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fix(eslint-plugin): [no-unused-vars] no is assigned a value but only used as a type error when it has a same name #11322

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fix(eslint-plugin): [no-unused-vars] no is assigned a value but only used as a type error when it has a same name #11322

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f7d55fd
test: add test case
nayounsang Jun 17, 2025
bc379fc
fix: strict checks on exports with same type and variable name
nayounsang Jun 20, 2025
bfffde3
Merge branch 'main' into type-unused
nayounsang Jun 20, 2025
2f474b3
refactor: resolve self-code-review
nayounsang Jun 20, 2025
2bfdd0b
Merge branch 'main' into type-unused
nayounsang Jul 1, 2025
52eede8
refactor: change ScopeVariable to Variable
nayounsang Jul 1, 2025
df466a4
refactor: improve perf when call isSafeUnusedExportCondition
nayounsang Jul 1, 2025
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42 changes: 37 additions & 5 deletions packages/eslint-plugin/src/util/collectUnusedVariables.ts
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Original file line number Diff line number Diff line change
@@ -1,10 +1,13 @@
import type {
ScopeManager,
ScopeVariable,
Variable,
} from '@typescript-eslint/scope-manager';
import type { TSESTree } from '@typescript-eslint/utils';

import {
DefinitionType,
ESLintScopeVariable,
ImplicitLibVariable,
ScopeType,
Visitor,
Expand Down Expand Up @@ -188,7 +191,7 @@ class UnusedVarsVisitor extends Visitor {
// basic exported variables
isExported(variable) ||
// variables implicitly exported via a merged declaration
isMergableExported(variable) ||
isMergeableExported(variable) ||
// used variables
isUsedVariable(variable)
) {
Expand Down Expand Up @@ -415,6 +418,26 @@ function isSelfReference(
return false;
}

const exportExceptDefTypes: DefinitionType[] = [
DefinitionType.Variable,
DefinitionType.Type,
];
/**
* In edge cases, the existing used logic does not work.
* When the type and variable name of the variable are the same
* @ref https://github.com/typescript-eslint/typescript-eslint/issues/10658
* @param variable the variable to check
* @returns true if it is an edge case
*/
function isSafeUnusedExportCondition(variable: Variable): boolean {
if (variable.isTypeVariable && variable.isValueVariable) {
return !variable.defs
.map(d => d.type)
.every(t => exportExceptDefTypes.includes(t));
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[Testing] If I comment out this .every, then all tests still pass. In fact, if the inside of the if just does return false; then tests still pass. So either this is unnecessary code or there's a gap in test coverage.

}
return true;
}

const MERGABLE_TYPES = new Set([
AST_NODE_TYPES.ClassDeclaration,
AST_NODE_TYPES.FunctionDeclaration,
Expand All @@ -426,7 +449,7 @@ const MERGABLE_TYPES = new Set([
* Determine if the variable is directly exported
* @param variable the variable to check
*/
function isMergableExported(variable: ScopeVariable): boolean {
function isMergeableExported(variable: Variable): boolean {
// If all of the merged things are of the same type, TS will error if not all of them are exported - so we only need to find one
for (const def of variable.defs) {
// parameters can never be exported.
Expand All @@ -441,7 +464,10 @@ function isMergableExported(variable: ScopeVariable): boolean {
def.node.parent?.type === AST_NODE_TYPES.ExportNamedDeclaration) ||
def.node.parent?.type === AST_NODE_TYPES.ExportDefaultDeclaration
) {
return true;
return (
def.node.type !== AST_NODE_TYPES.TSTypeAliasDeclaration ||
isSafeUnusedExportCondition(variable)
);
}
}

Expand All @@ -453,7 +479,7 @@ function isMergableExported(variable: ScopeVariable): boolean {
* @param variable eslint-scope variable object.
* @returns True if the variable is exported, false if not.
*/
function isExported(variable: ScopeVariable): boolean {
function isExported(variable: Variable): boolean {
return variable.defs.some(definition => {
let node = definition.node;

Expand All @@ -465,7 +491,13 @@ function isExported(variable: ScopeVariable): boolean {
}

// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
return node.parent!.type.startsWith('Export');
const isExportedFlag = node.parent!.type.startsWith('Export');
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@nayounsang nayounsang Jun 20, 2025 •
edited
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need advice

Is there a reason why didn't use optional chaining before?

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tl;dr: the ! is the right thing to use here. node.parent definitely always exists, so it'd be unnecessary to add extra runtime logic with a ?.. The types are wrong!

Other code using ?. isn't ideal, but is existing cruft that we'll clean up eventually.

Digging in for fun...

To see what node type(s) don't know that the parent property definitely exists, you can hover or use a twoslash query on:

node;
// ^? let node: TSESTree.CatchClause | TSESTree.ArrayPattern | TSESTree.ObjectPattern | TSESTree.Identifier | TSESTree.ClassDeclarationWithName | ... 192 more ... | TSESTree.YieldExpression

if (!node.parent) {
  node;
  // ^? let node: TSESTree.Program
}

TSESTree.Program is the AST root representing a file. Why is node allowed to be TSESTree.Program?

Its definition comes from:

typescript-eslint/packages/eslint-plugin/src/util/collectUnusedVariables.ts

Line 487 in 2f474b3

let node = definition.node;

  • definition.node is the DefinitionBase type parameter Node extends ESTree.Node
  • definition itself comes from variable.defs, which is the VariableBase property defs: Definition[]

I think the root issue, then, is that Definition says its node can be any TSESTree.Node, including TSESTree.Program - the only node type that doesn't have a parent. Which feels weird and wrong to me. What kind of scope-manager definition would come from a TSESTree.Program?

Filed: #11334. Once that's fixed then lint rules will force this code to remove unnecessary !.s and ?.s.


return (
isExportedFlag &&
(node.type !== AST_NODE_TYPES.TSTypeAliasDeclaration ||
isSafeUnusedExportCondition(variable))
);
});
}

Expand Down
26 changes: 26 additions & 0 deletions packages/eslint-plugin/tests/rules/no-unused-vars/no-unused-vars.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1715,6 +1715,24 @@ export {};
],
filename: 'foo.d.ts',
},
// https://github.com/typescript-eslint/typescript-eslint/issues/10658
{
code: `
const A = 0;
export type A = typeof A;
`,
errors: [
{
data: {
action: 'assigned a value',
additional: '',
varName: 'A',
},
line: 2,
messageId: 'usedOnlyAsType',
},
],
},
],

valid: [
Expand Down Expand Up @@ -3018,5 +3036,13 @@ declare class Bar {}
`,
filename: 'foo.d.ts',
},
{
code: `
const A = 0;

type A = typeof A;
export { A };
`,
},
],
});