Skip to content

fix(eslint-plugin): fix crash and false positives in no-useless-default-assignment #11845

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
ulrichstark wants to merge 10 commits into
base: main
Choose a base branch
from
+55 −73
Open

fix(eslint-plugin): fix crash and false positives in no-useless-default-assignment #11845

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
10 commits
Select commit Hold shift + click to select a range
9364244
fix(eslint-plugin): fix crash in `no-useless-default-assignment` if n…
ulrichstark Dec 15, 2025
4d5189f
fix false positives
ulrichstark Dec 16, 2025
1908ae6
shuffle code around to make diff shorter and increase test coverage
ulrichstark Dec 16, 2025
755c032
change comment to point to new issue
ulrichstark Dec 16, 2025
1cfcf21
reduce git diff
ulrichstark Dec 16, 2025
148ca95
increase test coverage
ulrichstark Dec 16, 2025
6921a1a
remove changes to fix issue 11847
ulrichstark Dec 17, 2025
5bf1247
bring back noUncheckedIndexedAccess tests
ulrichstark Dec 17, 2025
84419df
remove changes to fix issue 11847 (2.0)
ulrichstark Dec 17, 2025
f25f541
move elementIndex down
ulrichstark Dec 19, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
31 changes: 15 additions & 16 deletions packages/eslint-plugin/src/rules/no-useless-default-assignment.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -39,11 +39,6 @@ export default createRule<[], MessageId>({
create(context) {
const services = getParserServices(context);
const checker = services.program.getTypeChecker();
const compilerOptions = services.program.getCompilerOptions();
const isNoUncheckedIndexedAccess = tsutils.isCompilerOptionEnabled(
compilerOptions,
'noUncheckedIndexedAccess',
);

function canBeUndefined(type: ts.Type): boolean {
if (isTypeAnyType(type) || isTypeUnknownType(type)) {
Expand All @@ -60,10 +55,7 @@ export default createRule<[], MessageId>({
): ts.Type | null {
const symbol = objectType.getProperty(propertyName);
if (!symbol) {
if (isNoUncheckedIndexedAccess) {
return null;
}
return objectType.getStringIndexType() ?? null;
return null;
}
return checker.getTypeOfSymbol(symbol);
}
Expand All @@ -79,10 +71,6 @@ export default createRule<[], MessageId>({
}
}

if (isNoUncheckedIndexedAccess) {
return null;
}

return arrayType.getNumberIndexType() ?? null;
}

Expand Down Expand Up @@ -118,6 +106,13 @@ export default createRule<[], MessageId>({
}

const signatures = contextualType.getCallSignatures();
if (
signatures.length === 0 ||
signatures[0].getDeclaration() === tsFunc
) {
return;
}

const params = signatures[0].getParameters();
if (paramIndex < params.length) {
const paramSymbol = params[paramIndex];
Expand Down Expand Up @@ -152,12 +147,16 @@ export default createRule<[], MessageId>({
return;
}

const elementIndex = parent.elements.indexOf(node);
const elementType = getArrayElementType(sourceType, elementIndex);
if (!elementType) {
if (!checker.isTupleType(sourceType)) {
return;
}

const tupleArgs = checker.getTypeArguments(sourceType);
const elementIndex = parent.elements.indexOf(node);
if (elementIndex < 0 || elementIndex >= tupleArgs.length) {
return;
}
const elementType = tupleArgs[elementIndex];
if (!canBeUndefined(elementType)) {
reportUselessDefault(node, 'property', 'uselessDefaultAssignment');
}
Expand Down
97 changes: 40 additions & 57 deletions packages/eslint-plugin/tests/rules/no-useless-default-assignment.test.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -184,6 +184,46 @@ ruleTester.run('no-useless-default-assignment', rule, {
},
},
},
`
declare const g: Array<string>;
const [foo = ''] = g;
`,
`
declare const g: Record<string, string>;
const { foo = '' } = g;
`,
`
declare const h: { [key: string]: string };
const { bar = '' } = h;
`,
// https://github.com/typescript-eslint/typescript-eslint/issues/11849
`
type Merge = boolean | ((incoming: string[]) => void);

const policy: { merge: Merge } = {
merge: (incoming: string[] = []) => {
incoming;
},
};
`,
// https://github.com/typescript-eslint/typescript-eslint/issues/11846
`
const [a, b = ''] = 'somestr'.split('.');
`,
// https://github.com/typescript-eslint/typescript-eslint/issues/11846
`
declare const params: string[];
const [c = '123'] = params;
`,
// https://github.com/typescript-eslint/typescript-eslint/issues/11846
`
declare function useCallback<T>(callback: T);
useCallback((value: number[] = []) => {});
`,
`
declare const tuple: [string];
const [a, b = 'default'] = tuple;
Copy link
Member

@kirkwaiblinger kirkwaiblinger Dec 17, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

(praise) TIL that TS allows out-of-bounds tuple destructuring if a default value is present.

Comically it means that

const [a, outOfBounds = undefined] = ["foo"] as const;

is kind of a false positive if you really squint, but I think let's completely ignore that edge case as niche and unimportant.

`,
],
invalid: [
{
Expand Down Expand Up @@ -459,62 +499,5 @@ ruleTester.run('no-useless-default-assignment', rule, {
function foo({ a }) {}
`,
},
{
code: `
declare const g: Record<string, string>;
const { hello = '' } = g;
`,
errors: [
{
column: 25,
data: { type: 'property' },
endColumn: 27,
line: 3,
messageId: 'uselessDefaultAssignment',
},
],
output: `
declare const g: Record<string, string>;
const { hello } = g;
`,
},
{
code: `
declare const h: { [key: string]: string };
const { world = '' } = h;
`,
errors: [
{
column: 25,
data: { type: 'property' },
endColumn: 27,
line: 3,
messageId: 'uselessDefaultAssignment',
},
],
output: `
declare const h: { [key: string]: string };
const { world } = h;
`,
},
{
code: `
declare const g: Array<string>;
const [foo = ''] = g;
`,
errors: [
{
column: 22,
data: { type: 'property' },
endColumn: 24,
line: 3,
messageId: 'uselessDefaultAssignment',
},
],
output: `
declare const g: Array<string>;
const [foo] = g;
`,
},
],
});