feat(58561): Allow leading underscore for types to bypass noUnusedLocals warning #58884
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The TypeScript team hasn't accepted the linked issue #58561. If you can get it accepted, this PR will have a better chance of being reviewed. |
jakebailey
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jonshea
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Aug 22, 2025
This PR continues [Allow leading underscore for types...](microsoft#58884), taking into account feedback from https://github.com/microsoft/TypeScript/pull/58884/files#r1643108204. The initial commit on this PR is original work by @a-tarasyuk. The second commit enhances the test suite and reverts the change to checker.ts to get a new baseline on the test suite for easier comparison with the changes. The third commit changes checker.ts to allow any unused local if it is prefixed with an underscore. This has the effect of newly allowing the following unused declarations: ```ts // Variables were previously allowed only in destructuring and for-loops const _unusedVar = 2; let _unusedLet = 4; var _unusedVar2 = 6; function _unusedFunc() { } const _unusedArrow = () => { }; class _UnusedClass { } interface _UnusedInterface { } type _UnusedType = string; enum _UnusedEnum { A } namespace _UnusedNamespace { ... } ``` As far as I can tell, enum members and properties are not checked in the checkUnusedLocalsAndParameters function, and we do not need to special-case them. Closes microsoft#58561
jonshea
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Aug 23, 2025
This PR continues [Allow leading underscore for types...](microsoft#58884), taking into account feedback from https://github.com/microsoft/TypeScript/pull/58884/files#r1643108204. The initial commit on this PR is original work by @a-tarasyuk. The second commit enhances the test suite and reverts the change to checker.ts to get a new baseline on the test suite for easier comparison with the changes. The third commit changes checker.ts to allow any unused local if it is prefixed with an underscore. This has the effect of newly allowing the following unused declarations: ```ts // Variables were previously allowed only in destructuring and for-loops const _unusedVar = 2; let _unusedLet = 4; var _unusedVar2 = 6; // These two no longer raise // error TS6198: All destructured elements are unused const { _a, _b } = { _a: 1, _b: 1 }; function f2({_a, _b}) function _unusedFunc() { } const _unusedArrow = () => { }; class _UnusedClass { } interface _UnusedInterface { } type _UnusedType = string; enum _UnusedEnum { A } namespace _UnusedNamespace { ... } ``` As far as I can tell, enum members and properties are not checked in the checkUnusedLocalsAndParameters function, and we do not need to special-case them. Closes microsoft#58561
jonshea
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Aug 23, 2025
This PR continues [Allow leading underscore for types...](microsoft#58884), taking into account feedback from https://github.com/microsoft/TypeScript/pull/58884/files#r1643108204. The initial commit on this PR is original work by @a-tarasyuk. The second commit enhances the test suite and reverts the change to checker.ts to get a new baseline on the test suite for easier comparison with the changes. The third commit changes checker.ts to allow any unused local if it is prefixed with an underscore. This has the effect of newly allowing the following unused declarations: ```ts // Variables were previously allowed only in destructuring and for-loops const _unusedVar = 2; let _unusedLet = 4; var _unusedVar2 = 6; // These two no longer raise // error TS6198: All destructured elements are unused const { _a, _b } = { _a: 1, _b: 1 }; function f2({_a, _b}) function _unusedFunc() { } const _unusedArrow = () => { }; class _UnusedClass { } interface _UnusedInterface { } type _UnusedType = string; enum _UnusedEnum { A } namespace _UnusedNamespace { ... } ``` As far as I can tell, enum members and properties are not checked in the checkUnusedLocalsAndParameters function, and we do not need to special-case them. Closes microsoft#58561
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Fixes #58561