typescript-eslint · JoshuaKGoldberg · Nov 29, 2023 · Nov 29, 2023 · Nov 29, 2023 · bradzacher
diff --git a/.eslintrc.js b/.eslintrc.js
@@ -53,7 +53,6 @@ module.exports = {
     'deprecation/deprecation': 'error',
 
     // TODO(#7338): Investigate enabling these soon ✨
-    '@typescript-eslint/no-unnecessary-condition': 'off',
     '@typescript-eslint/no-dynamic-delete': 'off',
     '@typescript-eslint/prefer-nullish-coalescing': 'off',
 
@@ -85,6 +84,11 @@ module.exports = {
     ],
     '@typescript-eslint/no-explicit-any': 'error',
     '@typescript-eslint/no-non-null-assertion': 'off',
+    'no-constant-condition': 'off',
+    '@typescript-eslint/no-unnecessary-condition': [
+      'error',
+      { allowConstantLoopConditions: true },
+    ],
     '@typescript-eslint/no-var-requires': 'off',
     '@typescript-eslint/prefer-literal-enum-member': [
       'error',

diff --git a/packages/ast-spec/tests/util/serializers/Node.ts b/packages/ast-spec/tests/util/serializers/Node.ts
@@ -3,7 +3,9 @@ import type { NewPlugin } from 'pretty-format';
 import type * as TSESTree from '../../../src';
 import { AST_NODE_TYPES } from '../../../src';
 
-function sortKeys(node: TSESTree.Node): (keyof typeof node)[] {
+function sortKeys<Node extends TSESTree.Node>(
+  node: Node,
+): (keyof typeof node)[] {
   const keySet = new Set(Object.keys(node));
 
   // type place as first key
@@ -39,7 +41,14 @@ const serializer: NewPlugin = {
   test(val: unknown) {
     return isObject(val) && hasValidType(val.type);
   },
-  serialize(node: TSESTree.Node, config, indentation, depth, refs, printer) {
+  serialize(
+    node: TSESTree.Node & Record<string, unknown>,
+    config,
+    indentation,
+    depth,
+    refs,
+    printer,
+  ) {
     const keys = sortKeys(node);
     const type = node.type;
     const loc = node.loc;

diff --git a/packages/eslint-plugin-internal/src/rules/plugin-test-formatting.ts b/packages/eslint-plugin-internal/src/rules/plugin-test-formatting.ts
@@ -172,6 +172,7 @@ export default createRule<Options, MessageIds>({
       } catch (ex) {
         // ex instanceof Error is false as of @prettier/sync@0.3.0, as is ex instanceof SyntaxError
         if (
+          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
           (ex as Partial<Error> | undefined)?.constructor?.name !==
           'SyntaxError'
         ) {

diff --git a/packages/eslint-plugin/src/rules/consistent-type-exports.ts b/packages/eslint-plugin/src/rules/consistent-type-exports.ts
@@ -109,6 +109,7 @@ export default createRule<Options, MessageIds>({
       ExportNamedDeclaration(node: TSESTree.ExportNamedDeclaration): void {
         // Coerce the source into a string for use as a lookup entry.
         const source = getSourceFromExport(node) ?? 'undefined';
+        // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
         const sourceExports = (sourceExportsMap[source] ||= {
           source,
           reportValueExports: [],

diff --git a/packages/eslint-plugin/src/rules/consistent-type-imports.ts b/packages/eslint-plugin/src/rules/consistent-type-imports.ts
@@ -119,6 +119,7 @@ export default createRule<Options, MessageIds>({
             ImportDeclaration(node): void {
               const source = node.source.value;
               // sourceImports is the object containing all the specifics for a particular import source, type or value
+              // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
               sourceImportsMap[source] ??= {
                 source,
                 reportValueImports: [], // if there is a mismatch where type importKind but value specifiers
@@ -194,8 +195,9 @@ export default createRule<Options, MessageIds>({
                         }
                       }
                       if (ref.isValueReference) {
-                        let parent: TSESTree.Node | undefined =
-                          ref.identifier.parent;
+                        let parent = ref.identifier.parent as
+                          | TSESTree.Node
+                          | undefined;
                         let child: TSESTree.Node = ref.identifier;
                         while (parent) {
                           switch (parent.type) {

diff --git a/packages/eslint-plugin/src/rules/no-extra-parens.ts b/packages/eslint-plugin/src/rules/no-extra-parens.ts
@@ -277,6 +277,7 @@ export default createRule<Options, MessageIds>({
         }
       },
     };
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (rules.ForInStatement && rules.ForOfStatement) {
       overrides.ForInStatement = function (node): void {
         if (isTypeAssertion(node.right)) {

diff --git a/packages/eslint-plugin/src/rules/no-shadow.ts b/packages/eslint-plugin/src/rules/no-shadow.ts
@@ -412,7 +412,7 @@ export default createRule<Options, MessageIds>({
         return false;
       }
 
-      let node: TSESTree.Node | undefined = outerDef.name;
+      let node = outerDef.name as TSESTree.Node | undefined;
       const location = callExpression.range[1];
 
       while (node) {

diff --git a/packages/eslint-plugin/src/rules/prefer-readonly.ts b/packages/eslint-plugin/src/rules/prefer-readonly.ts
@@ -105,7 +105,7 @@ export default createRule<Options, MessageIds>({
     function isDestructuringAssignment(
       node: ts.PropertyAccessExpression,
     ): boolean {
-      let current: ts.Node = node.parent;
+      let current = node.parent as ts.Node | undefined;
 
       while (current) {
         const parent = current.parent;

diff --git a/packages/eslint-plugin/src/rules/return-await.ts b/packages/eslint-plugin/src/rules/return-await.ts
@@ -71,7 +71,7 @@ export default createRule({
     }
 
     function inTry(node: ts.Node): boolean {
-      let ancestor = node.parent;
+      let ancestor = node.parent as ts.Node | undefined;
 
       while (ancestor && !ts.isFunctionLike(ancestor)) {
         if (ts.isTryStatement(ancestor)) {
@@ -85,7 +85,7 @@ export default createRule({
     }
 
     function inCatch(node: ts.Node): boolean {
-      let ancestor = node.parent;
+      let ancestor = node.parent as ts.Node | undefined;
 
       while (ancestor && !ts.isFunctionLike(ancestor)) {
         if (ts.isCatchClause(ancestor)) {
@@ -99,7 +99,7 @@ export default createRule({
     }
 
     function isReturnPromiseInFinally(node: ts.Node): boolean {
-      let ancestor = node.parent;
+      let ancestor = node.parent as ts.Node | undefined;
 
       while (ancestor && !ts.isFunctionLike(ancestor)) {
         if (
@@ -116,7 +116,7 @@ export default createRule({
     }
 
     function hasFinallyBlock(node: ts.Node): boolean {
-      let ancestor = node.parent;
+      let ancestor = node.parent as ts.Node | undefined;
 
       while (ancestor && !ts.isFunctionLike(ancestor)) {
         if (ts.isTryStatement(ancestor)) {

diff --git a/packages/eslint-plugin/src/rules/unified-signatures.ts b/packages/eslint-plugin/src/rules/unified-signatures.ts
@@ -172,12 +172,12 @@ export default createRule<Options, MessageIds>({
       const isTypeParameter = getIsTypeParameter(typeParameters);
       for (const overloads of signatures) {
         forEachPair(overloads, (a, b) => {
-          const signature0 = (a as MethodDefinition).value ?? a;
-          const signature1 = (b as MethodDefinition).value ?? b;
+          const signature0 = (a as Partial<MethodDefinition>).value ?? a;
+          const signature1 = (b as Partial<MethodDefinition>).value ?? b;
 
           const unify = compareSignatures(
-            signature0,
-            signature1,
+            signature0 as SignatureDefinition,
+            signature1 as SignatureDefinition,
             isTypeParameter,
           );
           if (unify !== undefined) {

diff --git a/packages/eslint-plugin/src/util/getThisExpression.ts b/packages/eslint-plugin/src/util/getThisExpression.ts
@@ -4,7 +4,7 @@ import { AST_NODE_TYPES } from '@typescript-eslint/utils';
 export function getThisExpression(
   node: TSESTree.Node,
 ): TSESTree.ThisExpression | undefined {
-  while (node) {
+  while (true) {
     if (node.type === AST_NODE_TYPES.CallExpression) {
       node = node.callee;
     } else if (node.type === AST_NODE_TYPES.ThisExpression) {

diff --git a/packages/rule-tester/src/RuleTester.ts b/packages/rule-tester/src/RuleTester.ts
@@ -1,3 +1,4 @@
+/* eslint-disable @typescript-eslint/no-unnecessary-condition */
 // Forked from https://github.com/eslint/eslint/blob/ad9dd6a933fd098a0d99c6a9aa059850535c23ee/lib/rule-tester/rule-tester.js
 
 import assert from 'node:assert';

diff --git a/packages/scope-manager/src/referencer/Referencer.ts b/packages/scope-manager/src/referencer/Referencer.ts
@@ -88,6 +88,7 @@ class Referencer extends Visitor {
   private populateGlobalsFromLib(globalScope: GlobalScope): void {
     for (const lib of this.#lib) {
       const variables = TSLibraries[lib];
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       /* istanbul ignore if */ if (!variables) {
         throw new Error(`Invalid value for lib provided: ${lib}`);
       }

diff --git a/packages/scope-manager/src/referencer/TypeVisitor.ts b/packages/scope-manager/src/referencer/TypeVisitor.ts
@@ -53,6 +53,7 @@ class TypeVisitor extends Visitor {
       });
 
       // there are a few special cases where the type annotation is owned by the parameter, not the pattern
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
       if (!didVisitAnnotation && 'typeAnnotation' in param) {
         this.visit(param.typeAnnotation);
       }

diff --git a/packages/type-utils/src/getTypeArguments.ts b/packages/type-utils/src/getTypeArguments.ts
@@ -8,6 +8,7 @@ export function getTypeArguments(
   checker: ts.TypeChecker,
 ): readonly ts.Type[] {
   // getTypeArguments was only added in TS3.7
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (checker.getTypeArguments) {
     return checker.getTypeArguments(type);
   }

diff --git a/packages/typescript-estree/src/convert.ts b/packages/typescript-estree/src/convert.ts
@@ -1,3 +1,4 @@
+/* eslint-disable @typescript-eslint/no-unnecessary-condition */
 // There's lots of funny stuff due to the typing of ts.Node
 /* eslint-disable @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-assignment, @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-return, @typescript-eslint/no-unsafe-member-access */
 import * as ts from 'typescript';

diff --git a/packages/typescript-estree/src/create-program/shared.ts b/packages/typescript-estree/src/create-program/shared.ts
@@ -55,6 +55,7 @@ type CanonicalPath = string & { __brand: unknown };
 
 // typescript doesn't provide a ts.sys implementation for browser environments
 const useCaseSensitiveFileNames =
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   ts.sys !== undefined ? ts.sys.useCaseSensitiveFileNames : true;
 const correctPathCasing = useCaseSensitiveFileNames
   ? (filePath: string): string => filePath
@@ -118,6 +119,7 @@ function getAstFromProgram(
  */
 function createHash(content: string): string {
   // No ts.sys in browser environments.
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (ts.sys?.createHash) {
     return ts.sys.createHash(content);
   }

diff --git a/packages/typescript-estree/src/create-program/useProvidedPrograms.ts b/packages/typescript-estree/src/create-program/useProvidedPrograms.ts
@@ -56,6 +56,7 @@ function createProgramFromConfigFile(
   configFile: string,
   projectDirectory?: string,
 ): ts.Program {
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   if (ts.sys === undefined) {
     throw new Error(
       '`createProgramFromConfigFile` is only supported in a Node-like environment.',

diff --git a/packages/typescript-estree/src/node-utils.ts b/packages/typescript-estree/src/node-utils.ts
@@ -430,7 +430,7 @@ export function findFirstMatchingAncestor(
     if (predicate(current)) {
       return current;
     }
-    current = current.parent;
+    current = current.parent as ts.Node | undefined;
   }
   return undefined;
 }

diff --git a/packages/typescript-estree/src/parseSettings/createParseSettings.ts b/packages/typescript-estree/src/parseSettings/createParseSettings.ts
@@ -25,12 +25,15 @@ let TSSERVER_PROJECT_SERVICE: TypeScriptProjectService | null = null;
 
 // NOTE - we intentionally use "unnecessary" `?.` here because in TS<5.3 this enum doesn't exist
 // This object exists so we can centralize these for tracking and so we don't proliferate these across the file
+// https://github.com/microsoft/TypeScript/issues/56579
+/* eslint-disable @typescript-eslint/no-unnecessary-condition */
 const JSDocParsingMode = {
   ParseAll: ts.JSDocParsingMode?.ParseAll,
   ParseNone: ts.JSDocParsingMode?.ParseNone,
   ParseForTypeErrors: ts.JSDocParsingMode?.ParseForTypeErrors,
   ParseForTypeInfo: ts.JSDocParsingMode?.ParseForTypeInfo,
 } as const;
+/* eslint-enable @typescript-eslint/no-unnecessary-condition */
 
 export function createParseSettings(
   code: ts.SourceFile | string,

diff --git a/packages/typescript-estree/src/parseSettings/warnAboutTSVersion.ts b/packages/typescript-estree/src/parseSettings/warnAboutTSVersion.ts
@@ -33,6 +33,8 @@ export function warnAboutTSVersion(
 
   if (
     passedLoggerFn ||
+    // See https://github.com/typescript-eslint/typescript-eslint/issues/7896
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     (typeof process === 'undefined' ? false : process.stdout?.isTTY)
   ) {
     const border = '=============';

diff --git a/packages/utils/src/eslint-utils/context.ts b/packages/utils/src/eslint-utils/context.ts
@@ -1,6 +1,6 @@
 // Wrappers around ESLint's deprecation of existing methods
 // We'll be able to drop them once we no longer support ESLint <8.40.0.
-/* eslint-disable deprecation/deprecation */
+/* eslint-disable @typescript-eslint/no-unnecessary-condition, deprecation/deprecation */
 import type { Scope, SourceCode } from '../ts-eslint';
 import type { RuleContext } from '../ts-eslint/Rule';
 import type { TSESTree } from '../ts-estree';

diff --git a/packages/utils/src/eslint-utils/getParserServices.ts b/packages/utils/src/eslint-utils/getParserServices.ts
@@ -69,7 +69,7 @@ function getParserServices(
   if (
     // eslint-disable-next-line deprecation/deprecation -- TODO - support for ESLint v9 with backwards-compatible support for ESLint v8
     context.parserServices?.esTreeNodeToTSNodeMap == null ||
-    // eslint-disable-next-line deprecation/deprecation -- TODO - support for ESLint v9 with backwards-compatible support for ESLint v8
+    // eslint-disable-next-line deprecation/deprecation, @typescript-eslint/no-unnecessary-condition -- TODO - support for ESLint v9 with backwards-compatible support for ESLint v8
     context.parserServices.tsNodeToESTreeNodeMap == null
   ) {
     throw new Error(ERROR_MESSAGE);

diff --git a/packages/website/src/components/Playground.tsx b/packages/website/src/components/Playground.tsx
@@ -1,3 +1,5 @@
+// See https://github.com/typescript-eslint/typescript-eslint/issues/7630.
+/* eslint-disable @typescript-eslint/no-unnecessary-condition */
 import { useWindowSize } from '@docusaurus/theme-common';
 import clsx from 'clsx';
 import type * as ESQuery from 'esquery';

diff --git a/packages/website/src/components/ast/ASTViewer.tsx b/packages/website/src/components/ast/ASTViewer.tsx
@@ -21,6 +21,7 @@ export interface ASTViewerProps {
 
 function tryToApplyFilter<T>(value: T, filter?: ESQuery.Selector): T | T[] {
   try {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (window.esquery && filter) {
       // @ts-expect-error - esquery requires js ast types
       return window.esquery.match(value, filter);

diff --git a/packages/website/src/components/ast/selectedRange.ts b/packages/website/src/components/ast/selectedRange.ts
@@ -32,7 +32,7 @@ function findInObject(
   visited: Set<unknown>,
 ): {
   key: string[];
-  value: object;
+  value: unknown;
 } | null {
   const children = Object.entries(iter);
   for (const [name, child] of children) {
@@ -73,7 +73,7 @@ export function findSelectionPath(
 ): { path: string[]; node: object | null } {
   const nodePath = ['ast'];
   const visited = new Set<unknown>();
-  let currentNode: object | null = node;
+  let currentNode: unknown = node;
   while (currentNode) {
     // infinite loop guard
     if (visited.has(currentNode)) {

diff --git a/packages/website/src/components/config/ConfigTypeScript.tsx b/packages/website/src/components/config/ConfigTypeScript.tsx
@@ -35,6 +35,7 @@ function ConfigTypeScript(props: ConfigTypeScriptProps): React.JSX.Element {
       getTypescriptOptions().reduce<Record<string, ConfigOptionsType>>(
         (group, item) => {
           const category = item.category!.message;
+          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
           group[category] ??= {
             heading: category,
             fields: [],

diff --git a/packages/website/src/components/linter/config.ts b/packages/website/src/components/linter/config.ts
@@ -17,6 +17,8 @@ export const defaultParseSettings: ParseSettings = {
   EXPERIMENTAL_useSourceOfProjectReferenceRedirect: false,
   extraFileExtensions: [],
   filePath: '',
+  // JSDocParsingMode was added in TS 5.3.
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
   jsDocParsingMode: window.ts?.JSDocParsingMode?.ParseAll,
   jsx: true,
   loc: true,

diff --git a/packages/website/src/components/linter/createLinter.ts b/packages/website/src/components/linter/createLinter.ts
@@ -76,29 +76,27 @@ export function createLinter(
   const triggerLint = (filename: string): void => {
     console.info('[Editor] linting triggered for file', filename);
     const code = system.readFile(filename) ?? '\n';
-    if (code != null) {
-      try {
-        const messages = linter.verify(code, eslintConfig, filename);
-        onLint.trigger(filename, messages);
-      } catch (e) {
-        const lintMessage: Linter.LintMessage = {
-          source: 'eslint',
-          ruleId: '',
-          severity: 2,
-          nodeType: '',
-          column: 1,
-          line: 1,
-          message: String(e instanceof Error ? e.stack : e),
-        };
-        if (typeof e === 'object' && e && 'currentNode' in e) {
-          const node = e.currentNode as TSESTree.Node;
-          lintMessage.column = node.loc.start.column + 1;
-          lintMessage.line = node.loc.start.line;
-          lintMessage.endColumn = node.loc.end.column + 1;
-          lintMessage.endLine = node.loc.end.line;
-        }
-        onLint.trigger(filename, [lintMessage]);
+    try {
+      const messages = linter.verify(code, eslintConfig, filename);
+      onLint.trigger(filename, messages);
+    } catch (e) {
+      const lintMessage: Linter.LintMessage = {
+        source: 'eslint',
+        ruleId: '',
+        severity: 2,
+        nodeType: '',
+        column: 1,
+        line: 1,
+        message: String(e instanceof Error ? e.stack : e),
+      };
+      if (typeof e === 'object' && e && 'currentNode' in e) {
+        const node = e.currentNode as TSESTree.Node;
+        lintMessage.column = node.loc.start.column + 1;
+        lintMessage.line = node.loc.start.line;
+        lintMessage.endColumn = node.loc.end.column + 1;
+        lintMessage.endLine = node.loc.end.line;
       }
+      onLint.trigger(filename, [lintMessage]);
     }
   };
 

diff --git a/packages/website/src/components/linter/utils.ts b/packages/website/src/components/linter/utils.ts
@@ -92,6 +92,7 @@ export function parseMarkers(
           ? 'TypeScript'
           : marker.owner;
 
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!result[group]) {
       result[group] = {
         group: group,