stabilize const_extern_fn

Author: folkertdev

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, "CURRENT_RUSTC_VERSION", 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 {

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

@@ -1,13 +1,13 @@
 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();
    |         ^^^^^^^^^^^^^^^^^^
    |
    = 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; }
-//~^ ERROR pointers cannot be cast to integers
-
+const extern "C" fn ptr_cast(val: *const u8) {
+    val as usize;
+    //~^ 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