feat: add installDir variable for NsisUpdater

Author: panther7

docs/api/electron-builder.md

@@ -1599,6 +1599,9 @@ return path.join(target.outDir, <code>__${target.name}-${getArtifactArchName(arc
 <p>Currently false to prevent breaking the current API, but it should be changed to default true at some point that breaking changes are allowed.</p>
 </li>
 <li>
+<p><code id="AppUpdater-installDir">installDir</code> = <code>''</code> String - <em>NSIS updater only</em> - Install folder for NSIS updater</p>
+</li>
+<li>
 <p><code id="AppUpdater-currentVersion">currentVersion</code> SemVer - The current application version.</p>
 </li>
 <li>

packages/electron-updater/src/AppUpdater.ts

@@ -86,6 +86,12 @@ export abstract class AppUpdater extends (EventEmitter as new () => TypedEmitter
 
   disableWebInstaller = false
 
+  /**
+   * Install dir for Nsis Updater
+   *
+   */
+  installDir = ''
+
   /**
    * The current application version.
    */

packages/electron-updater/src/NsisUpdater.ts

@@ -109,6 +109,11 @@ export class NsisUpdater extends BaseUpdater {
       args.push("--force-run")
     }
 
+    if (this.installDir && typeof this.installDir === 'string') {
+      // maybe check if folder exists
+      args.push(`/D=${this.installDir}`)
+    }
+
     const packagePath = this.downloadedUpdateHelper == null ? null : this.downloadedUpdateHelper.packageFile
     if (packagePath != null) {
       // only = form is supported