.eslintrc.cjs

@@ -1,3 +1,8 @@
+// Airbnb's own bans, kept: a `no-restricted-syntax` entry below replaces the whole list.
+const airbnbRestrictedSyntax = require('eslint-config-airbnb-base/rules/style').rules[
+  'no-restricted-syntax'
+];
+
 module.exports = {
   env: {
     browser: true,
@@ -62,6 +67,21 @@ module.exports = {
     "@typescript-eslint/no-shadow": "error"
   },
   overrides: [
+    {
+      // The one join path: a join is `joinEstateRoom`, which files the DM before it sends the join.
+      files: ['src/**/*.ts', 'src/**/*.tsx'],
+      excludedFiles: ['src/app/features/estate/joinEstateRoom.ts', 'src/**/*.test.*'],
+      rules: {
+        'no-restricted-syntax': [
+          ...airbnbRestrictedSyntax,
+          {
+            selector: "CallExpression[callee.property.name='joinRoom']",
+            message:
+              'Join a room through joinEstateRoom (features/estate/joinEstateRoom.ts), the one join path.',
+          },
+        ],
+      },
+    },
     {
       files: ['*.ts'],
       rules: {

harness/estate/check.cjs

@@ -2,12 +2,17 @@
 // non-zero when the page or the fake homeserver's log says otherwise.
 const fs = require('fs');
 const fails = [];
+let asserted = 0;
 exports.expect = (label, ok, detail = '') => {
+  asserted += 1;
   console.log(`[ASSERT] ${ok ? 'PASS' : 'FAIL'} ${label}${ok ? '' : ` :: ${detail}`}`);
   if (!ok) fails.push(label);
 };
-/** Exit code for the drive: 4 when any assertion failed. */
-exports.done = () => (fails.length ? 4 : 0);
+/** Exit code for the drive: 4 when any assertion failed, 5 when none ran (a drive that asserts nothing proves nothing). */
+exports.done = () => {
+  if (fails.length) return 4;
+  return asserted === 0 ? 5 : 0;
+};
 /** The fake homeserver's request log (HSLOG is shared with the server process). */
 exports.hsLog = () => fs.readFileSync(process.env.HSLOG, 'utf8').split('\n');
 /** Bodies of the account-data PUTs for m.direct, in order. */

harness/estate/check.test.ts

@@ -0,0 +1,35 @@
+// @vitest-environment node
+import { createRequire } from 'module';
+import { describe, expect, it, vi } from 'vitest';
+
+// A drive that asserts nothing proves nothing: its exit code must say so.
+const fresh = () => {
+  const require = createRequire(import.meta.url);
+  const path = require.resolve('./check.cjs');
+  delete require.cache[path];
+  return require('./check.cjs') as {
+    expect: (label: string, ok: boolean, detail?: string) => void;
+    done: () => number;
+  };
+};
+
+describe('estate drive exit code', () => {
+  it('is 5 when no assertion ran', () => {
+    expect(fresh().done()).toBe(5);
+  });
+
+  it('is 0 when assertions ran and all held', () => {
+    vi.spyOn(console, 'log').mockImplementation(() => undefined);
+    const c = fresh();
+    c.expect('holds', true);
+    expect(c.done()).toBe(0);
+  });
+
+  it('is 4 when any assertion failed', () => {
+    vi.spyOn(console, 'log').mockImplementation(() => undefined);
+    const c = fresh();
+    c.expect('holds', true);
+    c.expect('breaks', false, 'detail');
+    expect(c.done()).toBe(4);
+  });
+});

src/app/features/estate/joinPath.lint.test.ts

@@ -0,0 +1,32 @@
+// @vitest-environment node
+import { describe, expect, it } from 'vitest';
+import { ESLint } from 'eslint';
+
+// The product rule is one join path: a join is joinEstateRoom, which files the DM before it sends the join.
+// This pins that the lint config enforces it, not just that the code happens to comply today.
+const lint = async (filePath: string, code: string) => {
+  const eslint = new ESLint({ cwd: process.cwd(), useEslintrc: true });
+  const [result] = await eslint.lintText(code, { filePath });
+  return result.messages.filter((m) => m.ruleId === 'no-restricted-syntax');
+};
+const JOIN = 'export const f = (mx: { joinRoom: (id: string) => void }) => mx.joinRoom("!a:b");\n';
+
+describe('the one join path is enforced by lint', () => {
+  it('rejects a joinRoom call anywhere but joinEstateRoom.ts', async () => {
+    const found = await lint('src/app/features/estate/EstateNavigator.tsx', JOIN);
+    expect(found).toHaveLength(1);
+    expect(found[0].message).toContain('joinEstateRoom');
+  });
+
+  it('allows the call inside joinEstateRoom.ts itself', async () => {
+    expect(await lint('src/app/features/estate/joinEstateRoom.ts', JOIN)).toHaveLength(0);
+  });
+
+  it('still applies the Airbnb syntax bans in the same files', async () => {
+    const found = await lint(
+      'src/app/foo.ts',
+      'export const g = (o: object) => { for (const k in o) { return k; } return 0; };\n'
+    );
+    expect(found.some((m) => m.message.includes('for..in'))).toBe(true);
+  });
+});