fix(eslint-plugin): [no-unnecessary-condition] fix false positive wit…

…h computed member access and branded key type
typescript-eslint · Sep 30, 2023 · de4ae83 · de4ae83
1 parent 4a6d841
commit de4ae83
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Showing 2 changed files with 50 additions and 6 deletions.
diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts b/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
@@ -534,12 +534,9 @@ export default createRule<Options, MessageId>({
         }
       }
       const typeName = getTypeName(checker, propertyType);
-      return !!(
-        (typeName === 'string' &&
-          checker.getIndexInfoOfType(objType, ts.IndexKind.String)) ||
-        (typeName === 'number' &&
-          checker.getIndexInfoOfType(objType, ts.IndexKind.Number))
-      );
+      return !!checker
+        .getIndexInfosOfType(objType)
+        .find(info => getTypeName(checker, info.keyType) === typeName);
     }
 
     // Checks whether a member expression is nullable or not regardless of it's previous node.

diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
@@ -507,6 +507,53 @@ type Key = 'bar' | 'foo' | 'baz';
 declare const foo: Foo;
 declare const key: Key;
 
+foo?.[key]?.trim();
+    `,
+    // https://github.com/typescript-eslint/typescript-eslint/issues/7700
+    `
+type BrandedKey = string & { __brand: string };
+type Foo = { [key: BrandedKey]: string } | null;
+declare const foo: Foo;
+const key = '1' as BrandedKey;
+foo?.[key]?.trim();
+    `,
+    `
+type BrandedKey<S extends string> = S & { __brand: string };
+type Foo = { [key: string]: string; foo: 'foo'; bar: 'bar' } | null;
+type Key = Branded<'bar'> | Branded<'foo'>;
+declare const foo: Foo;
+declare const key: Key;
+foo?.[key].trim();
+    `,
+    `
+type BrandedKey = string & { __brand: string };
+interface Outer {
+  inner?: {
+    [key: BrandedKey<string>]: string | undefined;
+  };
+}
+function Foo(outer: Outer, key: BrandedKey): number | undefined {
+  return outer.inner?.[key]?.charCodeAt(0);
+}
+    `,
+    `
+interface Outer {
+  inner?: {
+    [key: string & { __brand: string }]: string | undefined;
+    bar: 'bar';
+  };
+}
+type Foo = 'foo' & { __brand: string };
+function Foo(outer: Outer, key: Foo): number | undefined {
+  return outer.inner?.[key]?.charCodeAt(0);
+}
+    `,
+    `
+type BrandedKey<S extends string> = S & { __brand: string };
+type Foo = { [key: string]: string; foo: 'foo'; bar: 'bar' } | null;
+type Key = BrandedKey<'bar'> | BrandedKey<'foo'> | BrandedKey<'baz'>;
+declare const foo: Foo;
+declare const key: Key;
 foo?.[key]?.trim();
     `,
     `