@typescript-eslint/eslint-plugin/dist/rules/prefer-string-starts-ends-with.js

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const utils_1 = require("@typescript-eslint/utils");
const regexpp_1 = require("regexpp");
const util_1 = require("../util");
const EQ_OPERATORS = /^[=!]=/;
const regexpp = new regexpp_1.RegExpParser();
exports.default = (0, util_1.createRule)({
    name: 'prefer-string-starts-ends-with',
    defaultOptions: [],
    meta: {
        type: 'suggestion',
        docs: {
            description: 'Enforce the use of `String#startsWith` and `String#endsWith` instead of other equivalent methods of checking substrings',
            recommended: false,
            requiresTypeChecking: true,
        },
        messages: {
            preferStartsWith: "Use 'String#startsWith' method instead.",
            preferEndsWith: "Use the 'String#endsWith' method instead.",
        },
        schema: [],
        fixable: 'code',
    },
    create(context) {
        const globalScope = context.getScope();
        const sourceCode = context.getSourceCode();
        const service = (0, util_1.getParserServices)(context);
        const typeChecker = service.program.getTypeChecker();
        /**
         * Check if a given node is a string.
         * @param node The node to check.
         */
        function isStringType(node) {
            const objectType = typeChecker.getTypeAtLocation(service.esTreeNodeToTSNodeMap.get(node));
            return (0, util_1.getTypeName)(typeChecker, objectType) === 'string';
        }
        /**
         * Check if a given node is a `Literal` node that is null.
         * @param node The node to check.
         */
        function isNull(node) {
            const evaluated = (0, util_1.getStaticValue)(node, globalScope);
            return evaluated != null && evaluated.value === null;
        }
        /**
         * Check if a given node is a `Literal` node that is a given value.
         * @param node The node to check.
         * @param value The expected value of the `Literal` node.
         */
        function isNumber(node, value) {
            const evaluated = (0, util_1.getStaticValue)(node, globalScope);
            return evaluated != null && evaluated.value === value;
        }
        /**
         * Check if a given node is a `Literal` node that is a character.
         * @param node The node to check.
         * @param kind The method name to get a character.
         */
        function isCharacter(node) {
            const evaluated = (0, util_1.getStaticValue)(node, globalScope);
            return (evaluated != null &&
                typeof evaluated.value === 'string' &&
                // checks if the string is a character long
                evaluated.value[0] === evaluated.value);
        }
        /**
         * Check if a given node is `==`, `===`, `!=`, or `!==`.
         * @param node The node to check.
         */
        function isEqualityComparison(node) {
            return (node.type === utils_1.AST_NODE_TYPES.BinaryExpression &&
                EQ_OPERATORS.test(node.operator));
        }
        /**
         * Check if two given nodes are the same meaning.
         * @param node1 A node to compare.
         * @param node2 Another node to compare.
         */
        function isSameTokens(node1, node2) {
            const tokens1 = sourceCode.getTokens(node1);
            const tokens2 = sourceCode.getTokens(node2);
            if (tokens1.length !== tokens2.length) {
                return false;
            }
            for (let i = 0; i < tokens1.length; ++i) {
                const token1 = tokens1[i];
                const token2 = tokens2[i];
                if (token1.type !== token2.type || token1.value !== token2.value) {
                    return false;
                }
            }
            return true;
        }
        /**
         * Check if a given node is the expression of the length of a string.
         *
         * - If `length` property access of `expectedObjectNode`, it's `true`.
         *   E.g., `foo` → `foo.length` / `"foo"` → `"foo".length`
         * - If `expectedObjectNode` is a string literal, `node` can be a number.
         *   E.g., `"foo"` → `3`
         *
         * @param node The node to check.
         * @param expectedObjectNode The node which is expected as the receiver of `length` property.
         */
        function isLengthExpression(node, expectedObjectNode) {
            if (node.type === utils_1.AST_NODE_TYPES.MemberExpression) {
                return ((0, util_1.getPropertyName)(node, globalScope) === 'length' &&
                    isSameTokens(node.object, expectedObjectNode));
            }
            const evaluatedLength = (0, util_1.getStaticValue)(node, globalScope);
            const evaluatedString = (0, util_1.getStaticValue)(expectedObjectNode, globalScope);
            return (evaluatedLength != null &&
                evaluatedString != null &&
                typeof evaluatedLength.value === 'number' &&
                typeof evaluatedString.value === 'string' &&
                evaluatedLength.value === evaluatedString.value.length);
        }
        /**
         * Check if a given node is a negative index expression
         *
         * E.g. `s.slice(- <expr>)`, `s.substring(s.length - <expr>)`
         *
         * @param node The node to check.
         * @param expectedIndexedNode The node which is expected as the receiver of index expression.
         */
        function isNegativeIndexExpression(node, expectedIndexedNode) {
            return ((node.type === utils_1.AST_NODE_TYPES.UnaryExpression &&
                node.operator === '-') ||
                (node.type === utils_1.AST_NODE_TYPES.BinaryExpression &&
                    node.operator === '-' &&
                    isLengthExpression(node.left, expectedIndexedNode)));
        }
        /**
         * Check if a given node is the expression of the last index.
         *
         * E.g. `foo.length - 1`
         *
         * @param node The node to check.
         * @param expectedObjectNode The node which is expected as the receiver of `length` property.
         */
        function isLastIndexExpression(node, expectedObjectNode) {
            return (node.type === utils_1.AST_NODE_TYPES.BinaryExpression &&
                node.operator === '-' &&
                isLengthExpression(node.left, expectedObjectNode) &&
                isNumber(node.right, 1));
        }
        /**
         * Get the range of the property of a given `MemberExpression` node.
         *
         * - `obj[foo]` → the range of `[foo]`
         * - `obf.foo` → the range of `.foo`
         * - `(obj).foo` → the range of `.foo`
         *
         * @param node The member expression node to get.
         */
        function getPropertyRange(node) {
            const dotOrOpenBracket = sourceCode.getTokenAfter(node.object, util_1.isNotClosingParenToken);
            return [dotOrOpenBracket.range[0], node.range[1]];
        }
        /**
         * Parse a given `RegExp` pattern to that string if it's a static string.
         * @param pattern The RegExp pattern text to parse.
         * @param uFlag The Unicode flag of the RegExp.
         */
        function parseRegExpText(pattern, uFlag) {
            // Parse it.
            const ast = regexpp.parsePattern(pattern, undefined, undefined, uFlag);
            if (ast.alternatives.length !== 1) {
                return null;
            }
            // Drop `^`/`$` assertion.
            const chars = ast.alternatives[0].elements;
            const first = chars[0];
            if (first.type === 'Assertion' && first.kind === 'start') {
                chars.shift();
            }
            else {
                chars.pop();
            }
            // Check if it can determine a unique string.
            if (!chars.every(c => c.type === 'Character')) {
                return null;
            }
            // To string.
            return String.fromCodePoint(...chars.map(c => c.value));
        }
        /**
         * Parse a given node if it's a `RegExp` instance.
         * @param node The node to parse.
         */
        function parseRegExp(node) {
            const evaluated = (0, util_1.getStaticValue)(node, globalScope);
            if (evaluated == null || !(evaluated.value instanceof RegExp)) {
                return null;
            }
            const { source, flags } = evaluated.value;
            const isStartsWith = source.startsWith('^');
            const isEndsWith = source.endsWith('$');
            if (isStartsWith === isEndsWith ||
                flags.includes('i') ||
                flags.includes('m')) {
                return null;
            }
            const text = parseRegExpText(source, flags.includes('u'));
            if (text == null) {
                return null;
            }
            return { isEndsWith, isStartsWith, text };
        }
        function getLeftNode(node) {
            if (node.type === utils_1.AST_NODE_TYPES.ChainExpression) {
                return getLeftNode(node.expression);
            }
            let leftNode;
            if (node.type === utils_1.AST_NODE_TYPES.CallExpression) {
                leftNode = node.callee;
            }
            else {
                leftNode = node;
            }
            if (leftNode.type !== utils_1.AST_NODE_TYPES.MemberExpression) {
                throw new Error(`Expected a MemberExpression, got ${leftNode.type}`);
            }
            return leftNode;
        }
        /**
         * Fix code with using the right operand as the search string.
         * For example: `foo.slice(0, 3) === 'bar'` → `foo.startsWith('bar')`
         * @param fixer The rule fixer.
         * @param node The node which was reported.
         * @param kind The kind of the report.
         * @param isNegative The flag to fix to negative condition.
         */
        function* fixWithRightOperand(fixer, node, kind, isNegative, isOptional) {
            // left is CallExpression or MemberExpression.
            const leftNode = getLeftNode(node.left);
            const propertyRange = getPropertyRange(leftNode);
            if (isNegative) {
                yield fixer.insertTextBefore(node, '!');
            }
            yield fixer.replaceTextRange([propertyRange[0], node.right.range[0]], `${isOptional ? '?.' : '.'}${kind}sWith(`);
            yield fixer.replaceTextRange([node.right.range[1], node.range[1]], ')');
        }
        /**
         * Fix code with using the first argument as the search string.
         * For example: `foo.indexOf('bar') === 0` → `foo.startsWith('bar')`
         * @param fixer The rule fixer.
         * @param node The node which was reported.
         * @param kind The kind of the report.
         * @param negative The flag to fix to negative condition.
         */
        function* fixWithArgument(fixer, node, callNode, calleeNode, kind, negative, isOptional) {
            if (negative) {
                yield fixer.insertTextBefore(node, '!');
            }
            yield fixer.replaceTextRange(getPropertyRange(calleeNode), `${isOptional ? '?.' : '.'}${kind}sWith`);
            yield fixer.removeRange([callNode.range[1], node.range[1]]);
        }
        function getParent(node) {
            var _a;
            return (0, util_1.nullThrows)(((_a = node.parent) === null || _a === void 0 ? void 0 : _a.type) === utils_1.AST_NODE_TYPES.ChainExpression
                ? node.parent.parent
                : node.parent, util_1.NullThrowsReasons.MissingParent);
        }
        return {
            // foo[0] === "a"
            // foo.charAt(0) === "a"
            // foo[foo.length - 1] === "a"
            // foo.charAt(foo.length - 1) === "a"
            [[
                'BinaryExpression > MemberExpression.left[computed=true]',
                'BinaryExpression > CallExpression.left > MemberExpression.callee[property.name="charAt"][computed=false]',
                'BinaryExpression > ChainExpression.left > MemberExpression[computed=true]',
                'BinaryExpression > ChainExpression.left > CallExpression > MemberExpression.callee[property.name="charAt"][computed=false]',
            ].join(', ')](node) {
                let parentNode = getParent(node);
                let indexNode = null;
                if ((parentNode === null || parentNode === void 0 ? void 0 : parentNode.type) === utils_1.AST_NODE_TYPES.CallExpression) {
                    if (parentNode.arguments.length === 1) {
                        indexNode = parentNode.arguments[0];
                    }
                    parentNode = getParent(parentNode);
                }
                else {
                    indexNode = node.property;
                }
                if (indexNode == null ||
                    !isEqualityComparison(parentNode) ||
                    !isStringType(node.object)) {
                    return;
                }
                const isEndsWith = isLastIndexExpression(indexNode, node.object);
                const isStartsWith = !isEndsWith && isNumber(indexNode, 0);
                if (!isStartsWith && !isEndsWith) {
                    return;
                }
                const eqNode = parentNode;
                context.report({
                    node: parentNode,
                    messageId: isStartsWith ? 'preferStartsWith' : 'preferEndsWith',
                    fix(fixer) {
                        // Don't fix if it can change the behavior.
                        if (!isCharacter(eqNode.right)) {
                            return null;
                        }
                        return fixWithRightOperand(fixer, eqNode, isStartsWith ? 'start' : 'end', eqNode.operator.startsWith('!'), node.optional);
                    },
                });
            },
            // foo.indexOf('bar') === 0
            [[
                'BinaryExpression > CallExpression.left > MemberExpression.callee[property.name="indexOf"][computed=false]',
                'BinaryExpression > ChainExpression.left > CallExpression > MemberExpression.callee[property.name="indexOf"][computed=false]',
            ].join(', ')](node) {
                const callNode = getParent(node);
                const parentNode = getParent(callNode);
                if (callNode.arguments.length !== 1 ||
                    !isEqualityComparison(parentNode) ||
                    !isNumber(parentNode.right, 0) ||
                    !isStringType(node.object)) {
                    return;
                }
                context.report({
                    node: parentNode,
                    messageId: 'preferStartsWith',
                    fix(fixer) {
                        return fixWithArgument(fixer, parentNode, callNode, node, 'start', parentNode.operator.startsWith('!'), node.optional);
                    },
                });
            },
            // foo.lastIndexOf('bar') === foo.length - 3
            // foo.lastIndexOf(bar) === foo.length - bar.length
            [[
                'BinaryExpression > CallExpression.left > MemberExpression.callee[property.name="lastIndexOf"][computed=false]',
                'BinaryExpression > ChainExpression.left > CallExpression > MemberExpression.callee[property.name="lastIndexOf"][computed=false]',
            ].join(', ')](node) {
                const callNode = getParent(node);
                const parentNode = getParent(callNode);
                if (callNode.arguments.length !== 1 ||
                    !isEqualityComparison(parentNode) ||
                    parentNode.right.type !== utils_1.AST_NODE_TYPES.BinaryExpression ||
                    parentNode.right.operator !== '-' ||
                    !isLengthExpression(parentNode.right.left, node.object) ||
                    !isLengthExpression(parentNode.right.right, callNode.arguments[0]) ||
                    !isStringType(node.object)) {
                    return;
                }
                context.report({
                    node: parentNode,
                    messageId: 'preferEndsWith',
                    fix(fixer) {
                        return fixWithArgument(fixer, parentNode, callNode, node, 'end', parentNode.operator.startsWith('!'), node.optional);
                    },
                });
            },
            // foo.match(/^bar/) === null
            // foo.match(/bar$/) === null
            [[
                'BinaryExpression > CallExpression.left > MemberExpression.callee[property.name="match"][computed=false]',
                'BinaryExpression > ChainExpression.left > CallExpression > MemberExpression.callee[property.name="match"][computed=false]',
            ].join(', ')](node) {
                const callNode = getParent(node);
                const parentNode = getParent(callNode);
                if (!isEqualityComparison(parentNode) ||
                    !isNull(parentNode.right) ||
                    !isStringType(node.object)) {
                    return;
                }
                const parsed = callNode.arguments.length === 1
                    ? parseRegExp(callNode.arguments[0])
                    : null;
                if (parsed == null) {
                    return;
                }
                const { isStartsWith, text } = parsed;
                context.report({
                    node: callNode,
                    messageId: isStartsWith ? 'preferStartsWith' : 'preferEndsWith',
                    *fix(fixer) {
                        if (!parentNode.operator.startsWith('!')) {
                            yield fixer.insertTextBefore(parentNode, '!');
                        }
                        yield fixer.replaceTextRange(getPropertyRange(node), `${node.optional ? '?.' : '.'}${isStartsWith ? 'start' : 'end'}sWith`);
                        yield fixer.replaceText(callNode.arguments[0], JSON.stringify(text));
                        yield fixer.removeRange([callNode.range[1], parentNode.range[1]]);
                    },
                });
            },
            // foo.slice(0, 3) === 'bar'
            // foo.slice(-3) === 'bar'
            // foo.slice(-3, foo.length) === 'bar'
            // foo.substring(0, 3) === 'bar'
            // foo.substring(foo.length - 3) === 'bar'
            // foo.substring(foo.length - 3, foo.length) === 'bar'
            [[
                'BinaryExpression > CallExpression.left > MemberExpression.callee[property.name="slice"][computed=false]',
                'BinaryExpression > CallExpression.left > MemberExpression.callee[property.name="substring"][computed=false]',
                'BinaryExpression > ChainExpression.left > CallExpression > MemberExpression.callee[property.name="slice"][computed=false]',
                'BinaryExpression > ChainExpression.left > CallExpression > MemberExpression.callee[property.name="substring"][computed=false]',
            ].join(', ')](node) {
                const callNode = getParent(node);
                const parentNode = getParent(callNode);
                if (!isEqualityComparison(parentNode) || !isStringType(node.object)) {
                    return;
                }
                const isEndsWith = (callNode.arguments.length === 1 ||
                    (callNode.arguments.length === 2 &&
                        isLengthExpression(callNode.arguments[1], node.object))) &&
                    isNegativeIndexExpression(callNode.arguments[0], node.object);
                const isStartsWith = !isEndsWith &&
                    callNode.arguments.length === 2 &&
                    isNumber(callNode.arguments[0], 0) &&
                    !isNegativeIndexExpression(callNode.arguments[1], node.object);
                if (!isStartsWith && !isEndsWith) {
                    return;
                }
                const eqNode = parentNode;
                const negativeIndexSupported = node.property.name === 'slice';
                context.report({
                    node: parentNode,
                    messageId: isStartsWith ? 'preferStartsWith' : 'preferEndsWith',
                    fix(fixer) {
                        // Don't fix if it can change the behavior.
                        if (eqNode.operator.length === 2 &&
                            (eqNode.right.type !== utils_1.AST_NODE_TYPES.Literal ||
                                typeof eqNode.right.value !== 'string')) {
                            return null;
                        }
                        // code being checked is likely mistake:
                        // unequal length of strings being checked for equality
                        // or reliant on behavior of substring (negative indices interpreted as 0)
                        if (isStartsWith) {
                            if (!isLengthExpression(callNode.arguments[1], eqNode.right)) {
                                return null;
                            }
                        }
                        else {
                            const posNode = callNode.arguments[0];
                            const posNodeIsAbsolutelyValid = (posNode.type === utils_1.AST_NODE_TYPES.BinaryExpression &&
                                posNode.operator === '-' &&
                                isLengthExpression(posNode.left, node.object) &&
                                isLengthExpression(posNode.right, eqNode.right)) ||
                                (negativeIndexSupported &&
                                    posNode.type === utils_1.AST_NODE_TYPES.UnaryExpression &&
                                    posNode.operator === '-' &&
                                    isLengthExpression(posNode.argument, eqNode.right));
                            if (!posNodeIsAbsolutelyValid) {
                                return null;
                            }
                        }
                        return fixWithRightOperand(fixer, parentNode, isStartsWith ? 'start' : 'end', parentNode.operator.startsWith('!'), node.optional);
                    },
                });
            },
            // /^bar/.test(foo)
            // /bar$/.test(foo)
            'CallExpression > MemberExpression.callee[property.name="test"][computed=false]'(node) {
                const callNode = getParent(node);
                const parsed = callNode.arguments.length === 1 ? parseRegExp(node.object) : null;
                if (parsed == null) {
                    return;
                }
                const { isStartsWith, text } = parsed;
                const messageId = isStartsWith ? 'preferStartsWith' : 'preferEndsWith';
                const methodName = isStartsWith ? 'startsWith' : 'endsWith';
                context.report({
                    node: callNode,
                    messageId,
                    *fix(fixer) {
                        const argNode = callNode.arguments[0];
                        const needsParen = argNode.type !== utils_1.AST_NODE_TYPES.Literal &&
                            argNode.type !== utils_1.AST_NODE_TYPES.TemplateLiteral &&
                            argNode.type !== utils_1.AST_NODE_TYPES.Identifier &&
                            argNode.type !== utils_1.AST_NODE_TYPES.MemberExpression &&
                            argNode.type !== utils_1.AST_NODE_TYPES.CallExpression;
                        yield fixer.removeRange([callNode.range[0], argNode.range[0]]);
                        if (needsParen) {
                            yield fixer.insertTextBefore(argNode, '(');
                            yield fixer.insertTextAfter(argNode, ')');
                        }
                        yield fixer.insertTextAfter(argNode, `${node.optional ? '?.' : '.'}${methodName}(${JSON.stringify(text)}`);
                    },
                });
            },
        };
    },
});
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