don't let const_fn feature flag affect impl-block-level trait bounds

Author: RalfJung

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/rfc-2632-const-trait-impl/assoc-type.rs

@@ -5,7 +5,6 @@
 
 #![allow(incomplete_features)]
 #![feature(const_trait_impl)]
-#![feature(const_fn)]
 
 struct NonConstAdd(i32);
 

src/test/ui/rfc-2632-const-trait-impl/call-const-trait-method-fail.rs

@@ -1,6 +1,5 @@
 #![allow(incomplete_features)]
 #![feature(const_trait_impl)]
-#![feature(const_fn)]
 
 pub trait Plus {
     fn plus(self, rhs: Self) -> Self;

src/test/ui/rfc-2632-const-trait-impl/call-const-trait-method-fail.stderr

@@ -1,5 +1,5 @@
 error[E0015]: calls in constant functions are limited to constant functions, tuple structs and tuple variants
-  --> $DIR/call-const-trait-method-fail.rs:26:5
+  --> $DIR/call-const-trait-method-fail.rs:25:5
    |
 LL |     a.plus(b)
    |     ^^^^^^^^^

src/test/ui/rfc-2632-const-trait-impl/call-const-trait-method-pass.rs

@@ -2,7 +2,6 @@
 
 #![allow(incomplete_features)]
 #![feature(const_trait_impl)]
-#![feature(const_fn)]
 
 struct Int(i32);
 

src/test/ui/rfc-2632-const-trait-impl/call-generic-method-fail.rs

@@ -1,4 +1,4 @@
-#![feature(const_fn)]
+#![feature(const_fn_trait_bound)]
 #![feature(const_trait_impl)]
 #![feature(const_trait_bound_opt_out)]
 #![allow(incomplete_features)]

src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst-opt-out.rs

@@ -1,6 +1,6 @@
 // check-pass
 
-#![feature(const_fn)]
+#![feature(const_fn_trait_bound)]
 #![feature(const_trait_impl)]
 #![feature(const_trait_bound_opt_out)]
 #![allow(incomplete_features)]

src/test/ui/rfc-2632-const-trait-impl/call-generic-method-nonconst.rs

@@ -1,7 +1,6 @@
 // FIXME(jschievink): this is not rejected correctly (only when the non-const impl is actually used)
 // ignore-test
 
-#![feature(const_fn)]
 #![feature(const_trait_impl)]
 #![allow(incomplete_features)]
 

src/test/ui/rfc-2632-const-trait-impl/const-trait-bound-opt-out/feature-gate.rs

@@ -4,7 +4,7 @@
 #![cfg_attr(gated, feature(const_trait_bound_opt_out))]
 #![allow(incomplete_features)]
 #![feature(rustc_attrs)]
-#![feature(const_fn)]
+#![feature(const_fn_trait_bound)]
 
 trait T {
     const CONST: i32;