From 012bad107e7fb2fa9ab1184cbd8dc0bbdf4e79b4 Mon Sep 17 00:00:00 2001
From: Perryvw <perryvw@users.noreply.github.com>
Date: Sun, 15 Dec 2024 21:41:17 +0100
Subject: [PATCH] Fix missing index increment

---
 src/transformation/utils/typescript/types.ts | 18 ++++++++++++++----
 test/unit/builtins/array.spec.ts             | 14 ++++++++++++++
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/src/transformation/utils/typescript/types.ts b/src/transformation/utils/typescript/types.ts
index 5ba2a013c..4a356b972 100644
--- a/src/transformation/utils/typescript/types.ts
+++ b/src/transformation/utils/typescript/types.ts
@@ -56,6 +56,20 @@ export function isNumberType(context: TransformationContext, type: ts.Type): boo
 
 function isExplicitArrayType(context: TransformationContext, type: ts.Type): boolean {
     if (context.checker.isArrayType(type) || context.checker.isTupleType(type)) return true;
+
+    if (type.isUnionOrIntersection()) {
+        if (type.types.some(t => isExplicitArrayType(context, t))) {
+            return true;
+        }
+    }
+
+    const baseTypes = type.getBaseTypes();
+    if (baseTypes) {
+        if (baseTypes.some(t => isExplicitArrayType(context, t))) {
+            return true;
+        }
+    }
+
     if (type.symbol) {
         const baseConstraint = context.checker.getBaseConstraintOfType(type);
         if (baseConstraint && baseConstraint !== type) {
@@ -63,10 +77,6 @@ function isExplicitArrayType(context: TransformationContext, type: ts.Type): boo
         }
     }
 
-    if (type.isUnionOrIntersection()) {
-        return type.types.some(t => isExplicitArrayType(context, t));
-    }
-
     return false;
 }
 
diff --git a/test/unit/builtins/array.spec.ts b/test/unit/builtins/array.spec.ts
index 1e952a162..1784ed73b 100644
--- a/test/unit/builtins/array.spec.ts
+++ b/test/unit/builtins/array.spec.ts
@@ -884,3 +884,17 @@ describe("copying array methods", () => {
         });
     });
 });
+
+// https://github.com/TypeScriptToLua/TypeScriptToLua/issues/1605
+test("array indexing in optional chain (#1605)", () => {
+    util.testModule`
+        interface Foo extends Array<number> {}
+        const b: {arr?: Foo} = {arr:[1,2]};
+        export const t = b.arr?.[1];
+
+        const c: Foo | undefined = b.arr;
+        export const u = c?.[1];
+    `
+        .setOptions({ strict: true }) // crucial to reproducing for some reason
+        .expectToMatchJsResult();
+});