When render_widget gets invalidated, invalidate anyone would reads the value

Author: cpsievert

shinywidgets/_shinywidgets.py

@@ -29,6 +29,7 @@
 from shiny import Session, reactive, req
 from shiny.http_staticfiles import StaticFiles
 from shiny.module import resolve_id
+from shiny.reactive._core import Context, get_current_context
 from shiny.render.transformer import (
     TransformerMetadata,
     ValueFn,
@@ -209,20 +210,31 @@ def _restore_state():
 # Implement @render_widget()
 # --------------------------------------------------------------------------------------------
 
+# TODO: pass along IT/OT to get proper typing?
+UserValueFn = ValueFn[object | None]
 
 @output_transformer(default_ui=output_widget)
 async def WidgetTransformer(
     _meta: TransformerMetadata,
-    _fn: ValueFn[object | None],
+    _fn: UserValueFn,
 ) -> dict[str, Any] | None:
     value = await resolve_value_fn(_fn)
+
+    # Attach value/widget attributes to user func so they can be accessed (in other reactive contexts)
     _fn.value = value  # type: ignore
     _fn.widget = None  # type: ignore
+
+    # Invalidate any reactive contexts that have read these attributes
+    invalidate_contexts(_fn)
+
     if value is None:
         return None
+
+    # Ensure we have a widget & smart layout defaults
     widget = as_widget(value)
     widget, fill = set_layout_defaults(widget)
     _fn.widget = widget  # type: ignore
+
     return {"model_id": widget.model_id, "fill": fill}  # type: ignore
 
 
@@ -243,27 +255,62 @@ def render_widget(
     # Make the `res._value_fn.widget` attribute that we set in WidgetTransformer
     # accessible via `res.widget`
     def get_widget(*_: object) -> Optional[Widget]:
-        w = res._value_fn.widget  # type: ignore
-        if w is None:
+        vfn = res._value_fn  # pyright: ignore[reportFunctionMemberAccess]
+        vfn = register_current_context(vfn)
+        w = vfn.widget  # type: ignore
+        if w is not None:
+            return w
+        # If widget is None, we're reading in a reactive context, other than the render context, throw a silent exception
+        if has_current_context():
             req(False)
-            return None
-        return w
+        return None
 
     def set_widget(*_: object):
         raise RuntimeError("The widget attribute of a @render_widget function is read only.")
 
     setattr(res.__class__, "widget", property(get_widget, set_widget))
 
     def get_value(*_: object) -> object | None:
-        return res._value_fn.value  # type: ignore
+        vfn = res._value_fn  # pyright: ignore[reportFunctionMemberAccess]
+        vfn = register_current_context(vfn)
+        v = vfn.value  # type: ignore
+        if v is not None:
+            return v
+        if has_current_context():
+            req(False)
+        return None
 
     def set_value(*_: object):
         raise RuntimeError("The value attribute of a @render_widget function is read only.")
 
     setattr(res.__class__, "value", property(get_value, set_value))
 
+    # Define these attributes directly on the user function so they're defined, even
+    # if that function hasn't been called yet. (we don't want to raise an exception in that case)
+    fn.widget = None  # type: ignore
+    fn.value = None   # type: ignore
+
     return res
 
+
+def invalidate_contexts(fn: UserValueFn):
+    ctxs = getattr(fn, "_shinywidgets_contexts", set[Context]())
+    for ctx in ctxs:
+        # TODO: at what point should we be removing contexts?
+        ctx.invalidate()
+
+
+# If the widget/value is read in a reactive context, then we'll need to invalidate
+# that context when the widget's value changes
+def register_current_context(fn: UserValueFn):
+    if not has_current_context():
+        return fn
+    ctxs = getattr(fn, "_shinywidgets_contexts", set[Context]())
+    ctxs.add(get_current_context())
+    fn._shinywidgets_contexts = ctxs  # type: ignore
+    return fn
+
+
 def reactive_read(widget: Widget, names: Union[str, Sequence[str]]) -> Any:
     reactive_depend(widget, names)
     if isinstance(names, str):
@@ -282,7 +329,7 @@ def reactive_depend(
     """
 
     try:
-        ctx = reactive.get_current_context()  # pyright: ignore[reportPrivateImportUsage]
+        ctx = get_current_context()
     except RuntimeError:
         raise RuntimeError("reactive_read() must be called within a reactive context")
 
@@ -376,6 +423,14 @@ def set_layout_defaults(widget: Widget) -> Tuple[Widget, bool]:
 
     return (widget, fill)
 
+
+def has_current_context() -> bool:
+    try:
+        get_current_context()
+        return True
+    except RuntimeError:
+        return False
+
 # similar to base::system.file()
 def package_dir(package: str) -> str:
     with tempfile.TemporaryDirectory():