feat(github): pull request tool window, timeline and review flow (#477)

Replaces the Pull Requests tool window with a full review workflow on top of gh's authentication.

- List with search, quick filters and paging; a tab per pull request and a New Pull Request tab.
- Details: commit picker, changes tree with viewed state, CI and reviewer status, merge, close and reopen.
- Timeline editor: comments, review threads, reactions and suggested changes.
- Review in the diff viewer and, for the checked-out branch, in the editor (review mode).
- New generic vcs extension points: registerDiffViewerProvider, lineInlays, reviewGutter, branch widget extensions; new vcs_merge_base and gh_api commands.
- CSP: img-src allows https://avatars.githubusercontent.com for avatars.

Fixed while testing against a real repository: remotes behind an SSH host alias, mergeability stuck on UNKNOWN, Apply Locally staying disabled after a checkout, relative links navigating the app's page, and review inlays wider than the pane.

Co-authored-by: imacross <[email protected]>

src/features/github/toolwindow/store.ts

@@ -0,0 +1,74 @@
+/**
+ * Content tabs of the Pull Requests tool window (IntelliJ's `ReviewToolwindowTabsManager`):
+ * the list tab (not closable), one `#N` tab per opened pull request and the "New Pull
+ * Request" tab, each opened at most once. Also the list's selection, which actions such as
+ * Checkout Pull Request… use.
+ */
+import { create } from "zustand";
+import { setContext } from "@/platform/context";
+
+export type GhTab = { kind: "pr"; number: number } | { kind: "create" };
+export type GhTabId = "list" | `pr:${number}` | "create";
+
+interface TabsState {
+  tabs: GhTab[];
+  active: GhTabId;
+  /** The pull request selected in the list. */
+  listSelection: number | null;
+}
+
+export const useGhTabs = create<TabsState>(() => ({ tabs: [], active: "list", listSelection: null }));
+
+export const tabId = (t: GhTab): GhTabId => (t.kind === "pr" ? `pr:${t.number}` : "create");
+
+/** Opens (or selects) the `#N` tab. */
+export function openPullRequestTab(number: number) {
+  useGhTabs.setState((s) => ({
+    tabs: s.tabs.some((t) => t.kind === "pr" && t.number === number) ? s.tabs : [...s.tabs, { kind: "pr", number }],
+    active: `pr:${number}`,
+  }));
+}
+
+/** Opens (or selects) the "New Pull Request at {repo}" tab. */
+export function openCreateTab() {
+  useGhTabs.setState((s) => ({
+    tabs: s.tabs.some((t) => t.kind === "create") ? s.tabs : [...s.tabs, { kind: "create" }],
+    active: "create",
+  }));
+}
+
+export function selectTab(id: GhTabId) {
+  useGhTabs.setState({ active: id });
+}
+
+/** Closes a `#N` or the New Pull Request tab; the tab before it becomes active. */
+export function closeTab(id: GhTabId) {
+  if (id === "list") return;
+  useGhTabs.setState((s) => {
+    const i = s.tabs.findIndex((t) => tabId(t) === id);
+    if (i < 0) return s;
+    const tabs = s.tabs.filter((_, j) => j !== i);
+    const before = tabs[i - 1];
+    const active = s.active === id ? (before ? tabId(before) : "list") : s.active;
+    return { tabs, active };
+  });
+}
+
+export function setListSelection(number: number | null) {
+  useGhTabs.setState({ listSelection: number });
+}
+
+/** The pull request of the active `#N` tab, else the list's selection. */
+export function contextPullRequest(): number | null {
+  const s = useGhTabs.getState();
+  const m = /^pr:(\d+)$/.exec(s.active);
+  return m ? Number(m[1]) : s.listSelection;
+}
+
+/** Another repository or project: only the list tab stays. */
+export function resetTabs() {
+  useGhTabs.setState({ tabs: [], active: "list", listSelection: null });
+}
+
+/** `githubPrTab`: `list`, `pr` or `create`, for the tab-specific shortcuts (Refresh). */
+useGhTabs.subscribe((s) => setContext("githubPrTab", s.active.startsWith("pr:") ? "pr" : s.active));