295 lines
10 KiB
JavaScript
295 lines
10 KiB
JavaScript
/**
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* @fileoverview Rule to flag use constant conditions
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* @author Christian Schulz <http://rndm.de>
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*/
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"use strict";
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//------------------------------------------------------------------------------
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// Helpers
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//------------------------------------------------------------------------------
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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module.exports = {
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meta: {
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type: "problem",
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docs: {
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description: "disallow constant expressions in conditions",
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category: "Possible Errors",
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recommended: true,
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url: "https://eslint.org/docs/rules/no-constant-condition"
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},
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schema: [
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{
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type: "object",
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properties: {
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checkLoops: {
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type: "boolean",
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default: true
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}
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},
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additionalProperties: false
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}
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],
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messages: {
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unexpected: "Unexpected constant condition."
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}
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},
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create(context) {
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const options = context.options[0] || {},
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checkLoops = options.checkLoops !== false,
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loopSetStack = [];
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let loopsInCurrentScope = new Set();
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//--------------------------------------------------------------------------
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// Helpers
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//--------------------------------------------------------------------------
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/**
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* Returns literal's value converted to the Boolean type
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* @param {ASTNode} node any `Literal` node
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* @returns {boolean | null} `true` when node is truthy, `false` when node is falsy,
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* `null` when it cannot be determined.
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*/
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function getBooleanValue(node) {
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if (node.value === null) {
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/*
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* it might be a null literal or bigint/regex literal in unsupported environments .
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* https://github.com/estree/estree/blob/14df8a024956ea289bd55b9c2226a1d5b8a473ee/es5.md#regexpliteral
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* https://github.com/estree/estree/blob/14df8a024956ea289bd55b9c2226a1d5b8a473ee/es2020.md#bigintliteral
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*/
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if (node.raw === "null") {
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return false;
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}
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// regex is always truthy
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if (typeof node.regex === "object") {
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return true;
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}
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return null;
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}
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return !!node.value;
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}
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/**
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* Checks if a branch node of LogicalExpression short circuits the whole condition
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* @param {ASTNode} node The branch of main condition which needs to be checked
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* @param {string} operator The operator of the main LogicalExpression.
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* @returns {boolean} true when condition short circuits whole condition
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*/
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function isLogicalIdentity(node, operator) {
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switch (node.type) {
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case "Literal":
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return (operator === "||" && getBooleanValue(node) === true) ||
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(operator === "&&" && getBooleanValue(node) === false);
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case "UnaryExpression":
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return (operator === "&&" && node.operator === "void");
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case "LogicalExpression":
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/*
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* handles `a && false || b`
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* `false` is an identity element of `&&` but not `||`
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*/
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return operator === node.operator &&
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(
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isLogicalIdentity(node.left, operator) ||
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isLogicalIdentity(node.right, operator)
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);
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case "AssignmentExpression":
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return ["||=", "&&="].includes(node.operator) &&
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operator === node.operator.slice(0, -1) &&
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isLogicalIdentity(node.right, operator);
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// no default
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}
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return false;
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}
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/**
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* Checks if a node has a constant truthiness value.
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* @param {ASTNode} node The AST node to check.
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* @param {boolean} inBooleanPosition `false` if checking branch of a condition.
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* `true` in all other cases
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* @returns {Bool} true when node's truthiness is constant
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* @private
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*/
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function isConstant(node, inBooleanPosition) {
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// node.elements can return null values in the case of sparse arrays ex. [,]
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if (!node) {
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return true;
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}
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switch (node.type) {
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case "Literal":
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case "ArrowFunctionExpression":
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case "FunctionExpression":
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case "ObjectExpression":
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return true;
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case "TemplateLiteral":
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return (inBooleanPosition && node.quasis.some(quasi => quasi.value.cooked.length)) ||
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node.expressions.every(exp => isConstant(exp, inBooleanPosition));
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case "ArrayExpression": {
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if (node.parent.type === "BinaryExpression" && node.parent.operator === "+") {
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return node.elements.every(element => isConstant(element, false));
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}
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return true;
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}
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case "UnaryExpression":
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if (
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node.operator === "void" ||
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node.operator === "typeof" && inBooleanPosition
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) {
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return true;
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}
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if (node.operator === "!") {
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return isConstant(node.argument, true);
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}
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return isConstant(node.argument, false);
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case "BinaryExpression":
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return isConstant(node.left, false) &&
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isConstant(node.right, false) &&
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node.operator !== "in";
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case "LogicalExpression": {
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const isLeftConstant = isConstant(node.left, inBooleanPosition);
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const isRightConstant = isConstant(node.right, inBooleanPosition);
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const isLeftShortCircuit = (isLeftConstant && isLogicalIdentity(node.left, node.operator));
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const isRightShortCircuit = (inBooleanPosition && isRightConstant && isLogicalIdentity(node.right, node.operator));
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return (isLeftConstant && isRightConstant) ||
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isLeftShortCircuit ||
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isRightShortCircuit;
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}
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case "AssignmentExpression":
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if (node.operator === "=") {
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return isConstant(node.right, inBooleanPosition);
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}
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if (["||=", "&&="].includes(node.operator) && inBooleanPosition) {
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return isLogicalIdentity(node.right, node.operator.slice(0, -1));
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}
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return false;
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case "SequenceExpression":
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return isConstant(node.expressions[node.expressions.length - 1], inBooleanPosition);
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// no default
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}
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return false;
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}
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/**
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* Tracks when the given node contains a constant condition.
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* @param {ASTNode} node The AST node to check.
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* @returns {void}
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* @private
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*/
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function trackConstantConditionLoop(node) {
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if (node.test && isConstant(node.test, true)) {
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loopsInCurrentScope.add(node);
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}
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}
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/**
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* Reports when the set contains the given constant condition node
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* @param {ASTNode} node The AST node to check.
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* @returns {void}
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* @private
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*/
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function checkConstantConditionLoopInSet(node) {
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if (loopsInCurrentScope.has(node)) {
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loopsInCurrentScope.delete(node);
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context.report({ node: node.test, messageId: "unexpected" });
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}
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}
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/**
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* Reports when the given node contains a constant condition.
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* @param {ASTNode} node The AST node to check.
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* @returns {void}
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* @private
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*/
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function reportIfConstant(node) {
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if (node.test && isConstant(node.test, true)) {
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context.report({ node: node.test, messageId: "unexpected" });
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}
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}
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/**
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* Stores current set of constant loops in loopSetStack temporarily
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* and uses a new set to track constant loops
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* @returns {void}
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* @private
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*/
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function enterFunction() {
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loopSetStack.push(loopsInCurrentScope);
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loopsInCurrentScope = new Set();
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}
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/**
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* Reports when the set still contains stored constant conditions
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* @returns {void}
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* @private
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*/
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function exitFunction() {
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loopsInCurrentScope = loopSetStack.pop();
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}
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/**
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* Checks node when checkLoops option is enabled
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* @param {ASTNode} node The AST node to check.
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* @returns {void}
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* @private
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*/
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function checkLoop(node) {
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if (checkLoops) {
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trackConstantConditionLoop(node);
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}
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}
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//--------------------------------------------------------------------------
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// Public
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//--------------------------------------------------------------------------
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return {
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ConditionalExpression: reportIfConstant,
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IfStatement: reportIfConstant,
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WhileStatement: checkLoop,
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"WhileStatement:exit": checkConstantConditionLoopInSet,
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DoWhileStatement: checkLoop,
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"DoWhileStatement:exit": checkConstantConditionLoopInSet,
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ForStatement: checkLoop,
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"ForStatement > .test": node => checkLoop(node.parent),
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"ForStatement:exit": checkConstantConditionLoopInSet,
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FunctionDeclaration: enterFunction,
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"FunctionDeclaration:exit": exitFunction,
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FunctionExpression: enterFunction,
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"FunctionExpression:exit": exitFunction,
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YieldExpression: () => loopsInCurrentScope.clear()
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};
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}
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};
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