Fix save-as making it easy to save without extension for positron notebooks (#8858)

Addresses #8857.

@:notebooks

Adds proper file dialog configuration to `PositronNotebookEditorInput`
to prevent users from
saving notebooks without `.ipynb` extensions. Uses VS Code's
`showSaveDialog` with filters, title,
and localized labels to provide a native save experience that
automatically handles extension
enforcement. The dialog's built-in extension enforcement ensures users
cannot accidentally save
notebooks un-extensioned files that causes the file to display as raw
json.

### Release Notes

#### New Features

#### Bug Fixes
- Properly configured the save as dialog for positron notebooks to
prevent mangled file names

### QA Notes

Updated the positron notebook save e2e test to make sure this behavior
is working. At least for the case of saving without a file extension.

Test the enhanced save dialog by creating a new untitled notebook and
saving it. The dialog
should provide a native experience with proper labeling and automatic
extension handling.

1. Create a new untitled notebook
2. Add some content (e.g., a code cell with `print("test")`)
3. Use "Save As" and observe:
   - Dialog shows "Save Notebook As" title
   - Type `mynotebook` (should automatically become `mynotebook.ipynb`)

Expected behavior: The save dialog automatically enforces`.ipynb`
extensions, preventing users from accidentally saving raw JSON notebook
content.

Author: nstrayer

src/vs/workbench/contrib/positronNotebook/browser/PositronNotebookEditorInput.ts

@@ -172,7 +172,7 @@ export class PositronNotebookEditorInput extends EditorInput {
 	 */
 	override getName(): string {
 		const extUri = new ExtUri(() => false);
-		return extUri.basename(this.resource) ?? localize('positronNotebookInputName', "Positron Notebook");
+		return extUri.basename(this.resource) ?? localize('positron.notebook.inputName', "Positron Notebook");
 	}
 
 	/**
@@ -237,8 +237,16 @@ export class PositronNotebookEditorInput extends EditorInput {
 		const suggestedName = extUri.basename(this.resource);
 		const pathCandidate = await this._suggestName(provider, suggestedName);
 
-		// Ask the user where to save the file
-		const target = await this._fileDialogService.pickFileToSave(pathCandidate, options?.availableFileSystems);
+		// Ask the user where to save the file with proper filters
+		const target = await this._fileDialogService.showSaveDialog({
+			title: localize('positron.notebook.saveAs', "Save Notebook As"),
+			defaultUri: pathCandidate,
+			filters: [
+				// This will ensure that the saved file has the .ipynb extension.
+				{ name: localize('positron.notebook.fileType', 'Jupyter Notebook'), extensions: ['ipynb'] }
+			],
+			availableFileSystems: options?.availableFileSystems
+		});
 		if (!target) {
 			return undefined; // save cancelled
 		}

test/e2e/tests/notebook/positron-notebook-editor.test.ts

@@ -92,18 +92,22 @@ test.describe('Positron notebook opening and saving', {
 		// New notebooks should automatically be named "Untitled-1.ipynb" by default
 		await editors.waitForActiveTab('Untitled-1.ipynb', false);
 
-		// Save the notebook with a specific name
+		// Test save dialog functionality - save with a name that doesn't include .ipynb extension
+		// The enhanced save dialog should automatically handle extension enforcement
 		await runCommand('workbench.action.files.saveAs', { keepOpen: true });
 		await quickInput.waitForQuickInputOpened();
-		const newFileName = `saved-positron-notebook-${Math.random().toString(36).substring(7)}.ipynb`;
-		await quickInput.type(path.join(app.workspacePathOrFolder, newFileName));
+
+		// Type filename without extension to test automatic extension handling
+		const baseFileName = `saved-positron-notebook-${Math.random().toString(36).substring(7)}`;
+		await quickInput.type(path.join(app.workspacePathOrFolder, baseFileName));
 		await quickInput.clickOkButton();
 
-		// Verify the editor tab now shows the new filename instead of "Untitled" and it is a positron notebook
-		await editors.waitForActiveTab(newFileName, false);
+		// Verify the file was saved and the .ipynb extension was automatically added
+		const expectedFileName = `${baseFileName}.ipynb`;
+		await editors.waitForActiveTab(expectedFileName, false);
 		await notebooksPositron.expectToBeVisible();
 
 		// Keep the test workspace clean for subsequent test runs
-		await cleanup.removeTestFiles([newFileName]);
+		await cleanup.removeTestFiles([expectedFileName]);
 	});
 });