T33: the sessions and right columns resize by a drag on their border toward the terminal, 160 to 960 pixels, kept in the settings once a drag rests; Ely 5c2822c's resizable ShellColumn, whose handle occludes the header so the drag moves no window, and Ely 005faef's handle line, a filled hairline, since gpui paints a border no wider than half its box

src/workspace/widths.rs

@@ -0,0 +1,80 @@
+use std::time::Duration;
+
+use ely_gpui_component::shell::ShellColumn;
+use gpui::{Context, Pixels, Task, px};
+
+use super::Workspace;
+use crate::settings::{COLUMN, SettingsStore};
+
+/// How long a dragged border rests before its width is saved.
+const SETTLE: Duration = Duration::from_millis(500);
+
+/// A side column, whose border toward the terminal drags its width.
+#[derive(Clone, Copy, Debug)]
+pub(super) enum Side {
+    Sessions,
+    Panel,
+}
+
+/// Widths a drag shows that the settings do not hold yet.
+#[derive(Default)]
+pub(super) struct Dragged {
+    sessions: Option<f32>,
+    panel: Option<f32>,
+    saving: Option<Task<()>>,
+}
+
+impl Workspace {
+    /// Column `side`, as wide as it was dragged or saved.
+    pub(super) fn side_column(&self, side: Side, cx: &Context<Self>) -> ShellColumn {
+        let settings = SettingsStore::get(cx);
+        let (id, dragged, saved) = match side {
+            Side::Sessions => ("sessions", self.dragged.sessions, settings.sessions_width),
+            Side::Panel => ("panel", self.dragged.panel, settings.panel_width),
+        };
+        let workspace = cx.entity();
+        ShellColumn::new(id).resizable(
+            px(dragged.unwrap_or(saved)),
+            px(*COLUMN.start()),
+            px(*COLUMN.end()),
+            move |width, _, cx| workspace.update(cx, |this, cx| this.drag(side, width, cx)),
+        )
+    }
+
+    /// Shows `width` at once and saves it once the drag rests.
+    fn drag(&mut self, side: Side, width: Pixels, cx: &mut Context<Self>) {
+        let width = f32::from(width).round();
+        match side {
+            Side::Sessions => self.dragged.sessions = Some(width),
+            Side::Panel => self.dragged.panel = Some(width),
+        }
+        self.dragged.saving = Some(cx.spawn(async move |this, cx| {
+            cx.background_executor().timer(SETTLE).await;
+            if let Err(error) = this.update(cx, |this, cx| this.save(cx)) {
+                log::error!("app: the columns' widths were not saved: {error:#}");
+            }
+        }));
+        cx.notify();
+    }
+
+    fn save(&mut self, cx: &mut Context<Self>) {
+        let (sessions, panel) = (self.dragged.sessions.take(), self.dragged.panel.take());
+        let saved = SettingsStore::update(cx, |settings| {
+            settings.sessions_width = sessions.unwrap_or(settings.sessions_width);
+            settings.panel_width = panel.unwrap_or(settings.panel_width);
+        });
+        match saved {
+            Ok(()) => {
+                let settings = SettingsStore::get(cx);
+                log::info!(
+                    "app: the sessions column is {} px wide, the right column {} px",
+                    settings.sessions_width,
+                    settings.panel_width
+                );
+            }
+            // The columns go back to the saved widths.
+            Err(error) => log::error!("app: the columns' widths are not kept: {error:#}"),
+        }
+        cx.notify();
+    }
+}