Fix #4505 Notebooks: New Notebook will not work if existing untitled notebooks are rehydrated (#4506)

* Fix #4505 Notebooks: New Notebook will not work if existing untitled notebooks are rehydrated
* Also fixes #4508
* Unify behavior across New Notebook entry points
- Use Notebook-{n} as the standard in both entry points
- Use SQL as default provider in both
- Ensure both check for other names and only use free number

extensions/mssql/src/main.ts

@@ -172,19 +172,27 @@ function saveProfileAndCreateNotebook(profile: azdata.IConnectionProfile): Promi
 	return handleNewNotebookTask(undefined, profile);
 }
 
+function findNextUntitledEditorName(): string {
+	let nextVal = untitledCounter;
+	// Note: this will go forever if it's coded wrong, or you have inifinite Untitled notebooks!
+	while (true) {
+		let title = `Notebook-${nextVal++}`;
+		let hasTextDoc = vscode.workspace.textDocuments.findIndex(doc => doc.isUntitled && doc.fileName === title) > -1;
+		let hasNotebookDoc = azdata.nb.notebookDocuments.findIndex(doc => doc.isUntitled && doc.fileName === title) > -1;
+		if (!hasTextDoc && !hasNotebookDoc) {
+			untitledCounter = nextVal;
+			return title;
+		}
+	}
+}
 async function handleNewNotebookTask(oeContext?: azdata.ObjectExplorerContext, profile?: azdata.IConnectionProfile): Promise<void> {
 	// Ensure we get a unique ID for the notebook. For now we're using a different prefix to the built-in untitled files
 	// to handle this. We should look into improving this in the future
-	let untitledUri = vscode.Uri.parse(`untitled:Notebook-${untitledCounter++}`);
+	let title = findNextUntitledEditorName();
+	let untitledUri = vscode.Uri.parse(`untitled:${title}`);
 	let editor = await azdata.nb.showNotebookDocument(untitledUri, {
 		connectionProfile: profile,
-		providerId: jupyterNotebookProviderId,
-		preview: false,
-		defaultKernel: {
-			name: 'pyspark3kernel',
-			display_name: 'PySpark3',
-			language: 'python'
-		}
+		preview: false
 	});
 	if (oeContext && oeContext.nodeInfo && oeContext.nodeInfo.nodePath) {
 		// Get the file path after '/HDFS'
@@ -221,7 +229,6 @@ async function handleOpenNotebookTask(profile: azdata.IConnectionProfile): Promi
 		} else {
 			await azdata.nb.showNotebookDocument(fileUri, {
 				connectionProfile: profile,
-				providerId: jupyterNotebookProviderId,
 				preview: false
 			});
 		}