fix list render diff (#45)

pyproject.toml

@@ -5,7 +5,7 @@ packages = [
   { include = "pyview" },
 ]
 
-version = "0.0.24"
+version = "0.0.25"
 description = "LiveView in Python"
 authors = ["Larry Ogrodnek <[email protected]>"]
 license = "MIT"

pyview/template/render_diff.py

@@ -11,19 +11,24 @@ def calc_diff(old_tree: dict[str, Any], new_tree: dict[str, Any]) -> dict[str, A
             and "s" in new_tree[key]
             and "d" in new_tree[key]
         ):
+            if isinstance(old_tree[key], str):
+                diff[key] = new_tree[key]
+                continue
+
             # Handle special case of for loop
+            old_static = old_tree[key].get("s", [])
+            new_static = new_tree[key]["s"]
+
             old_dynamic = old_tree[key]["d"]
             new_dynamic = new_tree[key]["d"]
 
-            old_static = old_tree[key]["s"]
-            new_static = new_tree[key]["s"]
-
             if old_static != new_static:
                 diff[key] = {"s": new_static, "d": new_dynamic}
                 continue
 
             if old_dynamic != new_dynamic:
                 diff[key] = {"d": new_dynamic}
+
         elif isinstance(new_tree[key], dict):
             nested_diff = calc_diff(old_tree[key], new_tree[key])
             if nested_diff:

tests/template/test_diff.py

@@ -49,6 +49,35 @@ def test_loop_diff_no_change():
     assert calc_diff(old, new) == {}
 
 
+def test_loop_diff_empty_to_nonempty():
+    t = Template("<div>{% for item in items %}<span>{{item}}</span>{% endfor %}</div>")
+
+    old = t.tree({"items": []})
+    new = t.tree({"items": ["One", "Two", "Three"]})
+
+    assert calc_diff(old, new) == {
+        "0": {"d": [["One"], ["Two"], ["Three"]], "s": ["<span>", "</span>"]}
+    }
+
+
+def test_loop_diff_nonempty_to_empty():
+    t = Template("<div>{% for item in items %}<span>{{item}}</span>{% endfor %}</div>")
+
+    old = t.tree({"items": ["One", "Two", "Three"]})
+    new = t.tree({"items": []})
+
+    assert calc_diff(old, new) == {"0": ""}
+
+
+def test_loop_diff_size_change():
+    t = Template("<div>{% for item in items %}<span>{{item}}</span>{% endfor %}</div>")
+
+    old = t.tree({"items": ["One", "Two", "Three"]})
+    new = t.tree({"items": ["One"]})
+
+    assert calc_diff(old, new) == {"0": {"d": [["One"]]}}
+
+
 def test_loop_diff_static_change():
     t = Template("<div>{% for item in items %}<span>{{item}}</span>{% endfor %}</div>")
     t2 = Template("<div>{% for item in items %}<div>{{item}}</div>{% endfor %}</div>")