Bugfix and add test

Author: cpsievert

shiny/session/_session.py

@@ -188,7 +188,7 @@ class Session(ABC):
     groups: list[str] | None
 
     # Internal state for current_output_id()
-    _current_output_id: str | None
+    _current_output_id: str | None = None
 
     # TODO: not sure these should be directly exposed
     _outbound_message_queues: OutBoundMessageQueues

tests/playwright/shiny/session/current_output_info/app.py

@@ -0,0 +1,30 @@
+from shiny import App, Inputs, Outputs, Session, render, ui
+
+app_ui = ui.page_fluid(
+    ui.input_dark_mode(mode="light", id="dark_mode"),
+    ui.output_text("text1"),
+    ui.output_text("text2"),
+    ui.output_text("info").add_class("shiny-report-theme"),
+)
+
+
+def server(input: Inputs, output: Outputs, session: Session):
+
+    @render.text
+    def text1():
+        id = session.current_output_id() or "None"
+        return f"Output ID: {id}"
+
+    @output(id="text2")
+    @render.text
+    def _():
+        id = session.current_output_id() or "None"
+        return f"Output ID: {id}"
+
+    @render.text
+    def info():
+        bg_color = session.clientdata.output_bg_color()
+        return f"BG color: {bg_color}"
+
+
+app = App(app_ui, server)

tests/playwright/shiny/session/current_output_info/test_current_output_info.py

@@ -0,0 +1,29 @@
+from playwright.sync_api import Page
+
+from shiny.playwright import controller
+from shiny.run import ShinyAppProc
+
+
+def test_current_output_info(page: Page, local_app: ShinyAppProc) -> None:
+
+    page.goto(local_app.url)
+
+    # Check that the output ID is displayed correctly in the UI
+    text1 = controller.OutputText(page, "text1")
+    text2 = controller.OutputText(page, "text2")
+
+    text1.expect_value("Output ID: text1")
+    text2.expect_value("Output ID: text2")
+
+    # Check that we can get background color from clientdata
+    info = controller.OutputText(page, "info")
+    info.expect_value("BG color: rgb(255, 255, 255)")
+
+    # Click the dark mode button to change the background color
+    dark_mode = controller.InputDarkMode(page, "dark_mode")
+    dark_mode.expect_mode("light")
+    dark_mode.click()
+    dark_mode.expect_mode("dark")
+
+    # Check that the background color has changed
+    info.expect_value("BG color: rgb(29, 31, 33)")