From c0d8828be093406ef4f9ca4fdd3073737e44f783 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Sun, 23 Aug 2026 19:52:25 +0200
Subject: [PATCH] interpret: make validate_c_variadic_compatible_ty public

---
 .../rustc_const_eval/src/interpret/intrinsics.rs    | 13 ++-----------
 compiler/rustc_const_eval/src/interpret/mod.rs      |  1 +
 2 files changed, 3 insertions(+), 11 deletions(-)

diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index f8c308ece55b7..00057dc503827 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -60,7 +60,7 @@ pub(crate) enum MinMax {
 
 /// Whether two types `T` and `U` are compatible when a value of type `T` is passed as a c-variadic
 /// argument and read as a value of type `U`.
-enum VarArgCompatible {
+pub enum VarArgCompatible {
     /// `T` and `U` are compatible, e.g.
     ///
     /// - They're the same type.
@@ -829,15 +829,6 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             return interp_ok(());
         }
 
-        // Types of different sizes can never be compatible.
-        if arg_mplace.layout.size != callee_type.size {
-            throw_ub_format!(
-                "va_arg type mismatch: requested `{}` is incompatible with next argument of type `{}`",
-                callee_ty,
-                caller_ty,
-            )
-        }
-
         match self.validate_c_variadic_compatible_ty(arg_mplace.layout.ty, callee_type.ty)? {
             VarArgCompatible::Compatible => interp_ok(()),
             VarArgCompatible::Incompatible => throw_ub_format!(
@@ -875,7 +866,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     /// - `T` and `U` are both pointers, and their target types are compatible.
     /// - `T` is a pointer to [`std::ffi::c_void`] and `U` is a pointer to [`i8`] or [`u8`],
     /// or vice versa.
-    fn validate_c_variadic_compatible_ty(
+    pub fn validate_c_variadic_compatible_ty(
         &mut self,
         caller_type: Ty<'tcx>,
         callee_type: Ty<'tcx>,
diff --git a/compiler/rustc_const_eval/src/interpret/mod.rs b/compiler/rustc_const_eval/src/interpret/mod.rs
index cd1a5cf6a46d5..1eceff75e092b 100644
--- a/compiler/rustc_const_eval/src/interpret/mod.rs
+++ b/compiler/rustc_const_eval/src/interpret/mod.rs
@@ -29,6 +29,7 @@ pub use self::intern::{
     HasStaticRootDefId, InternError, InternKind, intern_const_alloc_for_constprop,
     intern_const_alloc_recursive,
 };
+pub use self::intrinsics::VarArgCompatible;
 pub use self::machine::{
     AllocMap, Machine, MayLeak, RetagMode, ReturnAction, compile_time_machine,
 };