree);
 
        if (result != 0) { /* non-trivial merge (with or without conflicts) */
                /* Commit (partial) result */
diff --git a/packfile.c b/packfile.c
index b1d33b646a..3eb9c4a36e 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1925,7 +1925,7 @@ static int add_promisor_object(const struct object_id 
*oid,
                struct commit *commit = (struct commit *) obj;
                struct commit_list *parents = commit->parents;
 
-               oidset_insert(set, &commit->tree->object.oid);
+               oidset_insert(set, &commit->maybe_tree->object.oid);
                for (; parents; parents = parents->next)
                        oidset_insert(set, &parents->item->object.oid);
        } else if (obj->type == OBJ_TAG) {
diff --git a/pretty.c b/pretty.c
index f7ce490230..42095ea495 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1161,10 +1161,10 @@ static size_t format_commit_one(struct strbuf *sb, /* 
in UTF-8 */
                strbuf_addstr(sb, diff_get_color(c->auto_color, DIFF_RESET));
                return 1;
        case 'T':               /* tree hash */
-               strbuf_addstr(sb, oid_to_hex(&commit->tree->object.oid));
+               strbuf_addstr(sb, oid_to_hex(&commit->maybe_tree->object.oid));
                return 1;
        case 't':               /* abbreviated tree hash */
-               strbuf_add_unique_abbrev(sb, commit->tree->object.oid.hash,
+               strbuf_add_unique_abbrev(sb, 
commit->maybe_tree->object.oid.hash,
                                         c->pretty_ctx->abbrev);
                return 1;
        case 'P':               /* parent hashes */
diff --git a/ref-filter.c b/ref-filter.c
index 45fc56216a..783a3ee6cf 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -815,7 +815,7 @@ static void grab_commit_values(struct atom_value *val, int 
deref, struct object
                if (deref)
                        name++;
                if (!strcmp(name, "tree")) {
-                       v->s = xstrdup(oid_to_hex(&commit->tree->object.oid));
+                       v->s = 
xstrdup(oid_to_hex(&commit->maybe_tree->object.oid));
                }
                else if (!strcmp(name, "numparent")) {
                        v->value = commit_list_count(commit->parents);
diff --git a/revision.c b/revision.c
index b42c836d7a..7d66e32e83 100644
--- a/revision.c
+++ b/revision.c
@@ -440,8 +440,8 @@ static void file_change(struct diff_options *options,
 static int rev_compare_tree(struct rev_info *revs,
                            struct commit *parent, struct commit *commit)
 {
-       struct tree *t1 = parent->tree;
-       struct tree *t2 = commit->tree;
+       struct tree *t1 = parent->maybe_tree;
+       struct tree *t2 = commit->maybe_tree;
 
        if (!t1)
                return REV_TREE_NEW;
@@ -477,7 +477,7 @@ static int rev_compare_tree(struct rev_info *revs,
 static int rev_same_tree_as_empty(struct rev_info *revs, struct commit *commit)
 {
        int retval;
-       struct tree *t1 = commit->tree;
+       struct tree *t1 = commit->maybe_tree;
 
        if (!t1)
                return 0;
@@ -615,7 +615,7 @@ static void try_to_simplify_commit(struct rev_info *revs, 
struct commit *commit)
        if (!revs->prune)
                return;
 
-       if (!commit->tree)
+       if (!commit->maybe_tree)
                return;
 
        if (!commit->parents) {
diff --git a/sequencer.c b/sequencer.c
index f9d1001dee..3b2823c8b5 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -499,8 +499,8 @@ static int do_recursive_merge(struct commit *base, struct 
commit *next,
        o.show_rename_progress = 1;
 
        head_tree = parse_tree_indirect(head);
-       next_tree = next ? next->tree : empty_tree();
-       base_tree = base ? base->tree : empty_tree();
+       next_tree = next ? next->maybe_tree : empty_tree();
+       base_tree = base ? base->maybe_tree : empty_tree();
 
        for (xopt = opts->xopts; xopt != opts->xopts + opts->xopts_nr; xopt++)
                parse_merge_opt(&o, *xopt);
@@ -561,7 +561,7 @@ static int is_index_unchanged(void)
                        return error(_("unable to update cache tree"));
 
        return !oidcmp(&active_cache_tree->oid,
-                      &head_commit->tree->object.oid);
+                      &head_commit->maybe_tree->object.oid);
 }
 
 static int write_author_script(const char *message)
@@ -1118,7 +1118,7 @@ static int try_to_commit(struct strbuf *msg, const char 
*author,
        }
 
        if (!(flags & ALLOW_EMPTY) && !oidcmp(current_head ?
-                                             &current_head->tree->object.oid :
+                                             
&current_head->maybe_tree->object.oid :
                                              &empty_tree_oid, &tree)) {
                res = 1; /* run 'git commit' to display error message */
                goto out;
@@ -1216,12 +1216,12 @@ static int is_original_commit_empty(struct commit 
*commit)
                if (parse_commit(parent))
                        return error(_("could not parse parent commit %s"),
                                oid_to_hex(&parent->object.oid));
-               ptree_oid = &parent->tree->object.oid;
+               ptree_oid = &parent->maybe_tree->object.oid;
        } else {
                ptree_oid = the_hash_algo->empty_tree; /* commit is root */
        }
 
-       return !oidcmp(ptree_oid, &commit->tree->object.oid);
+       return !oidcmp(ptree_oid, &commit->maybe_tree->object.oid);
 }
 
 /*
diff --git a/sha1_name.c b/sha1_name.c
index 735c1c0b8e..26b22cb628 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -896,7 +896,7 @@ struct object *peel_to_type(const char *name, int namelen,
                if (o->type == OBJ_TAG)
                        o = ((struct tag*) o)->tagged;
                else if (o->type == OBJ_COMMIT)
-                       o = &(((struct commit *) o)->tree->object);
+                       o = &(((struct commit *) o)->maybe_tree->object);
                else {
                        if (name)
                                error("%.*s: expected %s type, but the object "
diff --git a/tree.c b/tree.c
index b224115e0f..dbc5e0be54 100644
--- a/tree.c
+++ b/tree.c
@@ -109,7 +109,7 @@ static int read_tree_1(struct tree *tree, struct strbuf 
*base,
                                    oid_to_hex(entry.oid),
                                    base->buf, entry.path);
 
-                       oidcpy(&oid, &commit->tree->object.oid);
+                       oidcpy(&oid, &commit->maybe_tree->object.oid);
                }
                else
                        continue;
@@ -248,7 +248,7 @@ struct tree *parse_tree_indirect(const struct object_id 
*oid)
                if (obj->type == OBJ_TREE)
                        return (struct tree *) obj;
                else if (obj->type == OBJ_COMMIT)
-                       obj = &(((struct commit *) obj)->tree->object);
+                       obj = &(((struct commit *) obj)->maybe_tree->object);
                else if (obj->type == OBJ_TAG)
                        obj = ((struct tag *) obj)->tagged;
                else
diff --git a/walker.c b/walker.c
index dffb9c8e37..1d5f3059a2 100644
--- a/walker.c
+++ b/walker.c
@@ -87,7 +87,7 @@ static int process_commit(struct walker *walker, struct 
commit *commit)
        walker_say(walker, "walk %s\n", oid_to_hex(&commit->object.oid));
 
        if (walker->get_tree) {
-               if (process(walker, &commit->tree->object))
+               if (process(walker, &commit->maybe_tree->object))
                        return -1;
                if (!walker->get_all)
                        walker->get_tree = 0;
-- 
2.17.0

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