add lint rule to prevent type discrimination properties in API types (#180829)

re https://github.com/microsoft/vscode/issues/63943 and other

.eslintplugin/vscode-dts-string-type-literals.ts

@@ -0,0 +1,34 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as eslint from 'eslint';
+import { TSESTree } from '@typescript-eslint/experimental-utils';
+
+export = new class ApiTypeDiscrimination implements eslint.Rule.RuleModule {
+
+	readonly meta: eslint.Rule.RuleMetaData = {
+		docs: { url: 'https://github.com/microsoft/vscode/wiki/Extension-API-guidelines' },
+		messages: {
+			noTypeDiscrimination: 'Do not use type descrimination properties'
+		}
+	};
+
+	create(context: eslint.Rule.RuleContext): eslint.Rule.RuleListener {
+		return {
+			['TSPropertySignature[optional=undefined] TSTypeAnnotation TSLiteralType Literal']: (node: any) => {
+
+				const raw = String((<TSESTree.Literal>node).raw)
+
+				if (/^('|").*\1$/.test(raw)) {
+
+					context.report({
+						node: node,
+						messageId: 'noTypeDiscrimination'
+					});
+				}
+			}
+		}
+	}
+};

.eslintrc.json

@@ -130,6 +130,7 @@
 			"rules": {
 				"local/vscode-dts-create-func": "warn",
 				"local/vscode-dts-literal-or-types": "warn",
+				"local/vscode-dts-string-type-literals": "warn",
 				"local/vscode-dts-interface-naming": "warn",
 				"local/vscode-dts-cancellation": "warn",
 				"local/vscode-dts-use-thenable": "warn",

src/vscode-dts/vscode.proposed.debugFocus.d.ts

@@ -8,6 +8,7 @@ declare module 'vscode' {
 	// See https://github.com/microsoft/vscode/issues/63943
 
 	export interface ThreadFocus {
+		// eslint-disable-next-line local/vscode-dts-string-type-literals
 		kind: 'thread';
 
 		/**
@@ -22,6 +23,7 @@ declare module 'vscode' {
 	}
 
 	export interface StackFrameFocus {
+		// eslint-disable-next-line local/vscode-dts-string-type-literals
 		kind: 'stackFrame';
 
 		/**

src/vscode-dts/vscode.proposed.interactive.d.ts

@@ -159,6 +159,7 @@ declare module 'vscode' {
 	}
 
 	export interface InteractiveSessionVoteAction {
+		// eslint-disable-next-line local/vscode-dts-string-type-literals
 		kind: 'vote';
 		responseId: string;
 		direction: InteractiveSessionVoteDirection;
@@ -171,6 +172,7 @@ declare module 'vscode' {
 	}
 
 	export interface InteractiveSessionCopyAction {
+		// eslint-disable-next-line local/vscode-dts-string-type-literals
 		kind: 'copy';
 		responseId: string;
 		codeBlockIndex: number;
@@ -181,6 +183,7 @@ declare module 'vscode' {
 	}
 
 	export interface InteractiveSessionInsertAction {
+		// eslint-disable-next-line local/vscode-dts-string-type-literals
 		kind: 'insert';
 		responseId: string;
 		codeBlockIndex: number;
@@ -189,6 +192,7 @@ declare module 'vscode' {
 	}
 
 	export interface InteractiveSessionTerminalAction {
+		// eslint-disable-next-line local/vscode-dts-string-type-literals
 		kind: 'runInTerminal';
 		responseId: string;
 		codeBlockIndex: number;
@@ -196,6 +200,7 @@ declare module 'vscode' {
 	}
 
 	export interface InteractiveSessionCommandAction {
+		// eslint-disable-next-line local/vscode-dts-string-type-literals
 		kind: 'command';
 		command: InteractiveResponseCommand;
 	}

src/vscode-dts/vscode.proposed.resolvers.d.ts

@@ -173,7 +173,7 @@ declare module 'vscode' {
 	export interface ResourceLabelFormatting {
 		label: string; // myLabel:/${path}
 		// For historic reasons we use an or string here. Once we finalize this API we should start using enums instead and adopt it in extensions.
-		// eslint-disable-next-line local/vscode-dts-literal-or-types
+		// eslint-disable-next-line local/vscode-dts-literal-or-types, local/vscode-dts-string-type-literals
 		separator: '/' | '\\' | '';
 		tildify?: boolean;
 		normalizeDriveLetter?: boolean;