Auto merge of #129753 - folkertdev:stabilize-const-extern-fn, r=RalfJung

stabilize `const_extern_fn`

closes https://github.com/rust-lang/rust/issues/64926

tracking issue: https://github.com/rust-lang/rust/issues/64926
reference PR: https://github.com/rust-lang/reference/pull/1596

## Stabilizaton Report

### Summary

Using `const extern "Rust"` and `const extern "C"` was already stabilized (since version 1.62.0, see https://github.com/rust-lang/rust/pull/95346). This PR stabilizes the other calling conventions: it is now possible to write  `const unsafe extern "calling-convention" fn` and `const extern "calling-convention" fn` for any supported calling convention:

```rust
const extern "C-unwind" fn foo1(val: u8) -> u8 { val + 1}
const extern "stdcall" fn foo2(val: u8) -> u8 { val + 1}
const unsafe extern "C-unwind" fn bar1(val: bool) -> bool { !val }
const unsafe extern "stdcall" fn bar2(val: bool) -> bool { !val }
```

This can be used to const-ify an `extern fn`, or conversely, to make a `const fn` callable from external code.

r? T-lang

cc `@RalfJung`

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -75,22 +75,9 @@ struct PostExpansionVisitor<'a> {
 
 impl<'a> PostExpansionVisitor<'a> {
     #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
-    fn check_abi(&self, abi: ast::StrLit, constness: ast::Const) {
+    fn check_abi(&self, abi: ast::StrLit) {
         let ast::StrLit { symbol_unescaped, span, .. } = abi;
 
-        if let ast::Const::Yes(_) = constness {
-            match symbol_unescaped {
-                // Stable
-                sym::Rust | sym::C => {}
-                abi => gate!(
-                    &self,
-                    const_extern_fn,
-                    span,
-                    format!("`{}` as a `const fn` ABI is unstable", abi)
-                ),
-            }
-        }
-
         match abi::is_enabled(self.features, span, symbol_unescaped.as_str()) {
             Ok(()) => (),
             Err(abi::AbiDisabled::Unstable { feature, explain }) => {
@@ -110,9 +97,9 @@ impl<'a> PostExpansionVisitor<'a> {
         }
     }
 
-    fn check_extern(&self, ext: ast::Extern, constness: ast::Const) {
+    fn check_extern(&self, ext: ast::Extern) {
         if let ast::Extern::Explicit(abi, _) = ext {
-            self.check_abi(abi, constness);
+            self.check_abi(abi);
         }
     }
 
@@ -239,7 +226,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         match &i.kind {
             ast::ItemKind::ForeignMod(foreign_module) => {
                 if let Some(abi) = foreign_module.abi {
-                    self.check_abi(abi, ast::Const::No);
+                    self.check_abi(abi);
                 }
             }
 
@@ -341,7 +328,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         match &ty.kind {
             ast::TyKind::BareFn(bare_fn_ty) => {
                 // Function pointers cannot be `const`
-                self.check_extern(bare_fn_ty.ext, ast::Const::No);
+                self.check_extern(bare_fn_ty.ext);
                 self.check_late_bound_lifetime_defs(&bare_fn_ty.generic_params);
             }
             ast::TyKind::Never => {
@@ -446,7 +433,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
         if let Some(header) = fn_kind.header() {
             // Stability of const fn methods are covered in `visit_assoc_item` below.
-            self.check_extern(header.ext, header.constness);
+            self.check_extern(header.ext);
         }
 
         if let FnKind::Closure(ast::ClosureBinder::For { generic_params, .. }, ..) = fn_kind {

compiler/rustc_feature/src/accepted.rs

@@ -115,6 +115,8 @@ declare_features! (
     (accepted, conservative_impl_trait, "1.26.0", Some(34511)),
     /// Allows calling constructor functions in `const fn`.
     (accepted, const_constructor, "1.40.0", Some(61456)),
+    /// Allows the definition of `const extern fn` and `const unsafe extern fn`.
+    (accepted, const_extern_fn, "CURRENT_RUSTC_VERSION", Some(64926)),
     /// Allows basic arithmetic on floating point types in a `const fn`.
     (accepted, const_fn_floating_point_arithmetic, "1.82.0", Some(57241)),
     /// Allows using and casting function pointers in a `const fn`.

compiler/rustc_feature/src/unstable.rs

@@ -401,8 +401,6 @@ declare_features! (
     (unstable, const_async_blocks, "1.53.0", Some(85368)),
     /// Allows `const || {}` closures in const contexts.
     (incomplete, const_closures, "1.68.0", Some(106003)),
-    /// Allows the definition of `const extern fn` and `const unsafe extern fn`.
-    (unstable, const_extern_fn, "1.40.0", Some(64926)),
     /// Allows `for _ in _` loops in const contexts.
     (unstable, const_for, "1.56.0", Some(87575)),
     /// Allows using `&mut` in constant functions.

compiler/rustc_parse/src/parser/ty.rs

@@ -607,9 +607,6 @@ impl<'a> Parser<'a> {
         let decl = self.parse_fn_decl(|_| false, AllowPlus::No, recover_return_sign)?;
         let whole_span = lo.to(self.prev_token.span);
         if let ast::Const::Yes(span) = constness {
-            // If we ever start to allow `const fn()`, then update
-            // feature gating for `#![feature(const_extern_fn)]` to
-            // cover it.
             self.dcx().emit_err(FnPointerCannotBeConst { span: whole_span, qualifier: span });
         }
         if let Some(ast::CoroutineKind::Async { span, .. }) = coroutine_kind {

src/tools/clippy/clippy_config/src/msrvs.rs

@@ -17,6 +17,7 @@ macro_rules! msrv_aliases {
 
 // names may refer to stabilized feature flags or library items
 msrv_aliases! {
+    1,83,0 { CONST_EXTERN_FN }
     1,83,0 { CONST_FLOAT_BITS_CONV }
     1,81,0 { LINT_REASONS_STABILIZATION }
     1,80,0 { BOX_INTO_ITER}
@@ -27,7 +28,7 @@ msrv_aliases! {
     1,68,0 { PATH_MAIN_SEPARATOR_STR }
     1,65,0 { LET_ELSE, POINTER_CAST_CONSTNESS }
     1,63,0 { CLONE_INTO }
-    1,62,0 { BOOL_THEN_SOME, DEFAULT_ENUM_ATTRIBUTE, CONST_EXTERN_FN }
+    1,62,0 { BOOL_THEN_SOME, DEFAULT_ENUM_ATTRIBUTE, CONST_EXTERN_C_FN }
     1,59,0 { THREAD_LOCAL_CONST_INIT }
     1,58,0 { FORMAT_ARGS_CAPTURE, PATTERN_TRAIT_CHAR_ARRAY, CONST_RAW_PTR_DEREF }
     1,56,0 { CONST_FN_UNION }

src/tools/clippy/clippy_lints/src/missing_const_for_fn.rs

@@ -119,9 +119,7 @@ impl<'tcx> LateLintPass<'tcx> for MissingConstForFn {
                     .iter()
                     .any(|param| matches!(param.kind, GenericParamKind::Const { .. }));
 
-                if already_const(header)
+                if already_const(header) || has_const_generic_params || !could_be_const_with_abi(&self.msrv, header.abi)
-                    || has_const_generic_params
-                    || !could_be_const_with_abi(cx, &self.msrv, header.abi)
                 {
                     return;
                 }
@@ -183,13 +181,13 @@ fn already_const(header: hir::FnHeader) -> bool {
     header.constness == Constness::Const
 }
 
-fn could_be_const_with_abi(cx: &LateContext<'_>, msrv: &Msrv, abi: Abi) -> bool {
+fn could_be_const_with_abi(msrv: &Msrv, abi: Abi) -> bool {
     match abi {
         Abi::Rust => true,
         // `const extern "C"` was stabilized after 1.62.0
-        Abi::C { unwind: false } => msrv.meets(msrvs::CONST_EXTERN_FN),
+        Abi::C { unwind: false } => msrv.meets(msrvs::CONST_EXTERN_C_FN),
         // Rest ABIs are still unstable and need the `const_extern_fn` feature enabled.
-        _ => cx.tcx.features().const_extern_fn,
+        _ => msrv.meets(msrvs::CONST_EXTERN_FN),
     }
 }
 

src/tools/clippy/tests/ui/missing_const_for_fn/cant_be_const.rs

@@ -186,12 +186,6 @@ mod msrv {
     extern "C" fn c() {}
 }
 
-mod with_extern {
-    extern "C-unwind" fn c_unwind() {}
-    extern "system" fn system() {}
-    extern "system-unwind" fn system_unwind() {}
-}
-
 mod with_ty_alias {
     type Foo = impl std::fmt::Debug;
 

src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.fixed

@@ -1,5 +1,6 @@
 #![warn(clippy::missing_const_for_fn)]
 #![allow(incomplete_features, clippy::let_and_return, clippy::missing_transmute_annotations)]
+#![allow(unsupported_calling_conventions)]
 #![feature(const_mut_refs)]
 #![feature(const_trait_impl)]
 
@@ -204,3 +205,16 @@ mod with_ty_alias {
     // in this test.
     const fn alias_ty_is_projection(bar: <() as FooTrait>::Foo) {}
 }
+
+mod extern_fn {
+    const extern "C-unwind" fn c_unwind() {}
+    //~^ ERROR: this could be a `const fn`
+    const extern "system" fn system() {}
+    //~^ ERROR: this could be a `const fn`
+    const extern "system-unwind" fn system_unwind() {}
+    //~^ ERROR: this could be a `const fn`
+    pub const extern "stdcall" fn std_call() {}
+    //~^ ERROR: this could be a `const fn`
+    pub const extern "stdcall-unwind" fn std_call_unwind() {}
+    //~^ ERROR: this could be a `const fn`
+}

src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.rs

@@ -1,5 +1,6 @@
 #![warn(clippy::missing_const_for_fn)]
 #![allow(incomplete_features, clippy::let_and_return, clippy::missing_transmute_annotations)]
+#![allow(unsupported_calling_conventions)]
 #![feature(const_mut_refs)]
 #![feature(const_trait_impl)]
 
@@ -204,3 +205,16 @@ mod with_ty_alias {
     // in this test.
     fn alias_ty_is_projection(bar: <() as FooTrait>::Foo) {}
 }
+
+mod extern_fn {
+    extern "C-unwind" fn c_unwind() {}
+    //~^ ERROR: this could be a `const fn`
+    extern "system" fn system() {}
+    //~^ ERROR: this could be a `const fn`
+    extern "system-unwind" fn system_unwind() {}
+    //~^ ERROR: this could be a `const fn`
+    pub extern "stdcall" fn std_call() {}
+    //~^ ERROR: this could be a `const fn`
+    pub extern "stdcall-unwind" fn std_call_unwind() {}
+    //~^ ERROR: this could be a `const fn`
+}

src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.stderr

@@ -1,5 +1,5 @@
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:14:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:15:5
    |
 LL | /     pub fn new() -> Self {
 LL | |
@@ -16,7 +16,7 @@ LL |     pub const fn new() -> Self {
    |         +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:20:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:21:5
    |
 LL | /     fn const_generic_params<'a, T, const N: usize>(&self, b: &'a [T; N]) -> &'a [T; N] {
 LL | |
@@ -30,7 +30,7 @@ LL |     const fn const_generic_params<'a, T, const N: usize>(&self, b: &'a [T;
    |     +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:27:1
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:28:1
    |
 LL | / fn one() -> i32 {
 LL | |
@@ -44,7 +44,7 @@ LL | const fn one() -> i32 {
    | +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:33:1
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:34:1
    |
 LL | / fn two() -> i32 {
 LL | |
@@ -59,7 +59,7 @@ LL | const fn two() -> i32 {
    | +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:40:1
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:41:1
    |
 LL | / fn string() -> String {
 LL | |
@@ -73,7 +73,7 @@ LL | const fn string() -> String {
    | +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:46:1
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:47:1
    |
 LL | / unsafe fn four() -> i32 {
 LL | |
@@ -87,7 +87,7 @@ LL | const unsafe fn four() -> i32 {
    | +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:52:1
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:53:1
    |
 LL | / fn generic<T>(t: T) -> T {
 LL | |
@@ -101,7 +101,7 @@ LL | const fn generic<T>(t: T) -> T {
    | +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:61:1
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:62:1
    |
 LL | / fn generic_arr<T: Copy>(t: [T; 1]) -> T {
 LL | |
@@ -115,7 +115,7 @@ LL | const fn generic_arr<T: Copy>(t: [T; 1]) -> T {
    | +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:75:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:76:9
    |
 LL | /         pub fn b(self, a: &A) -> B {
 LL | |
@@ -129,7 +129,7 @@ LL |         pub const fn b(self, a: &A) -> B {
    |             +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:85:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:86:5
    |
 LL | /     fn const_fn_stabilized_before_msrv(byte: u8) {
 LL | |
@@ -143,7 +143,7 @@ LL |     const fn const_fn_stabilized_before_msrv(byte: u8) {
    |     +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:97:1
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:98:1
    |
 LL | / fn msrv_1_46() -> i32 {
 LL | |
@@ -157,7 +157,7 @@ LL | const fn msrv_1_46() -> i32 {
    | +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:117:1
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:118:1
    |
 LL | fn d(this: D) {}
    | ^^^^^^^^^^^^^^^^
@@ -168,7 +168,7 @@ LL | const fn d(this: D) {}
    | +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:125:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:126:9
    |
 LL | /         fn deref_ptr_can_be_const(self) -> usize {
 LL | |
@@ -182,7 +182,7 @@ LL |         const fn deref_ptr_can_be_const(self) -> usize {
    |         +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:130:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:131:9
    |
 LL | /         fn deref_copied_val(self) -> usize {
 LL | |
@@ -196,7 +196,7 @@ LL |         const fn deref_copied_val(self) -> usize {
    |         +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:141:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:142:5
    |
 LL | /     fn union_access_can_be_const() {
 LL | |
@@ -211,7 +211,7 @@ LL |     const fn union_access_can_be_const() {
    |     +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:149:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:150:9
    |
 LL |         extern "C" fn c() {}
    |         ^^^^^^^^^^^^^^^^^^^^
@@ -222,7 +222,7 @@ LL |         const extern "C" fn c() {}
    |         +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:153:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:154:9
    |
 LL |         extern fn implicit_c() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -233,7 +233,7 @@ LL |         const extern fn implicit_c() {}
    |         +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:170:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:171:9
    |
 LL | /         pub fn new(strings: Vec<String>) -> Self {
 LL | |             Self { strings }
@@ -246,7 +246,7 @@ LL |         pub const fn new(strings: Vec<String>) -> Self {
    |             +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:175:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:176:9
    |
 LL | /         pub fn empty() -> Self {
 LL | |             Self { strings: Vec::new() }
@@ -259,7 +259,7 @@ LL |         pub const fn empty() -> Self {
    |             +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:186:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:187:9
    |
 LL | /         pub fn new(text: String) -> Self {
 LL | |             let vec = Vec::new();
@@ -273,7 +273,7 @@ LL |         pub const fn new(text: String) -> Self {
    |             +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:205:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:206:5
    |
 LL |     fn alias_ty_is_projection(bar: <() as FooTrait>::Foo) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -283,5 +283,60 @@ help: make the function `const`
 LL |     const fn alias_ty_is_projection(bar: <() as FooTrait>::Foo) {}
    |     +++++
 
-error: aborting due to 21 previous errors
+error: this could be a `const fn`
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:210:5
+   |
+LL |     extern "C-unwind" fn c_unwind() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: make the function `const`
+   |
+LL |     const extern "C-unwind" fn c_unwind() {}
+   |     +++++
+
+error: this could be a `const fn`
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:212:5
+   |
+LL |     extern "system" fn system() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: make the function `const`
+   |
+LL |     const extern "system" fn system() {}
+   |     +++++
+
+error: this could be a `const fn`
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:214:5
+   |
+LL |     extern "system-unwind" fn system_unwind() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: make the function `const`
+   |
+LL |     const extern "system-unwind" fn system_unwind() {}
+   |     +++++
+
+error: this could be a `const fn`
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:216:5
+   |
+LL |     pub extern "stdcall" fn std_call() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: make the function `const`
+   |
+LL |     pub const extern "stdcall" fn std_call() {}
+   |         +++++
+
+error: this could be a `const fn`
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:218:5
+   |
+LL |     pub extern "stdcall-unwind" fn std_call_unwind() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: make the function `const`
+   |
+LL |     pub const extern "stdcall-unwind" fn std_call_unwind() {}
+   |         +++++
+
+error: aborting due to 26 previous errors
 

src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const_with_const_extern_fn.fixed

@@ -1,14 +0,0 @@
-#![warn(clippy::missing_const_for_fn)]
-#![allow(unsupported_calling_conventions)]
-#![feature(const_extern_fn)]
-
-const extern "C-unwind" fn c_unwind() {}
-//~^ ERROR: this could be a `const fn`
-const extern "system" fn system() {}
-//~^ ERROR: this could be a `const fn`
-const extern "system-unwind" fn system_unwind() {}
-//~^ ERROR: this could be a `const fn`
-pub const extern "stdcall" fn std_call() {}
-//~^ ERROR: this could be a `const fn`
-pub const extern "stdcall-unwind" fn std_call_unwind() {}
-//~^ ERROR: this could be a `const fn`

src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const_with_const_extern_fn.rs

@@ -1,14 +0,0 @@
-#![warn(clippy::missing_const_for_fn)]
-#![allow(unsupported_calling_conventions)]
-#![feature(const_extern_fn)]
-
-extern "C-unwind" fn c_unwind() {}
-//~^ ERROR: this could be a `const fn`
-extern "system" fn system() {}
-//~^ ERROR: this could be a `const fn`
-extern "system-unwind" fn system_unwind() {}
-//~^ ERROR: this could be a `const fn`
-pub extern "stdcall" fn std_call() {}
-//~^ ERROR: this could be a `const fn`
-pub extern "stdcall-unwind" fn std_call_unwind() {}
-//~^ ERROR: this could be a `const fn`

src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const_with_const_extern_fn.stderr

@@ -1,59 +0,0 @@
-error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const_with_const_extern_fn.rs:5:1
-   |
-LL | extern "C-unwind" fn c_unwind() {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: `-D clippy::missing-const-for-fn` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(clippy::missing_const_for_fn)]`
-help: make the function `const`
-   |
-LL | const extern "C-unwind" fn c_unwind() {}
-   | +++++
-
-error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const_with_const_extern_fn.rs:7:1
-   |
-LL | extern "system" fn system() {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-help: make the function `const`
-   |
-LL | const extern "system" fn system() {}
-   | +++++
-
-error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const_with_const_extern_fn.rs:9:1
-   |
-LL | extern "system-unwind" fn system_unwind() {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-help: make the function `const`
-   |
-LL | const extern "system-unwind" fn system_unwind() {}
-   | +++++
-
-error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const_with_const_extern_fn.rs:11:1
-   |
-LL | pub extern "stdcall" fn std_call() {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-help: make the function `const`
-   |
-LL | pub const extern "stdcall" fn std_call() {}
-   |     +++++
-
-error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const_with_const_extern_fn.rs:13:1
-   |
-LL | pub extern "stdcall-unwind" fn std_call_unwind() {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-help: make the function `const`
-   |
-LL | pub const extern "stdcall-unwind" fn std_call_unwind() {}
-   |     +++++
-
-error: aborting due to 5 previous errors
-

tests/ui/consts/const-eval/unwind-abort.rs

@@ -1,5 +1,3 @@
-#![feature(const_extern_fn)]
-
 const extern "C" fn foo() {
     panic!() //~ ERROR evaluation of constant value failed
 }

tests/ui/consts/const-eval/unwind-abort.stderr

@@ -1,16 +1,16 @@
 error[E0080]: evaluation of constant value failed
-  --> $DIR/unwind-abort.rs:4:5
+  --> $DIR/unwind-abort.rs:2:5
    |
 LL |     panic!()
-   |     ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/unwind-abort.rs:4:5
+   |     ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/unwind-abort.rs:2:5
    |
 note: inside `foo`
-  --> $DIR/unwind-abort.rs:4:5
+  --> $DIR/unwind-abort.rs:2:5
    |
 LL |     panic!()
    |     ^^^^^^^^
 note: inside `_`
-  --> $DIR/unwind-abort.rs:7:15
+  --> $DIR/unwind-abort.rs:5:15
    |
 LL | const _: () = foo();
    |               ^^^^^

tests/ui/consts/const-extern-fn/const-extern-fn-call-extern-fn.rs

@@ -1,5 +1,3 @@
-#![feature(const_extern_fn)]
-
 extern "C" {
     fn regular_in_block();
 }

tests/ui/consts/const-extern-fn/const-extern-fn-call-extern-fn.stderr

@@ -1,5 +1,5 @@
 error[E0015]: cannot call non-const fn `regular_in_block` in constant functions
-  --> $DIR/const-extern-fn-call-extern-fn.rs:9:9
+  --> $DIR/const-extern-fn-call-extern-fn.rs:7:9
    |
 LL |         regular_in_block();
    |         ^^^^^^^^^^^^^^^^^^
@@ -7,7 +7,7 @@ LL |         regular_in_block();
    = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
 
 error[E0015]: cannot call non-const fn `regular` in constant functions
-  --> $DIR/const-extern-fn-call-extern-fn.rs:18:9
+  --> $DIR/const-extern-fn-call-extern-fn.rs:16:9
    |
 LL |         regular();
    |         ^^^^^^^^^

tests/ui/consts/const-extern-fn/const-extern-fn-min-const-fn.rs

@@ -1,7 +1,6 @@
-#![feature(const_extern_fn)]
+const extern "C" fn ptr_cast(val: *const u8) {
-
+    val as usize;
-const extern "C" fn ptr_cast(val: *const u8) { val as usize; }
+    //~^ ERROR pointers cannot be cast to integers
-//~^ ERROR pointers cannot be cast to integers
+}
-
 
 fn main() {}

tests/ui/consts/const-extern-fn/const-extern-fn-min-const-fn.stderr

@@ -1,8 +1,8 @@
 error: pointers cannot be cast to integers during const eval
-  --> $DIR/const-extern-fn-min-const-fn.rs:3:48
+  --> $DIR/const-extern-fn-min-const-fn.rs:2:5
    |
-LL | const extern "C" fn ptr_cast(val: *const u8) { val as usize; }
+LL |     val as usize;
-   |                                                ^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^
    |
    = note: at compile-time, pointers do not have an integer value
    = note: avoiding this restriction via `transmute`, `union`, or raw pointers leads to compile-time undefined behavior

tests/ui/consts/const-extern-fn/const-extern-fn-requires-unsafe.rs

@@ -1,12 +1,18 @@
-#![feature(const_extern_fn)]
-
 const unsafe extern "C" fn foo() -> usize {
     5
 }
 
+const unsafe extern "C-unwind" fn bar() -> usize {
+    5
+}
+
 fn main() {
     let a: [u8; foo()];
     //~^ call to unsafe function `foo` is unsafe and requires unsafe function or block
     foo();
     //~^ ERROR call to unsafe function `foo` is unsafe and requires unsafe function or block
+    let b: [u8; bar()];
+    //~^ call to unsafe function `bar` is unsafe and requires unsafe function or block
+    bar();
+    //~^ ERROR call to unsafe function `bar` is unsafe and requires unsafe function or block
 }

tests/ui/consts/const-extern-fn/const-extern-fn-requires-unsafe.stderr

@@ -1,19 +1,35 @@
 error[E0133]: call to unsafe function `foo` is unsafe and requires unsafe function or block
-  --> $DIR/const-extern-fn-requires-unsafe.rs:10:5
+  --> $DIR/const-extern-fn-requires-unsafe.rs:12:5
    |
 LL |     foo();
    |     ^^^^^ call to unsafe function
    |
    = note: consult the function's documentation for information on how to avoid undefined behavior
 
+error[E0133]: call to unsafe function `bar` is unsafe and requires unsafe function or block
+  --> $DIR/const-extern-fn-requires-unsafe.rs:16:5
+   |
+LL |     bar();
+   |     ^^^^^ call to unsafe function
+   |
+   = note: consult the function's documentation for information on how to avoid undefined behavior
+
 error[E0133]: call to unsafe function `foo` is unsafe and requires unsafe function or block
-  --> $DIR/const-extern-fn-requires-unsafe.rs:8:17
+  --> $DIR/const-extern-fn-requires-unsafe.rs:10:17
    |
 LL |     let a: [u8; foo()];
    |                 ^^^^^ call to unsafe function
    |
    = note: consult the function's documentation for information on how to avoid undefined behavior
 
-error: aborting due to 2 previous errors
+error[E0133]: call to unsafe function `bar` is unsafe and requires unsafe function or block
+  --> $DIR/const-extern-fn-requires-unsafe.rs:14:17
+   |
+LL |     let b: [u8; bar()];
+   |                 ^^^^^ call to unsafe function
+   |
+   = note: consult the function's documentation for information on how to avoid undefined behavior
+
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0133`.

tests/ui/consts/const-extern-fn/const-extern-fn.rs

@@ -1,5 +1,4 @@
 //@ run-pass
-#![feature(const_extern_fn)]
 
 const extern "C" fn foo1(val: u8) -> u8 {
     val + 1
@@ -47,6 +46,10 @@ fn main() {
     let _bar2_cast: unsafe extern "C" fn(bool) -> bool = bar2;
 
     unsize(&[0, 1, 2]);
-    unsafe { closure(); }
+    unsafe {
-    unsafe { use_float(); }
+        closure();
+    }
+    unsafe {
+        use_float();
+    }
 }

tests/ui/consts/const-extern-fn/feature-gate-const_extern_fn.rs

@@ -1,13 +0,0 @@
-// Check that `const extern fn` and `const unsafe extern fn` are feature-gated
-// for certain ABIs.
-
-const extern fn foo1() {}
-const extern "C" fn foo2() {}
-const extern "Rust" fn foo3() {}
-const extern "cdecl" fn foo4() {} //~ ERROR `cdecl` as a `const fn` ABI is unstable
-const unsafe extern fn bar1() {}
-const unsafe extern "C" fn bar2() {}
-const unsafe extern "Rust" fn bar3() {}
-const unsafe extern "cdecl" fn bar4() {} //~ ERROR `cdecl` as a `const fn` ABI is unstable
-
-fn main() {}

tests/ui/consts/const-extern-fn/feature-gate-const_extern_fn.stderr

@@ -1,23 +0,0 @@
-error[E0658]: `cdecl` as a `const fn` ABI is unstable
-  --> $DIR/feature-gate-const_extern_fn.rs:7:14
-   |
-LL | const extern "cdecl" fn foo4() {}
-   |              ^^^^^^^
-   |
-   = note: see issue #64926 <https://github.com/rust-lang/rust/issues/64926> for more information
-   = help: add `#![feature(const_extern_fn)]` 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]: `cdecl` as a `const fn` ABI is unstable
-  --> $DIR/feature-gate-const_extern_fn.rs:11:21
-   |
-LL | const unsafe extern "cdecl" fn bar4() {}
-   |                     ^^^^^^^
-   |
-   = note: see issue #64926 <https://github.com/rust-lang/rust/issues/64926> for more information
-   = help: add `#![feature(const_extern_fn)]` 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 2 previous errors
-
-For more information about this error, try `rustc --explain E0658`.

tests/ui/consts/miri_unleashed/abi-mismatch.rs

@@ -1,8 +1,6 @@
 // Checks that we report ABI mismatches for "const extern fn"
 //@ compile-flags: -Z unleash-the-miri-inside-of-you
 
-#![feature(const_extern_fn)]
-
 const extern "C" fn c_fn() {}
 
 const fn call_rust_fn(my_fn: extern "Rust" fn()) {

tests/ui/consts/miri_unleashed/abi-mismatch.stderr

@@ -1,16 +1,16 @@
 error[E0080]: could not evaluate static initializer
-  --> $DIR/abi-mismatch.rs:9:5
+  --> $DIR/abi-mismatch.rs:7:5
    |
 LL |     my_fn();
    |     ^^^^^^^ calling a function with calling convention C using calling convention Rust
    |
 note: inside `call_rust_fn`
-  --> $DIR/abi-mismatch.rs:9:5
+  --> $DIR/abi-mismatch.rs:7:5
    |
 LL |     my_fn();
    |     ^^^^^^^
 note: inside `VAL`
-  --> $DIR/abi-mismatch.rs:15:18
+  --> $DIR/abi-mismatch.rs:13:18
    |
 LL | static VAL: () = call_rust_fn(unsafe { std::mem::transmute(c_fn as extern "C" fn()) });
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -18,7 +18,7 @@ LL | static VAL: () = call_rust_fn(unsafe { std::mem::transmute(c_fn as extern "
 warning: skipping const checks
    |
 help: skipping check that does not even have a feature gate
-  --> $DIR/abi-mismatch.rs:9:5
+  --> $DIR/abi-mismatch.rs:7:5
    |
 LL |     my_fn();
    |     ^^^^^^^

tests/ui/consts/unwind-abort.rs

@@ -1,7 +1,5 @@
 //@ check-pass
 
-#![feature(const_extern_fn)]
-
 // We don't unwind in const-eval anyways.
 const extern "C" fn foo() {
     panic!()

tests/ui/parser/fn-header-semantic-fail.rs

@@ -2,8 +2,6 @@
 
 //@ edition:2018
 
-#![feature(const_extern_fn)]
-
 fn main() {
     async fn ff1() {} // OK.
     unsafe fn ff2() {} // OK.

tests/ui/parser/fn-header-semantic-fail.stderr

@@ -1,5 +1,5 @@
 error: functions cannot be both `const` and `async`
-  --> $DIR/fn-header-semantic-fail.rs:12:5
+  --> $DIR/fn-header-semantic-fail.rs:10:5
    |
 LL |     const async unsafe extern "C" fn ff5() {}
    |     ^^^^^-^^^^^------------------------------
@@ -8,7 +8,7 @@ LL |     const async unsafe extern "C" fn ff5() {}
    |     `const` because of this
 
 error[E0379]: functions in traits cannot be declared const
-  --> $DIR/fn-header-semantic-fail.rs:18:9
+  --> $DIR/fn-header-semantic-fail.rs:16:9
    |
 LL |         const fn ft3();
    |         ^^^^^-
@@ -17,7 +17,7 @@ LL |         const fn ft3();
    |         help: remove the `const`
 
 error[E0379]: functions in traits cannot be declared const
-  --> $DIR/fn-header-semantic-fail.rs:20:9
+  --> $DIR/fn-header-semantic-fail.rs:18:9
    |
 LL |         const async unsafe extern "C" fn ft5();
    |         ^^^^^-
@@ -26,7 +26,7 @@ LL |         const async unsafe extern "C" fn ft5();
    |         help: remove the `const`
 
 error: functions cannot be both `const` and `async`
-  --> $DIR/fn-header-semantic-fail.rs:20:9
+  --> $DIR/fn-header-semantic-fail.rs:18:9
    |
 LL |         const async unsafe extern "C" fn ft5();
    |         ^^^^^-^^^^^----------------------------
@@ -35,7 +35,7 @@ LL |         const async unsafe extern "C" fn ft5();
    |         `const` because of this
 
 error[E0379]: functions in trait impls cannot be declared const
-  --> $DIR/fn-header-semantic-fail.rs:29:9
+  --> $DIR/fn-header-semantic-fail.rs:27:9
    |
 LL |         const fn ft3() {}
    |         ^^^^^-
@@ -44,7 +44,7 @@ LL |         const fn ft3() {}
    |         help: remove the `const`
 
 error[E0379]: functions in trait impls cannot be declared const
-  --> $DIR/fn-header-semantic-fail.rs:31:9
+  --> $DIR/fn-header-semantic-fail.rs:29:9
    |
 LL |         const async unsafe extern "C" fn ft5() {}
    |         ^^^^^-
@@ -53,7 +53,7 @@ LL |         const async unsafe extern "C" fn ft5() {}
    |         help: remove the `const`
 
 error: functions cannot be both `const` and `async`
-  --> $DIR/fn-header-semantic-fail.rs:31:9
+  --> $DIR/fn-header-semantic-fail.rs:29:9
    |
 LL |         const async unsafe extern "C" fn ft5() {}
    |         ^^^^^-^^^^^------------------------------
@@ -62,7 +62,7 @@ LL |         const async unsafe extern "C" fn ft5() {}
    |         `const` because of this
 
 error: functions cannot be both `const` and `async`
-  --> $DIR/fn-header-semantic-fail.rs:41:9
+  --> $DIR/fn-header-semantic-fail.rs:39:9
    |
 LL |         const async unsafe extern "C" fn fi5() {}
    |         ^^^^^-^^^^^------------------------------
@@ -71,7 +71,7 @@ LL |         const async unsafe extern "C" fn fi5() {}
    |         `const` because of this
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:46:9
+  --> $DIR/fn-header-semantic-fail.rs:44:9
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -79,7 +79,7 @@ LL |         async fn fe1();
    |         ^^^^^ help: remove this qualifier
 
 error: items in unadorned `extern` blocks cannot have safety qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:47:9
+  --> $DIR/fn-header-semantic-fail.rs:45:9
    |
 LL |         unsafe fn fe2();
    |         ^^^^^^^^^^^^^^^^
@@ -90,7 +90,7 @@ LL |     unsafe extern "C" {
    |     ++++++
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:48:9
+  --> $DIR/fn-header-semantic-fail.rs:46:9
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -99,7 +99,7 @@ LL |         const fn fe3();
    |         ^^^^^ help: remove this qualifier
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:49:9
+  --> $DIR/fn-header-semantic-fail.rs:47:9
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -108,7 +108,7 @@ LL |         extern "C" fn fe4();
    |         ^^^^^^^^^^ help: remove this qualifier
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:50:15
+  --> $DIR/fn-header-semantic-fail.rs:48:15
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -117,7 +117,7 @@ LL |         const async unsafe extern "C" fn fe5();
    |               ^^^^^ help: remove this qualifier
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:50:9
+  --> $DIR/fn-header-semantic-fail.rs:48:9
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -126,7 +126,7 @@ LL |         const async unsafe extern "C" fn fe5();
    |         ^^^^^ help: remove this qualifier
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:50:28
+  --> $DIR/fn-header-semantic-fail.rs:48:28
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -135,7 +135,7 @@ LL |         const async unsafe extern "C" fn fe5();
    |                            ^^^^^^^^^^ help: remove this qualifier
 
 error: items in unadorned `extern` blocks cannot have safety qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:50:9
+  --> $DIR/fn-header-semantic-fail.rs:48:9
    |
 LL |         const async unsafe extern "C" fn fe5();
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -146,7 +146,7 @@ LL |     unsafe extern "C" {
    |     ++++++
 
 error: functions cannot be both `const` and `async`
-  --> $DIR/fn-header-semantic-fail.rs:50:9
+  --> $DIR/fn-header-semantic-fail.rs:48:9
    |
 LL |         const async unsafe extern "C" fn fe5();
    |         ^^^^^-^^^^^----------------------------