T16 round 2 fixes: synced charts move their shared window once per append, Fibonacci labels sit in a box clipped to the price pane and flip below near its top, and prices show every place their tick needs

src/finance/tests.rs

@@ -0,0 +1,66 @@
+use std::rc::Rc;
+
+use gpui::{
+    AppContext as _, Context, Entity, IntoElement, ParentElement, Render, Styled, TestAppContext,
+    Window, div, px,
+};
+use jiff::Timestamp;
+
+use crate::finance::{CandlestickChart, ChartSync, candles::Candle, stage::Visible};
+use crate::theme::Theme;
+
+fn candles(count: usize) -> Rc<Vec<Candle>> {
+    Rc::new(
+        (0..count)
+            .map(|ix| {
+                let time = Timestamp::from_second(ix as i64 * 86_400).expect("a day");
+                Candle::new(time, (10.0, 11.0, 9.0, 10.0 + ix as f64 * 0.01), 100.0)
+            })
+            .collect(),
+    )
+}
+
+struct Pair {
+    candles: Rc<Vec<Candle>>,
+    sync: Entity<ChartSync>,
+}
+
+impl Render for Pair {
+    fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
+        div()
+            .w(px(800.))
+            .child(CandlestickChart::new("first", self.candles.clone()).sync(&self.sync))
+            .child(CandlestickChart::new("second", self.candles.clone()).sync(&self.sync))
+    }
+}
+
+#[gpui::test]
+fn synced_charts_move_their_shared_window_once_per_append(cx: &mut TestAppContext) {
+    cx.update(Theme::init);
+    let sync = cx.new(|_| ChartSync::default());
+    let shared = sync.clone();
+    let (view, cx) = cx.add_window_view(|_, _| Pair {
+        candles: candles(40),
+        sync: shared,
+    });
+    cx.run_until_parked();
+    sync.update(cx, |sync, cx| {
+        sync.visible = Some(Visible {
+            start: 20.0,
+            count: 20.0,
+        });
+        cx.notify();
+    });
+    view.update(cx, |_, cx| cx.notify());
+    cx.run_until_parked();
+    view.update(cx, |pair, cx| {
+        pair.candles = candles(45);
+        cx.notify();
+    });
+    cx.run_until_parked();
+    let start = sync.read_with(cx, |sync, _| sync.visible.expect("held").start);
+    assert_eq!(
+        start, 25.0,
+        "five new candles move the shared window five, not ten"
+    );
+}