Show only the newest repository when replies arrive out of order

Every reload and every open takes a number before asking git; a reply is
used only if no newer request was sent after it, and an out-of-date error
is not shown. Commit details and diffs that come back after another
repository was opened are neither kept nor shown.

src/App.vue

@@ -11,6 +11,7 @@ import { layout } from "./lib/layout";
 import { textWidth } from "./lib/measure";
 import { colorOf } from "./lib/palette";
 import { addRecent, mergeRecents } from "./lib/recents";
+import { tickets } from "./lib/latest";
 import type { FileDiff, Layout } from "./lib/diff";
 import type { ChangedFile, CommitDetails, FilterState, Ref, RefKind, RepoData } from "./lib/types";
 import DiffView from "./components/DiffView.vue";
@@ -104,6 +105,12 @@ function startDrag(e: PointerEvent, axis: "x" | "y") {
 let filtersLoadedFor: string | null = null;
 
 let loading = false;
+/**
+ * Git runs away from the window, so replies can arrive in another order than the requests
+ * went out. Every request that can put a new repository on screen (a reload or opening one)
+ * takes a ticket; a reply is used only if no newer such request was sent after it.
+ */
+const repoRequests = tickets();
 /** False until the first load answers, so the welcome screen does not flash up at start. */
 const started = ref(false);
 
@@ -111,11 +118,14 @@ async function load() {
   // The window gets focus often; one reload at a time is enough.
   if (loading) return;
   loading = true;
+  const ticket = repoRequests.take();
   try {
     // null: gites was started outside a repository and none is open yet.
     const data = await invoke<RepoData | null>("load_repo");
-    if (data) await applyRepo(data);
+    if (data) await applyRepo(data, ticket);
   } catch (e) {
+    // A newer request replaced this one; its error no longer matters.
+    if (!repoRequests.isLatest(ticket)) return;
     // A repository already on screen stays, for example when a connection drops.
     if (repo.value) showToast(`could not reload: ${e}`, { error: true });
     else error.value = String(e);
@@ -127,9 +137,12 @@ async function load() {
 
 async function openRepo(path: string) {
   menuOpen.value = false;
+  const ticket = repoRequests.take();
   try {
-    await applyRepo(await invoke<RepoData>("open_repo", { path }));
+    await applyRepo(await invoke<RepoData>("open_repo", { path }), ticket);
   } catch (e) {
+    // A newer request replaced this one; its error no longer matters.
+    if (!repoRequests.isLatest(ticket)) return;
     // The repository that was open stays open.
     showToast(`could not open ${path}: ${e}`, { error: true });
   }
@@ -144,12 +157,16 @@ async function browse() {
 
 const menuOpen = ref(false);
 
-async function applyRepo(data: RepoData) {
+/** Puts `data` on screen, unless a request newer than the one holding `ticket` was sent. */
+async function applyRepo(data: RepoData, ticket: number) {
+  if (!repoRequests.isLatest(ticket)) return;
   error.value = null;
   if (filtersLoadedFor !== data.root) {
     const saved = await invoke<Partial<FilterState & { collapseAll: boolean }> | null>("load_filters", {
       repo: data.root,
     });
+    // Another repository may have been asked for while the filters were read.
+    if (!repoRequests.isLatest(ticket)) return;
     filters.hidden = saved?.hidden ?? [];
     filters.rules = saved?.rules ?? [];
     filters.hideTags = saved?.hideTags ?? false;
@@ -161,7 +178,11 @@ async function applyRepo(data: RepoData) {
     diffCache.clear();
     if (scroller.value) scroller.value.scrollTop = 0;
     settings.recents = addRecent(settings.recents, data.root);
+    // The caches were emptied just above; the new root goes on screen in the same step, so a
+    // late reply for the old repository sees that the root changed and is not kept.
+    repo.value = data;
     await getCurrentWindow().setTitle(`gites — ${data.root}`);
+    return;
   }
   repo.value = data;
 }
@@ -275,14 +296,18 @@ watch([selectedHash, () => settings.previewShown], ([hash, shown]) => {
   }
   // Wait a moment, so holding a key down does not run git for every row passed.
   detailsTimer = window.setTimeout(async () => {
+    // A reply that comes after another repository was opened belongs to the old one.
+    const root = repo.value?.root;
     try {
       const d = await invoke<CommitDetails>("commit_details", { hash });
+      if (repo.value?.root !== root) return;
       detailsCache.set(hash, d);
       if (selectedHash.value === hash) {
         details.value = d;
         detailsError.value = null;
       }
     } catch (e) {
+      if (repo.value?.root !== root) return;
       if (selectedHash.value === hash) detailsError.value = String(e);
     }
   }, 120);
@@ -308,11 +333,15 @@ async function openDiff(file: ChangedFile, force = false) {
     return;
   }
   diffData.value = null;
+  // A reply that comes after another repository was opened belongs to the old one.
+  const root = repo.value?.root;
   try {
     const d = await invoke<FileDiff>("file_diff", { hash, path: file.path, oldPath: file.old_path, force });
+    if (repo.value?.root !== root) return;
     diffCache.set(key, d);
     if (diffFile.value === file && details.value?.hash === hash) diffData.value = d;
   } catch (e) {
+    if (repo.value?.root !== root) return;
     if (diffFile.value === file) diffError.value = String(e);
   }
 }

src/lib/latest.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+import { tickets } from "./latest";
+
+describe("tickets", () => {
+  it("treats the only ticket taken as the newest", () => {
+    const t = tickets();
+    const a = t.take();
+    expect(t.isLatest(a)).toBe(true);
+  });
+  it("treats an older ticket as out of date once a newer one is taken", () => {
+    const t = tickets();
+    const older = t.take();
+    const newer = t.take();
+    expect(t.isLatest(older)).toBe(false);
+    expect(t.isLatest(newer)).toBe(true);
+  });
+  it("keeps an older ticket out of date after more tickets are taken", () => {
+    const t = tickets();
+    const first = t.take();
+    t.take();
+    const last = t.take();
+    expect(t.isLatest(first)).toBe(false);
+    expect(t.isLatest(last)).toBe(true);
+  });
+  it("keeps separate sets of tickets apart", () => {
+    const a = tickets();
+    const b = tickets();
+    const fromA = a.take();
+    b.take();
+    b.take();
+    expect(a.isLatest(fromA)).toBe(true);
+  });
+});

src/lib/latest.ts

@@ -0,0 +1,17 @@
+/**
+ * Numbers requests so that only the reply to the newest one is used. Take a ticket before
+ * sending a request; when its reply arrives, use it only if `isLatest` says no newer ticket
+ * was taken in the meantime.
+ */
+export interface Tickets {
+  take(): number;
+  isLatest(ticket: number): boolean;
+}
+
+export function tickets(): Tickets {
+  let newest = 0;
+  return {
+    take: () => ++newest,
+    isLatest: (ticket) => ticket === newest,
+  };
+}