Rollup merge of #144066 - RalfJung:extern-c-variadics, r=workingjubilee

stabilize c-style varargs for sysv64, win64, efiapi, aapcs

This has been split up so the PR now only contains the extended_varargs_abi_support stabilization; "system" has been moved to https://github.com/rust-lang/rust/pull/145954.

**Previous (combined) PR description:**

This stabilizes extern block declarations of variadic functions with the system, sysv64, win64, efiapi, aapcs ABIs. This corresponds to the extended_varargs_abi_support and extern_system_varargs feature gates.

The feature gates were split up since it seemed like there might be further discussion needed for what exactly "system" ABI variadic functions should do, but a [consensus](https://github.com/rust-lang/rust/issues/136946#issuecomment-2967847553) has meanwhile been reached: they shall behave like "C" functions. IOW, the ABI of a "system" function is (bold part is new in this PR):
- "stdcall" for win32 targets **for non-variadic functions**
- "C" for everything else

This had been previously stabilized *without FCP* in https://github.com/rust-lang/rust/pull/116161, which got reverted in https://github.com/rust-lang/rust/pull/136897. There was also a "fun" race condition involved with the system ABI being [added](https://github.com/rust-lang/rust/pull/119587) to the list of variadic-supporting ABIs between the creation and merge of rust-lang/rust#116161.

There was a question raised [here](https://github.com/rust-lang/rust/pull/116161#issuecomment-1983829513) whether t-lang even needs to be involved for a change like this. Not sure if that has meanwhile been clarified? The behavior of the "system" ABI (a Rust-specific ABI) definitely feels like t-lang territory to me.

Fixes rust-lang/rust#100189
Cc `@rust-lang/lang`

# Stabilization report

> ## General design

>  ### What is the RFC for this feature and what changes have occurred to the user-facing design since the RFC was finalized?

AFAIK there is no RFC. The tracking issues are
- https://github.com/rust-lang/rust/issues/100189
- https://github.com/rust-lang/rust/issues/136946

>  ### What behavior are we committing to that has been controversial? Summarize the major arguments pro/con.

The only controversial point is whether "system" ABI functions should support variadics.
- Pro: This allows crates like windows-rs to consistently use "system", see e.g. https://github.com/microsoft/windows-rs/issues/3626.
- Cons: `@workingjubilee` had some implementation concerns, but I think those have been [resolved](https://github.com/rust-lang/rust/issues/136946#issuecomment-2967847553). EDIT: turns out Jubilee still has concerns (she mentioned that in a DM); I'll let her express those.

Note that "system" is already a magic ABI we introduced to "do the right thing". This just makes it do the right thing in more cases. In particular, it means that on Windows one can almost always just do
```rust
extern "system" {
  // put all the things here
}
```
and it'll do the right thing, rather than having to split imports into non-varargs and varargs, with the varargs in a separate `extern "C"` block (and risking accidentally putting a non-vararg there).

(I am saying "almost" always because some Windows API functions actually use cdecl, not stdcall, on x86. Those of course need to go in `extern "C"` blocks.)

> ### Are there extensions to this feature that remain unstable? How do we know that we are not accidentally committing to those?

Actually defining variadic functions in Rust remains unstable, under the [c_variadic feature gate](https://github.com/rust-lang/rust/issues/44930).

> ## Has a Call for Testing period been conducted? If so, what feedback was received?
>
> Does any OSS nightly users use this feature? For instance, a useful indication might be "search <grep.app> for `#![feature(FEATURE_NAME)]` and had `N` results".

There was no call for testing.

A search brings up https://github.com/rust-osdev/uefi-rs/blob/main/uefi-raw/src/table/boot.rs using this for "efiapi". This doesn't seem widely used, but it is an "obvious" gap in our support for c-variadics.

> ## Implementation quality

All rustc does here is forward the ABI to LLVM so there's lot a lot to say here...

> ### Summarize the major parts of the implementation and provide links into the code (or to PRs)
>
> An example for async closures: <https://rustc-dev-guide.rust-lang.org/coroutine-closures.html>.

The check for allowed variadic ABIs is [here](https://github.com/rust-lang/rust/blob/9c870d30e2d6434c9e9a004b450c5ccffdf3d844/compiler/rustc_hir_analysis/src/lib.rs#L109-L126).

The special handling of "system" is [here](https://github.com/rust-lang/rust/blob/c24914ec8329b22ec7bcaa6ab534a784b2bd8ab9/compiler/rustc_target/src/spec/abi_map.rs#L82-L85).

> ### Summarize existing test coverage of this feature
>
> Consider what the "edges" of this feature are.  We're particularly interested in seeing tests that assure us about exactly what nearby things we're not stabilizing.
>
> Within each test, include a comment at the top describing the purpose of the test and what set of invariants it intends to demonstrate. This is a great help to those reviewing the tests at stabilization time.
>
> - What does the test coverage landscape for this feature look like?
>   - Tests for compiler errors when you use the feature wrongly or make mistakes?
>   - Tests for the feature itself:
>       - Limits of the feature (so failing compilation)
>       - Exercises of edge cases of the feature
>       - Tests that checks the feature works as expected (where applicable, `//@ run-pass`).
>   - Are there any intentional gaps in test coverage?
>
> Link to test folders or individual tests (ui/codegen/assembly/run-make tests, etc.).

Prior PRs add a codegen test for all ABIs and tests actually calling extern variadic functions for sysv64 and win64:
- https://github.com/rust-lang/rust/pull/144359
- https://github.com/rust-lang/rust/pull/144379

We don't have a way of executing uefi target code in the test suite, so it's unclear how to fully test efiapi. aapcs could probably be done? (But note that we have hardly an such actually-calling-functions tests for ABI things, we almost entirely rely on codegen tests.)

The test ensuring that we do *not* stabilize *defining* c-variadic functions is `tests/ui/feature-gates/feature-gate-c_variadic.rs`.

> ### What outstanding bugs in the issue tracker involve this feature? Are they stabilization-blocking?

None that I am aware of.

> ### What FIXMEs are still in the code for that feature and why is it ok to leave them there?

None that I am aware of.

> ### Summarize contributors to the feature by name for recognition and assuredness that people involved in the feature agree with stabilization

`@Soveu` added sysv64, win64, efiapi, aapcs to the list of ABIs that allow variadics, `@beepster4096` added system.  `@workingjubilee` recently refactored the ABI handling in the compiler, also affecting this feature.

> ### Which tools need to be adjusted to support this feature. Has this work been done?
>
> Consider rustdoc, clippy, rust-analyzer, rustfmt, rustup, docs.rs.

Maybe RA needs to be taught about the new allowed ABIs? No idea how precisely they mirror what exactly rustc accepts and rejects here.

> ## Type system and execution rules

> ### What compilation-time checks are done that are needed to prevent undefined behavior?
>
>  (Be sure to link to tests demonstrating that these tests are being done.)

Nothing new here, this just expands the existing support for calling variadic functions to more ABIs.

> ### Does the feature's implementation need checks to prevent UB or is it sound by default and needs opt in in places to perform the dangerous/unsafe operations? If it is not sound by default, what is the rationale?

Nothing new here, this just expands the existing support for calling variadic functions to more ABIs.

> ### Can users use this feature to introduce undefined behavior, or use this feature to break the abstraction of Rust and expose the underlying assembly-level implementation? (Describe.)

Nothing new here, this just expands the existing support for calling variadic functions to more ABIs.

> ### What updates are needed to the reference/specification? (link to PRs when they exist)

- https://github.com/rust-lang/reference/pull/1936

> ## Common interactions

> ### Does this feature introduce new expressions and can they produce temporaries? What are the lifetimes of those temporaries?

No.

> ### What other unstable features may be exposed by this feature?

None.

28 files changed, 128 insertions, 162 deletions

diff --git a/compiler/rustc_abi/src/extern_abi.rs b/compiler/rustc_abi/src/extern_abi.rs
index 41d744e1946..e3b2b1eff72 100644
--- a/compiler/rustc_abi/src/extern_abi.rs
+++ b/compiler/rustc_abi/src/extern_abi.rs
@@ -6,6 +6,8 @@ use std::hash::{Hash, Hasher};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher, StableOrd};
 #[cfg(feature = "nightly")]
 use rustc_macros::{Decodable, Encodable};
+#[cfg(feature = "nightly")]
+use rustc_span::Symbol;
 
 use crate::AbiFromStrErr;
 
@@ -226,6 +228,13 @@ impl StableOrd for ExternAbi {
 #[cfg(feature = "nightly")]
 rustc_error_messages::into_diag_arg_using_display!(ExternAbi);
 
+#[cfg(feature = "nightly")]
+pub enum CVariadicStatus {
+    NotSupported,
+    Stable,
+    Unstable { feature: Symbol },
+}
+
 impl ExternAbi {
     /// An ABI "like Rust"
     ///
@@ -238,23 +247,33 @@ impl ExternAbi {
         matches!(self, Rust | RustCall | RustCold)
     }
 
-    pub fn supports_varargs(self) -> bool {
+    /// Returns whether the ABI supports C variadics. This only controls whether we allow *imports*
+    /// of such functions via `extern` blocks; there's a separate check during AST construction
+    /// guarding *definitions* of variadic functions.
+    #[cfg(feature = "nightly")]
+    pub fn supports_c_variadic(self) -> CVariadicStatus {
         // * C and Cdecl obviously support varargs.
         // * C can be based on Aapcs, SysV64 or Win64, so they must support varargs.
         // * EfiApi is based on Win64 or C, so it also supports it.
+        // * System automatically falls back to C when used with variadics, therefore supports it.
         //
         // * Stdcall does not, because it would be impossible for the callee to clean
         //   up the arguments. (callee doesn't know how many arguments are there)
         // * Same for Fastcall, Vectorcall and Thiscall.
         // * Other calling conventions are related to hardware or the compiler itself.
+        //
+        // All of the supported ones must have a test in `tests/codegen/cffi/c-variadic-ffi.rs`.
         match self {
             Self::C { .. }
             | Self::Cdecl { .. }
             | Self::Aapcs { .. }
             | Self::Win64 { .. }
             | Self::SysV64 { .. }
-            | Self::EfiApi => true,
-            _ => false,
+            | Self::EfiApi => CVariadicStatus::Stable,
+            Self::System { .. } => {
+                CVariadicStatus::Unstable { feature: rustc_span::sym::extern_system_varargs }
+            }
+            _ => CVariadicStatus::NotSupported,
         }
     }
 }
diff --git a/compiler/rustc_abi/src/lib.rs b/compiler/rustc_abi/src/lib.rs
index a1a0de5aaf8..369874521e5 100644
--- a/compiler/rustc_abi/src/lib.rs
+++ b/compiler/rustc_abi/src/lib.rs
@@ -63,6 +63,8 @@ mod tests;
 
 pub use callconv::{Heterogeneous, HomogeneousAggregate, Reg, RegKind};
 pub use canon_abi::{ArmCall, CanonAbi, InterruptKind, X86Call};
+#[cfg(feature = "nightly")]
+pub use extern_abi::CVariadicStatus;
 pub use extern_abi::{ExternAbi, all_names};
 #[cfg(feature = "nightly")]
 pub use layout::{FIRST_VARIANT, FieldIdx, Layout, TyAbiInterface, TyAndLayout, VariantIdx};
diff --git a/compiler/rustc_ast_passes/messages.ftl b/compiler/rustc_ast_passes/messages.ftl
index a95f1443968..e5f1fcdc4b4 100644
--- a/compiler/rustc_ast_passes/messages.ftl
+++ b/compiler/rustc_ast_passes/messages.ftl
@@ -57,7 +57,7 @@ ast_passes_auto_super_lifetime = auto traits cannot have super traits or lifetim
     .label = {ast_passes_auto_super_lifetime}
     .suggestion = remove the super traits or lifetime bounds
 
-ast_passes_bad_c_variadic = only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+ast_passes_bad_c_variadic = defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 
 ast_passes_body_in_extern = incorrect `{$kind}` inside `extern` block
     .cannot_have = cannot have a body
diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
index 9fe55216f93..6af4cfb0e56 100644
--- a/compiler/rustc_feature/src/accepted.rs
+++ b/compiler/rustc_feature/src/accepted.rs
@@ -203,6 +203,9 @@ declare_features! (
     (accepted, expr_fragment_specifier_2024, "1.83.0", Some(123742)),
     /// Allows arbitrary expressions in key-value attributes at parse time.
     (accepted, extended_key_value_attributes, "1.54.0", Some(78835)),
+    /// Allows using `aapcs`, `efiapi`, `sysv64` and `win64` as calling conventions
+    /// for functions with varargs.
+    (accepted, extended_varargs_abi_support, "CURRENT_RUSTC_VERSION", Some(100189)),
     /// Allows resolving absolute paths as paths from other crates.
     (accepted, extern_absolute_paths, "1.30.0", Some(44660)),
     /// Allows `extern crate foo as bar;`. This puts `bar` into extern prelude.
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 92b435b4b01..573e9aab055 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -492,9 +492,6 @@ declare_features! (
     (incomplete, explicit_tail_calls, "1.72.0", Some(112788)),
     /// Allows using `#[export_stable]` which indicates that an item is exportable.
     (incomplete, export_stable, "1.88.0", Some(139939)),
-    /// Allows using `aapcs`, `efiapi`, `sysv64` and `win64` as calling conventions
-    /// for functions with varargs.
-    (unstable, extended_varargs_abi_support, "1.65.0", Some(100189)),
     /// Allows using `system` as a calling convention with varargs.
     (unstable, extern_system_varargs, "1.86.0", Some(136946)),
     /// Allows defining `extern type`s.
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index eccb88a938f..08b344638dd 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -978,7 +978,7 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(),
                         tcx.ensure_ok().fn_sig(def_id);
                         let item = tcx.hir_foreign_item(item);
                         let hir::ForeignItemKind::Fn(sig, ..) = item.kind else { bug!() };
-                        require_c_abi_if_c_variadic(tcx, sig.decl, abi, item.span);
+                        check_c_variadic_abi(tcx, sig.decl, abi, item.span);
                     }
                     DefKind::Static { .. } => {
                         tcx.ensure_ok().codegen_fn_attrs(def_id);
diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index 2e4b151d4dc..b5c0ca4727c 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -98,7 +98,7 @@ use tracing::debug;
 
 use self::compare_impl_item::collect_return_position_impl_trait_in_trait_tys;
 use self::region::region_scope_tree;
-use crate::{errors, require_c_abi_if_c_variadic};
+use crate::{check_c_variadic_abi, errors};
 
 /// Adds query implementations to the [Providers] vtable, see [`rustc_middle::query`]
 pub(super) fn provide(providers: &mut Providers) {
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index c7b984d9b25..c5e079fe89a 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -52,11 +52,11 @@ use rustc_trait_selection::traits::{self, FulfillmentError};
 use tracing::{debug, instrument};
 
 use crate::check::check_abi;
+use crate::check_c_variadic_abi;
 use crate::errors::{AmbiguousLifetimeBound, BadReturnTypeNotation};
 use crate::hir_ty_lowering::errors::{GenericsArgsErrExtend, prohibit_assoc_item_constraint};
 use crate::hir_ty_lowering::generics::{check_generic_arg_count, lower_generic_args};
 use crate::middle::resolve_bound_vars as rbv;
-use crate::require_c_abi_if_c_variadic;
 
 /// A path segment that is semantically allowed to have generic arguments.
 #[derive(Debug)]
@@ -2412,7 +2412,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 Ty::new_tup_from_iter(tcx, fields.iter().map(|t| self.lower_ty(t)))
             }
             hir::TyKind::FnPtr(bf) => {
-                require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, hir_ty.span);
+                check_c_variadic_abi(tcx, bf.decl, bf.abi, hir_ty.span);
 
                 Ty::new_fn_ptr(
                     tcx,
diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index 44a5ceed469..2562ab7542a 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -90,7 +90,7 @@ mod outlives;
 mod variance;
 
 pub use errors::NoVariantNamed;
-use rustc_abi::ExternAbi;
+use rustc_abi::{CVariadicStatus, ExternAbi};
 use rustc_hir::def::DefKind;
 use rustc_hir::lints::DelayedLint;
 use rustc_hir::{self as hir};
@@ -99,7 +99,6 @@ use rustc_middle::mir::interpret::GlobalId;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{self, Const, Ty, TyCtxt};
 use rustc_session::parse::feature_err;
-use rustc_span::symbol::sym;
 use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::traits;
 
@@ -108,46 +107,34 @@ use crate::hir_ty_lowering::{FeedConstTy, HirTyLowerer};
 
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
 
-fn require_c_abi_if_c_variadic(
-    tcx: TyCtxt<'_>,
-    decl: &hir::FnDecl<'_>,
-    abi: ExternAbi,
-    span: Span,
-) {
-    // ABIs which can stably use varargs
-    if !decl.c_variadic || matches!(abi, ExternAbi::C { .. } | ExternAbi::Cdecl { .. }) {
+fn check_c_variadic_abi(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: ExternAbi, span: Span) {
+    if !decl.c_variadic {
+        // Not even a variadic function.
         return;
     }
 
-    // ABIs with feature-gated stability
-    let extended_abi_support = tcx.features().extended_varargs_abi_support();
-    let extern_system_varargs = tcx.features().extern_system_varargs();
-
-    // If the feature gate has been enabled, we can stop here
-    if extern_system_varargs && let ExternAbi::System { .. } = abi {
-        return;
-    };
-    if extended_abi_support && abi.supports_varargs() {
-        return;
-    };
-
-    // Looks like we need to pick an error to emit.
-    // Is there any feature which we could have enabled to make this work?
-    let unstable_explain =
-        format!("C-variadic functions with the {abi} calling convention are unstable");
-    match abi {
-        ExternAbi::System { .. } => {
-            feature_err(&tcx.sess, sym::extern_system_varargs, span, unstable_explain)
+    match abi.supports_c_variadic() {
+        CVariadicStatus::Stable => {}
+        CVariadicStatus::NotSupported => {
+            tcx.dcx()
+                .create_err(errors::VariadicFunctionCompatibleConvention {
+                    span,
+                    convention: &format!("{abi}"),
+                })
+                .emit();
         }
-        abi if abi.supports_varargs() => {
-            feature_err(&tcx.sess, sym::extended_varargs_abi_support, span, unstable_explain)
+        CVariadicStatus::Unstable { feature } => {
+            if !tcx.features().enabled(feature) {
+                feature_err(
+                    &tcx.sess,
+                    feature,
+                    span,
+                    format!("C-variadic functions with the {abi} calling convention are unstable"),
+                )
+                .emit();
+            }
         }
-        _ => tcx.dcx().create_err(errors::VariadicFunctionCompatibleConvention {
-            span,
-            convention: &format!("{abi}"),
-        }),
     }
-    .emit();
 }
 
 /// Adds query implementations to the [Providers] vtable, see [`rustc_middle::query`]
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 3771699c59f..7bdc6ff7882 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -290,7 +290,6 @@
 #![feature(doc_masked)]
 #![feature(doc_notable_trait)]
 #![feature(dropck_eyepatch)]
-#![feature(extended_varargs_abi_support)]
 #![feature(f16)]
 #![feature(f128)]
 #![feature(ffi_const)]
diff --git a/src/doc/unstable-book/src/language-features/extended-varargs-abi-support.md b/src/doc/unstable-book/src/language-features/extended-varargs-abi-support.md
deleted file mode 100644
index b20c30ec8f1..00000000000
--- a/src/doc/unstable-book/src/language-features/extended-varargs-abi-support.md
+++ /dev/null
@@ -1,10 +0,0 @@
-# `extended_varargs_abi_support`
-
-The tracking issue for this feature is: [#100189]
-
-[#100189]: https://github.com/rust-lang/rust/issues/100189
-
-------------------------
-
-This feature adds the possibility of using `sysv64`, `win64` or `efiapi` calling
-conventions on functions with varargs.
diff --git a/tests/codegen-llvm/cffi/c-variadic-ffi.rs b/tests/codegen-llvm/cffi/c-variadic-ffi.rs
index 3e99c9fb84e..1dee477e9ed 100644
--- a/tests/codegen-llvm/cffi/c-variadic-ffi.rs
+++ b/tests/codegen-llvm/cffi/c-variadic-ffi.rs
@@ -14,7 +14,7 @@
 //@[arm32] needs-llvm-components: arm
 #![crate_type = "lib"]
 #![feature(no_core)]
-#![feature(extended_varargs_abi_support, extern_system_varargs)]
+#![feature(extern_system_varargs)]
 #![no_core]
 
 extern crate minicore;
diff --git a/tests/ui/abi/unsupported-varargs-fnptr.rs b/tests/ui/abi/unsupported-varargs-fnptr.rs
index 1d23916d039..ac3913b3ef8 100644
--- a/tests/ui/abi/unsupported-varargs-fnptr.rs
+++ b/tests/ui/abi/unsupported-varargs-fnptr.rs
@@ -6,8 +6,6 @@
 // We have to use this flag to force ABI computation of an invalid ABI
 //@ compile-flags: -Clink-dead-code
 
-#![feature(extended_varargs_abi_support)]
-
 // sometimes fn ptrs with varargs make layout and ABI computation ICE
 // as found in https://github.com/rust-lang/rust/issues/142107
 
diff --git a/tests/ui/abi/unsupported-varargs-fnptr.stderr b/tests/ui/abi/unsupported-varargs-fnptr.stderr
index 238f2b31330..c05c55df82e 100644
--- a/tests/ui/abi/unsupported-varargs-fnptr.stderr
+++ b/tests/ui/abi/unsupported-varargs-fnptr.stderr
@@ -1,5 +1,5 @@
 error[E0570]: "aapcs" is not a supported ABI for the current target
-  --> $DIR/unsupported-varargs-fnptr.rs:14:20
+  --> $DIR/unsupported-varargs-fnptr.rs:12:20
    |
 LL | fn aapcs(f: extern "aapcs" fn(usize, ...)) {
    |                    ^^^^^^^
diff --git a/tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.rs b/tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.rs
deleted file mode 100644
index 1e0576b2186..00000000000
--- a/tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.rs
+++ /dev/null
@@ -1,16 +0,0 @@
-//@ only-x86_64
-
-fn efiapi(f: extern "efiapi" fn(usize, ...)) {
-    //~^ ERROR: unstable
-    f(22, 44);
-}
-fn sysv(f: extern "sysv64" fn(usize, ...)) {
-    //~^ ERROR: unstable
-    f(22, 44);
-}
-fn win(f: extern "win64" fn(usize, ...)) {
-    //~^ ERROR: unstable
-    f(22, 44);
-}
-
-fn main() {}
diff --git a/tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.stderr b/tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.stderr
deleted file mode 100644
index 7ef54b639ad..00000000000
--- a/tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.stderr
+++ /dev/null
@@ -1,33 +0,0 @@
-error[E0658]: C-variadic functions with the "efiapi" calling convention are unstable
-  --> $DIR/feature-gate-extended_varargs_abi_support.rs:3:14
-   |
-LL | fn efiapi(f: extern "efiapi" fn(usize, ...)) {
-   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #100189 <https://github.com/rust-lang/rust/issues/100189> for more information
-   = help: add `#![feature(extended_varargs_abi_support)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error[E0658]: C-variadic functions with the "sysv64" calling convention are unstable
-  --> $DIR/feature-gate-extended_varargs_abi_support.rs:7:12
-   |
-LL | fn sysv(f: extern "sysv64" fn(usize, ...)) {
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #100189 <https://github.com/rust-lang/rust/issues/100189> for more information
-   = help: add `#![feature(extended_varargs_abi_support)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error[E0658]: C-variadic functions with the "win64" calling convention are unstable
-  --> $DIR/feature-gate-extended_varargs_abi_support.rs:11:11
-   |
-LL | fn win(f: extern "win64" fn(usize, ...)) {
-   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #100189 <https://github.com/rust-lang/rust/issues/100189> for more information
-   = help: add `#![feature(extended_varargs_abi_support)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error: aborting due to 3 previous errors
-
-For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/c-variadic/issue-86053-1.rs b/tests/ui/c-variadic/issue-86053-1.rs
index 8eeb99a4cc1..537d0263adf 100644
--- a/tests/ui/c-variadic/issue-86053-1.rs
+++ b/tests/ui/c-variadic/issue-86053-1.rs
@@ -13,6 +13,6 @@ fn ordering4 < 'a , 'b     > ( a :            ,   self , self ,   self ,
     //~| ERROR unexpected `self` parameter in function
     //~| ERROR unexpected `self` parameter in function
     //~| ERROR `...` must be the last argument of a C-variadic function
-    //~| ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~| ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     //~| ERROR cannot find type `F` in this scope
 }
diff --git a/tests/ui/c-variadic/issue-86053-1.stderr b/tests/ui/c-variadic/issue-86053-1.stderr
index 3bf8b7ba5d8..675dfd335c4 100644
--- a/tests/ui/c-variadic/issue-86053-1.stderr
+++ b/tests/ui/c-variadic/issue-86053-1.stderr
@@ -46,7 +46,7 @@ error: `...` must be the last argument of a C-variadic function
 LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
    |            ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/issue-86053-1.rs:11:12
    |
 LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
diff --git a/tests/ui/c-variadic/same-program-multiple-abis-arm.rs b/tests/ui/c-variadic/same-program-multiple-abis-arm.rs
index 1b0bdecabfb..1445bbb47bb 100644
--- a/tests/ui/c-variadic/same-program-multiple-abis-arm.rs
+++ b/tests/ui/c-variadic/same-program-multiple-abis-arm.rs
@@ -1,4 +1,3 @@
-#![feature(extended_varargs_abi_support)]
 //@ run-pass
 //@ only-arm
 //@ ignore-thumb (this test uses arm assembly)
diff --git a/tests/ui/c-variadic/same-program-multiple-abis-x86_64.rs b/tests/ui/c-variadic/same-program-multiple-abis-x86_64.rs
index b21accb999e..aff8ab613c4 100644
--- a/tests/ui/c-variadic/same-program-multiple-abis-x86_64.rs
+++ b/tests/ui/c-variadic/same-program-multiple-abis-x86_64.rs
@@ -1,4 +1,3 @@
-#![feature(extended_varargs_abi_support)]
 //@ run-pass
 //@ only-x86_64
 
diff --git a/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/generics.rs b/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/generics.rs
index 800dd580af2..ad4fca8252d 100644
--- a/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/generics.rs
+++ b/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/generics.rs
@@ -71,6 +71,6 @@ extern "cmse-nonsecure-entry" fn wrapped_trait_object(
 }
 
 extern "cmse-nonsecure-entry" fn c_variadic(_: u32, _: ...) {
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     //~| ERROR requires `va_list` lang_item
 }
diff --git a/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/generics.stderr b/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/generics.stderr
index f0190671b5a..7aeb6969feb 100644
--- a/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/generics.stderr
+++ b/tests/ui/cmse-nonsecure/cmse-nonsecure-entry/generics.stderr
@@ -1,4 +1,4 @@
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/generics.rs:73:53
    |
 LL | extern "cmse-nonsecure-entry" fn c_variadic(_: u32, _: ...) {
diff --git a/tests/ui/feature-gates/feature-gate-c_variadic.rs b/tests/ui/feature-gates/feature-gate-c_variadic.rs
index f189f02a26d..45c68842093 100644
--- a/tests/ui/feature-gates/feature-gate-c_variadic.rs
+++ b/tests/ui/feature-gates/feature-gate-c_variadic.rs
@@ -2,3 +2,9 @@
 
 pub unsafe extern "C" fn test(_: i32, ap: ...) { }
 //~^ ERROR C-variadic functions are unstable
+
+trait Trait {
+    unsafe extern "C" fn trait_test(_: i32, ap: ...) { }
+    //~^ ERROR C-variadic functions are unstable
+    //~| ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
+}
diff --git a/tests/ui/feature-gates/feature-gate-c_variadic.stderr b/tests/ui/feature-gates/feature-gate-c_variadic.stderr
index 1b6a8c92af5..e30a2f1ede3 100644
--- a/tests/ui/feature-gates/feature-gate-c_variadic.stderr
+++ b/tests/ui/feature-gates/feature-gate-c_variadic.stderr
@@ -1,3 +1,9 @@
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
+  --> $DIR/feature-gate-c_variadic.rs:7:45
+   |
+LL |     unsafe extern "C" fn trait_test(_: i32, ap: ...) { }
+   |                                             ^^^^^^^
+
 error[E0658]: C-variadic functions are unstable
   --> $DIR/feature-gate-c_variadic.rs:3:1
    |
@@ -8,6 +14,16 @@ LL | pub unsafe extern "C" fn test(_: i32, ap: ...) { }
    = help: add `#![feature(c_variadic)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 1 previous error
+error[E0658]: C-variadic functions are unstable
+  --> $DIR/feature-gate-c_variadic.rs:7:5
+   |
+LL |     unsafe extern "C" fn trait_test(_: i32, ap: ...) { }
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #44930 <https://github.com/rust-lang/rust/issues/44930> for more information
+   = help: add `#![feature(c_variadic)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/mir/issue-83499-input-output-iteration-ice.rs b/tests/ui/mir/issue-83499-input-output-iteration-ice.rs
index 78e5c961802..9277994d9b3 100644
--- a/tests/ui/mir/issue-83499-input-output-iteration-ice.rs
+++ b/tests/ui/mir/issue-83499-input-output-iteration-ice.rs
@@ -5,6 +5,6 @@
 fn main() {}
 
 fn foo(_: Bar, ...) -> impl {}
-//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 //~| ERROR cannot find type `Bar` in this scope
 //~| ERROR at least one trait must be specified
diff --git a/tests/ui/mir/issue-83499-input-output-iteration-ice.stderr b/tests/ui/mir/issue-83499-input-output-iteration-ice.stderr
index 80a8a94aea4..4a1aa49eb6e 100644
--- a/tests/ui/mir/issue-83499-input-output-iteration-ice.stderr
+++ b/tests/ui/mir/issue-83499-input-output-iteration-ice.stderr
@@ -1,4 +1,4 @@
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/issue-83499-input-output-iteration-ice.rs:7:16
    |
 LL | fn foo(_: Bar, ...) -> impl {}
diff --git a/tests/ui/parser/variadic-ffi-semantic-restrictions.rs b/tests/ui/parser/variadic-ffi-semantic-restrictions.rs
index 1cd6d13d56b..e7a0248cffa 100644
--- a/tests/ui/parser/variadic-ffi-semantic-restrictions.rs
+++ b/tests/ui/parser/variadic-ffi-semantic-restrictions.rs
@@ -4,29 +4,29 @@
 fn main() {}
 
 fn f1_1(x: isize, ...) {}
-//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 
 fn f1_2(...) {}
-//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 
 extern "C" fn f2_1(x: isize, ...) {}
-//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 
 extern "C" fn f2_2(...) {}
-//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 
 extern "C" fn f2_3(..., x: isize) {}
-//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 //~| ERROR `...` must be the last argument of a C-variadic function
 
 extern "C" fn f3_1(x: isize, ...) {}
-//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 
 extern "C" fn f3_2(...) {}
-//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 
 extern "C" fn f3_3(..., x: isize) {}
-//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 //~| ERROR `...` must be the last argument of a C-variadic function
 
 const unsafe extern "C" fn f4_1(x: isize, ...) {}
@@ -35,12 +35,12 @@ const unsafe extern "C" fn f4_1(x: isize, ...) {}
 
 const extern "C" fn f4_2(x: isize, ...) {}
 //~^ ERROR functions cannot be both `const` and C-variadic
-//~| ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~| ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 //~| ERROR destructor of `VaListImpl<'_>` cannot be evaluated at compile-time
 
 const extern "C" fn f4_3(..., x: isize, ...) {}
 //~^ ERROR functions cannot be both `const` and C-variadic
-//~| ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+//~| ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
 //~| ERROR `...` must be the last argument of a C-variadic function
 
 extern "C" {
@@ -52,34 +52,34 @@ struct X;
 
 impl X {
     fn i_f1(x: isize, ...) {}
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     fn i_f2(...) {}
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     fn i_f3(..., x: isize, ...) {}
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     //~| ERROR `...` must be the last argument of a C-variadic function
     fn i_f4(..., x: isize, ...) {}
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     //~| ERROR `...` must be the last argument of a C-variadic function
     const fn i_f5(x: isize, ...) {}
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     //~| ERROR functions cannot be both `const` and C-variadic
     //~| ERROR destructor of `VaListImpl<'_>` cannot be evaluated at compile-time
 }
 
 trait T {
     fn t_f1(x: isize, ...) {}
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     fn t_f2(x: isize, ...);
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     fn t_f3(...) {}
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     fn t_f4(...);
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     fn t_f5(..., x: isize) {}
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     //~| ERROR `...` must be the last argument of a C-variadic function
     fn t_f6(..., x: isize);
-    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+    //~^ ERROR defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
     //~| ERROR `...` must be the last argument of a C-variadic function
 }
diff --git a/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr b/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr
index b740cef0200..5379045967a 100644
--- a/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr
+++ b/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr
@@ -1,22 +1,22 @@
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:6:19
    |
 LL | fn f1_1(x: isize, ...) {}
    |                   ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:9:9
    |
 LL | fn f1_2(...) {}
    |         ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:12:30
    |
 LL | extern "C" fn f2_1(x: isize, ...) {}
    |                              ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:15:20
    |
 LL | extern "C" fn f2_2(...) {}
@@ -28,19 +28,19 @@ error: `...` must be the last argument of a C-variadic function
 LL | extern "C" fn f2_3(..., x: isize) {}
    |                    ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:18:20
    |
 LL | extern "C" fn f2_3(..., x: isize) {}
    |                    ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:22:30
    |
 LL | extern "C" fn f3_1(x: isize, ...) {}
    |                              ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:25:20
    |
 LL | extern "C" fn f3_2(...) {}
@@ -52,7 +52,7 @@ error: `...` must be the last argument of a C-variadic function
 LL | extern "C" fn f3_3(..., x: isize) {}
    |                    ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:28:20
    |
 LL | extern "C" fn f3_3(..., x: isize) {}
@@ -70,7 +70,7 @@ error: functions cannot be both `const` and C-variadic
 LL | const extern "C" fn f4_2(x: isize, ...) {}
    | ^^^^^ `const` because of this      ^^^ C-variadic because of this
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:36:36
    |
 LL | const extern "C" fn f4_2(x: isize, ...) {}
@@ -91,7 +91,7 @@ LL | const extern "C" fn f4_3(..., x: isize, ...) {}
    | |                        C-variadic because of this
    | `const` because of this
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:41:26
    |
 LL | const extern "C" fn f4_3(..., x: isize, ...) {}
@@ -103,13 +103,13 @@ error: `...` must be the last argument of a C-variadic function
 LL |     fn e_f2(..., x: isize);
    |             ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:54:23
    |
 LL |     fn i_f1(x: isize, ...) {}
    |                       ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:56:13
    |
 LL |     fn i_f2(...) {}
@@ -121,7 +121,7 @@ error: `...` must be the last argument of a C-variadic function
 LL |     fn i_f3(..., x: isize, ...) {}
    |             ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:58:13
    |
 LL |     fn i_f3(..., x: isize, ...) {}
@@ -133,7 +133,7 @@ error: `...` must be the last argument of a C-variadic function
 LL |     fn i_f4(..., x: isize, ...) {}
    |             ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:61:13
    |
 LL |     fn i_f4(..., x: isize, ...) {}
@@ -147,31 +147,31 @@ LL |     const fn i_f5(x: isize, ...) {}
    |     |
    |     `const` because of this
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:64:29
    |
 LL |     const fn i_f5(x: isize, ...) {}
    |                             ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:71:23
    |
 LL |     fn t_f1(x: isize, ...) {}
    |                       ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:73:23
    |
 LL |     fn t_f2(x: isize, ...);
    |                       ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:75:13
    |
 LL |     fn t_f3(...) {}
    |             ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:77:13
    |
 LL |     fn t_f4(...);
@@ -183,7 +183,7 @@ error: `...` must be the last argument of a C-variadic function
 LL |     fn t_f5(..., x: isize) {}
    |             ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:79:13
    |
 LL |     fn t_f5(..., x: isize) {}
@@ -195,7 +195,7 @@ error: `...` must be the last argument of a C-variadic function
 LL |     fn t_f6(..., x: isize);
    |             ^^^
 
-error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
+error: defining functions with C-variadic arguments is only allowed for free functions with the "C" or "C-unwind" calling convention
   --> $DIR/variadic-ffi-semantic-restrictions.rs:82:13
    |
 LL |     fn t_f6(..., x: isize);