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Diffstat (limited to 'tools/node_modules/eslint/lib/rules/no-constant-binary-expression.js')
| -rw-r--r-- | tools/node_modules/eslint/lib/rules/no-constant-binary-expression.js | 500 |
1 files changed, 500 insertions, 0 deletions
diff --git a/tools/node_modules/eslint/lib/rules/no-constant-binary-expression.js b/tools/node_modules/eslint/lib/rules/no-constant-binary-expression.js new file mode 100644 index 00000000000..d550bcf1d91 --- /dev/null +++ b/tools/node_modules/eslint/lib/rules/no-constant-binary-expression.js @@ -0,0 +1,500 @@ +/** + * @fileoverview Rule to flag constant comparisons and logical expressions that always/never short circuit + * @author Jordan Eldredge <https://jordaneldredge.com> + */ + +"use strict"; + +const globals = require("globals"); +const { isNullLiteral, isConstant, isReferenceToGlobalVariable, isLogicalAssignmentOperator } = require("./utils/ast-utils"); + +const NUMERIC_OR_STRING_BINARY_OPERATORS = new Set(["+", "-", "*", "/", "%", "|", "^", "&", "**", "<<", ">>", ">>>"]); + +//------------------------------------------------------------------------------ +// Helpers +//------------------------------------------------------------------------------ + +/** + * Test if an AST node has a statically knowable constant nullishness. Meaning, + * it will always resolve to a constant value of either: `null`, `undefined` + * or not `null` _or_ `undefined`. An expression that can vary between those + * three states at runtime would return `false`. + * @param {Scope} scope The scope in which the node was found. + * @param {ASTNode} node The AST node being tested. + * @returns {boolean} Does `node` have constant nullishness? + */ +function hasConstantNullishness(scope, node) { + switch (node.type) { + case "ObjectExpression": // Objects are never nullish + case "ArrayExpression": // Arrays are never nullish + case "ArrowFunctionExpression": // Functions never nullish + case "FunctionExpression": // Functions are never nullish + case "ClassExpression": // Classes are never nullish + case "NewExpression": // Objects are never nullish + case "Literal": // Nullish, or non-nullish, literals never change + case "TemplateLiteral": // A string is never nullish + case "UpdateExpression": // Numbers are never nullish + case "BinaryExpression": // Numbers, strings, or booleans are never nullish + return true; + case "CallExpression": { + if (node.callee.type !== "Identifier") { + return false; + } + const functionName = node.callee.name; + + return (functionName === "Boolean" || functionName === "String" || functionName === "Number") && + isReferenceToGlobalVariable(scope, node.callee); + } + case "AssignmentExpression": + if (node.operator === "=") { + return hasConstantNullishness(scope, node.right); + } + + /* + * Handling short-circuiting assignment operators would require + * walking the scope. We won't attempt that (for now...) / + */ + if (isLogicalAssignmentOperator(node.operator)) { + return false; + } + + /* + * The remaining assignment expressions all result in a numeric or + * string (non-nullish) value: + * "+=", "-=", "*=", "/=", "%=", "<<=", ">>=", ">>>=", "|=", "^=", "&=" + */ + + return true; + case "UnaryExpression": + + /* + * "void" Always returns `undefined` + * "typeof" All types are strings, and thus non-nullish + * "!" Boolean is never nullish + * "delete" Returns a boolean, which is never nullish + * Math operators always return numbers or strings, neither of which + * are non-nullish "+", "-", "~" + */ + + return true; + case "SequenceExpression": { + const last = node.expressions[node.expressions.length - 1]; + + return hasConstantNullishness(scope, last); + } + case "Identifier": + return node.name === "undefined" && isReferenceToGlobalVariable(scope, node); + case "JSXElement": // ESLint has a policy of not assuming any specific JSX behavior. + case "JSXFragment": + return false; + default: + return false; + } +} + +/** + * Test if an AST node is a boolean value that never changes. Specifically we + * test for: + * 1. Literal booleans (`true` or `false`) + * 2. Unary `!` expressions with a constant value + * 3. Constant booleans created via the `Boolean` global function + * @param {Scope} scope The scope in which the node was found. + * @param {ASTNode} node The node to test + * @returns {boolean} Is `node` guaranteed to be a boolean? + */ +function isStaticBoolean(scope, node) { + switch (node.type) { + case "Literal": + return typeof node.value === "boolean"; + case "CallExpression": + return node.callee.type === "Identifier" && node.callee.name === "Boolean" && + isReferenceToGlobalVariable(scope, node.callee) && + (node.arguments.length === 0 || isConstant(scope, node.arguments[0], true)); + case "UnaryExpression": + return node.operator === "!" && isConstant(scope, node.argument, true); + default: + return false; + } +} + + +/** + * Test if an AST node will always give the same result when compared to a + * bolean value. Note that comparison to boolean values is different than + * truthiness. + * https://262.ecma-international.org/5.1/#sec-11.9.3 + * + * Javascript `==` operator works by converting the boolean to `1` (true) or + * `+0` (false) and then checks the values `==` equality to that number. + * @param {Scope} scope The scope in which node was found. + * @param {ASTNode} node The node to test. + * @returns {boolean} Will `node` always coerce to the same boolean value? + */ +function hasConstantLooseBooleanComparison(scope, node) { + switch (node.type) { + case "ObjectExpression": + case "ClassExpression": + + /** + * In theory objects like: + * + * `{toString: () => a}` + * `{valueOf: () => a}` + * + * Or a classes like: + * + * `class { static toString() { return a } }` + * `class { static valueOf() { return a } }` + * + * Are not constant verifiably when `inBooleanPosition` is + * false, but it's an edge case we've opted not to handle. + */ + return true; + case "ArrayExpression": { + const nonSpreadElements = node.elements.filter(e => + + // Elements can be `null` in sparse arrays: `[,,]`; + e !== null && e.type !== "SpreadElement"); + + + /* + * Possible future direction if needed: We could check if the + * single value would result in variable boolean comparison. + * For now we will err on the side of caution since `[x]` could + * evaluate to `[0]` or `[1]`. + */ + return node.elements.length === 0 || nonSpreadElements.length > 1; + } + case "ArrowFunctionExpression": + case "FunctionExpression": + return true; + case "UnaryExpression": + if (node.operator === "void" || // Always returns `undefined` + node.operator === "typeof" // All `typeof` strings, when coerced to number, are not 0 or 1. + ) { + return true; + } + if (node.operator === "!") { + return isConstant(scope, node.argument, true); + } + + /* + * We won't try to reason about +, -, ~, or delete + * In theory, for the mathematical operators, we could look at the + * argument and try to determine if it coerces to a constant numeric + * value. + */ + return false; + case "NewExpression": // Objects might have custom `.valueOf` or `.toString`. + return false; + case "CallExpression": { + if (node.callee.type === "Identifier" && + node.callee.name === "Boolean" && + isReferenceToGlobalVariable(scope, node.callee) + ) { + return node.arguments.length === 0 || isConstant(scope, node.arguments[0], true); + } + return false; + } + case "Literal": // True or false, literals never change + return true; + case "Identifier": + return node.name === "undefined" && isReferenceToGlobalVariable(scope, node); + case "TemplateLiteral": + + /* + * In theory we could try to check if the quasi are sufficient to + * prove that the expression will always be true, but it would be + * tricky to get right. For example: `000.${foo}000` + */ + return node.expressions.length === 0; + case "AssignmentExpression": + if (node.operator === "=") { + return hasConstantLooseBooleanComparison(scope, node.right); + } + + /* + * Handling short-circuiting assignment operators would require + * walking the scope. We won't attempt that (for now...) + * + * The remaining assignment expressions all result in a numeric or + * string (non-nullish) values which could be truthy or falsy: + * "+=", "-=", "*=", "/=", "%=", "<<=", ">>=", ">>>=", "|=", "^=", "&=" + */ + return false; + case "SequenceExpression": { + const last = node.expressions[node.expressions.length - 1]; + + return hasConstantLooseBooleanComparison(scope, last); + } + case "JSXElement": // ESLint has a policy of not assuming any specific JSX behavior. + case "JSXFragment": + return false; + default: + return false; + } +} + + +/** + * Test if an AST node will always give the same result when _strictly_ compared + * to a bolean value. This can happen if the expression can never be boolean, or + * if it is always the same boolean value. + * @param {Scope} scope The scope in which the node was found. + * @param {ASTNode} node The node to test + * @returns {boolean} Will `node` always give the same result when compared to a + * static boolean value? + */ +function hasConstantStrictBooleanComparison(scope, node) { + switch (node.type) { + case "ObjectExpression": // Objects are not booleans + case "ArrayExpression": // Arrays are not booleans + case "ArrowFunctionExpression": // Functions are not booleans + case "FunctionExpression": + case "ClassExpression": // Classes are not booleans + case "NewExpression": // Objects are not booleans + case "TemplateLiteral": // Strings are not booleans + case "Literal": // True, false, or not boolean, literals never change. + case "UpdateExpression": // Numbers are not booleans + return true; + case "BinaryExpression": + return NUMERIC_OR_STRING_BINARY_OPERATORS.has(node.operator); + case "UnaryExpression": { + if (node.operator === "delete") { + return false; + } + if (node.operator === "!") { + return isConstant(scope, node.argument, true); + } + + /* + * The remaining operators return either strings or numbers, neither + * of which are boolean. + */ + return true; + } + case "SequenceExpression": { + const last = node.expressions[node.expressions.length - 1]; + + return hasConstantStrictBooleanComparison(scope, last); + } + case "Identifier": + return node.name === "undefined" && isReferenceToGlobalVariable(scope, node); + case "AssignmentExpression": + if (node.operator === "=") { + return hasConstantStrictBooleanComparison(scope, node.right); + } + + /* + * Handling short-circuiting assignment operators would require + * walking the scope. We won't attempt that (for now...) + */ + if (isLogicalAssignmentOperator(node.operator)) { + return false; + } + + /* + * The remaining assignment expressions all result in either a number + * or a string, neither of which can ever be boolean. + */ + return true; + case "CallExpression": { + if (node.callee.type !== "Identifier") { + return false; + } + const functionName = node.callee.name; + + if ( + (functionName === "String" || functionName === "Number") && + isReferenceToGlobalVariable(scope, node.callee) + ) { + return true; + } + if (functionName === "Boolean" && isReferenceToGlobalVariable(scope, node.callee)) { + return ( + node.arguments.length === 0 || isConstant(scope, node.arguments[0], true)); + } + return false; + } + case "JSXElement": // ESLint has a policy of not assuming any specific JSX behavior. + case "JSXFragment": + return false; + default: + return false; + } +} + +/** + * Test if an AST node will always result in a newly constructed object + * @param {Scope} scope The scope in which the node was found. + * @param {ASTNode} node The node to test + * @returns {boolean} Will `node` always be new? + */ +function isAlwaysNew(scope, node) { + switch (node.type) { + case "ObjectExpression": + case "ArrayExpression": + case "ArrowFunctionExpression": + case "FunctionExpression": + case "ClassExpression": + return true; + case "NewExpression": { + if (node.callee.type !== "Identifier") { + return false; + } + + /* + * All the built-in constructors are always new, but + * user-defined constructors could return a sentinel + * object. + * + * Catching these is especially useful for primitive constructures + * which return boxed values, a surprising gotcha' in JavaScript. + */ + return Object.hasOwnProperty.call(globals.builtin, node.callee.name) && + isReferenceToGlobalVariable(scope, node.callee); + } + case "Literal": + + // Regular expressions are objects, and thus always new + return typeof node.regex === "object"; + case "SequenceExpression": { + const last = node.expressions[node.expressions.length - 1]; + + return isAlwaysNew(scope, last); + } + case "AssignmentExpression": + if (node.operator === "=") { + return isAlwaysNew(scope, node.right); + } + return false; + case "ConditionalExpression": + return isAlwaysNew(scope, node.consequent) && isAlwaysNew(scope, node.alternate); + case "JSXElement": // ESLint has a policy of not assuming any specific JSX behavior. + case "JSXFragment": + return false; + default: + return false; + } +} + +/** + * Checks whether or not a node is `null` or `undefined`. Similar to the one + * found in ast-utils.js, but this one correctly handles the edge case that + * `undefined` has been redefined. + * @param {Scope} scope Scope in which the expression was found. + * @param {ASTNode} node A node to check. + * @returns {boolean} Whether or not the node is a `null` or `undefined`. + * @public + */ +function isNullOrUndefined(scope, node) { + return ( + isNullLiteral(node) || + (node.type === "Identifier" && node.name === "undefined" && isReferenceToGlobalVariable(scope, node)) || + (node.type === "UnaryExpression" && node.operator === "void") + ); +} + + +/** + * Checks if one operand will cause the result to be constant. + * @param {Scope} scope Scope in which the expression was found. + * @param {ASTNode} a One side of the expression + * @param {ASTNode} b The other side of the expression + * @param {string} operator The binary expression operator + * @returns {ASTNode | null} The node which will cause the expression to have a constant result. + */ +function findBinaryExpressionConstantOperand(scope, a, b, operator) { + if (operator === "==" || operator === "!=") { + if ( + (isNullOrUndefined(scope, a) && hasConstantNullishness(scope, b)) || + (isStaticBoolean(scope, a) && hasConstantLooseBooleanComparison(scope, b)) + ) { + return b; + } + } else if (operator === "===" || operator === "!==") { + if ( + (isNullOrUndefined(scope, a) && hasConstantNullishness(scope, b)) || + (isStaticBoolean(scope, a) && hasConstantStrictBooleanComparison(scope, b)) + ) { + return b; + } + } + return null; +} + +//------------------------------------------------------------------------------ +// Rule Definition +//------------------------------------------------------------------------------ + +/** @type {import('../shared/types').Rule} */ +module.exports = { + meta: { + type: "problem", + docs: { + description: "disallow expressions where the operation doesn't affect the value", + recommended: false, + url: "https://eslint.org/docs/rules/no-constant-binary-expression" + }, + schema: [], + messages: { + constantBinaryOperand: "Unexpected constant binary expression. Compares constantly with the {{otherSide}}-hand side of the `{{operator}}`.", + constantShortCircuit: "Unexpected constant {{property}} on the left-hand side of a `{{operator}}` expression.", + alwaysNew: "Unexpected comparison to newly constructed object. These two values can never be equal.", + bothAlwaysNew: "Unexpected comparison of two newly constructed objects. These two values can never be equal." + } + }, + + create(context) { + return { + LogicalExpression(node) { + const { operator, left } = node; + const scope = context.getScope(); + + if ((operator === "&&" || operator === "||") && isConstant(scope, left, true)) { + context.report({ node: left, messageId: "constantShortCircuit", data: { property: "truthiness", operator } }); + } else if (operator === "??" && hasConstantNullishness(scope, left)) { + context.report({ node: left, messageId: "constantShortCircuit", data: { property: "nullishness", operator } }); + } + }, + BinaryExpression(node) { + const scope = context.getScope(); + const { right, left, operator } = node; + const rightConstantOperand = findBinaryExpressionConstantOperand(scope, left, right, operator); + const leftConstantOperand = findBinaryExpressionConstantOperand(scope, right, left, operator); + + if (rightConstantOperand) { + context.report({ node: rightConstantOperand, messageId: "constantBinaryOperand", data: { operator, otherSide: "left" } }); + } else if (leftConstantOperand) { + context.report({ node: leftConstantOperand, messageId: "constantBinaryOperand", data: { operator, otherSide: "right" } }); + } else if (operator === "===" || operator === "!==") { + if (isAlwaysNew(scope, left)) { + context.report({ node: left, messageId: "alwaysNew" }); + } else if (isAlwaysNew(scope, right)) { + context.report({ node: right, messageId: "alwaysNew" }); + } + } else if (operator === "==" || operator === "!=") { + + /* + * If both sides are "new", then both sides are objects and + * therefore they will be compared by reference even with `==` + * equality. + */ + if (isAlwaysNew(scope, left) && isAlwaysNew(scope, right)) { + context.report({ node: left, messageId: "bothAlwaysNew" }); + } + } + + } + + /* + * In theory we could handle short circuting assignment operators, + * for some constant values, but that would require walking the + * scope to find the value of the variable being assigned. This is + * dependant on https://github.com/eslint/eslint/issues/13776 + * + * AssignmentExpression() {}, + */ + }; + } +}; |