From f005b451c2eeb018e3c2c6e6653636981cfa7f1a Mon Sep 17 00:00:00 2001
From: Veera <sveera.2001@gmail.com>
Date: Tue, 16 Apr 2024 18:53:05 -0400
Subject: [PATCH] Support C23's Variadics Without a Named Parameter

This PR removes the static check that disallowed extern functions
with ellipsis (varargs) as the only parameter since this is now
valid in C23.

Also, adds a doc comment for `check_decl_cvariadic_pos()` and
fixes the name of the function (`varadic` -> `variadic`).
---
 compiler/rustc_ast_passes/messages.ftl          |  3 ---
 compiler/rustc_ast_passes/src/ast_validation.rs | 12 +++++-------
 compiler/rustc_ast_passes/src/errors.rs         |  7 -------
 3 files changed, 5 insertions(+), 17 deletions(-)

diff --git a/compiler/rustc_ast_passes/messages.ftl b/compiler/rustc_ast_passes/messages.ftl
index a3731e94276b5..f578165f369cb 100644
--- a/compiler/rustc_ast_passes/messages.ftl
+++ b/compiler/rustc_ast_passes/messages.ftl
@@ -97,9 +97,6 @@ ast_passes_fn_body_extern = incorrect function inside `extern` block
 ast_passes_fn_param_c_var_args_not_last =
     `...` must be the last argument of a C-variadic function
 
-ast_passes_fn_param_c_var_args_only =
-    C-variadic function must be declared with at least one named argument
-
 ast_passes_fn_param_doc_comment =
     documentation comments cannot be applied to function parameters
     .label = doc comments are not allowed here
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index 495e90e967b93..63aed6493dc49 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -365,7 +365,7 @@ impl<'a> AstValidator<'a> {
 
     fn check_fn_decl(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
         self.check_decl_num_args(fn_decl);
-        self.check_decl_cvaradic_pos(fn_decl);
+        self.check_decl_cvariadic_pos(fn_decl);
         self.check_decl_attrs(fn_decl);
         self.check_decl_self_param(fn_decl, self_semantic);
     }
@@ -380,13 +380,11 @@ impl<'a> AstValidator<'a> {
         }
     }
 
-    fn check_decl_cvaradic_pos(&self, fn_decl: &FnDecl) {
+    /// Emits an error if a function declaration has a variadic parameter in the
+    /// beginning or middle of parameter list.
+    /// Example: `fn foo(..., x: i32)` will emit an error.
+    fn check_decl_cvariadic_pos(&self, fn_decl: &FnDecl) {
         match &*fn_decl.inputs {
-            [Param { ty, span, .. }] => {
-                if let TyKind::CVarArgs = ty.kind {
-                    self.dcx().emit_err(errors::FnParamCVarArgsOnly { span: *span });
-                }
-            }
             [ps @ .., _] => {
                 for Param { ty, span, .. } in ps {
                     if let TyKind::CVarArgs = ty.kind {
diff --git a/compiler/rustc_ast_passes/src/errors.rs b/compiler/rustc_ast_passes/src/errors.rs
index f397c949e0486..0e4599f55ba5b 100644
--- a/compiler/rustc_ast_passes/src/errors.rs
+++ b/compiler/rustc_ast_passes/src/errors.rs
@@ -92,13 +92,6 @@ pub struct FnParamTooMany {
     pub max_num_args: usize,
 }
 
-#[derive(Diagnostic)]
-#[diag(ast_passes_fn_param_c_var_args_only)]
-pub struct FnParamCVarArgsOnly {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(ast_passes_fn_param_c_var_args_not_last)]
 pub struct FnParamCVarArgsNotLast {