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fix(eslint-plugin): [no-unnecessary-type-parameters] descend into all parts of mapped types in no-unnecessary-type-parameters #9530

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Merged
merged 6 commits into from
Jul 14, 2024
Merged

fix(eslint-plugin): [no-unnecessary-type-parameters] descend into all parts of mapped types in no-unnecessary-type-parameters #9530

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7b5bb63
recurse into mapped types
danvk Jul 9, 2024
cc7ae25
one failure
danvk Jul 9, 2024
9cd559d
all tests passing
danvk Jul 9, 2024
d5b35e9
add new invalid tests
danvk Jul 10, 2024
9e99ed0
Merge branch 'main' into fix-9524
danvk Jul 10, 2024
9af9db6
remove zero use test
danvk Jul 10, 2024
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10 changes: 9 additions & 1 deletion packages/eslint-plugin/src/rules/no-unnecessary-type-parameters.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -271,10 +271,16 @@ function collectTypeParameterUsageCounts(
// `isTypeReference` to avoid descending into all the properties of a
// generic interface/class, e.g. `Map<K, V>`.
else if (tsutils.isObjectType(type)) {
visitSymbolsListOnce(type.getProperties(), false);
const properties = type.getProperties();
visitSymbolsListOnce(properties, false);

if (isMappedType(type)) {
visitType(type.typeParameter, false);
if (properties.length === 0) {
// TS treats mapped types like `{[k in "a"]: T}` like `{a: T}`.
// They have properties, so we need to avoid double-counting.
visitType(type.templateType, false);
}
}

for (const typeArgument of type.aliasTypeArguments ?? []) {
Expand Down Expand Up @@ -372,6 +378,8 @@ function collectTypeParameterUsageCounts(

interface MappedType extends ts.ObjectType {
typeParameter?: ts.Type;
constraintType?: ts.Type;
templateType?: ts.Type;
}

function isMappedType(type: ts.Type): type is MappedType {
Expand Down
15 changes: 15 additions & 0 deletions packages/eslint-plugin/tests/rules/no-unnecessary-type-parameters.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -342,6 +342,12 @@ ruleTester.run('no-unnecessary-type-parameters', rule, {
(token): token is Exclude<TSESTree.Token, Conditions & ExtractedToken> =>
tokenType in conditions;
`,
`
declare function mapObj<K extends string, V>(
obj: { [key in K]?: V },
fn: (key: K, val: V) => number,
): number[];
`,
],

invalid: [
Expand Down Expand Up @@ -608,5 +614,14 @@ ruleTester.run('no-unnecessary-type-parameters', rule, {
code: 'type Fn = <T extends string>() => `a${T}b`;',
errors: [{ messageId: 'sole', data: { name: 'T' } }],
},
{
code: `
declare function mapObj<K extends string, V>(
obj: { [key in K]?: V },
fn: (key: K) => number,
): number[];
`,
errors: [{ messageId: 'sole', data: { name: 'V' } }],
},
],
});
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