fix(tasks): Make every background task cancellable, queued or running (#177)

Background tasks often couldn't be cancelled, or cancelling didn't stop them:
- A cancel that arrived before the backend registered the request was dropped (build while saving files, multi-repository fetch/pull between repositories). The host now remembers early cancels (bounded, 2 min), and request ids start at a random value per page.
- There was no queue and no common cancel path: backend-reported tasks (LSP progress, deployment transfers) couldn't be cancelled, and tool installs, VCS operations and update checks had no cancel button in Background Tasks.
- Only the direct child process was killed, and JDK / tool archives were extracted without checking for cancellation.

Tool installs and JDK downloads now share a downloads queue; cancelling a queued task removes it without starting any work. Every task cancels through one path that shows "Cancelling…" and then removes it; tasks that can't be interrupted show a disabled cancel button with the reason. IdeEvent::Task carries `cancellable` with a cancel_task command, cancellable LSP progress sends window/workDoneProgress/cancel, installers, curl and tar run in their own process group and are killed as a group, and extraction checks for cancellation between entries.

Claude-Session: https://claude.ai/code/session_01Dq6jQQn8ZhRfkkyj3PRutA

src/features/app/updates.ts

@@ -39,9 +39,13 @@ export function checkForUpdates(): Promise<void> {
 
 async function runCheck() {
   const title = t("app.update.checking");
-  upsertTask({ id: CHECK_TASK_ID, title, message: null, fraction: null, done: false });
+  // The check only reads: cancelling drops its answer (the request finishes on its own).
+  let abandon = () => {};
+  const abandoned = new Promise<"cancelled">((resolve) => (abandon = () => resolve("cancelled")));
+  upsertTask({ id: CHECK_TASK_ID, title, message: null, fraction: null, done: false, cancel: () => abandon() });
   try {
-    const r = await call(commands.appCheckUpdate());
+    const r = await Promise.race([call(commands.appCheckUpdate()), abandoned]);
+    if (r === "cancelled") return;
     if (!r.enabled) {
       notifications().notify({
         level: "info",
@@ -122,6 +126,8 @@ async function runInstall(version: string) {
       fraction,
       done: false,
       cancel: p.type === "installing" ? undefined : cancel,
+      // Replacing the app happens in one step that must not be cut short.
+      uncancellable: p.type === "installing" ? t("app.update.installUncancellable") : undefined,
     });
   };
   // The notification's action is spent: progress lives in the status bar from here.

src/features/build-tools/store.ts

@@ -23,7 +23,7 @@ import {
 import { downloadJdkActions } from "@/platform/jdk";
 import { useProject } from "@/platform/project";
 import { editorService, notifications } from "@/workbench/contributions";
-import { removeTask, upsertTask } from "@/workbench/tasks";
+import { cancelTask, removeTask, upsertTask, useTasks } from "@/workbench/tasks";
 import { profilesList, type GradleRunOptions, type MavenRunOptions } from "./model";
 
 export interface BuildSettings {
@@ -231,7 +231,10 @@ export async function syncTool(tool: BuildTool): Promise<void> {
 
 export function cancelSync(tool: BuildTool) {
   const s = useBuild.getState().syncing[tool];
-  if (s) void commands.cancelRequest(s.request);
+  if (!s) return;
+  const taskId = `build-sync:${tool}`;
+  if (useTasks.getState().tasks.some((t) => t.id === taskId && t.cancel)) cancelTask(taskId);
+  else void commands.cancelRequest(s.request);
 }
 
 export function resetBuild() {

src/features/build/store.ts

@@ -25,7 +25,7 @@ import {
 } from "@/platform/ipc";
 import { useProject } from "@/platform/project";
 import { maybeEditorService, notifications, toolWindowService } from "@/workbench/contributions";
-import { removeTask, upsertTask } from "@/workbench/tasks";
+import { cancelTask, removeTask, upsertTask, useTasks } from "@/workbench/tasks";
 import { appendOutput, finishSummary, firstError, messageFiles, type BuildStatus, type ConsoleLine } from "./model";
 
 export const BUILD_TASK_ID = "build:compile";
@@ -248,7 +248,10 @@ function showFailure() {
 
 export function stopBuild() {
   const { request } = useBuildRun.getState();
-  if (request != null) backend.cancel(request);
+  if (request == null) return;
+  // Through the task, so its progress says "Cancelling…" until the build has stopped.
+  if (useTasks.getState().tasks.some((t) => t.id === BUILD_TASK_ID && t.cancel)) cancelTask(BUILD_TASK_ID);
+  else backend.cancel(request);
 }
 
 /** Runs the last build again (the tool window's rerun button). */

src/features/tools/__tests__/tools.test.tsx

@@ -70,6 +70,22 @@ describe("tools store", () => {
     expect(useTools.getState().tools.find((t) => t.name === "gopls")?.status).toBe("missing");
   });
 
+  it("installs one at a time; one cancelled while it waits never starts", async () => {
+    backend.stepMs = 10;
+    await refreshTools();
+    const install = vi.spyOn(backend, "install");
+    const first = installTool("gopls");
+    const queued = installTool("vtsls");
+    expect(useTasks.getState().tasks.find((t) => t.id === "tools:vtsls")).toMatchObject({ queued: true });
+    cancelInstall("vtsls");
+    expect(useTasks.getState().tasks.find((t) => t.id === "tools:vtsls")).toBeUndefined();
+    expect(await queued).toBeNull();
+    expect(useTools.getState().logs["vtsls"]?.error).toBe("Cancelled");
+    expect((await first)?.status).toBe("installed");
+    expect(install.mock.calls.map((c) => c[0])).toEqual(["gopls"]);
+    expect(notes.filter((n) => n.level === "error")).toHaveLength(0);
+  });
+
   it("uninstalls", async () => {
     await refreshTools();
     expect(await uninstallTool("rust-analyzer")).toBe(true);

src/features/tools/jdk.ts

@@ -17,10 +17,12 @@ import {
   requiredJdk,
   TEMURIN,
   type DownloadJdkArgs,
+  type JdkDownload,
 } from "@/platform/jdk";
 import { useProject } from "@/platform/project";
 import { notifications } from "@/workbench/contributions";
-import { upsertTask } from "@/workbench/tasks";
+import { queueTask, upsertTask } from "@/workbench/tasks";
+import { DOWNLOAD_QUEUE } from "./store";
 import { tx } from "@/platform/i18n";
 
 const JAVA_SETTINGS = "languages.java";
@@ -42,16 +44,19 @@ export function downloadJdkFor(args: DownloadJdkArgs): Promise<Sdk | null> {
   const title = `Downloading JDK ${args.version}`;
   const taskId = `jdk-download:${args.version}`;
   const key = `jdk-download-${args.version}`;
-  const cancel = () => job.cancel();
-  const job = downloadJdk(TEMURIN, args.version, null, (e) => {
-    const message = e.type === "line" ? e.text : e.message;
-    const fraction = e.type === "progress" ? e.fraction : null;
-    upsertTask({ id: taskId, title, message, fraction, done: false, cancel });
-  });
-  upsertTask({ id: taskId, title, message: "Eclipse Temurin", fraction: null, done: false, cancel });
   const p = (async () => {
     try {
-      const sdk = await job.promise;
+      // Waits for the downloads ahead of it; cancelling it there means it never starts.
+      const sdk = await queueTask(DOWNLOAD_QUEUE, { id: taskId, title }, () => {
+        const cancel = () => job.cancel();
+        upsertTask({ id: taskId, title, message: "Eclipse Temurin", fraction: null, done: false, cancel });
+        const job: JdkDownload = downloadJdk(TEMURIN, args.version, null, (e) => {
+          const message = e.type === "line" ? e.text : e.message;
+          const fraction = e.type === "progress" ? e.fraction : null;
+          upsertTask({ id: taskId, title, message, fraction, done: false, cancel });
+        });
+        return job.promise;
+      });
       if (args.languageServer) await chooseForLanguageServer(sdk.path);
       notifications().notify({
         group: "tools",

src/features/tools/store.ts

@@ -4,11 +4,13 @@ import type { RequestId, ToolInfo } from "@/bindings";
 import { executeAction } from "@/platform/actions";
 import { isCancelled, nextRequestId } from "@/platform/ipc";
 import { notifications } from "@/workbench/contributions";
-import { upsertTask } from "@/workbench/tasks";
+import { cancelTask, queueTask, upsertTask, useTasks } from "@/workbench/tasks";
 import { toolsBackend } from "./backend";
 import { tx } from "@/platform/i18n";
 
 export const SETTINGS_PAGE_ID = "languages.servers";
+/** Tool installs and JDK downloads take turns (one network download / package manager at a time). */
+export const DOWNLOAD_QUEUE = "downloads";
 const MAX_LOG_LINES = 400;
 
 export interface InstallJob {
@@ -100,24 +102,25 @@ export function installTool(name: string, opts: { notificationKey?: string } = {
   const taskId = `tools:${name}`;
   const key = opts.notificationKey ?? `tools-install-${name}`;
   useTools.setState((s) => ({ jobs: { ...s.jobs, [name]: { request, lines: [], fraction: null, message: null } } }));
-  upsertTask({ id: taskId, title: tx`Installing ${display}`, message: null, fraction: null, done: false });
+  const title = tx`Installing ${display}`;
+  const cancel = () => toolsBackend().cancel(request);
+  const task = (message: string | null, fraction: number | null) =>
+    upsertTask({ id: taskId, title, message, fraction, done: false, cancel });
 
   const p = (async () => {
     try {
-      const info = await toolsBackend().install(name, request, (e) => {
-        if (e.type === "line") {
-          patchJob(name, (j) => ({ ...j, lines: [...j.lines, e.text].slice(-MAX_LOG_LINES), message: e.text }));
-          upsertTask({ id: taskId, title: tx`Installing ${display}`, message: e.text, fraction: null, done: false });
-        } else {
-          patchJob(name, (j) => ({ ...j, fraction: e.fraction, message: e.message }));
-          upsertTask({
-            id: taskId,
-            title: tx`Installing ${display}`,
-            message: e.message,
-            fraction: e.fraction,
-            done: false,
-          });
-        }
+      // Downloads and package managers run one at a time; the rest wait, cancellable.
+      const info = await queueTask(DOWNLOAD_QUEUE, { id: taskId, title }, () => {
+        task(null, null);
+        return toolsBackend().install(name, request, (e) => {
+          if (e.type === "line") {
+            patchJob(name, (j) => ({ ...j, lines: [...j.lines, e.text].slice(-MAX_LOG_LINES), message: e.text }));
+            task(e.text, null);
+          } else {
+            patchJob(name, (j) => ({ ...j, fraction: e.fraction, message: e.message }));
+            task(e.message, e.fraction);
+          }
+        });
       });
       upsertTool(info);
       endJob(name, null);
@@ -151,7 +154,7 @@ export function installTool(name: string, opts: { notificationKey?: string } = {
       });
       return null;
     } finally {
-      upsertTask({ id: taskId, title: tx`Installing ${display}`, message: null, fraction: 1, done: true });
+      upsertTask({ id: taskId, title, message: null, fraction: 1, done: true });
       running.delete(name);
     }
   })();
@@ -159,7 +162,10 @@ export function installTool(name: string, opts: { notificationKey?: string } = {
   return p;
 }
 
+/** Cancels the install of `name`, queued or running (as the task's Cancel does). */
 export function cancelInstall(name: string) {
+  const taskId = `tools:${name}`;
+  if (useTasks.getState().tasks.some((t) => t.id === taskId)) return cancelTask(taskId);
   const job = useTools.getState().jobs[name];
   if (job) toolsBackend().cancel(job.request);
 }

src/features/vcs/ops.ts

@@ -6,9 +6,10 @@ import { Channel } from "@tauri-apps/api/core";
 import { create } from "zustand";
 import type { GitOperation, RemoteOp } from "@/bindings";
 import { tx } from "@/platform/i18n";
-import { call, commands, emitLocalIdeEvent, isCancelled, nextRequestId } from "@/platform/ipc";
+import { call, commands, isCancelled, nextRequestId } from "@/platform/ipc";
 import { editorsFor } from "@/editor/api";
 import { maybeEditorService, notifications } from "@/workbench/contributions";
+import { cancelTask, upsertTaskSoon, useTasks } from "@/workbench/tasks";
 import { progressFraction } from "./model";
 import { currentRepo, refreshNow, repoName, useVcs } from "./store";
 
@@ -129,7 +130,10 @@ export function lastRemoteFailure(): string | null {
 }
 
 export function cancelRemote() {
-  if (activeRemote !== null) void commands.cancelRequest(activeRemote);
+  if (activeRemote === null) return;
+  const taskId = `vcs:${activeRemote}`;
+  if (useTasks.getState().tasks.some((t) => t.id === taskId)) cancelTask(taskId);
+  else void commands.cancelRequest(activeRemote);
 }
 
 /** Every repository of the project (Fetch and Update Project act on all of them, as in IDEA). */
@@ -154,11 +158,12 @@ export async function runRemote(
   const [progressText, doneTitle] = REMOTE_TITLE[op.op];
   const progressTitle = tx(progressText);
   const request = nextRequestId();
-  const taskId = 900_000 + request;
+  const taskId = `vcs:${request}`;
   activeRemote = request;
   useVcs.setState({ remoteBusy: progressTitle });
+  const cancel = () => void commands.cancelRequest(request);
   const task = (message: string | null, fraction: number | null, done: boolean) =>
-    emitLocalIdeEvent({ type: "task", id: taskId, title: progressTitle, message, fraction, done });
+    upsertTaskSoon({ id: taskId, title: progressTitle, message, fraction, done, cancel });
   task(detail ?? null, null, false);
   notifications().notify({
     group: "vcs",
@@ -220,13 +225,16 @@ export async function runRemote(
     const cancelled = isCancelled(e);
     lastRemoteError = cancelled ? null : errorMessage(e);
     logConsole(cancelled ? "info" : "err", cancelled ? `${doneTitle} cancelled` : errorMessage(e));
-    notifications().notify({
-      group: "vcs",
-      level: cancelled ? "warning" : "error",
-      key: "vcs.remote",
-      title: cancelled ? `${doneTitle} cancelled` : `${doneTitle} failed`,
-      body: cancelled ? undefined : errorMessage(e),
-    });
+    // The user asked for it: the progress balloon just goes away.
+    if (cancelled) notifications().expire?.("vcs.remote");
+    else
+      notifications().notify({
+        group: "vcs",
+        level: "error",
+        key: "vcs.remote",
+        title: `${doneTitle} failed`,
+        body: errorMessage(e),
+      });
     return false;
   } finally {
     task(null, 1, true);
@@ -320,12 +328,13 @@ export async function runGitOperation(op: GitOperation, opts: GitOperationOption
   }
   await saveAll();
   const request = nextRequestId();
-  const taskId = 900_000 + request;
+  const taskId = `vcs:${request}`;
   activeRemote = request;
   const progress = tx(opts.progress);
   useVcs.setState({ remoteBusy: progress });
+  const cancel = () => void commands.cancelRequest(request);
   const task = (message: string | null, done: boolean) =>
-    emitLocalIdeEvent({ type: "task", id: taskId, title: progress, message, fraction: done ? 1 : null, done });
+    upsertTaskSoon({ id: taskId, title: progress, message, fraction: done ? 1 : null, done, cancel });
   task(null, false);
   notifications().notify({
     group: "vcs",
@@ -357,14 +366,14 @@ export async function runGitOperation(op: GitOperation, opts: GitOperationOption
     logConsole(cancelled ? "info" : "err", cancelled ? `${opts.failure}: cancelled` : message);
     notifications().expire?.("vcs.operation");
     await refreshNow();
-    const handled = !cancelled && opts.onError ? await opts.onError(message) : false;
+    const handled = cancelled || (opts.onError ? await opts.onError(message) : false);
     if (!handled)
       notifications().notify({
         group: "vcs",
-        level: cancelled ? "warning" : "error",
+        level: "error",
         key: "vcs.operation",
-        title: cancelled ? `${opts.progress} cancelled` : opts.failure,
-        body: cancelled ? undefined : message,
+        title: opts.failure,
+        body: message,
       });
     return false;
   } finally {