feat(eslint-plugin): [no-unused-private-class-members] new extension rule #10913

bradzacher · 2025-03-03T02:18:05Z

PR Checklist

Addresses an existing open issue: fixes Rule proposal: no-unused-private-class-members #4571
That issue was marked as accepting prs
Steps in Contributing were taken

Overview

This PR implements an extension rule for no-unused-private-class-members that introduces support for private members.

…rule

typescript-eslint · 2025-03-03T02:18:08Z

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JoshuaKGoldberg

packages/eslint-plugin/src/rules/no-unused-private-class-members.ts

ronami · 2025-03-06T15:02:41Z

packages/eslint-plugin/src/rules/no-unused-private-class-members.ts

+      // mark the first member we encounter as used. If you were to delete the
+      // member, then any subsequent usage could incorrectly mark the member of
+      // an encapsulating parent class as used, which is incorrect.
+      trackedClassMembersUsed.add(memberDefinition.declaredNode);


[Bug]: I've noticed some missed reports with functions that have a different this than the class instance (deploy preview playground link):

class Test1 { // should be reported but doesn't? private bar: number; foo = function () { return this.bar; } }

This is because the base rule doesn't support that case because this.#bar is a syntax error inside a function expression!!

It's worth noting that TS doesn't actually catch this case either and reports bar as unused because the type of the this in the function expression is any!
If you turn on noImplicitThis then TS will error on that this

We could support this if we wanted to. I'm leaning towards not because TS itself doesn't catch it either.

Yes! I think the rule should report bar as unused in this case. I've mentioned this since TypeScript reports it as unused but the rule doesn't report it as unused (regardless of the type error).

Coming back to this -- my code handles this correctly because realistically it is an actual usage of the parameter.

For example new Test1().foo() will return the value of bar.
There's an implicit binding here and so I think this is fine to keep not reporting on.

packages/eslint-plugin/src/rules/no-unused-private-class-members.ts

ronami

Looks amazing! Excited to enable this on projects I work on 🚀🚀🚀

(I accidentally posted the review earlier while still adding comments 🙈)

packages/eslint-plugin/docs/rules/no-unused-private-class-members.mdx

bradzacher · 2025-03-10T10:28:12Z

FYI I'm going to make @Josh-Cena very happy - I'm going to build a "class scope analyser" so we can do this right rather than just hacking it in.

This does mean that I'm going to rewrite the rule from the ground up -- but it'll be worht it

kirkwaiblinger · 2025-03-19T06:34:57Z

FYI I'm going to make @Josh-Cena very happy - I'm going to build a "class scope analyser" so we can do this right rather than just hacking it in.

This does mean that I'm going to rewrite the rule from the ground up -- but it'll be worht it

Do you intend for this to proceed as-is, with this work intended to happen in the future, or should we pause/draft it pending this work?

bradzacher · 2025-03-19T07:57:54Z

Let's draft it.
We need to at least handle the static property case.
Might have some time soon to pick the work back up.

ronami

Looks amazing and a very beneficial rule to have; just a few small comments from me 🚀🚀🚀

packages/eslint-plugin/src/rules/no-unused-private-class-members.ts

packages/eslint-plugin/src/util/class-scope-analyzer/classScopeAnalyzer.ts

ronami · 2025-08-24T06:41:29Z

packages/eslint-plugin/src/rules/no-unused-private-class-members.ts

+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'Disallow unused private class members',


I think this is a bug and shouldn't be reported (deploy preview playground link):

class Test1 { // reported but shouldn't? private foo: number | null; public bar() { this.foo ??= 1; } }

This is a weird case that isn't currently reported by no-unused-vars but really should be.

It is reported by the base no-unused-private-class-members rule

There was just a recent eslint bug report about these; I guess it's intentional for no-unused-vars since x ?? = y reads x first (equivalent to x != null ? x : (x = y)) rather than unconditionally assigning (x = x != null ? x : y). See eslint/eslint#20029. But presumably the two rules should agree?

Oh, but do note that these are reported by no-useless-assignment so 🤷‍♂️ 🤷‍♂️

(playground)

we should probably file a bug for NUPCM then so it matches NUV?

JoshuaKGoldberg

I have very little to add that Kirk and Ronami didn't already. Very exciting!! ⚡

packages/eslint-plugin/src/util/class-scope-analyzer/extractComputedName.ts

JoshuaKGoldberg · 2025-09-29T15:25:19Z

packages/eslint-plugin/src/util/class-scope-analyzer/extractComputedName.ts

+ */
+export function extractNameForMember(node: MemberNode): [Key, string] | null {
+  if (node.computed) {
+    return extractComputedName(node.key);


Just noting, #11006 has some other logic around computed keys. It might be useful to unify?

bradzacher · 2025-10-20T11:36:35Z

@ronami / @JoshuaKGoldberg / @kirkwaiblinger

Added support for:

Parameter properties

class Test1 {
  constructor(
    // errors
    private parameterPropertyUnused: number,
    // no error
    private parameterPropertyUsed: number,   
  ) {}

  method() {
    return this.parameterPropertyUsed;
  }
}

Usage of a private class member via explicitly and simply annotated variables:

class Foo {
  // no longer reported
  private prop: number;
  // no longer reported
  private staticProp: number;

  method1(thing: Foo) {
    return thing.prop;
  }
  method2(thing: typeof Foo) {
    return thing.staticProp;
  }
}

Usage of a private class member via simple assignment:

class Foo {
  // no longer reported
  private prop: number;
  method() {
    const self = this;
    return self.prop;
  }
}

JoshuaKGoldberg

Lint complaints notwithstanding, this looks great to me! I'll defer to the other reviewers on the finer points they're calling out. But the overall scope analyzer looks great and I'm very happy with the clean rule implementation. Nicely done! 👏

packages/eslint-plugin/src/util/class-scope-analyzer/types.ts

ronami

Looking great 👏👏👏

codecov · 2025-11-11T16:33:31Z

Codecov Report

❌ Patch coverage is 82.10181% with 109 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.56%. Comparing base (0fac889) to head (f7beddc).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...rc/util/class-scope-analyzer/classScopeAnalyzer.ts	82.45%	82 Missing and 1 partial ⚠️
...c/util/class-scope-analyzer/extractComputedName.ts	65.33%	26 Missing ⚠️

❌ Your patch status has failed because the patch coverage (82.10%) 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   #10913      +/-   ##
==========================================
- Coverage   90.66%   90.56%   -0.10%     
==========================================
  Files         518      522       +4     
  Lines       52454    53063     +609     
  Branches     8694     8838     +144     
==========================================
+ Hits        47558    48058     +500     
- Misses       4882     4990     +108     
- Partials       14       15       +1

Flag	Coverage Δ
unittest	`90.56% <82.10%> (-0.10%)`	⬇️

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

Files with missing lines	Coverage Δ
packages/eslint-plugin/src/configs/eslintrc/all.ts	`100.00% <100.00%> (ø)`
packages/eslint-plugin/src/configs/flat/all.ts	`100.00% <100.00%> (ø)`
...lugin/src/rules/no-unused-private-class-members.ts	`100.00% <100.00%> (ø)`
...lint-plugin/src/util/class-scope-analyzer/types.ts	`100.00% <100.00%> (ø)`
...c/util/class-scope-analyzer/extractComputedName.ts	`65.33% <65.33%> (ø)`
...rc/util/class-scope-analyzer/classScopeAnalyzer.ts	`82.45% <82.45%> (ø)`

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feat(eslint-plugin): [no-unused-private-class-members] new extension …

34b77b8

…rule

bradzacher added the enhancement: new base rule extension New base rule extension required to handle a TS specific case label Mar 3, 2025

JoshuaKGoldberg previously approved these changes Mar 3, 2025

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JoshuaKGoldberg added the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Mar 3, 2025

ronami reviewed Mar 6, 2025

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packages/eslint-plugin/docs/rules/no-unused-private-class-members.mdx Show resolved Hide resolved

support accessor properties

0854007

kirkwaiblinger added the awaiting response Issues waiting for a reply from the OP or another party label Mar 19, 2025

kirkwaiblinger marked this pull request as draft March 19, 2025 09:39

JoshuaKGoldberg removed the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Mar 24, 2025

WIP class scope analyser

df85b86

bradzacher dismissed JoshuaKGoldberg’s stale review via df85b86 July 6, 2025 02:52

bradzacher added 2 commits July 6, 2025 16:34

WIP

8710810

WIP

fe8c300

bradzacher removed the awaiting response Issues waiting for a reply from the OP or another party label Jul 13, 2025

got it all working

e72b89a

bradzacher marked this pull request as ready for review August 10, 2025 05:39

Merge branch 'main' into no-unused-private-class-members

a43dc70

bradzacher requested review from JoshuaKGoldberg and ronami August 10, 2025 05:39

ronami reviewed Aug 23, 2025

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ronami reviewed Aug 24, 2025

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kirkwaiblinger mentioned this pull request Sep 12, 2025

feat(eslint-plugin): [no-unused-private-class-members] new extension rule #11598

Closed

3 tasks

JoshuaKGoldberg added the awaiting response Issues waiting for a reply from the OP or another party label Sep 29, 2025

JoshuaKGoldberg requested changes Sep 29, 2025

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bradzacher added 4 commits October 20, 2025 20:27

Merge branch 'main' into no-unused-private-class-members

34e50d5

support parameter properties

db7e2a8

handle some simple scope analysis cases

73a1c8e

comment

73a1f53

bradzacher requested review from JoshuaKGoldberg, kirkwaiblinger and ronami October 20, 2025 11:36

bradzacher removed the awaiting response Issues waiting for a reply from the OP or another party label Oct 20, 2025

JoshuaKGoldberg previously approved these changes Nov 3, 2025

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packages/eslint-plugin/src/util/class-scope-analyzer/types.ts Outdated Show resolved Hide resolved

JoshuaKGoldberg added the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Nov 3, 2025

ronami previously approved these changes Nov 5, 2025

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bradzacher added 3 commits November 11, 2025 11:17

lint

d3077cb

Merge branch 'main' into no-unused-private-class-members

a7d1705

test

2ccb638

bradzacher dismissed stale reviews from ronami and JoshuaKGoldberg via 2ccb638 November 11, 2025 16:21

bradzacher force-pushed the no-unused-private-class-members branch from 408410c to 2ccb638 Compare November 11, 2025 16:21

review

f7beddc

bradzacher merged commit 6c6db24 into main Nov 11, 2025
66 of 69 checks passed

bradzacher deleted the no-unused-private-class-members branch November 11, 2025 16:34

bradzacher linked an issue Nov 11, 2025 that may be closed by this pull request

Rule proposal: no-unused-private-class-members #4571

Closed

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feat(eslint-plugin): [no-unused-private-class-members] new extension rule #10913

feat(eslint-plugin): [no-unused-private-class-members] new extension rule #10913

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bradzacher commented Mar 3, 2025

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