typescript-eslint · JoshuaKGoldberg · Oct 19, 2023 · Sep 24, 2023 · Sep 27, 2023 · Sep 27, 2023
diff --git a/packages/eslint-plugin/src/rules/enum-utils/shared.ts b/packages/eslint-plugin/src/rules/enum-utils/shared.ts
@@ -20,6 +20,23 @@ function getBaseEnumType(typeChecker: ts.TypeChecker, type: ts.Type): ts.Type {
   return typeChecker.getTypeAtLocation(symbol.valueDeclaration!.parent);
 }
 
+/**
+ * Retrieve only the Enum literals from a type. for example:
+ * - 123 --> []
+ * - {} --> []
+ * - Fruit.Apple --> [Fruit.Apple]
+ * - Fruit.Apple | Vegetable.Lettuce --> [Fruit.Apple, Vegetable.Lettuce]
+ * - Fruit.Apple | Vegetable.Lettuce | 123 --> [Fruit.Apple, Vegetable.Lettuce]
+ * - T extends Fruit --> [Fruit]
+ */
+export function getEnumLiterals(type: ts.Type): ts.LiteralType[] {
+  return tsutils
+    .unionTypeParts(type)
+    .filter((subType): subType is ts.LiteralType =>
+      isTypeFlagSet(subType, ts.TypeFlags.EnumLiteral),
+    );
+}
+
 /**
  * A type can have 0 or more enum types. For example:
  * - 123 --> []
@@ -33,8 +50,55 @@ export function getEnumTypes(
   typeChecker: ts.TypeChecker,
   type: ts.Type,
 ): ts.Type[] {
-  return tsutils
-    .unionTypeParts(type)
-    .filter(subType => isTypeFlagSet(subType, ts.TypeFlags.EnumLiteral))
-    .map(type => getBaseEnumType(typeChecker, type));
+  return getEnumLiterals(type).map(type => getBaseEnumType(typeChecker, type));
+}
+
+/**
+ * Returns the enum key that matches the given literal node, or null if none
+ * match. For example:
+ * ```ts
+ * enum Fruit {
+ *   Apple = 'apple',
+ *   Banana = 'banana',
+ * }
+ *
+ * getEnumKeyForLiteral([Fruit.Apple, Fruit.Banana], 'apple') --> 'Fruit.Apple'
+ * getEnumKeyForLiteral([Fruit.Apple, Fruit.Banana], 'banana') --> 'Fruit.Banana'
+ * getEnumKeyForLiteral([Fruit.Apple, Fruit.Banana], 'cherry') --> null
+ * ```
+ */
+export function getEnumKeyForLiteral(
+  enumLiterals: ts.LiteralType[],
+  literal: unknown,
+): string | null {
+  for (const enumLiteral of enumLiterals) {
+    if (enumLiteral.value === literal) {
+      const { symbol } = enumLiteral;
+
+      const memberDeclaration = symbol.valueDeclaration as ts.EnumMember;
+      const enumDeclaration = memberDeclaration.parent;
+
+      const memberNameIdentifier = memberDeclaration.name;
+      const enumName = enumDeclaration.name.text;
+
+      switch (memberNameIdentifier.kind) {
+        case ts.SyntaxKind.Identifier:
+          return `${enumName}.${memberNameIdentifier.text}`;
+
+        case ts.SyntaxKind.StringLiteral: {
+          const memberName = memberNameIdentifier.text.replace(/'/g, "\\'");
+
+          return `${enumName}['${memberName}']`;
+        }
+
+        case ts.SyntaxKind.ComputedPropertyName:
+          return `${enumName}[${memberNameIdentifier.expression.getText()}]`;
+
+        default:
+          break;
+      }
+    }
+  }
+
+  return null;
 }
diff --git a/packages/eslint-plugin/src/rules/no-unsafe-enum-comparison.ts b/packages/eslint-plugin/src/rules/no-unsafe-enum-comparison.ts
@@ -1,9 +1,13 @@
-import type { TSESTree } from '@typescript-eslint/utils';
+import type { TSESLint, TSESTree } from '@typescript-eslint/utils';
 import * as tsutils from 'ts-api-utils';
 import * as ts from 'typescript';
 
-import { createRule, getParserServices } from '../util';
-import { getEnumTypes } from './enum-utils/shared';
+import { createRule, getParserServices, getStaticValue } from '../util';
+import {
+  getEnumKeyForLiteral,
+  getEnumLiterals,
+  getEnumTypes,
+} from './enum-utils/shared';
 
 /**
  * @returns Whether the right type is an unsafe comparison against any left type.
@@ -39,6 +43,7 @@ function getEnumValueType(type: ts.Type): ts.TypeFlags | undefined {
 export default createRule({
   name: 'no-unsafe-enum-comparison',
   meta: {
+    hasSuggestions: true,
     type: 'suggestion',
     docs: {
       description: 'Disallow comparing an enum value with a non-enum value',
@@ -48,6 +53,7 @@ export default createRule({
     messages: {
       mismatched:
         'The two values in this comparison do not have a shared enum type.',
+      replaceValueWithEnum: 'Replace with an enum value comparison.',
     },
     schema: [],
   },
@@ -107,6 +113,43 @@ export default createRule({
           context.report({
             messageId: 'mismatched',
             node,
+            suggest: [
+              {
+                messageId: 'replaceValueWithEnum',
+                fix(fixer): TSESLint.RuleFix | null {
+                  // Replace the right side with an enum key if possible:
+                  //
+                  // ```ts
+                  // Fruit.Apple === 'apple'; // Fruit.Apple === Fruit.Apple
+                  // ```
+                  const leftEnumKey = getEnumKeyForLiteral(
+                    getEnumLiterals(left),
+                    getStaticValue(node.right)?.value,
+                  );
+
+                  if (leftEnumKey) {
+                    return fixer.replaceText(node.right, leftEnumKey);
+                  }
+
+                  // Replace the left side with an enum key if possible:
+                  //
+                  // ```ts
+                  // declare const fruit: Fruit;
+                  // 'apple' === Fruit.Apple; // Fruit.Apple === Fruit.Apple
+                  // ```
+                  const rightEnumKey = getEnumKeyForLiteral(
+                    getEnumLiterals(right),
+                    getStaticValue(node.left)?.value,
+                  );
+
+                  if (rightEnumKey) {
+                    return fixer.replaceText(node.left, rightEnumKey);
+                  }
+
+                  return null;
+                },
+              },
+            ],
           });
         }
       },