Auto merge of #84556 - RalfJung:const-fn-trait-bound, r=oli-obk

use correct feature flag for impl-block-level trait bounds on const fn

I am not sure what that special hack was needed for, but it doesn't seem needed any more...

This removes the last use of the `const_fn` feature flag -- Cc #84510
r? `@oli-obk`

Author: bors

compiler/rustc_mir/src/transform/check_consts/validation.rs

@@ -426,7 +426,7 @@ impl Validator<'mir, 'tcx> {
                     ty::PredicateKind::Subtype(_) => {
                         bug!("subtype predicate on function: {:#?}", predicate)
                     }
-                    ty::PredicateKind::Trait(pred, constness) => {
+                    ty::PredicateKind::Trait(pred, _constness) => {
                         if Some(pred.def_id()) == tcx.lang_items().sized_trait() {
                             continue;
                         }
@@ -440,16 +440,7 @@ impl Validator<'mir, 'tcx> {
                                 // arguments when determining importance.
                                 let kind = LocalKind::Arg;
 
-                                if constness == hir::Constness::Const {
-                                    self.check_op_spanned(ops::ty::TraitBound(kind), span);
-                                } else if !tcx.features().const_fn
-                                    || self.ccx.is_const_stable_const_fn()
-                                {
-                                    // HACK: We shouldn't need the conditional above, but trait
-                                    // bounds on containing impl blocks are wrongly being marked as
-                                    // "not-const".
-                                    self.check_op_spanned(ops::ty::TraitBound(kind), span);
-                                }
+                                self.check_op_spanned(ops::ty::TraitBound(kind), span);
                             }
                             // other kinds of bounds are either tautologies
                             // or cause errors in other passes

library/proc_macro/src/lib.rs

@@ -21,7 +21,8 @@
 #![feature(rustc_allow_const_fn_unstable)]
 #![feature(nll)]
 #![feature(staged_api)]
-#![feature(const_fn)]
+#![cfg_attr(bootstrap, feature(const_fn))]
+#![cfg_attr(not(bootstrap), feature(const_fn_trait_bound))]
 #![feature(const_fn_fn_ptr_basics)]
 #![feature(allow_internal_unstable)]
 #![feature(decl_macro)]

src/test/ui/array-slice-vec/subslice-patterns-const-eval-match.rs

@@ -2,8 +2,6 @@
 
 // run-pass
 
-#![feature(const_fn)]
-
 #[derive(PartialEq, Debug, Clone)]
 struct N(u8);
 

src/test/ui/associated-consts/associated-const-in-trait.rs

@@ -1,6 +1,6 @@
 // #29924
 
-#![feature(const_fn, associated_consts)]
+#![feature(associated_consts)]
 
 trait Trait {
     const N: usize;

src/test/ui/consts/const-eval/auxiliary/stability.rs

@@ -3,7 +3,6 @@
 #![crate_type="rlib"]
 #![stable(feature = "rust1", since = "1.0.0")]
 
-#![feature(const_fn)]
 #![feature(staged_api)]
 
 #[stable(feature = "rust1", since = "1.0.0")]

src/test/ui/consts/const-eval/const_fn_ptr.rs

@@ -1,6 +1,5 @@
 // run-pass
 // compile-flags: -Zunleash-the-miri-inside-of-you
-#![feature(const_fn)]
 
 fn double(x: usize) -> usize { x * 2 }
 const fn double_const(x: usize) -> usize { x * 2 }

src/test/ui/consts/const-eval/const_fn_ptr.stderr

@@ -1,27 +1,27 @@
 warning: skipping const checks
    |
 help: skipping check that does not even have a feature gate
-  --> $DIR/const_fn_ptr.rs:12:5
+  --> $DIR/const_fn_ptr.rs:11:5
    |
 LL |     X(x)
    |     ^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/const_fn_ptr.rs:16:5
+  --> $DIR/const_fn_ptr.rs:15:5
    |
 LL |     X_CONST(x)
    |     ^^^^^^^^^^
 help: skipping check for `const_fn_fn_ptr_basics` feature
-  --> $DIR/const_fn_ptr.rs:19:14
+  --> $DIR/const_fn_ptr.rs:18:14
    |
 LL | const fn foo(x: fn(usize) -> usize, y: usize)  -> usize {
    |              ^
 help: skipping check for `const_fn_fn_ptr_basics` feature
-  --> $DIR/const_fn_ptr.rs:20:5
+  --> $DIR/const_fn_ptr.rs:19:5
    |
 LL |     x(y)
    |     ^
 help: skipping check that does not even have a feature gate
-  --> $DIR/const_fn_ptr.rs:20:5
+  --> $DIR/const_fn_ptr.rs:19:5
    |
 LL |     x(y)
    |     ^^^^

src/test/ui/consts/const-eval/const_fn_ptr_fail.rs

@@ -1,6 +1,5 @@
 // run-pass
 // compile-flags: -Zunleash-the-miri-inside-of-you
-#![feature(const_fn)]
 #![allow(unused)]
 
 fn double(x: usize) -> usize { x * 2 }

src/test/ui/consts/const-eval/const_fn_ptr_fail.stderr

@@ -1,7 +1,7 @@
 warning: skipping const checks
    |
 help: skipping check that does not even have a feature gate
-  --> $DIR/const_fn_ptr_fail.rs:10:5
+  --> $DIR/const_fn_ptr_fail.rs:9:5
    |
 LL |     X(x) // FIXME: this should error someday
    |     ^^^^

src/test/ui/consts/const-eval/const_fn_ptr_fail2.rs

@@ -1,7 +1,6 @@
 // build-fail
 // compile-flags: -Zunleash-the-miri-inside-of-you
 
-#![feature(const_fn)]
 #![allow(const_err)]
 
 fn double(x: usize) -> usize {