treewide: rename tree to maybe_tree

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

5 files changed, 13 insertions, 13 deletions

diff --git a/builtin/checkout.c b/builtin/checkout.c
index a52af2e507..ca6aa29794 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 46b4ca13e5..a1fbc608bc 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1064,8 +1064,8 @@ 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 ac3dcd7a51..29d80a35a1 100644
--- a/builtin/reflog.c
+++ b/builtin/reflog.c
@@ -153,7 +153,7 @@ 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;
 			}