Revert "Stabilize `extended_varargs_abi_support`"

This reverts commit 685f189b4307435b83d625fea397ef36dff4e955.

16 files changed, 124 insertions, 12 deletions

diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
index 217a7aeb2d7..95b711c894e 100644
--- a/compiler/rustc_feature/src/accepted.rs
+++ b/compiler/rustc_feature/src/accepted.rs
@@ -197,9 +197,6 @@ 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 `efiapi`, `aapcs`, `sysv64` and `win64` as calling
-    /// convention for functions with varargs.
-    (accepted, extended_varargs_abi_support, "1.85.0", 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 4131812fc3b..d6915d21b29 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -479,6 +479,9 @@ declare_features! (
     (unstable, exhaustive_patterns, "1.13.0", Some(51085)),
     /// Allows explicit tail calls via `become` expression.
     (incomplete, explicit_tail_calls, "1.72.0", Some(112788)),
+    /// Allows using `efiapi`, `sysv64` and `win64` as calling convention
+    /// for functions with varargs.
+    (unstable, extended_varargs_abi_support, "1.65.0", Some(100189)),
     /// Allows defining `extern type`s.
     (unstable, extern_types, "1.23.0", Some(43467)),
     /// Allow using 128-bit (quad precision) floating point numbers.
diff --git a/compiler/rustc_hir_analysis/messages.ftl b/compiler/rustc_hir_analysis/messages.ftl
index 0c3ed9b5c60..9a87ea87e50 100644
--- a/compiler/rustc_hir_analysis/messages.ftl
+++ b/compiler/rustc_hir_analysis/messages.ftl
@@ -602,7 +602,7 @@ hir_analysis_value_of_associated_struct_already_specified =
     .label = re-bound here
     .previous_bound_label = `{$item_name}` bound here first
 
-hir_analysis_variadic_function_compatible_convention = C-variadic function must have a compatible calling convention, like `C`, `cdecl`, `system`, `aapcs`, `win64`, `sysv64` or `efiapi`
+hir_analysis_variadic_function_compatible_convention = C-variadic function must have a compatible calling convention, like {$conventions}
     .label = C-variadic function must have a compatible calling convention
 
 hir_analysis_variances_of = {$variances}
diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index 00ba1741ed7..63f2a8adbde 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -688,10 +688,11 @@ pub(crate) struct MainFunctionGenericParameters {
 
 #[derive(Diagnostic)]
 #[diag(hir_analysis_variadic_function_compatible_convention, code = E0045)]
-pub(crate) struct VariadicFunctionCompatibleConvention {
+pub(crate) struct VariadicFunctionCompatibleConvention<'a> {
     #[primary_span]
     #[label]
     pub span: Span,
+    pub conventions: &'a str,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index 87fd4de26a5..b4a7b8083ed 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -100,6 +100,8 @@ use rustc_middle::middle;
 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::Span;
 use rustc_trait_selection::traits;
 
@@ -113,9 +115,34 @@ fn require_c_abi_if_c_variadic(
     abi: ExternAbi,
     span: Span,
 ) {
-    if decl.c_variadic && !abi.supports_varargs() {
-        tcx.dcx().emit_err(errors::VariadicFunctionCompatibleConvention { span });
+    const CONVENTIONS_UNSTABLE: &str =
+        "`C`, `cdecl`, `system`, `aapcs`, `win64`, `sysv64` or `efiapi`";
+    const CONVENTIONS_STABLE: &str = "`C` or `cdecl`";
+    const UNSTABLE_EXPLAIN: &str =
+        "using calling conventions other than `C` or `cdecl` for varargs functions is unstable";
+
+    if !decl.c_variadic || matches!(abi, ExternAbi::C { .. } | ExternAbi::Cdecl { .. }) {
+        return;
     }
+
+    let extended_abi_support = tcx.features().extended_varargs_abi_support();
+    let conventions = match (extended_abi_support, abi.supports_varargs()) {
+        // User enabled additional ABI support for varargs and function ABI matches those ones.
+        (true, true) => return,
+
+        // Using this ABI would be ok, if the feature for additional ABI support was enabled.
+        // Return CONVENTIONS_STABLE, because we want the other error to look the same.
+        (false, true) => {
+            feature_err(&tcx.sess, sym::extended_varargs_abi_support, span, UNSTABLE_EXPLAIN)
+                .emit();
+            CONVENTIONS_STABLE
+        }
+
+        (false, false) => CONVENTIONS_STABLE,
+        (true, false) => CONVENTIONS_UNSTABLE,
+    };
+
+    tcx.dcx().emit_err(errors::VariadicFunctionCompatibleConvention { span, conventions });
 }
 
 pub fn provide(providers: &mut Providers) {
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 2f8f5c5c581..a193ff5b8a5 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -289,6 +289,7 @@
 #![feature(doc_masked)]
 #![feature(doc_notable_trait)]
 #![feature(dropck_eyepatch)]
+#![feature(extended_varargs_abi_support)]
 #![feature(f128)]
 #![feature(f16)]
 #![feature(formatting_options)]
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
new file mode 100644
index 00000000000..b20c30ec8f1
--- /dev/null
+++ b/src/doc/unstable-book/src/language-features/extended-varargs-abi-support.md
@@ -0,0 +1,10 @@
+# `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/ui/c-variadic/feature-gate-extended_varargs_abi_support.rs b/tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.rs
new file mode 100644
index 00000000000..d47a8e085fd
--- /dev/null
+++ b/tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.rs
@@ -0,0 +1,19 @@
+//@ only-x86_64
+
+fn efiapi(f: extern "efiapi" fn(usize, ...)) {
+    //~^ ERROR: C-variadic function must have a compatible calling convention, like `C` or `cdecl`
+    //~^^ ERROR: using calling conventions other than `C` or `cdecl` for varargs functions is unstable
+    f(22, 44);
+}
+fn sysv(f: extern "sysv64" fn(usize, ...)) {
+    //~^ ERROR: C-variadic function must have a compatible calling convention, like `C` or `cdecl`
+    //~^^ ERROR: using calling conventions other than `C` or `cdecl` for varargs functions is unstable
+    f(22, 44);
+}
+fn win(f: extern "win64" fn(usize, ...)) {
+    //~^ ERROR: C-variadic function must have a compatible calling convention, like `C` or `cdecl`
+    //~^^ ERROR: using calling conventions other than `C` or `cdecl` for varargs functions is 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
new file mode 100644
index 00000000000..41be3784245
--- /dev/null
+++ b/tests/ui/c-variadic/feature-gate-extended_varargs_abi_support.stderr
@@ -0,0 +1,52 @@
+error[E0658]: using calling conventions other than `C` or `cdecl` for varargs functions is 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[E0045]: C-variadic function must have a compatible calling convention, like `C` or `cdecl`
+  --> $DIR/feature-gate-extended_varargs_abi_support.rs:3:14
+   |
+LL | fn efiapi(f: extern "efiapi" fn(usize, ...)) {
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ C-variadic function must have a compatible calling convention
+
+error[E0658]: using calling conventions other than `C` or `cdecl` for varargs functions is unstable
+  --> $DIR/feature-gate-extended_varargs_abi_support.rs:8:12
+   |
+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[E0045]: C-variadic function must have a compatible calling convention, like `C` or `cdecl`
+  --> $DIR/feature-gate-extended_varargs_abi_support.rs:8:12
+   |
+LL | fn sysv(f: extern "sysv64" fn(usize, ...)) {
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ C-variadic function must have a compatible calling convention
+
+error[E0658]: using calling conventions other than `C` or `cdecl` for varargs functions is unstable
+  --> $DIR/feature-gate-extended_varargs_abi_support.rs:13:11
+   |
+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[E0045]: C-variadic function must have a compatible calling convention, like `C` or `cdecl`
+  --> $DIR/feature-gate-extended_varargs_abi_support.rs:13:11
+   |
+LL | fn win(f: extern "win64" fn(usize, ...)) {
+   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ C-variadic function must have a compatible calling convention
+
+error: aborting due to 6 previous errors
+
+Some errors have detailed explanations: E0045, E0658.
+For more information about an error, try `rustc --explain E0045`.
diff --git a/tests/ui/c-variadic/variadic-ffi-1.stderr b/tests/ui/c-variadic/variadic-ffi-1.stderr
index 7a54d043356..194710dfd21 100644
--- a/tests/ui/c-variadic/variadic-ffi-1.stderr
+++ b/tests/ui/c-variadic/variadic-ffi-1.stderr
@@ -1,4 +1,4 @@
-error[E0045]: C-variadic function must have a compatible calling convention, like `C`, `cdecl`, `system`, `aapcs`, `win64`, `sysv64` or `efiapi`
+error[E0045]: C-variadic function must have a compatible calling convention, like `C` or `cdecl`
   --> $DIR/variadic-ffi-1.rs:9:5
    |
 LL |     fn printf(_: *const u8, ...);
diff --git a/tests/ui/c-variadic/variadic-ffi-2-arm.rs b/tests/ui/c-variadic/variadic-ffi-2-arm.rs
index 82f9df5053c..3b0a71007a0 100644
--- a/tests/ui/c-variadic/variadic-ffi-2-arm.rs
+++ b/tests/ui/c-variadic/variadic-ffi-2-arm.rs
@@ -1,5 +1,6 @@
 //@ only-arm
 //@ build-pass
+#![feature(extended_varargs_abi_support)]
 
 fn aapcs(f: extern "aapcs" fn(usize, ...)) {
     f(22, 44);
diff --git a/tests/ui/c-variadic/variadic-ffi-2.rs b/tests/ui/c-variadic/variadic-ffi-2.rs
index 17a1065279f..bafb7e2b20c 100644
--- a/tests/ui/c-variadic/variadic-ffi-2.rs
+++ b/tests/ui/c-variadic/variadic-ffi-2.rs
@@ -1,4 +1,5 @@
 //@ ignore-arm stdcall isn't supported
+#![feature(extended_varargs_abi_support)]
 
 #[allow(unsupported_fn_ptr_calling_conventions)]
 fn baz(f: extern "stdcall" fn(usize, ...)) {
diff --git a/tests/ui/c-variadic/variadic-ffi-2.stderr b/tests/ui/c-variadic/variadic-ffi-2.stderr
index fbf273b1f1d..e52de93a926 100644
--- a/tests/ui/c-variadic/variadic-ffi-2.stderr
+++ b/tests/ui/c-variadic/variadic-ffi-2.stderr
@@ -1,5 +1,5 @@
 error[E0045]: C-variadic function must have a compatible calling convention, like `C`, `cdecl`, `system`, `aapcs`, `win64`, `sysv64` or `efiapi`
-  --> $DIR/variadic-ffi-2.rs:4:11
+  --> $DIR/variadic-ffi-2.rs:5:11
    |
 LL | fn baz(f: extern "stdcall" fn(usize, ...)) {
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ C-variadic function must have a compatible calling convention
diff --git a/tests/ui/cmse-nonsecure/cmse-nonsecure-call/generics.rs b/tests/ui/cmse-nonsecure/cmse-nonsecure-call/generics.rs
index da1327dace5..9e0ffa75c22 100644
--- a/tests/ui/cmse-nonsecure/cmse-nonsecure-call/generics.rs
+++ b/tests/ui/cmse-nonsecure/cmse-nonsecure-call/generics.rs
@@ -39,4 +39,4 @@ type WithTransparentTraitObject =
 //~^ ERROR return value of `"C-cmse-nonsecure-call"` function too large to pass via registers [E0798]
 
 type WithVarArgs = extern "C-cmse-nonsecure-call" fn(u32, ...);
-//~^ ERROR C-variadic function must have a compatible calling convention, like `C`, `cdecl`, `system`, `aapcs`, `win64`, `sysv64` or `efiapi` [E0045]
+//~^ ERROR C-variadic function must have a compatible calling convention, like `C` or `cdecl` [E0045]
diff --git a/tests/ui/cmse-nonsecure/cmse-nonsecure-call/generics.stderr b/tests/ui/cmse-nonsecure/cmse-nonsecure-call/generics.stderr
index f20e67e3d94..7cb8e135ea3 100644
--- a/tests/ui/cmse-nonsecure/cmse-nonsecure-call/generics.stderr
+++ b/tests/ui/cmse-nonsecure/cmse-nonsecure-call/generics.stderr
@@ -68,7 +68,7 @@ LL |     extern "C-cmse-nonsecure-call" fn(WrapperTransparent) -> WrapperTranspa
    = note: functions with the `"C-cmse-nonsecure-call"` ABI must pass their result via the available return registers
    = note: the result must either be a (transparently wrapped) i64, u64 or f64, or be at most 4 bytes in size
 
-error[E0045]: C-variadic function must have a compatible calling convention, like `C`, `cdecl`, `system`, `aapcs`, `win64`, `sysv64` or `efiapi`
+error[E0045]: C-variadic function must have a compatible calling convention, like `C` or `cdecl`
   --> $DIR/generics.rs:41:20
    |
 LL | type WithVarArgs = extern "C-cmse-nonsecure-call" fn(u32, ...);
diff --git a/tests/ui/error-codes/E0045.stderr b/tests/ui/error-codes/E0045.stderr
index b8ee31a4049..25b2f2654da 100644
--- a/tests/ui/error-codes/E0045.stderr
+++ b/tests/ui/error-codes/E0045.stderr
@@ -1,4 +1,4 @@
-error[E0045]: C-variadic function must have a compatible calling convention, like `C`, `cdecl`, `system`, `aapcs`, `win64`, `sysv64` or `efiapi`
+error[E0045]: C-variadic function must have a compatible calling convention, like `C` or `cdecl`
   --> $DIR/E0045.rs:1:17
    |
 LL | extern "Rust" { fn foo(x: u8, ...); }