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Merged
ArnaudBarre merged 1 commit into from
Nov 19, 2025
Merged

Catch useless ?? null and ?? undefined #13

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4 changes: 4 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,5 +1,9 @@
# Changelog

## Unreleased

- `noUnnecessaryCondition`: Catch useless `?? null` and `?? undefined` coalescing and add "Remove unnecessary nullish coalescing" suggestion.

## 1.0.27

- `preferOptionalChain`: fix chain analysis when the chain ends with `=== null`
Expand Down
201 changes: 186 additions & 15 deletions src/rules/noUnnecessaryCondition/noUnnecessaryCondition.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -934,6 +934,7 @@ function test<T>(arg: T | { value: string }) {
}
}
`,
`declare const foo: string | undefined; const bar = foo ?? null;`,
],
invalid: [
// Ensure that it's checking in all the right places
Expand Down Expand Up @@ -1556,38 +1557,104 @@ function test<T extends object>(a: T) {
column: 15,
},
],
}, // Nullish coalescing operator
},
// Nullish coalescing operator
{
code: `
function test(a: string) {
return a ?? 'default';
}
`,
errors: [{ message: messages.neverNullish, line: 3, column: 10 }],
errors: [
{
message: messages.neverNullish,
line: 3,
column: 12,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
function test(a: string) {
return a;
}
`,
},
],
},
],
},
{
code: `
function test(a: string | false) {
return a ?? 'default';
}
`,
errors: [{ message: messages.neverNullish, line: 3, column: 10 }],
errors: [
{
message: messages.neverNullish,
line: 3,
column: 12,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
function test(a: string | false) {
return a;
}
`,
},
],
},
],
},
{
code: `
function test<T extends string>(a: T) {
return a ?? 'default';
}
`,
errors: [{ message: messages.neverNullish, line: 3, column: 10 }],
}, // nullish + array index without optional chaining
errors: [
{
message: messages.neverNullish,
line: 3,
column: 12,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
function test<T extends string>(a: T) {
return a;
}
`,
},
],
},
],
},
// nullish + array index without optional chaining
{
code: `
function test(a: { foo: string }[]) {
return a[0].foo ?? 'default';
}
`,
errors: [{ message: messages.neverNullish, line: 3, column: 10 }],
errors: [
{
message: messages.neverNullish,
line: 3,
column: 19,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
function test(a: { foo: string }[]) {
return a[0].foo;
}
`,
},
],
},
],
},
{
code: `
Expand Down Expand Up @@ -1619,16 +1686,49 @@ function test(a: never) {
return a ?? 'default';
}
`,
errors: [{ message: messages.never, line: 3, column: 10 }],
errors: [
{
message: messages.never,
line: 3,
column: 12,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
function test(a: never) {
return a;
}
`,
},
],
},
],
},
{
code: `
function test<T extends { foo: number }, K extends 'foo'>(num: T[K]) {
num ?? 'default';
}
`,
errors: [{ message: messages.neverNullish, line: 3, column: 3 }],
}, // Predicate functions
errors: [
{
message: messages.neverNullish,
line: 3,
column: 7,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
function test<T extends { foo: number }, K extends 'foo'>(num: T[K]) {
num;
}
`,
},
],
},
],
},
// Predicate functions
{
code: `
[1, 3, 5].filter(() => true);
Expand Down Expand Up @@ -2757,9 +2857,18 @@ foo ??= 1;
{
message: messages.neverNullish,
line: 3,
column: 1,
endColumn: 4,
column: 5,
endLine: 3,
endColumn: 10,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
declare let foo: {};
foo;
`,
},
],
},
],
},
Expand All @@ -2772,9 +2881,18 @@ foo ??= 1;
{
message: messages.neverNullish,
line: 3,
column: 1,
endColumn: 4,
column: 5,
endLine: 3,
endColumn: 10,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
declare let foo: number;
foo;
`,
},
],
},
],
},
Expand Down Expand Up @@ -2863,9 +2981,18 @@ foo.bar ??= 1;
{
message: messages.neverNullish,
line: 3,
column: 1,
endColumn: 8,
column: 9,
endLine: 3,
endColumn: 14,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
declare const foo: { bar: number };
foo.bar;
`,
},
],
},
],
},
Expand Down Expand Up @@ -3185,5 +3312,49 @@ if (arr[42] && arr[42]) {}
`,
errors: [{ message: messages.alwaysTruthy, line: 3, column: 16 }],
},
{
code: `
declare const foo: string | null;
const bar = foo ?? null;
`,
errors: [
{
message: messages.uselessNullCoalescing,
line: 3,
column: 17,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
declare const foo: string | null;
const bar = foo;
`,
},
],
},
],
},
{
code: `
declare const foo: string | undefined;
const bar = foo ?? undefined;
`,
errors: [
{
message: messages.uselessUndefinedCoalescing,
line: 3,
column: 17,
suggestions: [
{
message: messages.removeNullishCoalescing,
output: `
declare const foo: string | undefined;
const bar = foo;
`,
},
],
},
],
},
],
});
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