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

nayounsang · 2025-06-20T07:37:44Z

PR Checklist

Addresses an existing open issue: fixes Bug: [no-unused-vars] no is assigned a value but only used as a type error when it has a same name type alias declaration exported #10658
That issue was marked as accepting prs
Steps in Contributing were taken

Overview

Strict checks on exports with same type and variable name

If the name is the same, the variable is isTypeVariable && isValueVariable.
ClassName, TSEnumName, TSModuleName, ImportBinding and arguments also have same characteristics
Therefore, only the cases that correspond to the issue are properly verified.

Perform additional validating for abnormal cases

def.node.type !== AST_NODE_TYPES.TSTypeAliasDeclaration

Add test cases

tc mentioned in issue and similar but valid

typescript-eslint · 2025-06-20T07:37:48Z

Thanks for the PR, @nayounsang!

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The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

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nx-cloud · 2025-06-20T07:39:13Z

View your CI Pipeline Execution ↗ for commit 2f474b3.

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`nx run-many -t typecheck`	✅ Succeeded	2m 6s	View ↗
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☁️ Nx Cloud last updated this comment at 2025-06-20 12:53:10 UTC

codecov · 2025-06-20T07:48:57Z

Codecov Report

Attention: Patch coverage is 88.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 90.84%. Comparing base (76cc62c) to head (2f474b3).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
...s/eslint-plugin/src/util/collectUnusedVariables.ts	88.00%	3 Missing ⚠️

❌ Your patch check has failed because the patch coverage (88.00%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #11322   +/-   ##
=======================================
  Coverage   90.84%   90.84%           
=======================================
  Files         501      501           
  Lines       50911    50932   +21     
  Branches     8383     8391    +8     
=======================================
+ Hits        46248    46269   +21     
  Misses       4648     4648           
  Partials       15       15

Flag	Coverage Δ
unittest	`90.84% <88.00%> (+<0.01%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...s/eslint-plugin/src/util/collectUnusedVariables.ts	`96.34% <88.00%> (+0.15%)`	⬆️

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nayounsang · 2025-06-20T07:53:10Z

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

+function isSafeUnusedExportCondition(variable: ScopeVariable): boolean {
+  if (variable instanceof ESLintScopeVariable) {
+    return true;
+  }


need advice

I don't know why this condition is necessary. Can't the arg type of isExported, isMergableExported be used as Variable?
Actually, it is used as Variable only.

it is used as Variable only

👍 any reason not to change its type from ScopeVariable to Variable? I tried the three : ScopeVariable parameters to : Variable locally and everything looked happy.

nayounsang · 2025-06-20T07:53:48Z

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

@@ -465,7 +495,12 @@ 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');


need advice

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

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.

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

nayounsang · 2025-06-27T10:43:45Z

Its a different issue:#8315, but we need to figure out if this is a workable solution.

nayounsang · 2025-06-27T15:03:03Z

Its a different issue:#8315, but we need to figure out if this is a workable solution.

Ah, it is different. should change validate logic.
I think I need to work on another PR. If this PR is headed in the right direction.

JoshuaKGoldberg · 2025-06-30T11:55:21Z

I think I need to work on another PR. If this PR is headed in the right direction.

@nayounsang apologies, I'm not following - are you suggesting we should or shouldn't review this PR?

nayounsang · 2025-06-30T12:09:18Z

@JoshuaKGoldberg
Oh, please review this PR. I'm ready.

The comments are my own monologue. I tend to take notes of everything and I just saw another issue that seemed related to this PR. After looking into it, it seems that even if this PR is resolved, there will be additional work needed to resolve the other issues.

JoshuaKGoldberg

🙌 Looks like a good start! I didn't review deeply because the .every line looks like it's either unnecessary or not fully tested. Which makes me suspect things might change up a bit. Could you please take a look?

JoshuaKGoldberg · 2025-06-23T16:31:11Z

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

@@ -441,7 +467,9 @@ function isMergableExported(variable: ScopeVariable): boolean {
        def.node.parent?.type === AST_NODE_TYPES.ExportNamedDeclaration) ||
      def.node.parent?.type === AST_NODE_TYPES.ExportDefaultDeclaration
    ) {
-      return true;
+      return (
+        safeFlag || def.node.type !== AST_NODE_TYPES.TSTypeAliasDeclaration


[Performance] There's no need to run through isSafeUnusedExportCondition(...) until it's used:

Suggested change

safeFlag || def.node.type !== AST_NODE_TYPES.TSTypeAliasDeclaration

def.node.type !== AST_NODE_TYPES.TSTypeAliasDeclaration || isSafeUnusedExportCondition(variable)

JoshuaKGoldberg · 2025-06-23T16:45:37Z

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

@@ -465,7 +495,12 @@ 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');


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.

JoshuaKGoldberg · 2025-06-23T16:49:39Z

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

+function isSafeUnusedExportCondition(variable: ScopeVariable): boolean {
+  if (variable instanceof ESLintScopeVariable) {
+    return true;
+  }


it is used as Variable only

👍 any reason not to change its type from ScopeVariable to Variable? I tried the three : ScopeVariable parameters to : Variable locally and everything looked happy.

JoshuaKGoldberg · 2025-06-30T14:47:13Z

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

+  if (variable.isTypeVariable && variable.isValueVariable) {
+    return !variable.defs
+      .map(d => d.type)
+      .every(t => exportExceptDefTypes.includes(t));


[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.

nayounsang added 2 commits June 20, 2025 16:28

test: add test case

f7d55fd

fix: strict checks on exports with same type and variable name

bc379fc

nayounsang commented Jun 20, 2025

View reviewed changes

Merge branch 'main' into type-unused

bfffde3

nayounsang commented Jun 20, 2025

View reviewed changes

packages/eslint-plugin/src/util/collectUnusedVariables.ts Outdated Show resolved Hide resolved

refactor: resolve self-code-review

2f474b3

nayounsang mentioned this pull request Jun 27, 2025

Bug: [consistent-type-imports] False negatives when type name also refers to a local value #8315

Open

4 tasks

JoshuaKGoldberg requested changes Jun 30, 2025

View reviewed changes

JoshuaKGoldberg added the awaiting response Issues waiting for a reply from the OP or another party label Jun 30, 2025

	safeFlag \|\| def.node.type !== AST_NODE_TYPES.TSTypeAliasDeclaration
	def.node.type !== AST_NODE_TYPES.TSTypeAliasDeclaration \|\| isSafeUnusedExportCondition(variable)

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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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PR Checklist

Overview

Strict checks on exports with same type and variable name

Perform additional validating for abnormal cases

Add test cases

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need advice

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need advice

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nayounsang commented Jun 27, 2025

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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

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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