From d5839115e2e72fa2d2be8499d7dccef6ff37992a Mon Sep 17 00:00:00 2001
From: Drew Rife <darife@jlg.com>
Date: Sun, 11 Oct 2026 18:11:32 +0000
Subject: [PATCH] fix: prevent invalid variant visit dispatch

---
 include/etl/infinite_loop.h            |  3 ++-
 include/etl/private/variant_variadic.h | 22 ++++++++++++++---
 test/test_variant_variadic.cpp         | 34 ++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 4 deletions(-)

diff --git a/include/etl/infinite_loop.h b/include/etl/infinite_loop.h
index 530e9b4c..4c91255d 100644
--- a/include/etl/infinite_loop.h
+++ b/include/etl/infinite_loop.h
@@ -55,7 +55,8 @@ namespace etl
   #elif defined(ETL_COMPILER_MICROSOFT)
       _ReadWriteBarrier();
   #else
-    #error "Infinite loop not supported for this compiler and platform"
+      volatile bool prevent_optimisation = true;
+      static_cast<void>(prevent_optimisation);
   #endif
 #endif
     }
diff --git a/include/etl/private/variant_variadic.h b/include/etl/private/variant_variadic.h
index 4161aa31..86c4a293 100644
--- a/include/etl/private/variant_variadic.h
+++ b/include/etl/private/variant_variadic.h
@@ -33,6 +33,7 @@ SOFTWARE.
 #include "../compare.h"
 #include "../error_handler.h"
 #include "../exception.h"
+#include "../infinite_loop.h"
 #include "../initializer_list.h"
 #include "../integral_limits.h"
 #include "../largest.h"
@@ -473,6 +474,17 @@ namespace etl
 
   namespace private_variant
   {
+    //***************************************************************************
+    /// Reports an invalid visit and prevents execution from continuing if the
+    /// configured error policy returns or runtime checks are disabled.
+    //***************************************************************************
+    ETL_NORETURN
+    inline void invalid_visit()
+    {
+      ETL_ASSERT_FAIL(ETL_ERROR(bad_variant_access));
+      etl::infinite_loop();
+    }
+
     //***************************************************************************
     /// variant_base for non-trivially destructible types.
     /// Uses uninitialized_buffer (char array) storage and switch-based
@@ -2188,7 +2200,6 @@ namespace etl
 
     //***************************************************************************
     /// Makes a call to TCallable using tIndex alternative to the variant.
-    /// Instantiated as function pointer in the `do_visit` function.
     //***************************************************************************
     template <typename TRet, typename TCallable, typename TVariant, size_t tIndex>
     constexpr TRet do_visit_single(TCallable&& f, TVariant&& v)
@@ -2219,14 +2230,19 @@ namespace etl
     template <typename TRet, typename TCallable, typename TVariant, size_t... tIndices, typename... TVarRest>
     static ETL_CONSTEXPR14 TRet do_visit(TCallable&& f, TVariant&& v, index_sequence<tIndices...>, TVarRest&&... variants)
     {
-      ETL_ASSERT(!v.valueless_by_exception(), ETL_ERROR(bad_variant_access));
+      const size_t index = v.index();
+
+      if (index >= sizeof...(tIndices)) ETL_UNLIKELY
+      {
+        invalid_visit();
+      }
 
       using helper_t = do_visit_helper<TRet, TCallable, TVariant, TVarRest...>;
       using func_ptr = typename helper_t::function_pointer;
 
       constexpr func_ptr jmp_table[]{helper_t::template fptr<tIndices>()...};
 
-      return jmp_table[v.index()](static_cast<TCallable&&>(f), static_cast<TVariant&&>(v), static_cast<TVarRest&&>(variants)...);
+      return jmp_table[index](static_cast<TCallable&&>(f), static_cast<TVariant&&>(v), static_cast<TVarRest&&>(variants)...);
     }
 
     template <typename TRet, typename TCallable, typename TVariant, typename... TVs>
diff --git a/test/test_variant_variadic.cpp b/test/test_variant_variadic.cpp
index 8e81a606..a5701fd0 100644
--- a/test/test_variant_variadic.cpp
+++ b/test/test_variant_variadic.cpp
@@ -2548,6 +2548,31 @@ namespace
       CHECK_EQUAL(70, type);
     }
 
+    //*************************************************************************
+    TEST(test_variant_visit_dispatches_every_alternative)
+    {
+      etl::variant<int8_t, uint8_t, int16_t> variant;
+      variant_test_visit_dispatcher          visitor;
+
+      variant = int8_t{};
+      CHECK_EQUAL(5, etl::visit(visitor, variant));
+
+      variant = uint8_t{};
+      CHECK_EQUAL(6, etl::visit(visitor, variant));
+
+      variant = int16_t{};
+      CHECK_EQUAL(7, etl::visit(visitor, variant));
+    }
+
+    //*************************************************************************
+    TEST(test_variant_visit_rejects_valueless_variant)
+    {
+      etl::variant<int8_t, uint8_t> variant(etl::private_variant::valueless_t{});
+      variant_test_visit_dispatcher visitor;
+
+      CHECK_THROW(etl::visit(visitor, variant), etl::bad_variant_access);
+    }
+
     //*************************************************************************
     struct test_variant_multiple_visit_helper
     {
@@ -2590,6 +2615,15 @@ namespace
       CHECK_EQUAL(32, res);
     }
 
+    //*************************************************************************
+    TEST(test_variant_multiple_visit_rejects_valueless_later_variant)
+    {
+      etl::variant<int8_t, uint8_t>           variant1;
+      etl::variant<int8_t, uint16_t, uint8_t> variant2(etl::private_variant::valueless_t{});
+
+      CHECK_THROW(etl::visit<int16_t>(test_variant_multiple_visit_helper{}, variant1, variant2), etl::bad_variant_access);
+    }
+
   #if ETL_USING_CPP14
     //*************************************************************************
     TEST(test_variant_multiple_visit_auto_return)