From 01b5b06874591dde9c5caa3406e6f59a4eb96d64 Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Mon, 2 Feb 2026 23:42:11 +0100
Subject: [PATCH] Assert that index is valid in wxArray::operator[]

Restore compatibility with all the previous wxWidgets versions that had
this assert and make sure that errors in the code using this operator
don't go unnoticed, as it happened with #26148.

Closes #26149.
---
 include/wx/dynarray.h   | 12 ++++++++++++
 tests/arrays/arrays.cpp |  5 +++++
 2 files changed, 17 insertions(+)

diff --git a/include/wx/dynarray.h b/include/wx/dynarray.h
index afd25b7e68..611655e602 100644
--- a/include/wx/dynarray.h
+++ b/include/wx/dynarray.h
@@ -122,6 +122,18 @@ public:
     bool IsEmpty() const { return this->empty(); }
     size_t Count() const { return this->size(); }
 
+    T& operator[](size_t uiIndex)
+    {
+        wxASSERT( uiIndex < this->size() );
+        return base_vec::operator[](uiIndex);
+    }
+
+    const T& operator[](size_t uiIndex) const
+    {
+        wxASSERT( uiIndex < this->size() );
+        return base_vec::operator[](uiIndex);
+    }
+
     T& Item(size_t uiIndex) const
     {
         wxASSERT( uiIndex < this->size() );
diff --git a/tests/arrays/arrays.cpp b/tests/arrays/arrays.cpp
index 5875c4f1ad..3ada06fb64 100644
--- a/tests/arrays/arrays.cpp
+++ b/tests/arrays/arrays.cpp
@@ -321,6 +321,11 @@ TEST_CASE("wxArrayString", "[dynarray]")
     CHECK( a5.size() == 3 );
     CHECK( a5[2] == "Foo" );
 
+    // This is undefined behaviour but because the array has just been resized
+    // down, its memory hopefully hasn't been reallocated yet, so we shouldn't
+    // crash accessing it. But we must assert due to the index being invalid.
+    WX_ASSERT_FAILS_WITH_ASSERT( a5[3].clear() );
+
     wxArrayString a6;
     a6.Add("Foo");
     a6.Insert(a6[0], 1, 100);