typescript-eslint · JoshuaKGoldberg · Feb 1, 2024 · Jan 14, 2024 · Feb 1, 2024
diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts b/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
@@ -197,6 +197,28 @@ export default createRule<Options, MessageId>({
       );
     }
 
+    function isNullableMemberExpression(
+      node: TSESTree.MemberExpression,
+    ): boolean {
+      const objectType = services.getTypeAtLocation(node.object);
+      if (node.computed) {
+        const propertyType = services.getTypeAtLocation(node.property);
+        return isNullablePropertyType(objectType, propertyType);
+      }
+      const property = node.property;
+
+      if (property.type === AST_NODE_TYPES.Identifier) {
+        const propertyType = objectType.getProperty(property.name);
+        if (
+          propertyType &&
+          tsutils.isSymbolFlagSet(propertyType, ts.SymbolFlags.Optional)
+        ) {
+          return true;
+        }
+      }
+      return false;
+    }
+
     /**
      * Checks if a conditional node is necessary:
      * if the type of the node is always true or always false, it's not necessary.
@@ -283,7 +305,13 @@ export default createRule<Options, MessageId>({
       let messageId: MessageId | null = null;
       if (isTypeFlagSet(type, ts.TypeFlags.Never)) {
         messageId = 'never';
-      } else if (!isPossiblyNullish(type)) {
+      } else if (
+        !isPossiblyNullish(type) &&
+        !(
+          node.type === AST_NODE_TYPES.MemberExpression &&
+          isNullableMemberExpression(node)
+        )
+      ) {
         // Since typescript array index signature types don't represent the
         //  possibility of out-of-bounds access, if we're indexing into an array
         //  just skip the check, to avoid false positives

diff --git a/packages/eslint-plugin/tests/fixtures/tsconfig.exactOptionalPropertyTypes.json b/packages/eslint-plugin/tests/fixtures/tsconfig.exactOptionalPropertyTypes.json
@@ -0,0 +1,6 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "exactOptionalPropertyTypes": true
+  }
+}
diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
@@ -22,6 +22,11 @@ const ruleTester = new RuleTester({
   },
 });
 
+const optionsWithExactOptionalPropertyTypes = {
+  tsconfigRootDir: rootPath,
+  project: './tsconfig.exactOptionalPropertyTypes.json',
+};
+
 const ruleError = (
   line: number,
   column: number,
@@ -748,6 +753,48 @@ declare let foo: number;
 foo ||= 1;
     `,
     `
+declare const foo: { bar: { baz?: number; qux: number } };
+type Key = 'baz' | 'qux';
+declare const key: Key;
+foo.bar[key] ??= 1;
+    `,
+    `
+enum Keys {
+  A = 'A',
+  B = 'B',
+}
+type Foo = {
+  [Keys.A]: number | null;
+  [Keys.B]: number;
+};
+declare const foo: Foo;
+declare const key: Keys;
+foo[key] ??= 1;
+    `,
+    {
+      code: `
+declare const foo: { bar?: number };
+foo.bar ??= 1;
+      `,
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
+    {
+      code: `
+declare const foo: { bar: { baz?: number } };
+foo['bar'].baz ??= 1;
+      `,
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
+    {
+      code: `
+declare const foo: { bar: { baz?: number; qux: number } };
+type Key = 'baz' | 'qux';
+declare const key: Key;
+foo.bar[key] ??= 1;
+      `,
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+    },
+    `
 declare let foo: number;
 foo &&= 1;
     `,
@@ -2035,6 +2082,22 @@ foo &&= null;
         },
       ],
     },
+    {
+      code: `
+declare const foo: { bar: number };
+foo.bar ??= 1;
+      `,
+      parserOptions: optionsWithExactOptionalPropertyTypes,
+      errors: [
+        {
+          messageId: 'neverNullish',
+          line: 3,
+          endLine: 3,
+          column: 1,
+          endColumn: 8,
+        },
+      ],
+    },
     {
       code: noFormat`
 type Foo = { bar: () => number } | null;