Re-enable running our eslint rules using ts-node (#159495)

Resubmission of #157532 with the following changes:

- Use `eslint-plugin-local` instead of `yarn` link to run our plugins
- Move our plugins to a top level `.eslintplugin` dir (as required by `eslint-plugin-local`)
- Update all names to `local/`

.eslintplugin/code-no-unused-expressions.ts

@@ -0,0 +1,151 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+// FORKED FROM https://github.com/eslint/eslint/blob/b23ad0d789a909baf8d7c41a35bc53df932eaf30/lib/rules/no-unused-expressions.js
+// and added support for `OptionalCallExpression`, see https://github.com/facebook/create-react-app/issues/8107 and https://github.com/eslint/eslint/issues/12642
+
+/**
+ * @fileoverview Flag expressions in statement position that do not side effect
+ * @author Michael Ficarra
+ */
+
+import * as eslint from 'eslint';
+import { TSESTree } from '@typescript-eslint/experimental-utils';
+import * as ESTree from 'estree';
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+	meta: {
+		type: 'suggestion',
+
+		docs: {
+			description: 'disallow unused expressions',
+			category: 'Best Practices',
+			recommended: false,
+			url: 'https://eslint.org/docs/rules/no-unused-expressions'
+		},
+
+		schema: [
+			{
+				type: 'object',
+				properties: {
+					allowShortCircuit: {
+						type: 'boolean',
+						default: false
+					},
+					allowTernary: {
+						type: 'boolean',
+						default: false
+					},
+					allowTaggedTemplates: {
+						type: 'boolean',
+						default: false
+					}
+				},
+				additionalProperties: false
+			}
+		]
+	},
+
+	create(context: eslint.Rule.RuleContext) {
+		const config = context.options[0] || {},
+			allowShortCircuit = config.allowShortCircuit || false,
+			allowTernary = config.allowTernary || false,
+			allowTaggedTemplates = config.allowTaggedTemplates || false;
+
+		// eslint-disable-next-line jsdoc/require-description
+		/**
+		 * @param node any node
+		 * @returns whether the given node structurally represents a directive
+		 */
+		function looksLikeDirective(node: TSESTree.Node): boolean {
+			return node.type === 'ExpressionStatement' &&
+				node.expression.type === 'Literal' && typeof node.expression.value === 'string';
+		}
+
+		// eslint-disable-next-line jsdoc/require-description
+		/**
+		 * @param predicate ([a] -> Boolean) the function used to make the determination
+		 * @param list the input list
+		 * @returns the leading sequence of members in the given list that pass the given predicate
+		 */
+		function takeWhile<T>(predicate: (item: T) => boolean, list: T[]): T[] {
+			for (let i = 0; i < list.length; ++i) {
+				if (!predicate(list[i])) {
+					return list.slice(0, i);
+				}
+			}
+			return list.slice();
+		}
+
+		// eslint-disable-next-line jsdoc/require-description
+		/**
+		 * @param node a Program or BlockStatement node
+		 * @returns the leading sequence of directive nodes in the given node's body
+		 */
+		function directives(node: TSESTree.Program | TSESTree.BlockStatement): TSESTree.Node[] {
+			return takeWhile(looksLikeDirective, node.body);
+		}
+
+		// eslint-disable-next-line jsdoc/require-description
+		/**
+		 * @param node any node
+		 * @param ancestors the given node's ancestors
+		 * @returns whether the given node is considered a directive in its current position
+		 */
+		function isDirective(node: TSESTree.Node, ancestors: TSESTree.Node[]): boolean {
+			const parent = ancestors[ancestors.length - 1],
+				grandparent = ancestors[ancestors.length - 2];
+
+			return (parent.type === 'Program' || parent.type === 'BlockStatement' &&
+				(/Function/u.test(grandparent.type))) &&
+				directives(parent).indexOf(node) >= 0;
+		}
+
+		/**
+		 * Determines whether or not a given node is a valid expression. Recurses on short circuit eval and ternary nodes if enabled by flags.
+		 * @param node any node
+		 * @returns whether the given node is a valid expression
+		 */
+		function isValidExpression(node: TSESTree.Node): boolean {
+			if (allowTernary) {
+
+				// Recursive check for ternary and logical expressions
+				if (node.type === 'ConditionalExpression') {
+					return isValidExpression(node.consequent) && isValidExpression(node.alternate);
+				}
+			}
+
+			if (allowShortCircuit) {
+				if (node.type === 'LogicalExpression') {
+					return isValidExpression(node.right);
+				}
+			}
+
+			if (allowTaggedTemplates && node.type === 'TaggedTemplateExpression') {
+				return true;
+			}
+
+			if (node.type === 'ExpressionStatement') {
+				return isValidExpression(node.expression);
+			}
+
+			return /^(?:Assignment|OptionalCall|Call|New|Update|Yield|Await|Chain)Expression$/u.test(node.type) ||
+				(node.type === 'UnaryExpression' && ['delete', 'void'].indexOf(node.operator) >= 0);
+		}
+
+		return {
+			ExpressionStatement(node: TSESTree.ExpressionStatement) {
+				if (!isValidExpression(node.expression) && !isDirective(node, <TSESTree.Node[]>context.getAncestors())) {
+					context.report({ node: <ESTree.Node>node, message: `Expected an assignment or function call and instead saw an expression. ${node.expression}` });
+				}
+			}
+		};
+
+	}
+};