typescript-eslint · bradzacher · Apr 11, 2019 · Feb 18, 2019 · Feb 18, 2019 · Feb 18, 2019
diff --git a/packages/eslint-plugin/docs/rules/prefer-includes.md b/packages/eslint-plugin/docs/rules/prefer-includes.md
@@ -0,0 +1,71 @@
+# Enforce `includes` method over `indexOf` method (@typescript-eslint/prefer-includes)
+
+Until ES5, we were using `String#indexOf` method to check whether a string contains an arbitrary substring or not.
+Until ES2015, we were using `Array#indexOf` method to check whether an array contains an arbitrary value or not.
+
+ES2015 has added `String#includes` and ES2016 has added `Array#includes`.
+It makes code more understandable if we use those `includes` methods for the purpose.
+
+## Rule Details
+
+This rule is aimed at suggesting `includes` method if `indexOf` method was used to check whether an object contains an arbitrary value or not.
+
+If the receiver object of the `indexOf` method call has `includes` method and the two methods have the same parameters, this rule does suggestion.
+There are such types: `String`, `Array`, `ReadonlyArray`, and typed arrays.
+
+Additionally, this rule reports the tests of simple regular expressions in favor of `String#includes`.
+
+Examples of **incorrect** code for this rule:
+
+```ts
+let str: string;
+let array: any[];
+let readonlyArray: ReadonlyArray<any>;
+let typedArray: UInt8Array;
+let userDefined: {
+  indexOf(x: any): number;
+  includes(x: any): boolean;
+};
+
+str.indexOf(value) !== -1;
+array.indexOf(value) !== -1;
+readonlyArray.indexOf(value) === -1;
+typedArray.indexOf(value) > -1;
+userDefined.indexOf(value) >= 0;
+
+// simple RegExp test
+/foo/.test(str);
+```
+
+Examples of **correct** code for this rule:
+
+```ts
+let array: any[];
+let readonlyArray: ReadonlyArray<any>;
+let typedArray: UInt8Array;
+let userDefined: {
+  indexOf(x: any): number;
+  includes(x: any): boolean;
+};
+let mismatchExample: {
+  indexOf(x: any, fromIndex?: number): number;
+  includes(x: any): boolean;
+};
+
+str.includes(value);
+array.includes(value);
+readonlyArray.includes(value);
+typedArray.includes(value);
+userDefined.includes(value);
+
+// the two methods have different parameters.
+mismatchExample.indexOf(value) >= 0;
+```
+
+## Options
+
+There are no options.
+
+## When Not To Use It
+
+If you don't want to suggest `includes`, you can safely turn this rule off.
diff --git a/packages/eslint-plugin/package.json b/packages/eslint-plugin/package.json
@@ -37,6 +37,8 @@
   "dependencies": {
     "@typescript-eslint/parser": "1.6.0",
     "@typescript-eslint/typescript-estree": "1.6.0",
+    "eslint-utils": "^1.3.1",
+    "regexpp": "^2.0.1",
     "requireindex": "^1.2.0",
     "tsutils": "^3.7.0"
   },

diff --git a/packages/eslint-plugin/src/rules/prefer-includes.ts b/packages/eslint-plugin/src/rules/prefer-includes.ts
@@ -0,0 +1,209 @@
+import { TSESTree } from '@typescript-eslint/typescript-estree';
+import { getStaticValue } from 'eslint-utils';
+import { AST as RegExpAST, parseRegExpLiteral } from 'regexpp';
+import ts from 'typescript';
+import { createRule, getParserServices } from '../util';
+
+export default createRule({
+  name: 'prefer-includes',
+  defaultOptions: [],
+
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'Enforce `includes` method over `indexOf` method',
+      category: 'Best Practices',
+      recommended: false,
+    },
+    fixable: 'code',
+    messages: {
+      preferIncludes: "Use 'includes()' method instead.",
+      preferStringIncludes:
+        'Use `String#includes()` method with a string instead.',
+    },
+    schema: [],
+  },
+
+  create(context) {
+    const globalScope = context.getScope();
+    const services = getParserServices(context);
+    const types = services.program.getTypeChecker();
+
+    function isNumber(node: TSESTree.Node, value: number): boolean {
+      const evaluated = getStaticValue(node, globalScope);
+      return evaluated !== null && evaluated.value === value;
+    }
+
+    function isPositiveCheck(node: TSESTree.BinaryExpression): boolean {
+      switch (node.operator) {
+        case '!==':
+        case '!=':
+        case '>':
+          return isNumber(node.right, -1);
+        case '>=':
+          return isNumber(node.right, 0);
+        default:
+          return false;
+      }
+    }
+    function isNegativeCheck(node: TSESTree.BinaryExpression): boolean {
+      switch (node.operator) {
+        case '===':
+        case '==':
+        case '<=':
+          return isNumber(node.right, -1);
+        case '<':
+          return isNumber(node.right, 0);
+        default:
+          return false;
+      }
+    }
+
+    function hasSameParameters(
+      nodeA: ts.Declaration,
+      nodeB: ts.Declaration,
+    ): boolean {
+      if (!ts.isFunctionLike(nodeA) || !ts.isFunctionLike(nodeB)) {
+        return false;
+      }
+
+      const paramsA = nodeA.parameters;
+      const paramsB = nodeB.parameters;
+      if (paramsA.length !== paramsB.length) {
+        return false;
+      }
+
+      for (let i = 0; i < paramsA.length; ++i) {
+        const paramA = paramsA[i];
+        const paramB = paramsB[i];
+
+        // Check name, type, and question token once.
+        if (paramA.getText() !== paramB.getText()) {
+          return false;
+        }
+      }
+
+      return true;
+    }
+
+    /**
+     * Parse a given node if it's a `RegExp` instance.
+     * @param node The node to parse.
+     */
+    function parseRegExp(node: TSESTree.Node): string | null {
+      const evaluated = getStaticValue(node, globalScope);
+      if (evaluated == null || !(evaluated.value instanceof RegExp)) {
+        return null;
+      }
+
+      const { pattern, flags } = parseRegExpLiteral(evaluated.value);
+      if (
+        pattern.alternatives.length !== 1 ||
+        flags.ignoreCase ||
+        flags.global
+      ) {
+        return null;
+      }
+
+      // Check if it can determine a unique string.
+      const chars = pattern.alternatives[0].elements;
+      if (!chars.every(c => c.type === 'Character')) {
+        return null;
+      }
+
+      // To string.
+      return String.fromCodePoint(
+        ...chars.map(c => (c as RegExpAST.Character).value),
+      );
+    }
+
+    return {
+      "BinaryExpression > CallExpression.left > MemberExpression.callee[property.name='indexOf'][computed=false]"(
+        node: TSESTree.MemberExpression,
+      ): void {
+        // Check if the comparison is equivalent to `includes()`.
+        const callNode = node.parent as TSESTree.CallExpression;
+        const compareNode = callNode.parent as TSESTree.BinaryExpression;
+        const negative = isNegativeCheck(compareNode);
+        if (!negative && !isPositiveCheck(compareNode)) {
+          return;
+        }
+
+        // Get the symbol of `indexOf` method.
+        const tsNode = services.esTreeNodeToTSNodeMap.get(node.property);
+        const indexofMethodSymbol = types.getSymbolAtLocation(tsNode);
+        if (
+          indexofMethodSymbol == null ||
+          indexofMethodSymbol.declarations.length === 0
+        ) {
+          return;
+        }
+
+        // Check if every declaration of `indexOf` method has `includes` method
+        // and the two methods have the same parameters.
+        for (const instanceofMethodDecl of indexofMethodSymbol.declarations) {
+          const typeDecl = instanceofMethodDecl.parent;
+          const type = types.getTypeAtLocation(typeDecl);
+          const includesMethodSymbol = type.getProperty('includes');
+          if (
+            includesMethodSymbol == null ||
+            !includesMethodSymbol.declarations.some(includesMethodDecl =>
+              hasSameParameters(includesMethodDecl, instanceofMethodDecl),
+            )
+          ) {
+            return;
+          }
+        }
+
+        // Report it.
+        context.report({
+          node: compareNode,
+          messageId: 'preferIncludes',
+          *fix(fixer) {
+            if (negative) {
+              yield fixer.insertTextBefore(callNode, '!');
+            }
+            yield fixer.replaceText(node.property, 'includes');
+            yield fixer.removeRange([callNode.range[1], compareNode.range[1]]);
+          },
+        });
+      },
+
+      // /bar/.test(foo)
+      'CallExpression > MemberExpression.callee[property.name="test"][computed=false]'(
+        node: TSESTree.MemberExpression,
+      ): void {
+        const callNode = node.parent as TSESTree.CallExpression;
+        const text =
+          callNode.arguments.length === 1 ? parseRegExp(node.object) : null;
+        if (text == null) {
+          return;
+        }
+
+        context.report({
+          node: callNode,
+          messageId: 'preferStringIncludes',
+          *fix(fixer) {
+            const argNode = callNode.arguments[0];
+            const needsParen =
+              argNode.type !== 'Literal' &&
+              argNode.type !== 'TemplateLiteral' &&
+              argNode.type !== 'Identifier' &&
+              argNode.type !== 'MemberExpression' &&
+              argNode.type !== 'CallExpression';
+
+            yield fixer.removeRange([callNode.range[0], argNode.range[0]]);
+            if (needsParen) {
+              yield fixer.insertTextBefore(argNode, '(');
+              yield fixer.insertTextAfter(argNode, ')');
+            }
+            yield fixer.insertTextAfter(
+              argNode,
+              `.includes(${JSON.stringify(text)}`,
+            );
+          },
+        });
+      },
+    };
+  },
+});