feat: multi-project workspaces and project window groups (#448)

Workspaces open several local project folders in one IDE session (File › New / Open / Manage Workspace…, or Attach when opening a project, which creates a workspace automatically for a plain project window). Member folders are the Project view roots and take part in indexing, Find in Files, Git, language servers, run configurations and builds; agent tasks choose which member they work in. Window › Merge All Project Windows groups project windows into one window with project tabs (switch, reorder, close, move to a new window), restored on reopen.

Closes #241
Closes #198
Closes #286

src/workbench/projectWindow.ts

@@ -2,14 +2,14 @@
 import { t } from "@/platform/i18n";
 import { call, commands } from "@/platform/ipc";
 import { confirmLeaveProject, useProject } from "@/platform/project";
-import { connectRemote } from "@/platform/remote";
+import { connectRemote, isRemoteWindow } from "@/platform/remote";
 import { ask } from "./messages";
 import { maybeEditorService } from "./contributions";
 
-/** "Open project in": `new` | `same` | `ask`. */
-export function openPolicy(): "ask" | "new" | "same" {
+/** "Open project in": `new` | `same` | `attach` | `ask`. */
+export function openPolicy(): "ask" | "new" | "same" | "attach" {
   const v = useProject.getState().settings?.general?.openProjectIn;
-  return v === "new" || v === "same" ? v : "ask";
+  return v === "new" || v === "same" || v === "attach" ? v : "ask";
 }
 
 /**
@@ -17,22 +17,26 @@ export function openPolicy(): "ask" | "new" | "same" {
  * per "Open project in", asking when set to (and remembering "Don't ask again").
  * `null`: cancelled.
  */
-export async function chooseProjectWindow(name: string): Promise<"new" | "same" | null> {
+export async function chooseProjectWindow(name: string, allowAttach = true): Promise<"new" | "same" | "attach" | null> {
   const { project, lightEdit } = useProject.getState();
   if (!project && !lightEdit) return "same";
-  const mode = openPolicy();
+  const canAttach = allowAttach && !!project && !isRemoteWindow();
+  const policy = openPolicy();
+  const mode = policy === "attach" && !canAttach ? "ask" : policy;
   if (mode !== "ask") return mode;
   const r = await ask({
     title: t("app.window.askTitle"),
+    width: canAttach ? 640 : undefined,
     body: t("app.window.askBody", { name }),
     buttons: [
+      { id: "cancel", label: t("common.cancel") },
+      ...(canAttach ? [{ id: "attach", label: t("app.window.askAttach") }] : []),
       { id: "new", label: t("app.window.askNew") },
       { id: "same", label: t("app.window.askThis"), primary: true },
-      { id: "cancel", label: t("common.cancel") },
     ],
     checkbox: t("app.window.askRemember"),
   });
-  if (r.button !== "same" && r.button !== "new") return null;
+  if (r.button !== "same" && r.button !== "new" && r.button !== "attach") return null;
   if (r.checked) {
     try {
       useProject.setState({
@@ -56,7 +60,7 @@ export async function openRemoteProject(
   here: () => Promise<unknown> = () => connectRemote(sshConfig, path),
 ): Promise<boolean> {
   if ((await call(commands.windowOpenRemote(sshConfig, path, false))).kind === "focused") return true;
-  const mode = await chooseProjectWindow(path.replace(/\/+$/, "").split("/").pop() || path);
+  const mode = await chooseProjectWindow(path.replace(/\/+$/, "").split("/").pop() || path, false);
   if (!mode) return false;
   if (mode === "new") {
     await call(commands.windowOpenRemote(sshConfig, path, true));