Handle case when all available ranks are filtered out in make_tree()

HISTORY.md

@@ -9,8 +9,9 @@
 * Add `User.annotated_observations_count` field
 * Add `root_id` filter to `taxon.make_tree()` to explicitly set the root taxon instead of determining it automatically
 * Fix `taxon.make_tree()` rank filtering to allow skipping any number of rank levels
-* `taxon.make_tree()` now returns copies of original taxon objects instead of modifying them in-place
-* `Taxon.flatten(hide_root=True)` now only hides the root taxon if it was automatically inserted by `make_tree()`
+* Fix `taxon.make_tree()` rank filtering to handle all available ranks filtered out
+* Update `taxon.make_tree()` to return copies of original taxon objects instead of modifying them in-place
+* Update `Taxon.flatten(hide_root=True)` to only hide the root taxon if it was automatically inserted by `make_tree()`
 * Add shortcut properties to `Taxon` for ancestors of common ranks:
   `Taxon.kingdom`, `phylum`, `class_` (note the `_`; 'class' is a reserved keyword), `order`, `family`, `genus`
 * Update `Observation.taxon.ancestors` based on identification data, if available

pyinaturalist/models/taxon.py

@@ -522,8 +522,11 @@ def _find_root(
 
 def _find_and_graft_root(taxa: Iterable[Taxon], include_ranks: Optional[List[str]] = None) -> Taxon:
     taxa_by_id = {t.id: t for t in taxa}
-    max_rank = max(t.rank_level for t in taxa if not include_ranks or t.rank in include_ranks)
-    root_taxa = [t for t in taxa if t.rank_level == max_rank]
+    rank_levels = [t.rank_level for t in taxa if not include_ranks or t.rank in include_ranks]
+    if not rank_levels:
+        logger.warning('All taxon ranks excluded; returning default root')
+        return deepcopy(DEFAULT_ROOT)
+    root_taxa = [t for t in taxa if t.rank_level == max(rank_levels)]
 
     # Add any ungrafted taxa and deduplicate
     ungrafted = [

test/test_models.py

@@ -1205,6 +1205,15 @@ def test_make_tree__filtered():
     ]
 
 
+def test_make_tree__all_filtered():
+    """When all available ranks are filtered out, a single root node should be created"""
+    root = make_tree(
+        Taxon.from_json_list(j_life_list_2),
+        include_ranks=['infraclass'],
+    )
+    assert root.name == 'Life' and not root.children
+
+
 def test_make_tree__preserves_originals():
     """Children/ancestors of original taxon objects should be preserved"""
     taxa = Taxon.from_json_list(j_life_list_2)