enable @typescript-eslint/no-unused-vars

.eslintrc.json

@@ -105,9 +105,14 @@
                 }
             }
         ],
-
-        // Todo: For each of these, investigate whether we want to enable them ✨
-        "@typescript-eslint/no-unused-vars": "off",
+        "@typescript-eslint/no-unused-vars": [
+            "error",
+            {
+                "argsIgnorePattern": "^_([^_]|_*$)",
+                "varsIgnorePattern": "^_[^_]",
+                "ignoreRestSiblings": true
+            }
+        ],
 
         // Pending https://github.com/typescript-eslint/typescript-eslint/issues/4820
         "@typescript-eslint/prefer-optional-chain": "off",

scripts/eslint/rules/argument-trivia.cjs

@@ -1,4 +1,5 @@
-const { AST_NODE_TYPES, TSESTree, ESLintUtils } = require("@typescript-eslint/utils");
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+const { AST_NODE_TYPES, /* used in JSDoc */ TSESTree, ESLintUtils } = require("@typescript-eslint/utils");
 const { createRule } = require("./utils.cjs");
 const ts = require("typescript");
 

scripts/eslint/rules/debug-assert.cjs

@@ -1,4 +1,5 @@
-const { AST_NODE_TYPES, TSESTree } = require("@typescript-eslint/utils");
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+const { AST_NODE_TYPES, TSESTree /* used in JSDoc */ } = require("@typescript-eslint/utils");
 const { createRule } = require("./utils.cjs");
 
 module.exports = createRule({

scripts/eslint/rules/jsdoc-format.cjs

@@ -1,4 +1,5 @@
-const { TSESTree } = require("@typescript-eslint/utils");
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+const { TSESTree /* used in JSDoc */ } = require("@typescript-eslint/utils");
 const { createRule } = require("./utils.cjs");
 
 module.exports = createRule({

scripts/eslint/rules/no-in-operator.cjs

@@ -1,4 +1,5 @@
-const { TSESTree } = require("@typescript-eslint/utils");
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+const { TSESTree /* used in JSDoc */ } = require("@typescript-eslint/utils");
 const { createRule } = require("./utils.cjs");
 
 module.exports = createRule({

scripts/eslint/rules/no-keywords.cjs

@@ -1,4 +1,5 @@
-const { TSESTree, AST_NODE_TYPES } = require("@typescript-eslint/utils");
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+const { /* used in JSDoc */ TSESTree, AST_NODE_TYPES } = require("@typescript-eslint/utils");
 const { createRule } = require("./utils.cjs");
 
 module.exports = createRule({

scripts/eslint/rules/only-arrow-functions.cjs

@@ -1,4 +1,5 @@
-const { AST_NODE_TYPES, TSESTree } = require("@typescript-eslint/utils");
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+const { AST_NODE_TYPES, TSESTree /* used in JSDoc */ } = require("@typescript-eslint/utils");
 const { createRule } = require("./utils.cjs");
 
 module.exports = createRule({

src/compiler/core.ts

@@ -1,5 +1,4 @@
 import {
-    __String,
     CharacterCodes,
     Comparer,
     Comparison,
@@ -286,6 +285,7 @@ export function filter<T>(array: T[], f: (x: T) => boolean): T[];
 /** @internal */
 export function filter<T, U extends T>(array: readonly T[], f: (x: T) => x is U): readonly U[];
 /** @internal */
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
 export function filter<T, U extends T>(array: readonly T[], f: (x: T) => boolean): readonly T[];
 /** @internal */
 export function filter<T, U extends T>(array: T[] | undefined, f: (x: T) => x is U): U[] | undefined;
@@ -294,6 +294,7 @@ export function filter<T>(array: T[] | undefined, f: (x: T) => boolean): T[] | u
 /** @internal */
 export function filter<T, U extends T>(array: readonly T[] | undefined, f: (x: T) => x is U): readonly U[] | undefined;
 /** @internal */
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
 export function filter<T, U extends T>(array: readonly T[] | undefined, f: (x: T) => boolean): readonly T[] | undefined;
 /** @internal */
 export function filter<T>(array: readonly T[] | undefined, f: (x: T) => boolean): readonly T[] | undefined {
@@ -830,6 +831,7 @@ export function insertSorted<T>(array: SortedArray<T>, insert: T, compare: Compa
 }
 
 /** @internal */
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
 export function sortAndDeduplicate<T>(array: readonly string[]): SortedReadonlyArray<string>;
 /** @internal */
 export function sortAndDeduplicate<T>(array: readonly T[], comparer: Comparer<T>, equalityComparer?: EqualityComparer<T>): SortedReadonlyArray<T>;

src/compiler/emitter.ts

@@ -4131,7 +4131,7 @@ export function createPrinter(printerOptions: PrinterOptions = {}, handlers: Pri
         writeSpace();
         nextPos = emitTokenWithComment(SyntaxKind.AsKeyword, nextPos, writeKeyword, node);
         writeSpace();
-        nextPos = emitTokenWithComment(SyntaxKind.NamespaceKeyword, nextPos, writeKeyword, node);
+        emitTokenWithComment(SyntaxKind.NamespaceKeyword, nextPos, writeKeyword, node);
         writeSpace();
         emit(node.name);
         writeTrailingSemicolon();

src/compiler/factory/utilities.ts

@@ -160,7 +160,8 @@ import {
     ReadonlyKeyword,
     RelationalOperator,
     RelationalOperatorOrHigher,
-    SetAccessorDeclaration,
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    SetAccessorDeclaration, // used in JSDoc
     setOriginalNode,
     setParent,
     setStartsOnNewLine,

src/compiler/moduleNameResolver.ts

@@ -348,6 +348,7 @@ interface PackageJson extends PackageJsonPathFields {
     version?: string;
 }
 
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
 function readPackageJsonField<TMatch, K extends MatchingKeys<PackageJson, string | undefined>>(jsonContent: PackageJson, fieldName: K, typeOfTag: "string", state: ModuleResolutionState): PackageJson[K] | undefined;
 function readPackageJsonField<K extends MatchingKeys<PackageJson, object | undefined>>(jsonContent: PackageJson, fieldName: K, typeOfTag: "object", state: ModuleResolutionState): PackageJson[K] | undefined;
 function readPackageJsonField<K extends keyof PackageJson>(jsonContent: PackageJson, fieldName: K, typeOfTag: "string" | "object", state: ModuleResolutionState): PackageJson[K] | undefined {

src/compiler/watchPublic.ts

@@ -264,6 +264,7 @@ export interface ProgramHost<T extends BuilderProgram> {
  *
  * @internal
  */
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
 export interface ProgramHost<T extends BuilderProgram> {
     // TODO: GH#18217 Optional methods are frequently asserted
     createDirectory?(path: string): void;

src/harness/collectionsImpl.ts

@@ -243,6 +243,7 @@ export class Metadata {
     public get size(): number {
         if (this._size === -1 || (this._parent && this._parent._version !== this._parentVersion)) {
             let size = 0;
+            // eslint-disable-next-line @typescript-eslint/no-unused-vars
             for (const _ in this._map) size++;
             this._size = size;
             if (this._parent) {

src/services/codefixes/fixAddMissingConstraint.ts

@@ -132,7 +132,7 @@ function addMissingConstraint(changes: textChanges.ChangeTracker, program: Progr
 }
 
 function tryGetConstraintFromDiagnosticMessage(messageText: string | DiagnosticMessageChain) {
-    const [_, constraint] = flattenDiagnosticMessageText(messageText, "\n", 0).match(/`extends (.*)`/) || [];
+    const [, constraint] = flattenDiagnosticMessageText(messageText, "\n", 0).match(/`extends (.*)`/) || [];
     return constraint;
 }
 

src/services/codefixes/fixNaNEquality.ts

@@ -87,6 +87,6 @@ function doChange(changes: textChanges.ChangeTracker, sourceFile: SourceFile, ar
 }
 
 function getSuggestion(messageText: string | DiagnosticMessageChain) {
-    const [_, suggestion] = flattenDiagnosticMessageText(messageText, "\n", 0).match(/'(.*)'/) || [];
+    const [, suggestion] = flattenDiagnosticMessageText(messageText, "\n", 0).match(/'(.*)'/) || [];
     return suggestion;
 }

src/services/refactors/moveToFile.ts

@@ -2,7 +2,6 @@ import {
     getModuleSpecifier,
 } from "../../compiler/moduleSpecifiers";
 import {
-    __String,
     AnyImportOrRequireStatement,
     append,
     ApplicableRefactorInfo,