From 2b9fce8c8cf4373ee9da938ad5eeb97e85ca2739 Mon Sep 17 00:00:00 2001
From: Folkert de Vries <folkert@folkertdev.nl>
Date: Sat, 6 Sep 2025 17:23:34 +0200
Subject: c-variadic: reject non-extern functions

---
 compiler/rustc_ast_passes/messages.ftl          | 2 ++
 compiler/rustc_ast_passes/src/ast_validation.rs | 3 ++-
 compiler/rustc_ast_passes/src/errors.rs         | 7 +++++++
 3 files changed, 11 insertions(+), 1 deletion(-)

(limited to 'compiler')

diff --git a/compiler/rustc_ast_passes/messages.ftl b/compiler/rustc_ast_passes/messages.ftl
index 6eb4e4bc452..958797a6089 100644
--- a/compiler/rustc_ast_passes/messages.ftl
+++ b/compiler/rustc_ast_passes/messages.ftl
@@ -68,6 +68,8 @@ ast_passes_bound_in_context = bounds on `type`s in {$ctx} have no effect
 
 ast_passes_c_variadic_associated_function = associated functions cannot have a C variable argument list
 
+ast_passes_c_variadic_no_extern = `...` is not supported for non-extern functions
+
 ast_passes_const_and_c_variadic = functions cannot be both `const` and C-variadic
     .const = `const` because of this
     .variadic = C-variadic because of this
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index 79947b514b1..bbba235a6d1 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -714,7 +714,8 @@ impl<'a> AstValidator<'a> {
                     self.dcx().emit_err(errors::BadCVariadic { span: variadic_param.span });
                 }
                 Extern::None => {
-                    self.dcx().emit_err(errors::BadCVariadic { span: variadic_param.span });
+                    let err = errors::CVariadicNoExtern { span: variadic_param.span };
+                    self.dcx().emit_err(err);
                 }
             },
             FnCtxt::Assoc(_) => {
diff --git a/compiler/rustc_ast_passes/src/errors.rs b/compiler/rustc_ast_passes/src/errors.rs
index a085e09fe94..6b57e5ef376 100644
--- a/compiler/rustc_ast_passes/src/errors.rs
+++ b/compiler/rustc_ast_passes/src/errors.rs
@@ -325,6 +325,13 @@ pub(crate) struct CVariadicAssociatedFunction {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(ast_passes_c_variadic_no_extern)]
+pub(crate) struct CVariadicNoExtern {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(ast_passes_bad_c_variadic)]
 pub(crate) struct BadCVariadic {
-- 
cgit 1.4.1-3-g733a5