validate the package if pre-release flag is passed (#666)

* fix: validate the package if pre-release flag is passed * Update src/publish.ts * Update src/publish.ts Co-authored-by: João Moreno <joao.moreno@microsoft.com>

Author: sandy081

src/publish.ts

@@ -51,6 +51,22 @@ export async function publish(options: IPublishOptions = {}): Promise<any> {
 throw new Error(`Invalid extension VSIX manifest. ${err}`);
 }
 
+if (options.preRelease) {
+let isPreReleasePackage = false;
+try {
+isPreReleasePackage = !!vsix.xmlManifest.PackageManifest.Metadata[0].Properties[0].Property.some(
+p => p.$.Id === 'Microsoft.VisualStudio.Code.PreRelease'
+);
+} catch (err) {
+throw new Error(`Invalid extension VSIX manifest. ${err}`);
+}
+if (!isPreReleasePackage) {
+throw new Error(
+`Cannot use '--pre-release' flag with a package that was not packaged as pre-release. Please package it using the '--pre-release' flag and publish again.`
+);
+}
+}
+
 await _publish(packagePath, vsix.manifest, { ...options, target });
 }
 } else {