Auto merge of #54835 - oli-obk:mögen_konstante_funktionen_doch_bitte_endlich_stabil_sein, r=Centril

Stabilize `min_const_fn`

tracking issue: #53555

r? @Centril

Author: bors

src/liballoc/lib.rs

@@ -86,7 +86,7 @@
 #![feature(box_syntax)]
 #![feature(cfg_target_has_atomic)]
 #![feature(coerce_unsized)]
-#![feature(min_const_fn)]
+#![cfg_attr(stage0, feature(min_const_fn))]
 #![feature(core_intrinsics)]
 #![feature(custom_attribute)]
 #![feature(dropck_eyepatch)]

src/liballoc/tests/lib.rs

@@ -11,7 +11,7 @@
 #![feature(allocator_api)]
 #![feature(alloc_system)]
 #![feature(box_syntax)]
-#![feature(min_const_fn)]
+#![cfg_attr(stage0, feature(min_const_fn))]
 #![feature(drain_filter)]
 #![feature(exact_size_is_empty)]
 #![feature(pattern)]

src/librustc/lib.rs

@@ -42,7 +42,7 @@
 
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(min_const_fn)]
+#![cfg_attr(stage0, feature(min_const_fn))]
 #![feature(core_intrinsics)]
 #![feature(drain_filter)]
 #![cfg_attr(windows, feature(libc))]

src/librustc/ty/constness.rs

@@ -65,7 +65,7 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
                 _ => true,
             }
         } else {
-            // users enabling the `const_fn` can do what they want
+            // users enabling the `const_fn` feature gate can do what they want
             !self.sess.features_untracked().const_fn
         }
     }

src/librustc_mir/diagnostics.rs

@@ -665,24 +665,6 @@ fn main() {
 ```
 "##,
 
-E0022: r##"
-Constant functions are not allowed to mutate anything. Thus, binding to an
-argument with a mutable pattern is not allowed. For example,
-
-```compile_fail
-const fn foo(mut x: u8) {
-    // do stuff
-}
-```
-
-Is incorrect because the function body may not mutate `x`.
-
-Remove any mutable bindings from the argument list to fix this error. In case
-you need to mutate the argument, try lazily initializing a global variable
-instead of using a `const fn`, or refactoring the code to a functional style to
-avoid mutation if possible.
-"##,
-
 E0133: r##"
 Unsafe code was used outside of an unsafe function or block.
 

src/librustc_target/lib.rs

@@ -22,7 +22,7 @@
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 
 #![feature(box_syntax)]
-#![feature(min_const_fn)]
+#![cfg_attr(stage0, feature(min_const_fn))]
 #![feature(nll)]
 #![feature(slice_patterns)]
 

src/libstd/lib.rs

@@ -250,7 +250,7 @@
 #![feature(cfg_target_vendor)]
 #![feature(char_error_internals)]
 #![feature(compiler_builtins_lib)]
-#![feature(min_const_fn)]
+#![cfg_attr(stage0, feature(min_const_fn))]
 #![feature(const_int_ops)]
 #![feature(const_ip)]
 #![feature(const_raw_ptr_deref)]

src/libsyntax/attr/builtin.rs

@@ -107,8 +107,7 @@ pub struct Stability {
     pub level: StabilityLevel,
     pub feature: Symbol,
     pub rustc_depr: Option<RustcDeprecation>,
-    /// `None` means the function is stable but needs to be allowed by the
-    /// `min_const_fn` feature
+    /// `None` means the function is stable but needs to be a stable const fn, too
     /// `Some` contains the feature gate required to be able to use the function
     /// as const fn
     pub const_stability: Option<Symbol>,

src/libsyntax/feature_gate.rs

@@ -40,16 +40,6 @@ use symbol::{keywords, Symbol};
 use std::{env};
 
 macro_rules! set {
-    // The const_fn feature also enables the min_const_fn feature, because `min_const_fn` allows
-    // the declaration `const fn`, but the `const_fn` feature gate enables things inside those
-    // functions that we do not want to expose to the user for now.
-    (const_fn) => {{
-        fn f(features: &mut Features, _: Span) {
-            features.const_fn = true;
-            features.min_const_fn = true;
-        }
-        f as fn(&mut Features, Span)
-    }};
     ($field: ident) => {{
         fn f(features: &mut Features, _: Span) {
             features.$field = true;
@@ -219,9 +209,6 @@ declare_features! (
     // Allows the definition of `const fn` functions with some advanced features.
     (active, const_fn, "1.2.0", Some(24111), None),
 
-    // Allows the definition of `const fn` functions.
-    (active, min_const_fn, "1.30.0", Some(53555), None),
-
     // Allows let bindings and destructuring in `const fn` functions and constants.
     (active, const_let, "1.22.1", Some(48821), None),
 
@@ -690,6 +677,8 @@ declare_features! (
     (accepted, extern_prelude, "1.30.0", Some(44660), None),
     // Parentheses in patterns
     (accepted, pattern_parentheses, "1.31.0", Some(51087), None),
+    // Allows the definition of `const fn` functions.
+    (accepted, min_const_fn, "1.31.0", Some(53555), None),
 );
 
 // If you change this, please modify src/doc/unstable-book as well. You must
@@ -1807,9 +1796,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 if header.asyncness.is_async() {
                     gate_feature_post!(&self, async_await, span, "async fn is unstable");
                 }
-                if header.constness.node == ast::Constness::Const {
-                    gate_feature_post!(&self, min_const_fn, span, "const fn is unstable");
-                }
                 // stability of const fn methods are covered in
                 // visit_trait_item and visit_impl_item below; this is
                 // because default methods don't pass through this
@@ -1864,11 +1850,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         }
 
         match ii.node {
-            ast::ImplItemKind::Method(ref sig, _) => {
-                if sig.header.constness.node == ast::Constness::Const {
-                    gate_feature_post!(&self, min_const_fn, ii.span, "const fn is unstable");
-                }
-            }
+            ast::ImplItemKind::Method(..) => {}
             ast::ImplItemKind::Existential(..) => {
                 gate_feature_post!(
                     &self,

src/test/codegen-units/item-collection/unreferenced-const-fn.rs

@@ -13,7 +13,6 @@
 
 // NB: We do not expect *any* monomorphization to be generated here.
 
-#![feature(min_const_fn)]
 #![deny(dead_code)]
 #![crate_type = "rlib"]