T44d Web · Gallery builds for wasm32: one story per section by URL, themed by the host

The gallery's entry runs natively or, on wasm32, from a wasm_bindgen start
through gpui_web, single-threaded with WebGL2 fallback. ?page, ?story and
?theme choose what shows; an unknown one fails in the page and the log.
set_theme switches the mode later. Pictures load from ELY_GALLERY_ASSETS.
scripts/stories.py writes examples/gallery/stories.json from the pages.

src/theme/mod.rs

@@ -136,6 +136,16 @@ impl Theme {
         Self::fade_to_target(cx);
     }
 
+    /// Sets `mode` without the fade, as before a window's first frame; a fade under way stops.
+    pub fn set_mode_now(mode: Mode, cx: &mut App) {
+        log::info!("theme: mode -> {mode:?}, at once");
+        let theme = cx.global_mut::<Theme>();
+        theme.mode = mode;
+        theme.transition += 1;
+        theme.colors = theme.target();
+        cx.refresh_windows();
+    }
+
     pub fn set_high_contrast(on: bool, cx: &mut App) {
         log::info!("theme: high contrast -> {on}");
         cx.global_mut::<Theme>().high_contrast = on;

src/theme/tests.rs

@@ -1,3 +1,5 @@
+use std::time::Duration;
+
 use gpui::{TestAppContext, hsla};
 
 use super::{ActiveTheme, Mode, Palette, Syntax, Theme};
@@ -19,6 +21,29 @@ fn an_owners_palette_serves_its_mode_alone(cx: &mut TestAppContext) {
     assert_eq!(cx.read(|cx| cx.theme().palette()), Palette::light(false));
 }
 
+/// A mode set at once wears its palette at once, and a fade under way cannot pull it back.
+#[gpui::test]
+fn a_mode_set_at_once_skips_the_fade(cx: &mut TestAppContext) {
+    cx.update(|cx| {
+        Theme::init(cx);
+        Theme::update(cx, |theme| theme.reduced_motion = true);
+        Theme::set_mode(Mode::Dark, cx);
+        Theme::set_mode_now(Mode::Light, cx);
+    });
+    assert_eq!(
+        cx.read(|cx| cx.theme().colors.clone()),
+        Palette::light(false)
+    );
+    std::thread::sleep(Duration::from_millis(2));
+    cx.executor().advance_clock(Duration::from_millis(100));
+    cx.run_until_parked();
+    assert!(!cx.read(|cx| cx.theme().is_dark()));
+    assert_eq!(
+        cx.read(|cx| cx.theme().colors.clone()),
+        Palette::light(false)
+    );
+}
+
 /// Every color of the palette and of code answers to its field's name, the quiet fills too.
 #[test]
 fn every_color_answers_to_its_name() {