Add ty to check for missing symbols and other simple errors

src/bonsai/scripts/bonsai_deps.py

@@ -0,0 +1,23 @@
+"""Clone or update Bonsai external dependencies.
+
+Must be run from the repository root.
+"""
+
+import subprocess
+from pathlib import Path
+
+DEPS = [
+    ("https://projects.blender.org/pioverfour/sun_position.git", "sun_position"),
+    ("https://github.com/kevancress/MeasureIt_ARCH", "MeasureIt_ARCH"),
+    ("https://github.com/nortikin/sverchok.git", "sverchok"),
+]
+
+base = Path("src/bonsai/external_dependencies")
+base.mkdir(parents=True, exist_ok=True)
+
+for url, name in DEPS:
+    path = base / name
+    if not path.exists():
+        subprocess.check_call(["git", "clone", url, str(path)])
+    else:
+        subprocess.check_call(["git", "-C", str(path), "pull", "--rebase"])