Set a read-only message from an extension (#185216)

* wip

* Allow extensions to provide a readonly message
Part of #166971

* Address feedback

* Further address feedback

* Fix some nits

* Add test

* Improve tests and respond to feedback

* Don't render editor.readOnlyMessage in the settings UI

* No need to validate the IMarkdownString

---------

Co-authored-by: Benjamin Pasero <benjamin.pasero@microsoft.com>
Co-authored-by: Alex Dima <alexdima@microsoft.com>

extensions/vscode-api-tests/src/singlefolder-tests/readonlyFileSystem.test.ts

@@ -0,0 +1,63 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as assert from 'assert';
+import * as vscode from 'vscode';
+import { TestFS } from '../memfs';
+import { assertNoRpc, closeAllEditors } from '../utils';
+
+suite('vscode API - file system', () => {
+
+	teardown(async function () {
+		assertNoRpc();
+		await closeAllEditors();
+	});
+
+	test('readonly file system - boolean', async function () {
+		const fs = new TestFS('this-fs', false);
+		const reg = vscode.workspace.registerFileSystemProvider(fs.scheme, fs, { isReadonly: true });
+		let error: any | undefined;
+		try {
+			await vscode.workspace.fs.writeFile(vscode.Uri.parse('this-fs:/foo.txt'), Buffer.from('Hello World'));
+		} catch (e) {
+			error = e;
+		}
+		assert.strictEqual(vscode.workspace.fs.isWritableFileSystem('this-fs'), false);
+		assert.strictEqual(error instanceof vscode.FileSystemError, true);
+		const fileError: vscode.FileSystemError = error;
+		assert.strictEqual(fileError.code, 'NoPermissions');
+		reg.dispose();
+	});
+
+	test('readonly file system - markdown', async function () {
+		const fs = new TestFS('this-fs', false);
+		const reg = vscode.workspace.registerFileSystemProvider(fs.scheme, fs, { isReadonly: new vscode.MarkdownString('This file is readonly.') });
+		let error: any | undefined;
+		try {
+			await vscode.workspace.fs.writeFile(vscode.Uri.parse('this-fs:/foo.txt'), Buffer.from('Hello World'));
+		} catch (e) {
+			error = e;
+		}
+		assert.strictEqual(vscode.workspace.fs.isWritableFileSystem('this-fs'), false);
+		assert.strictEqual(error instanceof vscode.FileSystemError, true);
+		const fileError: vscode.FileSystemError = error;
+		assert.strictEqual(fileError.code, 'NoPermissions');
+		reg.dispose();
+	});
+
+	test('writeable file system', async function () {
+		const fs = new TestFS('this-fs', false);
+		const reg = vscode.workspace.registerFileSystemProvider(fs.scheme, fs);
+		let error: any | undefined;
+		try {
+			await vscode.workspace.fs.writeFile(vscode.Uri.parse('this-fs:/foo.txt'), Buffer.from('Hello World'));
+		} catch (e) {
+			error = e;
+		}
+		assert.strictEqual(vscode.workspace.fs.isWritableFileSystem('this-fs'), true);
+		assert.strictEqual(error, undefined);
+		reg.dispose();
+	});
+});