@typescript-eslint/eslint-plugin
Version:
TypeScript plugin for ESLint
248 lines (247 loc) • 12.1 kB
JavaScript
;
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Object.defineProperty(exports, "__esModule", { value: true });
const utils_1 = require("@typescript-eslint/utils");
const tsutils = __importStar(require("ts-api-utils"));
const util_1 = require("../util");
exports.default = (0, util_1.createRule)({
name: 'prefer-find',
meta: {
type: 'suggestion',
docs: {
description: 'Enforce the use of Array.prototype.find() over Array.prototype.filter() followed by [0] when looking for a single result',
recommended: 'stylistic',
requiresTypeChecking: true,
},
hasSuggestions: true,
messages: {
preferFind: 'Prefer .find(...) instead of .filter(...)[0].',
preferFindSuggestion: 'Use .find(...) instead of .filter(...)[0].',
},
schema: [],
},
defaultOptions: [],
create(context) {
const globalScope = context.sourceCode.getScope(context.sourceCode.ast);
const services = (0, util_1.getParserServices)(context);
const checker = services.program.getTypeChecker();
function parseArrayFilterExpressions(expression) {
const node = (0, util_1.skipChainExpression)(expression);
if (node.type === utils_1.AST_NODE_TYPES.SequenceExpression) {
// Only the last expression in (a, b, [1, 2, 3].filter(condition))[0] matters
const lastExpression = (0, util_1.nullThrows)(node.expressions.at(-1), 'Expected to have more than zero expressions in a sequence expression');
return parseArrayFilterExpressions(lastExpression);
}
// This is the only reason we're returning a list rather than a single value.
if (node.type === utils_1.AST_NODE_TYPES.ConditionalExpression) {
// Both branches of the ternary _must_ return results.
const consequentResult = parseArrayFilterExpressions(node.consequent);
if (consequentResult.length === 0) {
return [];
}
const alternateResult = parseArrayFilterExpressions(node.alternate);
if (alternateResult.length === 0) {
return [];
}
// Accumulate the results from both sides and pass up the chain.
return [...consequentResult, ...alternateResult];
}
// Check if it looks like <<stuff>>(...), but not <<stuff>>?.(...)
if (node.type === utils_1.AST_NODE_TYPES.CallExpression && !node.optional) {
const callee = node.callee;
// Check if it looks like <<stuff>>.filter(...) or <<stuff>>['filter'](...),
// or the optional chaining variants.
if (callee.type === utils_1.AST_NODE_TYPES.MemberExpression) {
const isBracketSyntaxForFilter = callee.computed;
if ((0, util_1.isStaticMemberAccessOfValue)(callee, context, 'filter')) {
const filterNode = callee.property;
const filteredObjectType = (0, util_1.getConstrainedTypeAtLocation)(services, callee.object);
// As long as the object is a (possibly nullable) array,
// this is an Array.prototype.filter expression.
if (isArrayish(filteredObjectType)) {
return [
{
filterNode,
isBracketSyntaxForFilter,
},
];
}
}
}
}
// not a filter expression.
return [];
}
/**
* Tells whether the type is a possibly nullable array/tuple or union thereof.
*/
function isArrayish(type) {
let isAtLeastOneArrayishComponent = false;
for (const unionPart of tsutils.unionTypeParts(type)) {
if (tsutils.isIntrinsicNullType(unionPart) ||
tsutils.isIntrinsicUndefinedType(unionPart)) {
continue;
}
// apparently checker.isArrayType(T[] & S[]) => false.
// so we need to check the intersection parts individually.
const isArrayOrIntersectionThereof = tsutils
.intersectionTypeParts(unionPart)
.every(intersectionPart => checker.isArrayType(intersectionPart) ||
checker.isTupleType(intersectionPart));
if (!isArrayOrIntersectionThereof) {
// There is a non-array, non-nullish type component,
// so it's not an array.
return false;
}
isAtLeastOneArrayishComponent = true;
}
return isAtLeastOneArrayishComponent;
}
function getObjectIfArrayAtZeroExpression(node) {
// .at() should take exactly one argument.
if (node.arguments.length !== 1) {
return undefined;
}
const callee = node.callee;
if (callee.type === utils_1.AST_NODE_TYPES.MemberExpression &&
!callee.optional &&
(0, util_1.isStaticMemberAccessOfValue)(callee, context, 'at')) {
const atArgument = (0, util_1.getStaticValue)(node.arguments[0], globalScope);
if (atArgument != null && isTreatedAsZeroByArrayAt(atArgument.value)) {
return callee.object;
}
}
return undefined;
}
/**
* Implements the algorithm for array indexing by `.at()` method.
* @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/at#parameters
*/
function isTreatedAsZeroByArrayAt(value) {
// This would cause the number constructor coercion to throw. Other static
// values are safe.
if (typeof value === 'symbol') {
return false;
}
const asNumber = Number(value);
if (isNaN(asNumber)) {
return true;
}
return Math.trunc(asNumber) === 0;
}
function isMemberAccessOfZero(node) {
const property = (0, util_1.getStaticValue)(node.property, globalScope);
// Check if it looks like <<stuff>>[0] or <<stuff>>['0'], but not <<stuff>>?.[0]
return (!node.optional &&
property != null &&
isTreatedAsZeroByMemberAccess(property.value));
}
/**
* Implements the algorithm for array indexing by member operator.
* @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array#array_indices
*/
function isTreatedAsZeroByMemberAccess(value) {
return String(value) === '0';
}
function generateFixToRemoveArrayElementAccess(fixer, arrayNode, wholeExpressionBeingFlagged) {
const tokenToStartDeletingFrom = (0, util_1.nullThrows)(
// The next `.` or `[` is what we're looking for.
// think of (...).at(0) or (...)[0] or even (...)["at"](0).
context.sourceCode.getTokenAfter(arrayNode, token => token.value === '.' || token.value === '['), 'Expected to find a member access token!');
return fixer.removeRange([
tokenToStartDeletingFrom.range[0],
wholeExpressionBeingFlagged.range[1],
]);
}
function generateFixToReplaceFilterWithFind(fixer, filterExpression) {
return fixer.replaceText(filterExpression.filterNode, filterExpression.isBracketSyntaxForFilter ? '"find"' : 'find');
}
return {
// This query will be used to find things like `filteredResults.at(0)`.
CallExpression(node) {
const object = getObjectIfArrayAtZeroExpression(node);
if (object) {
const filterExpressions = parseArrayFilterExpressions(object);
if (filterExpressions.length !== 0) {
context.report({
node,
messageId: 'preferFind',
suggest: [
{
messageId: 'preferFindSuggestion',
fix: (fixer) => {
return [
...filterExpressions.map(filterExpression => generateFixToReplaceFilterWithFind(fixer, filterExpression)),
// Get rid of the .at(0) or ['at'](0).
generateFixToRemoveArrayElementAccess(fixer, object, node),
];
},
},
],
});
}
}
},
// This query will be used to find things like `filteredResults[0]`.
//
// Note: we're always looking for array member access to be "computed",
// i.e. `filteredResults[0]`, since `filteredResults.0` isn't a thing.
'MemberExpression[computed=true]'(node) {
if (isMemberAccessOfZero(node)) {
const object = node.object;
const filterExpressions = parseArrayFilterExpressions(object);
if (filterExpressions.length !== 0) {
context.report({
node,
messageId: 'preferFind',
suggest: [
{
messageId: 'preferFindSuggestion',
fix: (fixer) => {
return [
...filterExpressions.map(filterExpression => generateFixToReplaceFilterWithFind(fixer, filterExpression)),
// Get rid of the [0].
generateFixToRemoveArrayElementAccess(fixer, object, node),
];
},
},
],
});
}
}
},
};
},
});