fix(auto-updater): Autoupdates to lower version with allowPrerelease=…

…true using GitHub releases

Close #1497

docs/Auto Update.md

@@ -330,7 +330,7 @@ Emitted on progress. Only supported over Windows build, since `Squirrel.Mac` [do
 | --- | --- | --- |
 | autoDownload = <code>true</code>| <code>boolean</code> | <a name="AppUpdater-autoDownload"></a>Whether to automatically download an update when it is found. |
 | allowPrerelease| <code>boolean</code> | <a name="AppUpdater-allowPrerelease"></a>*GitHub provider only.* Whether to allow update to pre-release versions. Defaults to `true` if application version contains prerelease components (e.g. `0.12.1-alpha.1`, here `alpha` is a prerelease component), otherwise `false`.<br><br>If `true`, downgrade will be allowed (`allowDowngrade` will be set to `true`). |
-| allowDowngrade| <code>boolean</code> | <a name="AppUpdater-allowDowngrade"></a>Whether to allow version downgrade (when a user from the beta channel wants to go back to the stable channel). Defaults to `true` if application version contains prerelease components (e.g. `0.12.1-alpha.1`, here `alpha` is a prerelease component), otherwise `false`. |
+| allowDowngrade| <code>boolean</code> | <a name="AppUpdater-allowDowngrade"></a>Whether to allow version downgrade (when a user from the beta channel wants to go back to the stable channel). |
 | requestHeaders| <code>[RequestHeaders](electron-builder-http#RequestHeaders)</code> \| <code>null</code> | <a name="AppUpdater-requestHeaders"></a>The request headers. |
 | logger = <code>(&lt;any&gt;global).__test_app ? null : console</code>| <code>[Logger](#Logger)</code> \| <code>null</code> | <a name="AppUpdater-logger"></a>The logger. You can pass [electron-log](https://github.com/megahertz/electron-log), [winston](https://github.com/winstonjs/winston) or another logger with the following interface: `{ info(), warn(), error() }`. Set it to `null` if you would like to disable a logging feature. |
 | signals = <code>new UpdaterSignal(this)</code>| <code>[UpdaterSignal](#UpdaterSignal)</code> | <a name="AppUpdater-signals"></a>For type safety you can use signals, e.g. `autoUpdater.signals.updateDownloaded(() => {})` instead of `autoUpdater.on('update-available', () => {})` |

packages/electron-updater/src/AppUpdater.ts

@@ -38,7 +38,7 @@ export abstract class AppUpdater extends EventEmitter {
 
   /**
    * Whether to allow version downgrade (when a user from the beta channel wants to go back to the stable channel).
-   * Defaults to `true` if application version contains prerelease components (e.g. `0.12.1-alpha.1`, here `alpha` is a prerelease component), otherwise `false`.
+   * @default false
    */
   allowDowngrade = false
 
@@ -117,8 +117,7 @@ export abstract class AppUpdater extends EventEmitter {
       throw new Error(`App version is not valid semver version: "${currentVersionString}`)
     }
 
-    this.allowDowngrade = hasPrereleaseComponents(this.currentVersion)
-    this.allowPrerelease = this.allowDowngrade
+    this.allowPrerelease = hasPrereleaseComponents(this.currentVersion)
 
     if (options != null) {
       this.setFeedURL(options)

test/src/nsisUpdaterTest.ts

@@ -45,6 +45,7 @@ test("check updates - no versions at all", async () => {
 
 async function testUpdateFromBintray(app: any) {
   const updater = new NsisUpdater(null, app)
+  updater.allowDowngrade = true
   updater.updateConfigPath = await writeUpdateConfig(<BintrayOptions>{
     provider: "bintray",
     owner: "actperepo",