fix(channels): flatten the list and make the panes swipeable (#3832)

Author: puemos

packages/ui/src/features/canvas/AGENTS.md

@@ -44,7 +44,12 @@ The root `AGENTS.md` architecture rules still apply.
   (`ChannelPanes` in `ChannelsSidebar.tsx`): the searchable channel list, and the
   channel you're in (`ChannelSidebar`, headed by `ChannelBackRow`). Both panes
   stay mounted — the offscreen one is `inert` — so the slide has something to
-  slide and returning to the list doesn't rebuild every row.
+  slide and returning to the list doesn't rebuild every row. A two-finger
+  horizontal swipe moves between them (`useChannelPaneSwipe`, wheel `deltaX`
+  accumulated per gesture and locked until the wheel goes quiet).
+- In the list, "Starred"/"Channels" are headings, not parents: under the layout
+  the rows sit at the heading's level (no indent) and the "#"/lock glyph belongs
+  to the rows. The alpha's indented tree is unchanged.
 - One `ChannelsFab` serves both panes: given a `channelId` it creates inside
   that channel (task, canvas), and either way it can create a channel. Off the
   layout it keeps its original two-item menu. Archived moves out of the sidebar

packages/ui/src/features/canvas/components/ChannelsList.test.tsx

@@ -82,6 +82,26 @@ describe("ChannelsList", () => {
     expect(me.parentElement?.textContent).toMatch(/me(⌘|Ctrl)/);
   });
 
+  // "Starred" and "Channels" are headings over the rows, not parents of them —
+  // under the layout the rows sit at the heading's level and keep the "#" for
+  // themselves. The alpha's tree is unchanged.
+  describe("group headings", () => {
+    beforeEach(() => {
+      mocks.starredPaths = [ENG.path];
+    });
+
+    it("does not indent rows under the layout", () => {
+      renderList();
+      expect(screen.getByText("engineering").closest(".pl-5")).toBeNull();
+    });
+
+    it("keeps the indented tree off the layout", () => {
+      mocks.channelsLayout = false;
+      renderList();
+      expect(screen.getByText("engineering").closest(".pl-5")).toBeTruthy();
+    });
+  });
+
   describe("search", () => {
     // The list is the only way to switch channels now, so with a few dozen
     // channels it has to be filterable rather than only scrollable.

packages/ui/src/features/canvas/components/ChannelsList.tsx

@@ -399,7 +399,7 @@ function ChannelSection({
                 {channel.name}
               </span>
               {hotkeySlot != null && (
-                <Kbd className="ml-auto shrink-0 group-hover/chan:opacity-0">
+                <Kbd className="ml-auto shrink-0 opacity-50 group-hover/chan:opacity-0">
                   {formatHotkey(`mod+${hotkeySlot}`)}
                 </Kbd>
               )}
@@ -637,7 +637,7 @@ function PersonalChannelRow({ hotkeySlot }: { hotkeySlot?: number }) {
           {PERSONAL_CHANNEL_NAME}
         </span>
         {hotkeySlot != null && (
-          <Kbd className="ml-auto shrink-0 group-hover/chan:opacity-0">
+          <Kbd className="ml-auto shrink-0 opacity-50 group-hover/chan:opacity-0">
             {formatHotkey(`mod+${hotkeySlot}`)}
           </Kbd>
         )}
@@ -700,18 +700,23 @@ const CHANNELS_SECTION_ID = "channels:all";
 // the label styling) and animates the panel height (which janked on a list this
 // long). Unstyled parts give a plain label row that snaps.
 //
-// The whole header row is the trigger. It rests as a "#" and swaps to a chevron
-// on hover or keyboard focus, so the row only advertises the disclosure when
-// you're actually reaching for it.
+// The whole header row is the trigger. Under the layout the icon well rests
+// empty and fills with a chevron on hover or keyboard focus, so the row only
+// advertises the disclosure when you're reaching for it — a "#" there read as a
+// channel named "Starred", and the glyph belongs to the rows, not the label
+// above them.
 function ChannelGroup({
   sectionId,
   label,
   className,
+  flat,
   children,
 }: {
   sectionId: string;
   label: string;
   className?: string;
+  /** Layout-only: rows sit at the label's level instead of indented under it. */
+  flat?: boolean;
   children: ReactNode;
 }) {
   const collapsedSections = useSidebarStore((s) => s.collapsedSections);
@@ -736,10 +741,12 @@ function ChannelGroup({
         render={<MenuLabel render={<button type="button" />} />}
       >
         <span className="relative flex size-3.5 shrink-0 items-center justify-center">
-          <HashIcon
-            size={14}
-            className="group-hover/group-trigger:hidden group-focus-visible/group-trigger:hidden"
-          />
+          {!flat && (
+            <HashIcon
+              size={14}
+              className="group-hover/group-trigger:hidden group-focus-visible/group-trigger:hidden"
+            />
+          )}
           {isOpen ? (
             <CaretDownIcon
               size={14}
@@ -759,7 +766,7 @@ function ChannelGroup({
           makes each expand rebuild the lot (~940ms for 46 channels, vs ~80ms
           to collapse). */}
       <Collapsible.Panel keepMounted>
-        <div className="pl-5">{children}</div>
+        <div className={cn(!flat && "pl-5")}>{children}</div>
       </Collapsible.Panel>
     </Collapsible.Root>
   );
@@ -851,7 +858,11 @@ export function ChannelsList() {
               />
 
               {starred.length > 0 && (
-                <ChannelGroup sectionId={STARRED_SECTION_ID} label="Starred">
+                <ChannelGroup
+                  sectionId={STARRED_SECTION_ID}
+                  label="Starred"
+                  flat={channelsLayout}
+                >
                   {starred.map((channel) => (
                     <ChannelSection
                       key={channel.id}
@@ -863,7 +874,11 @@ export function ChannelsList() {
                 </ChannelGroup>
               )}
 
-              <ChannelGroup sectionId={CHANNELS_SECTION_ID} label="Channels">
+              <ChannelGroup
+                sectionId={CHANNELS_SECTION_ID}
+                label="Channels"
+                flat={channelsLayout}
+              >
                 {!isLoading && channels.length === 0 && (
                   <Empty className="px-2 py-1 text-subtle-foreground text-xs">
                     <EmptyHeader className="text-left">

packages/ui/src/features/canvas/components/ChannelsSidebar.test.tsx

@@ -1,6 +1,6 @@
 import { Theme } from "@radix-ui/themes";
 import { act, render, screen } from "@testing-library/react";
-import { beforeEach, describe, expect, it, vi } from "vitest";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
 const mocks = vi.hoisted(() => ({
   featureFlags: new Map<string, boolean>(),
@@ -169,6 +169,79 @@ describe("ChannelsSidebar", () => {
       expect(listIsInteractive()).toBe(true);
       expect(screen.queryByTestId("channel-sidebar")).toBeNull();
     });
+
+    // A trackpad swipe reaches the panes as a horizontal wheel. Right (negative
+    // deltaX, the platform "back" direction) leaves the channel; left returns to
+    // the one still scoped.
+    describe("swiping", () => {
+      // Wheel deltas within one gesture arrive back to back; a pause between
+      // them is what ends it. Fake timers let a test say which it's sending.
+      const wheel = (deltaX: number, deltaY = 0) =>
+        act(() => {
+          screen.getByTestId("channels-list").dispatchEvent(
+            new WheelEvent("wheel", {
+              deltaX,
+              deltaY,
+              bubbles: true,
+              cancelable: true,
+            }),
+          );
+        });
+      const pause = () => act(() => void vi.advanceTimersByTime(500));
+
+      beforeEach(() => {
+        vi.useFakeTimers();
+        mocks.routeChannelId = ENG.id;
+      });
+      afterEach(() => vi.useRealTimers());
+
+      it("goes back to the list and forward into the channel", () => {
+        renderSidebar();
+
+        wheel(-80);
+        expect(listIsInteractive()).toBe(true);
+        // The channel is browsed away from, not left.
+        expect(useCurrentChannelStore.getState().currentChannelId).toBe(ENG.id);
+
+        pause();
+        wheel(80);
+        expect(listIsInteractive()).toBe(false);
+      });
+
+      // One flick is dozens of small deltas, so the distance has to add up
+      // across them rather than be read off any one event.
+      it("adds a gesture's deltas up", () => {
+        renderSidebar();
+        wheel(-20);
+        expect(listIsInteractive()).toBe(false);
+        wheel(-20);
+        wheel(-20);
+        expect(listIsInteractive()).toBe(true);
+      });
+
+      it("ignores a mostly-vertical wheel", () => {
+        renderSidebar();
+        wheel(-80, -200);
+        expect(listIsInteractive()).toBe(false);
+      });
+
+      it("forgets a nudge once the gesture ends", () => {
+        renderSidebar();
+        wheel(-30);
+        pause();
+        wheel(-30);
+        expect(listIsInteractive()).toBe(false);
+      });
+
+      // The momentum tail of one flick keeps delivering deltas; read as fresh
+      // travel they'd swipe straight back to where the flick started.
+      it("does not let one flick's momentum swipe twice", () => {
+        renderSidebar();
+        wheel(-80);
+        wheel(200);
+        expect(listIsInteractive()).toBe(true);
+      });
+    });
   });
 
   describe("the Archived row", () => {

packages/ui/src/features/canvas/components/ChannelsSidebar.tsx

@@ -7,11 +7,13 @@ import { ChannelSidebar } from "@posthog/ui/features/canvas/components/ChannelSi
 import { ChannelsFab } from "@posthog/ui/features/canvas/components/ChannelsFab";
 import { ChannelsList } from "@posthog/ui/features/canvas/components/ChannelsList";
 import { useChannelsSidebarStore } from "@posthog/ui/features/canvas/components/channelsSidebarStore";
+import { useChannelPaneSwipe } from "@posthog/ui/features/canvas/hooks/useChannelPaneSwipe";
 import { useChannelsLayout } from "@posthog/ui/features/canvas/hooks/useChannelsLayout";
 import { useCurrentChannel } from "@posthog/ui/features/canvas/hooks/useCurrentChannel";
 import { PERSONAL_CHANNEL_NAME } from "@posthog/ui/features/canvas/hooks/useTaskChannels";
 import { useTrackChannelsSpaceViewed } from "@posthog/ui/features/canvas/hooks/useTrackChannelsSpaceViewed";
 import {
+  showChannelList,
   showChannelPane,
   useChannelPaneStore,
 } from "@posthog/ui/features/canvas/stores/channelPaneStore";
@@ -47,6 +49,10 @@ import { useDeferredValue, useEffect, useRef } from "react";
  * Both panes stay mounted so the slide has something to slide, and so coming
  * back to the list doesn't rebuild every row's menus and dialogs. The offscreen
  * one is `inert`, keeping it out of the tab order and off screen readers.
+ *
+ * A two-finger horizontal swipe moves between them, so the back row isn't the
+ * only way out of a channel — and swiping the other way returns to the channel
+ * that stayed scoped the whole time.
  */
 function ChannelPanes({
   channelId,
@@ -55,8 +61,17 @@ function ChannelPanes({
   channelId: string | null;
   showList: boolean;
 }) {
+  const panesRef = useRef<HTMLDivElement | null>(null);
+  useChannelPaneSwipe(panesRef, {
+    // With no channel to slide to, the list is all there is — leave the gesture
+    // to the platform rather than eat it for a slide that can't happen.
+    enabled: channelId != null,
+    onBack: showChannelList,
+    onForward: showChannelPane,
+  });
+
   return (
-    <Box className="min-h-0 flex-1 overflow-hidden">
+    <Box ref={panesRef} className="min-h-0 flex-1 overflow-hidden">
       <div
         className={cn(
           "flex h-full w-[200%] transition-transform duration-200 ease-out motion-reduce:transition-none",

packages/ui/src/features/canvas/hooks/useChannelPaneSwipe.ts

@@ -0,0 +1,65 @@
+import type { RefObject } from "react";
+import { useEffect } from "react";
+
+/** How far a horizontal gesture has to travel before it counts as a swipe. */
+const SWIPE_THRESHOLD_PX = 45;
+/** A pause this long ends the gesture, so momentum can't chain two swipes. */
+const GESTURE_GAP_MS = 180;
+
+/**
+ * Two-finger horizontal swipes over the sidebar, mapped to the pane slider.
+ *
+ * A trackpad swipe arrives as a `wheel` event carrying `deltaX`; the sidebar has
+ * nothing to scroll sideways, so we claim those and translate them into the
+ * same back/forward the back row and a channel click already do. Swipe right
+ * (the platform "back" direction, a negative `deltaX`) goes out to the list;
+ * swipe left goes back into the channel you're still scoped to.
+ *
+ * Distance is accumulated across the event stream rather than read off a single
+ * event — one flick is dozens of small deltas. Once a swipe fires, the gesture
+ * is locked until the wheel goes quiet, so the momentum tail doesn't bounce the
+ * panes back and forth.
+ */
+export function useChannelPaneSwipe(
+  ref: RefObject<HTMLElement | null>,
+  {
+    enabled,
+    onBack,
+    onForward,
+  }: { enabled: boolean; onBack: () => void; onForward: () => void },
+): void {
+  useEffect(() => {
+    const element = ref.current;
+    if (!element || !enabled) return;
+
+    let travelled = 0;
+    let lastEventAt = Number.NEGATIVE_INFINITY;
+    let locked = false;
+
+    const onWheel = (event: WheelEvent) => {
+      // A mostly-vertical wheel is someone scrolling the list, not swiping.
+      if (Math.abs(event.deltaX) <= Math.abs(event.deltaY)) return;
+      // Claim it before anything upstream reads it as history navigation.
+      event.preventDefault();
+
+      if (event.timeStamp - lastEventAt > GESTURE_GAP_MS) {
+        travelled = 0;
+        locked = false;
+      }
+      lastEventAt = event.timeStamp;
+      if (locked) return;
+
+      travelled += event.deltaX;
+      if (travelled <= -SWIPE_THRESHOLD_PX) {
+        locked = true;
+        onBack();
+      } else if (travelled >= SWIPE_THRESHOLD_PX) {
+        locked = true;
+        onForward();
+      }
+    };
+
+    element.addEventListener("wheel", onWheel, { passive: false });
+    return () => element.removeEventListener("wheel", onWheel);
+  }, [ref, enabled, onBack, onForward]);
+}