Merge pull request #265 from widgetti/fix_memoize_use_thread_none

fix: use_thread on memoize returning None after hit

solara/cache.py

@@ -128,8 +128,9 @@ def do_work():
                 self.storage[key] = new_value
                 return new_value
             else:
-                # we don't use the return value if value is _DOES_NOT_EXIST
-                return None
+                # although we don't use the return value directly, it's still used on the next time result_thread is
+                # returned.
+                return value
 
         result_thread: solara.Result[R] = solara.use_thread(do_work, dependencies=[key], intrusive_cancel=self.intrusive_cancel)
         if value is _DOES_NOT_EXIST:

tests/unit/cache_test.py

@@ -252,3 +252,41 @@ def f(x: int) -> int:
     # we should directly get the result from the cache, so we don't go into running state
     assert result_values[0].state == solara.ResultState.FINISHED
     assert result_values[0].value == 100
+
+
+def test_memoize_hook_no_None_after_hit():
+    has_been_none = False
+
+    selected = solara.Reactive("1")
+
+    @solara.memoize
+    def something(i):
+        return i
+
+    @solara.component
+    def Test():
+        result = something.use_thread(selected.value)
+
+        if result.state == solara.ResultState.FINISHED:
+            if result.value is None:
+                # this should not happen
+                nonlocal has_been_none
+                has_been_none = True
+
+            solara.Text(str(result.value))
+
+    box, rc = solara.render(Test(), handle_error=False)
+    rc.find(v.Html, children=["1"]).wait_for(timeout=2)
+
+    assert not has_been_none
+    selected.set("2")
+    rc.find(v.Html, children=["2"]).wait_for(timeout=2)
+    assert not has_been_none
+
+    selected.set("1")
+    rc.find(v.Html, children=["1"]).wait_for(timeout=2)
+    assert not has_been_none
+
+    selected.set("3")
+    rc.find(v.Html, children=["3"]).wait_for(timeout=2)
+    assert not has_been_none