fix(typescript-estree): forbid invalid `extends` and `implements` in interface declaration by fisker · Pull Request #11935 · typescript-eslint/typescript-eslint

fisker · 2026-01-06T17:23:52Z

PR Checklist

Addresses an existing open issue: fixes #000
That issue was marked as accepting prs
Steps in Contributing were taken

Overview

typescript-eslint · 2026-01-06T17:23:55Z

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nx-cloud · 2026-01-06T17:25:18Z

View your CI Pipeline Execution ↗ for commit 0d5e0ac

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codecov · 2026-01-06T18:27:40Z

Codecov Report

❌ Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.73%. Comparing base (674a76a) to head (0d5e0ac).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...kages/typescript-estree/src/check-syntax-errors.ts	0.00%	12 Missing ⚠️

❌ Your patch status has failed because the patch coverage (0.00%) 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   #11935      +/-   ##
==========================================
- Coverage   90.74%   90.73%   -0.02%     
==========================================
  Files         527      527              
  Lines       53651    53659       +8     
  Branches     9021     9021              
==========================================
  Hits        48685    48685              
- Misses       4953     4961       +8     
  Partials       13       13

Flag	Coverage Δ
unittest	`90.73% <0.00%> (-0.02%)`	⬇️

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

Files with missing lines	Coverage Δ
...kages/typescript-estree/src/check-syntax-errors.ts	`18.93% <0.00%> (-0.27%)`	⬇️

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bradzacher · 2026-01-06T22:57:53Z

packages/typescript-estree/src/check-syntax-errors.ts

+        if (token !== SyntaxKind.ExtendsKeyword) {
          throw createError(
            heritageClause,
            // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
-            heritageClause.token === SyntaxKind.ImplementsKeyword
+            token === SyntaxKind.ImplementsKeyword
              ? "Interface declaration cannot have 'implements' clause."
              : 'Unexpected token.',
          );
        }


probably should just split this out to avoid the nested condition:

eg

Suggested change

if (token !== SyntaxKind.ExtendsKeyword) {

throw createError(

heritageClause,

// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition

heritageClause.token === SyntaxKind.ImplementsKeyword

token === SyntaxKind.ImplementsKeyword

? "Interface declaration cannot have 'implements' clause."

: 'Unexpected token.',

);

}

if (token === SyntaxKind.ImplementsKeyword) {

throw createError(

heritageClause,

"Interface declaration cannot have 'implements' clause.",

);

} else if (token !== SyntaxKind.ExtendsKeyword) {

throw createError(

heritageClause,

'Unexpected token.',

);

}

Can't apply on website UI,

b08611a (#11935)

…interface declaration

bradzacher · 2026-01-07T00:01:51Z

just need to resolve conflicts and we can merge

# Conflicts: # packages/ast-spec/tests/fixtures-with-differences-ast.shot # packages/ast-spec/tests/fixtures-with-differences-errors.shot

@bradzacher

| datasource | package | from | to | | ---------- | -------------------------------- | ------ | ------ | | npm | @typescript-eslint/eslint-plugin | 8.52.0 | 8.53.0 | | npm | @typescript-eslint/parser | 8.52.0 | 8.53.0 | ## [v8.53.0](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8530-2026-01-12) ##### 🚀 Features - **eslint-plugin:** add rule \[strict-void-return] ([#9707](typescript-eslint/typescript-eslint#9707)) - **eslint-plugin:** \[no-unused-vars] add a fixer to remove unused imports ([#11922](typescript-eslint/typescript-eslint#11922)) ##### 🩹 Fixes - **eslint-plugin:** \[no-useless-default-assignment] fix false positive for parameters corresponding to a rest parameter ([#11916](typescript-eslint/typescript-eslint#11916)) - **eslint-plugin:** replace unclear "`error` typed" with more helpful description ([#11704](typescript-eslint/typescript-eslint#11704)) - **typescript-estree:** forbid invalid `extends` and `implements` in interface declaration ([#11935](typescript-eslint/typescript-eslint#11935)) - **typescript-estree:** forbid invalid class implements ([#11934](typescript-eslint/typescript-eslint#11934)) - **typescript-estree:** forbid type-only import with both default and named specifiers ([#11930](typescript-eslint/typescript-eslint#11930)) ##### ❤️ Thank You - Brad Zacher [@bradzacher](https://github.com/bradzacher) - fisker Cheung [@fisker](https://github.com/fisker) - Josh Goldberg - Josh Goldberg ✨ - Kirk Waiblinger - Niki [@phaux](https://github.com/phaux) - Nikita - SungHyun627 [@SungHyun627](https://github.com/SungHyun627) - Will Harney [@wjhsf](https://github.com/wjhsf) You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website.

@bradzacher

| datasource | package | from | to | | ---------- | -------------------------------- | ------ | ------ | | npm | @typescript-eslint/eslint-plugin | 8.52.0 | 8.53.0 | | npm | @typescript-eslint/parser | 8.52.0 | 8.53.0 | ## [v8.53.0](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8530-2026-01-12) ##### 🚀 Features - **eslint-plugin:** add rule \[strict-void-return] ([#9707](typescript-eslint/typescript-eslint#9707)) - **eslint-plugin:** \[no-unused-vars] add a fixer to remove unused imports ([#11922](typescript-eslint/typescript-eslint#11922)) ##### 🩹 Fixes - **eslint-plugin:** \[no-useless-default-assignment] fix false positive for parameters corresponding to a rest parameter ([#11916](typescript-eslint/typescript-eslint#11916)) - **eslint-plugin:** replace unclear "`error` typed" with more helpful description ([#11704](typescript-eslint/typescript-eslint#11704)) - **typescript-estree:** forbid invalid `extends` and `implements` in interface declaration ([#11935](typescript-eslint/typescript-eslint#11935)) - **typescript-estree:** forbid invalid class implements ([#11934](typescript-eslint/typescript-eslint#11934)) - **typescript-estree:** forbid type-only import with both default and named specifiers ([#11930](typescript-eslint/typescript-eslint#11930)) ##### ❤️ Thank You - Brad Zacher [@bradzacher](https://github.com/bradzacher) - fisker Cheung [@fisker](https://github.com/fisker) - Josh Goldberg - Josh Goldberg ✨ - Kirk Waiblinger - Niki [@phaux](https://github.com/phaux) - Nikita - SungHyun627 [@SungHyun627](https://github.com/SungHyun627) - Will Harney [@wjhsf](https://github.com/wjhsf) You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website.

fisker marked this pull request as ready for review January 6, 2026 19:07

bradzacher previously approved these changes Jan 6, 2026

View reviewed changes

bradzacher added the awaiting response Issues waiting for a reply from the OP or another party label Jan 6, 2026

fisker added 4 commits January 7, 2026 07:10

fix(typescript-estree): forbid invalid extends and implements in …

7aed0cf

…interface declaration

Add more tests

f9e0c21

Fix invalid test

c2df9a3

Linting

b361a35

fisker force-pushed the interface-invalid branch from 5c1bca2 to b361a35 Compare January 6, 2026 23:10

Apply suggestion

b08611a

fisker dismissed bradzacher’s stale review via b08611a January 6, 2026 23:14

Merge branch 'main' into interface-invalid

0d5e0ac

# Conflicts: # packages/ast-spec/tests/fixtures-with-differences-ast.shot # packages/ast-spec/tests/fixtures-with-differences-errors.shot

bradzacher merged commit 3ac7735 into typescript-eslint:main Jan 7, 2026
63 of 65 checks passed

fisker deleted the interface-invalid branch January 7, 2026 00:34

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fix(typescript-estree): forbid invalid `extends` and `implements` in interface declaration#11935

fix(typescript-estree): forbid invalid `extends` and `implements` in interface declaration#11935
bradzacher merged 6 commits intotypescript-eslint:mainfrom
fisker:interface-invalid

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