fix(node): Use better "isStable" function (#7157)

lib/versioning/node/index.spec.ts

-import { api as nodever } from '.';
+import { DateTime } from 'luxon';
+import { isStable, api as nodever } from '.';
 
 describe('semver.getNewValue()', () => {
+  let dtLocal: any;
+  beforeEach(() => {
+    dtLocal = DateTime.local;
+  });
+  afterEach(() => {
+    DateTime.local = dtLocal;
+  });
   it('returns normalized toVersion', () => {
     expect(
       nodever.getNewValue({
@@ -21,4 +29,29 @@ describe('semver.getNewValue()', () => {
       })
     ).toEqual('~8.2.0');
   });
+  it('isStable', () => {
+    const t1 = DateTime.fromISO('2020-09-01');
+    const t2 = DateTime.fromISO('2021-06-01');
+    [
+      ['16.0.0', t1, false],
+      ['15.0.0', t1, false],
+      ['14.9.0', t1, false],
+      ['14.0.0', t2, true],
+      ['12.0.3', t1, true],
+      ['v12.0.3', t1, true],
+      ['12.0.3a', t1, false],
+      ['11.0.0', t1, false],
+
+      ['10.0.0', t1, true],
+      ['10.0.999', t1, true],
+      ['10.1.0', t1, true],
+
+      ['10.0.0a', t1, false],
+      ['9.0.0', t1, false],
+    ].forEach(([version, time, result]) => {
+      DateTime.local = (...args) =>
+        args.length ? dtLocal.apply(DateTime, args) : time;
+      expect(isStable(version as string)).toBe(result);
+    });
+  });
 });

lib/versioning/node/index.ts

+import { DateTime } from 'luxon';
 import { NewValueConfig, VersioningApi } from '../common';
 import npm, { isValid, isVersion } from '../npm';
+import { nodeSchedule } from './schedule';
 
 export const id = 'node';
 export const displayName = 'Node.js';
@@ -27,8 +29,21 @@ function getNewValue({
 
 export { isValid };
 
+export function isStable(version: string): boolean {
+  if (npm.isStable(version)) {
+    const major = npm.getMajor(version);
+    const schedule = nodeSchedule[`v${major}`];
+    if (schedule?.lts) {
+      // TODO: use the exact release that started LTS
+      return DateTime.local() > DateTime.fromISO(schedule.lts);
+    }
+  }
+  return false;
+}
+
 export const api: VersioningApi = {
   ...npm,
+  isStable,
   getNewValue,
 };
 export default api;