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fix(eslint-plugin): [no-for-in-array] report on any type which may be an array or array-like #10535

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Merged
merged 10 commits into from
Jan 19, 2025
+311 −5
Merged

fix(eslint-plugin): [no-for-in-array] report on any type which may be an array or array-like #10535

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75d1ecb
report on for-in on 'Array<T> | undefined'
ronami Dec 21, 2024
4ded1c5
update the rule to report on anything that may be an array or array-like
ronami Dec 27, 2024
7efca69
nested test cases
ronami Dec 27, 2024
e126dab
refactor code to use 'isBuiltinSymbolLike' for checking the arguments…
ronami Dec 28, 2024
b612eef
refactor, add some more array-likes
ronami Dec 28, 2024
6466fb5
undo unrelated change
ronami Dec 28, 2024
2ce3cea
use lib-dom tsconfig only for tests that need it
ronami Dec 28, 2024
006eb4c
Merge branch 'main' into no-for-in-array-nullish
ronami Dec 28, 2024
762934d
fix failing tests
ronami Dec 28, 2024
599ac75
check array-like based on it having a length and a number-index-signa…
ronami Jan 11, 2025
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38 changes: 33 additions & 5 deletions packages/eslint-plugin/src/rules/no-for-in-array.ts
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Original file line number Diff line number Diff line change
@@ -1,10 +1,10 @@
import * as tsutils from 'ts-api-utils';
import * as ts from 'typescript';

import {
createRule,
getConstrainedTypeAtLocation,
getParserServices,
isTypeArrayTypeOrUnionOfArrayTypes,
} from '../util';
import { getForStatementHeadLoc } from '../util/getForStatementHeadLoc';

Expand Down Expand Up @@ -32,10 +32,7 @@ export default createRule({

const type = getConstrainedTypeAtLocation(services, node.right);

if (
isTypeArrayTypeOrUnionOfArrayTypes(type, checker) ||
(type.flags & ts.TypeFlags.StringLike) !== 0
) {
if (isArrayLike(checker, type)) {
context.report({
loc: getForStatementHeadLoc(context.sourceCode, node),
messageId: 'forInViolation',
Expand All @@ -45,3 +42,34 @@ export default createRule({
};
},
});

function isArrayLike(checker: ts.TypeChecker, type: ts.Type): boolean {
return isTypeRecurser(
type,
t => t.getNumberIndexType() != null && hasArrayishLength(checker, t),
);
}

function hasArrayishLength(checker: ts.TypeChecker, type: ts.Type): boolean {
const lengthProperty = type.getProperty('length');

if (lengthProperty == null) {
return false;
}

return tsutils.isTypeFlagSet(
checker.getTypeOfSymbol(lengthProperty),
ts.TypeFlags.NumberLike,
);
}

function isTypeRecurser(
type: ts.Type,
predicate: (t: ts.Type) => boolean,
): boolean {
if (type.isUnionOrIntersection()) {
return type.types.some(t => isTypeRecurser(t, predicate));
}

return predicate(type);
}
6 changes: 6 additions & 0 deletions packages/eslint-plugin/tests/fixtures/tsconfig.lib-dom.json
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
{
"extends": "./tsconfig.json",
"compilerOptions": {
"lib": ["es2015", "es2017", "esnext", "dom"]
}
}
Comment on lines +1 to +6
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Is there a better way to do this? Specifically dom is necessary for the two dom-array-likes.

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Yep, this is good!

272 changes: 272 additions & 0 deletions packages/eslint-plugin/tests/rules/no-for-in-array.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,23 @@ for (const x of [3, 4, 5]) {
`
for (const x in { a: 1, b: 2, c: 3 }) {
console.log(x);
}
`,
// this is normally a type error, this test is here to make sure the rule
// doesn't include an "extra" report for it
`
declare const nullish: null | undefined;
// @ts-expect-error
for (const k in nullish) {
}
`,
`
declare const obj: {
[key: number]: number;
};

for (const key in obj) {
console.log(key);
}
`,
],
Expand Down Expand Up @@ -177,5 +194,260 @@ for (const x
},
],
},
{
code: `
declare const array: string[] | null;

for (const key in array) {
console.log(key);
}
`,
errors: [
{
column: 1,
endColumn: 25,
endLine: 4,
line: 4,
messageId: 'forInViolation',
},
],
},
{
code: `
declare const array: number[] | undefined;

for (const key in array) {
console.log(key);
}
`,
errors: [
{
column: 1,
endColumn: 25,
endLine: 4,
line: 4,
messageId: 'forInViolation',
},
],
},
{
code: `
declare const array: boolean[] | { a: 1; b: 2; c: 3 };

for (const key in array) {
console.log(key);
}
`,
errors: [
{
column: 1,
endColumn: 25,
endLine: 4,
line: 4,
messageId: 'forInViolation',
},
],
},
{
code: `
declare const array: [number, string];

for (const key in array) {
console.log(key);
}
`,
errors: [
{
column: 1,
endColumn: 25,
endLine: 4,
line: 4,
messageId: 'forInViolation',
},
],
},
{
code: `
declare const array: [number, string] | { a: 1; b: 2; c: 3 };

for (const key in array) {
console.log(key);
}
`,
errors: [
{
column: 1,
endColumn: 25,
endLine: 4,
line: 4,
messageId: 'forInViolation',
},
],
},
{
code: `
declare const array: string[] | Record<number, string>;

for (const key in array) {
console.log(key);
}
`,
errors: [
{
column: 1,
endColumn: 25,
endLine: 4,
line: 4,
messageId: 'forInViolation',
},
],
},
{
code: `
const arrayLike = /fe/.exec('foo');

for (const x in arrayLike) {
console.log(x);
}
`,
errors: [
{
column: 1,
endColumn: 27,
endLine: 4,
line: 4,
messageId: 'forInViolation',
},
],
},
{
code: `
declare const arrayLike: HTMLCollection;

for (const x in arrayLike) {
console.log(x);
}
`,
errors: [
{
column: 1,
endColumn: 27,
endLine: 4,
line: 4,
messageId: 'forInViolation',
},
],
languageOptions: {
parserOptions: {
project: './tsconfig.lib-dom.json',
projectService: false,
tsconfigRootDir: rootDir,
},
},
},
{
code: `
declare const arrayLike: NodeList;

for (const x in arrayLike) {
console.log(x);
}
`,
errors: [
{
column: 1,
endColumn: 27,
endLine: 4,
line: 4,
messageId: 'forInViolation',
},
],
languageOptions: {
parserOptions: {
project: './tsconfig.lib-dom.json',
projectService: false,
tsconfigRootDir: rootDir,
},
},
},
{
code: `
function foo() {
for (const a in arguments) {
console.log(a);
}
}
`,
errors: [
{
column: 3,
endColumn: 29,
endLine: 3,
line: 3,
messageId: 'forInViolation',
},
],
},
{
code: `
declare const array:
| (({ a: string } & string[]) | Record<string, boolean>)
| Record<number, string>;

for (const key in array) {
console.log(key);
}
`,
errors: [
{
column: 1,
endColumn: 25,
endLine: 6,
line: 6,
messageId: 'forInViolation',
},
],
},
{
code: `
declare const array:
| (({ a: string } & RegExpExecArray) | Record<string, boolean>)
| Record<number, string>;

for (const key in array) {
console.log(k);
}
`,
errors: [
{
column: 1,
endColumn: 25,
endLine: 6,
line: 6,
messageId: 'forInViolation',
},
],
},
{
code: `
declare const obj: {
[key: number]: number;
length: 1;
};

for (const key in obj) {
console.log(key);
}
`,
errors: [
{
column: 1,
endColumn: 23,
endLine: 7,
line: 7,
messageId: 'forInViolation',
},
],
},
],
});
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