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fix(eslint-plugin): [prefer-find] stop throwing type errors when converting symbols to numbers #8390

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merged 2 commits into from Feb 6, 2024
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fix(eslint-plugin): [prefer-find] stop throwing type errors when converting symbols to numbers #8390

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1e86670
fix #8386: Stop throwing type errors when converting symbols to numbers
kirkwaiblinger Feb 6, 2024
a8d2c21
Address PR feedback
kirkwaiblinger Feb 6, 2024
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29 changes: 18 additions & 11 deletions packages/eslint-plugin/src/rules/prefer-find.ts
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Expand Up @@ -125,22 +125,22 @@ export default createRule({
return isAtLeastOneArrayishComponent;
}

function getObjectIfArrayAtExpression(
function getObjectIfArrayAtZeroExpression(
node: TSESTree.CallExpression,
): TSESTree.Expression | undefined {
// .at() should take exactly one argument.
if (node.arguments.length !== 1) {
return undefined;
}

const atArgument = getStaticValue(node.arguments[0], globalScope);
if (atArgument != null && isTreatedAsZeroByArrayAt(atArgument.value)) {
const callee = node.callee;
if (
callee.type === AST_NODE_TYPES.MemberExpression &&
!callee.optional &&
isStaticMemberAccessOfValue(callee, 'at', globalScope)
) {
const callee = node.callee;
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This change just reverses the order of whether .at, or the (0), are inspected first. It's not needed for the fix, but I found it surprising that foo(Symbol.for('throws')) would throw, since it's not even an at call; it's just any old function. WIth this change, you have to actually have
x.at(Symbol.for('throws')) in order to trigger the faulty code.

if (
callee.type === AST_NODE_TYPES.MemberExpression &&
!callee.optional &&
isStaticMemberAccessOfValue(callee, 'at', globalScope)
) {
const atArgument = getStaticValue(node.arguments[0], globalScope);
if (atArgument != null && isTreatedAsZeroByArrayAt(atArgument.value)) {
return callee.object;
}
}
Expand All @@ -153,7 +153,14 @@ export default createRule({
* @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/at#parameters
*/
function isTreatedAsZeroByArrayAt(value: unknown): boolean {
const asNumber = Number(value);
let asNumber: number;

try {
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[Refactor] I'm not a big fan of try/catch as a form of program control flow. It somewhat hides the intent of the code. Thrown errors are generally a sign of something truly breaking - IMO it's better to be intentional around code always working as expected.

Instead of generally catching all errors, how about checking if typeof value is 'symbol'?

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yep, I was 50/50 on which way to go on this. Changed!

asNumber = Number(value);
} catch (e) {
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this is all that's strictly necessary for the fix

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// This will happen if trying to convert a symbol.
return false;
}

if (isNaN(asNumber)) {
return true;
Expand Down Expand Up @@ -215,7 +222,7 @@ export default createRule({
return {
// This query will be used to find things like `filteredResults.at(0)`.
CallExpression(node): void {
const object = getObjectIfArrayAtExpression(node);
const object = getObjectIfArrayAtZeroExpression(node);
if (object) {
const filterExpression = parseIfArrayFilterExpression(object);
if (filterExpression) {
Expand Down
18 changes: 18 additions & 0 deletions packages/eslint-plugin/tests/rules/prefer-find.test.ts
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Expand Up @@ -56,6 +56,24 @@ ruleTester.run('prefer-find', rule, {
"['Just', 'a', 'find'].find(x => x.length > 4);",
'undefined.filter(x => x)[0];',
'null?.filter(x => x)[0];',
// Should not throw. See https://github.com/typescript-eslint/typescript-eslint/issues/8386
`
declare function foo(param: any): any;
foo(Symbol.for('foo'));
`,
// Specifically need to test Symbol.for(), not just Symbol(), since only
// Symbol.for() creates a static value that the rule inspects.
`
declare const arr: string[];
const s = Symbol.for("Don't throw!");
arr.filter(item => item === 'aha').at(s);
`,
`
[1, 2, 3].filter(x => x)[Symbol('0')];
`,
`
[1, 2, 3].filter(x => x)[Symbol.for('0')];
`,
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],

invalid: [
Expand Down