Error on unused vars in declaration files

.changeset/popular-mangos-run.md

@@ -0,0 +1,5 @@
+---
+"@definitelytyped/eslint-plugin": patch
+---
+
+Error on unused vars in declaration files

packages/eslint-plugin/src/configs/all.ts

@@ -185,5 +185,18 @@ export const all: Linter.BaseConfig = {
         ],
       },
     },
+    {
+      files: ["*.d.cts", "*.d.mts", "*.d.ts", "*.d.*.ts"],
+      rules: {
+        "@typescript-eslint/no-unused-vars": [
+          "error",
+          {
+              // Ignore: (solely underscores | starting with exactly one underscore)
+              "argsIgnorePattern": "^(_+$|_[^_])",
+              "varsIgnorePattern": "^(_+$|_[^_])"
+          }
+      ],
+      },
+    },
   ],
 };

packages/eslint-plugin/test/__file_snapshots__/types/export-just-namespace/bad3.d.ts.lint

@@ -1,12 +1,15 @@
 types/export-just-namespace/bad3.d.ts
-  3:1  error  Instead of `export =`-ing a namespace, use the body of the namespace as the module body  @definitelytyped/export-just-namespace
+  2:7  error  'other' is assigned a value but never used. Allowed unused vars must match /^(_+$|_[^_])/u  @typescript-eslint/no-unused-vars
+  3:1  error  Instead of `export =`-ing a namespace, use the body of the namespace as the module body     @definitelytyped/export-just-namespace
 
-✖ 1 problem (1 error, 0 warnings)
+✖ 2 problems (2 errors, 0 warnings)
 
 ==== types/export-just-namespace/bad3.d.ts ====
 
     namespace Stuff {}
     const other = "code";
+          ~~~~~
+!!! @typescript-eslint/no-unused-vars: 'other' is assigned a value but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
     export = Stuff;
     ~~~~~~~~~~~~~~~
 !!! @definitelytyped/export-just-namespace: Instead of `export =`-ing a namespace, use the body of the namespace as the module body.

packages/eslint-plugin/test/__file_snapshots__/types/export-just-namespace/good3.d.ts.lint

@@ -1,5 +1,10 @@
-No errors
+types/export-just-namespace/good3.d.ts
+  1:13  error  'fs' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u  @typescript-eslint/no-unused-vars
+
+✖ 1 problem (1 error, 0 warnings)
 
 ==== types/export-just-namespace/good3.d.ts ====
 
     import * as fs from "fs";
+                ~~
+!!! @typescript-eslint/no-unused-vars: 'fs' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.

packages/eslint-plugin/test/__file_snapshots__/types/export-just-namespace/good4.d.ts.lint

@@ -1,5 +1,10 @@
-No errors
+types/export-just-namespace/good4.d.ts
+  1:7  error  'value' is assigned a value but never used. Allowed unused vars must match /^(_+$|_[^_])/u  @typescript-eslint/no-unused-vars
+
+✖ 1 problem (1 error, 0 warnings)
 
 ==== types/export-just-namespace/good4.d.ts ====
 
     const value = 123;
+          ~~~~~
+!!! @typescript-eslint/no-unused-vars: 'value' is assigned a value but never used. Allowed unused vars must match /^(_+$|_[^_])/u.

packages/eslint-plugin/test/__file_snapshots__/types/no-bad-reference/v0.1/index.d.ts.lint

@@ -4,13 +4,20 @@ types/no-bad-reference/v0.1/index.d.ts
    2:22  error  The reference "../v1/index.d.ts" resolves outside of the package. Use a global reference to reference other packages           @definitelytyped/no-bad-reference
    3:22  error  The reference "../../foo/v0.1/index.d.ts" resolves outside of the package. Use a global reference to reference other packages  @definitelytyped/no-bad-reference
    4:22  error  The reference "../index.d.ts" resolves outside of the package. Use a global reference to reference other packages              @definitelytyped/no-bad-reference
+   6:13  error  'foo' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                                @typescript-eslint/no-unused-vars
    6:22  error  The import "../../foo" resolves outside of the package. Use a bare import to reference other packages                          @definitelytyped/no-bad-reference
+   7:13  error  'foo2' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                               @typescript-eslint/no-unused-vars
    7:23  error  The import "../v0.1" resolves to the current package, but uses relative paths                                                  @definitelytyped/no-bad-reference
+   8:13  error  'foo3' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                               @typescript-eslint/no-unused-vars
    8:23  error  The import "../../foo/v0.1" resolves outside of the package. Use a bare import to reference other packages                     @definitelytyped/no-bad-reference
+   9:13  error  'va4' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                                @typescript-eslint/no-unused-vars
    9:22  error  The import "../index" resolves outside of the package. Use a bare import to reference other packages                           @definitelytyped/no-bad-reference
+  12:10  error  'A' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                                  @typescript-eslint/no-unused-vars
+  13:10  error  'B' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                                  @typescript-eslint/no-unused-vars
+  14:10  error  'C' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                                  @typescript-eslint/no-unused-vars
   14:22  error  The import "../index" resolves outside of the package. Use a bare import to reference other packages                           @definitelytyped/no-bad-reference
 
-✖ 10 problems (10 errors, 0 warnings)
+✖ 17 problems (17 errors, 0 warnings)
 
 ==== types/no-bad-reference/v0.1/index.d.ts ====
 
@@ -30,22 +37,36 @@ types/no-bad-reference/v0.1/index.d.ts
 !!! @definitelytyped/no-bad-reference: The reference "../index.d.ts" resolves outside of the package. Use a global reference to reference other packages.
 
     import * as foo from "../../foo";
+                ~~~
+!!! @typescript-eslint/no-unused-vars: 'foo' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
                          ~~~~~~~~~~~
 !!! @definitelytyped/no-bad-reference: The import "../../foo" resolves outside of the package. Use a bare import to reference other packages.
     import * as foo2 from "../v0.1";
+                ~~~~
+!!! @typescript-eslint/no-unused-vars: 'foo2' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
                           ~~~~~~~~~
 !!! @definitelytyped/no-bad-reference: The import "../v0.1" resolves to the current package, but uses relative paths.
     import * as foo3 from "../../foo/v0.1";
+                ~~~~
+!!! @typescript-eslint/no-unused-vars: 'foo3' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
                           ~~~~~~~~~~~~~~~~
 !!! @definitelytyped/no-bad-reference: The import "../../foo/v0.1" resolves outside of the package. Use a bare import to reference other packages.
     import * as va4 from "../index";
+                ~~~
+!!! @typescript-eslint/no-unused-vars: 'va4' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
                          ~~~~~~~~~~
 !!! @definitelytyped/no-bad-reference: The import "../index" resolves outside of the package. Use a bare import to reference other packages.
 
     declare module "no-relative-references" {
       import A = require("no-relative-references/blah"); // Okay; relative
+             ~
+!!! @typescript-eslint/no-unused-vars: 'A' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
       import B = require("no-relative-references/v0.1"); // Okay; no versioned dir here
+             ~
+!!! @typescript-eslint/no-unused-vars: 'B' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
       import C = require("../index"); // Bad; parent dir
+             ~
+!!! @typescript-eslint/no-unused-vars: 'C' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
                          ~~~~~~~~~~
 !!! @definitelytyped/no-bad-reference: The import "../index" resolves outside of the package. Use a bare import to reference other packages.
     }

packages/eslint-plugin/test/__file_snapshots__/types/no-bad-reference/v11/index.d.ts.lint

@@ -4,13 +4,20 @@ types/no-bad-reference/v11/index.d.ts
    2:22  error  The reference "../v11/index.d.ts" resolves to the current package, but uses relative paths                                   @definitelytyped/no-bad-reference
    3:22  error  The reference "../../foo/v1/index.d.ts" resolves outside of the package. Use a global reference to reference other packages  @definitelytyped/no-bad-reference
    4:22  error  The reference "../index.d.ts" resolves outside of the package. Use a global reference to reference other packages            @definitelytyped/no-bad-reference
+   6:13  error  'foo' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                              @typescript-eslint/no-unused-vars
    6:22  error  The import "../../foo" resolves outside of the package. Use a bare import to reference other packages                        @definitelytyped/no-bad-reference
+   7:13  error  'foo2' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                             @typescript-eslint/no-unused-vars
    7:23  error  The import "../v11" resolves to the current package, but uses relative paths                                                 @definitelytyped/no-bad-reference
+   8:13  error  'foo3' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                             @typescript-eslint/no-unused-vars
    8:23  error  The import "../../foo/v11" resolves outside of the package. Use a bare import to reference other packages                    @definitelytyped/no-bad-reference
+   9:13  error  'va4' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                              @typescript-eslint/no-unused-vars
    9:22  error  The import "../index" resolves outside of the package. Use a bare import to reference other packages                         @definitelytyped/no-bad-reference
+  12:10  error  'A' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                                @typescript-eslint/no-unused-vars
+  13:10  error  'B' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                                @typescript-eslint/no-unused-vars
+  14:10  error  'C' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u                                                @typescript-eslint/no-unused-vars
   14:22  error  The import "../index" resolves outside of the package. Use a bare import to reference other packages                         @definitelytyped/no-bad-reference
 
-✖ 10 problems (10 errors, 0 warnings)
+✖ 17 problems (17 errors, 0 warnings)
 
 ==== types/no-bad-reference/v11/index.d.ts ====
 
@@ -30,22 +37,36 @@ types/no-bad-reference/v11/index.d.ts
 !!! @definitelytyped/no-bad-reference: The reference "../index.d.ts" resolves outside of the package. Use a global reference to reference other packages.
 
     import * as foo from "../../foo";
+                ~~~
+!!! @typescript-eslint/no-unused-vars: 'foo' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
                          ~~~~~~~~~~~
 !!! @definitelytyped/no-bad-reference: The import "../../foo" resolves outside of the package. Use a bare import to reference other packages.
     import * as foo2 from "../v11";
+                ~~~~
+!!! @typescript-eslint/no-unused-vars: 'foo2' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
                           ~~~~~~~~
 !!! @definitelytyped/no-bad-reference: The import "../v11" resolves to the current package, but uses relative paths.
     import * as foo3 from "../../foo/v11";
+                ~~~~
+!!! @typescript-eslint/no-unused-vars: 'foo3' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
                           ~~~~~~~~~~~~~~~
 !!! @definitelytyped/no-bad-reference: The import "../../foo/v11" resolves outside of the package. Use a bare import to reference other packages.
     import * as va4 from "../index";
+                ~~~
+!!! @typescript-eslint/no-unused-vars: 'va4' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
                          ~~~~~~~~~~
 !!! @definitelytyped/no-bad-reference: The import "../index" resolves outside of the package. Use a bare import to reference other packages.
 
     declare module "no-relative-references" {
       import A = require("no-relative-references/blah"); // Okay; relative
+             ~
+!!! @typescript-eslint/no-unused-vars: 'A' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
       import B = require("no-relative-references/v11"); // Okay; no versioned dir here
+             ~
+!!! @typescript-eslint/no-unused-vars: 'B' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
       import C = require("../index"); // Bad; parent dir
+             ~
+!!! @typescript-eslint/no-unused-vars: 'C' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
                          ~~~~~~~~~~
 !!! @definitelytyped/no-bad-reference: The import "../index" resolves outside of the package. Use a bare import to reference other packages.
     }

packages/eslint-plugin/test/__file_snapshots__/types/no-const-enum/bad.d.ts.lint

@@ -1,10 +1,13 @@
 types/no-const-enum/bad.d.ts
-  1:1  error  Use of `const enum` is forbidden  @definitelytyped/no-const-enum
+  1:1   error  Use of `const enum` is forbidden                                               @definitelytyped/no-const-enum
+  1:12  error  'E' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u  @typescript-eslint/no-unused-vars
 
-✖ 1 problem (1 error, 0 warnings)
+✖ 2 problems (2 errors, 0 warnings)
 
 ==== types/no-const-enum/bad.d.ts ====
 
     const enum E { }
     ~~~~~~~~~~~~~~~~
 !!! @definitelytyped/no-const-enum: Use of `const enum` is forbidden.
+               ~
+!!! @typescript-eslint/no-unused-vars: 'E' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.

packages/eslint-plugin/test/__file_snapshots__/types/no-const-enum/index.d.ts.lint

@@ -1,5 +1,10 @@
-No errors
+types/no-const-enum/index.d.ts
+  1:6  error  'F' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u  @typescript-eslint/no-unused-vars
+
+✖ 1 problem (1 error, 0 warnings)
 
 ==== types/no-const-enum/index.d.ts ====
 
     enum F {}
+         ~
+!!! @typescript-eslint/no-unused-vars: 'F' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.

packages/eslint-plugin/test/__file_snapshots__/types/no-import-default-of-export-equals/bad.d.ts.lint

@@ -1,17 +1,23 @@
 types/no-import-default-of-export-equals/bad.d.ts
-  7:12  error  The module a uses `export = `. Import with `import a = require(a)`  @definitelytyped/no-import-default-of-export-equals
+  2:15  error  'I' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u  @typescript-eslint/no-unused-vars
+  7:12  error  The module a uses `export = `. Import with `import a = require(a)`             @definitelytyped/no-import-default-of-export-equals
+  7:12  error  'a' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u  @typescript-eslint/no-unused-vars
 
-✖ 1 problem (1 error, 0 warnings)
+✖ 3 problems (3 errors, 0 warnings)
 
 ==== types/no-import-default-of-export-equals/bad.d.ts ====
 
     declare module "a" {
         interface I { i: any }
+                  ~
+!!! @typescript-eslint/no-unused-vars: 'I' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
         export = I;
     }
 
     declare module "b" {
         import a from "a";
                ~
 !!! @definitelytyped/no-import-default-of-export-equals: The module a uses `export = `. Import with `import a = require(a)`.
+               ~
+!!! @typescript-eslint/no-unused-vars: 'a' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
     }

packages/eslint-plugin/test/__file_snapshots__/types/no-import-default-of-export-equals/index.d.ts.lint

@@ -1,7 +1,8 @@
 types/no-import-default-of-export-equals/index.d.ts
-  1:1  error  Packages should contain value components, not just types  @definitelytyped/no-type-only-packages
+  1:1   error  Packages should contain value components, not just types                       @definitelytyped/no-type-only-packages
+  7:12  error  'a' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u  @typescript-eslint/no-unused-vars
 
-✖ 1 problem (1 error, 0 warnings)
+✖ 2 problems (2 errors, 0 warnings)
 
 ==== types/no-import-default-of-export-equals/index.d.ts ====
 
@@ -14,4 +15,6 @@ types/no-import-default-of-export-equals/index.d.ts
 
     declare module "bgood" {
         import a from "agood";
+               ~
+!!! @typescript-eslint/no-unused-vars: 'a' is defined but never used. Allowed unused vars must match /^(_+$|_[^_])/u.
     }