prefer-nullish-coalescing.js
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"use strict";
var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
if (k2 === undefined) k2 = k;
Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
}) : (function(o, m, k, k2) {
if (k2 === undefined) k2 = k;
o[k2] = m[k];
}));
var __setModuleDefault = (this && this.__setModuleDefault) || (Object.create ? (function(o, v) {
Object.defineProperty(o, "default", { enumerable: true, value: v });
}) : function(o, v) {
o["default"] = v;
});
var __importStar = (this && this.__importStar) || function (mod) {
if (mod && mod.__esModule) return mod;
var result = {};
if (mod != null) for (var k in mod) if (k !== "default" && Object.prototype.hasOwnProperty.call(mod, k)) __createBinding(result, mod, k);
__setModuleDefault(result, mod);
return result;
};
Object.defineProperty(exports, "__esModule", { value: true });
const experimental_utils_1 = require("@typescript-eslint/experimental-utils");
const util = __importStar(require("../util"));
exports.default = util.createRule({
name: 'prefer-nullish-coalescing',
meta: {
type: 'suggestion',
docs: {
description: 'Enforce the usage of the nullish coalescing operator instead of logical chaining',
category: 'Best Practices',
recommended: false,
suggestion: true,
requiresTypeChecking: true,
},
messages: {
preferNullish: 'Prefer using nullish coalescing operator (`??`) instead of a logical or (`||`), as it is a safer operator.',
suggestNullish: 'Fix to nullish coalescing operator (`??`).',
},
schema: [
{
type: 'object',
properties: {
ignoreConditionalTests: {
type: 'boolean',
},
ignoreMixedLogicalExpressions: {
type: 'boolean',
},
forceSuggestionFixer: {
type: 'boolean',
},
},
additionalProperties: false,
},
],
},
defaultOptions: [
{
ignoreConditionalTests: true,
ignoreMixedLogicalExpressions: true,
},
],
create(context, [{ ignoreConditionalTests, ignoreMixedLogicalExpressions }]) {
const parserServices = util.getParserServices(context);
const sourceCode = context.getSourceCode();
const checker = parserServices.program.getTypeChecker();
return {
'LogicalExpression[operator = "||"]'(node) {
const tsNode = parserServices.esTreeNodeToTSNodeMap.get(node);
const type = checker.getTypeAtLocation(tsNode.left);
const isNullish = util.isNullableType(type, { allowUndefined: true });
if (!isNullish) {
return;
}
if (ignoreConditionalTests === true && isConditionalTest(node)) {
return;
}
const isMixedLogical = isMixedLogicalExpression(node);
if (ignoreMixedLogicalExpressions === true && isMixedLogical) {
return;
}
const barBarOperator = util.nullThrows(sourceCode.getTokenAfter(node.left, token => token.type === experimental_utils_1.AST_TOKEN_TYPES.Punctuator &&
token.value === node.operator), util.NullThrowsReasons.MissingToken('operator', node.type));
function* fix(fixer) {
if (node.parent && util.isLogicalOrOperator(node.parent)) {
// '&&' and '??' operations cannot be mixed without parentheses (e.g. a && b ?? c)
if (node.left.type === experimental_utils_1.AST_NODE_TYPES.LogicalExpression &&
!util.isLogicalOrOperator(node.left.left)) {
yield fixer.insertTextBefore(node.left.right, '(');
}
else {
yield fixer.insertTextBefore(node.left, '(');
}
yield fixer.insertTextAfter(node.right, ')');
}
yield fixer.replaceText(barBarOperator, '??');
}
context.report({
node: barBarOperator,
messageId: 'preferNullish',
suggest: [
{
messageId: 'suggestNullish',
fix,
},
],
});
},
};
},
});
function isConditionalTest(node) {
const parents = new Set([node]);
let current = node.parent;
while (current) {
parents.add(current);
if ((current.type === experimental_utils_1.AST_NODE_TYPES.ConditionalExpression ||
current.type === experimental_utils_1.AST_NODE_TYPES.DoWhileStatement ||
current.type === experimental_utils_1.AST_NODE_TYPES.IfStatement ||
current.type === experimental_utils_1.AST_NODE_TYPES.ForStatement ||
current.type === experimental_utils_1.AST_NODE_TYPES.WhileStatement) &&
parents.has(current.test)) {
return true;
}
if ([
experimental_utils_1.AST_NODE_TYPES.ArrowFunctionExpression,
experimental_utils_1.AST_NODE_TYPES.FunctionExpression,
].includes(current.type)) {
/**
* This is a weird situation like:
* `if (() => a || b) {}`
* `if (function () { return a || b }) {}`
*/
return false;
}
current = current.parent;
}
return false;
}
function isMixedLogicalExpression(node) {
const seen = new Set();
const queue = [node.parent, node.left, node.right];
for (const current of queue) {
if (seen.has(current)) {
continue;
}
seen.add(current);
if (current && current.type === experimental_utils_1.AST_NODE_TYPES.LogicalExpression) {
if (current.operator === '&&') {
return true;
}
else if (current.operator === '||') {
// check the pieces of the node to catch cases like `a || b || c && d`
queue.push(current.parent, current.left, current.right);
}
}
}
return false;
}
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