stabilize member constraints

compiler/rustc_feature/src/accepted.rs

@@ -285,6 +285,8 @@ declare_features! (
     (accepted, extended_key_value_attributes, "1.54.0", Some(78835), None),
     /// Allows unsizing coercions in `const fn`.
     (accepted, const_fn_unsize, "1.54.0", Some(64992), None),
+    /// Allows `impl Trait` with multiple unrelated lifetimes.
+    (accepted, member_constraints, "1.54.0", Some(61997), None),
 
     // -------------------------------------------------------------------------
     // feature-group-end: accepted features

compiler/rustc_feature/src/active.rs

@@ -472,9 +472,6 @@ declare_features! (
     /// Allows explicit discriminants on non-unit enum variants.
     (active, arbitrary_enum_discriminant, "1.37.0", Some(60553), None),
 
-    /// Allows `impl Trait` with multiple unrelated lifetimes.
-    (active, member_constraints, "1.37.0", Some(61997), None),
-
     /// Allows `async || body` closures.
     (active, async_closure, "1.37.0", Some(62290), None),
 

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -140,15 +140,6 @@ pub trait InferCtxtExt<'tcx> {
         first_own_region_index: usize,
     );
 
-    /*private*/
-    fn member_constraint_feature_gate(
-        &self,
-        opaque_defn: &OpaqueTypeDecl<'tcx>,
-        opaque_type_def_id: DefId,
-        conflict1: ty::Region<'tcx>,
-        conflict2: ty::Region<'tcx>,
-    ) -> bool;
-
     fn infer_opaque_definition_from_instantiation(
         &self,
         def_id: DefId,
@@ -490,9 +481,6 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         // ['a, 'b, 'c]`, where `'a..'c` are the
                         // regions that appear in the impl trait.
 
-                        // For now, enforce a feature gate outside of async functions.
-                        self.member_constraint_feature_gate(opaque_defn, def_id, lr, subst_region);
-
                         return self.generate_member_constraint(
                             concrete_ty,
                             opaque_defn,
@@ -559,60 +547,6 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         });
     }
 
-    /// Member constraints are presently feature-gated except for
-    /// async-await. We expect to lift this once we've had a bit more
-    /// time.
-    fn member_constraint_feature_gate(
-        &self,
-        opaque_defn: &OpaqueTypeDecl<'tcx>,
-        opaque_type_def_id: DefId,
-        conflict1: ty::Region<'tcx>,
-        conflict2: ty::Region<'tcx>,
-    ) -> bool {
-        // If we have `#![feature(member_constraints)]`, no problems.
-        if self.tcx.features().member_constraints {
-            return false;
-        }
-
-        let span = self.tcx.def_span(opaque_type_def_id);
-
-        // Without a feature-gate, we only generate member-constraints for async-await.
-        let context_name = match opaque_defn.origin {
-            // No feature-gate required for `async fn`.
-            hir::OpaqueTyOrigin::AsyncFn => return false,
-
-            // Otherwise, generate the label we'll use in the error message.
-            hir::OpaqueTyOrigin::Binding
-            | hir::OpaqueTyOrigin::FnReturn
-            | hir::OpaqueTyOrigin::TyAlias
-            | hir::OpaqueTyOrigin::Misc => "impl Trait",
-        };
-        let msg = format!("ambiguous lifetime bound in `{}`", context_name);
-        let mut err = self.tcx.sess.struct_span_err(span, &msg);
-
-        let conflict1_name = conflict1.to_string();
-        let conflict2_name = conflict2.to_string();
-        let label_owned;
-        let label = match (&*conflict1_name, &*conflict2_name) {
-            ("'_", "'_") => "the elided lifetimes here do not outlive one another",
-            _ => {
-                label_owned = format!(
-                    "neither `{}` nor `{}` outlives the other",
-                    conflict1_name, conflict2_name,
-                );
-                &label_owned
-            }
-        };
-        err.span_label(span, label);
-
-        if self.tcx.sess.is_nightly_build() {
-            err.help("add #![feature(member_constraints)] to the crate attributes to enable");
-        }
-
-        err.emit();
-        true
-    }
-
     /// Given the fully resolved, instantiated type for an opaque
     /// type, i.e., the value of an inference variable like C1 or C2
     /// (*), computes the "definition type" for an opaque type

src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-fg.rs

@@ -1,10 +1,9 @@
 // edition:2018
 // run-pass
 
-// Test that a feature gate is needed to use `impl Trait` as the
-// return type of an async.
-
-#![feature(member_constraints)]
+// Test member constraints that appear in the `impl Trait`
+// return type of an async function.
+// (This used to require a feature gate.)
 
 trait Trait<'a, 'b> { }
 impl<T> Trait<'_, '_> for T { }

src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-one.nll.stderr

@@ -1,5 +1,5 @@
 error: lifetime may not live long enough
-  --> $DIR/ret-impl-trait-one.rs:12:80
+  --> $DIR/ret-impl-trait-one.rs:10:80
    |
 LL |   async fn async_ret_impl_trait1<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a> {
    |  ________________________________--__--__________________________________________^

src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-one.rs

@@ -3,8 +3,6 @@
 // Test that a feature gate is needed to use `impl Trait` as the
 // return type of an async.
 
-#![feature(member_constraints)]
-
 trait Trait<'a> { }
 impl<T> Trait<'_> for T { }
 

src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-one.stderr

@@ -1,5 +1,5 @@
 error[E0623]: lifetime mismatch
-  --> $DIR/ret-impl-trait-one.rs:12:65
+  --> $DIR/ret-impl-trait-one.rs:10:65
    |
 LL | async fn async_ret_impl_trait1<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a> {
    |                                           ------                ^^^^^^^^^^^^^^

src/test/ui/impl-trait/multiple-lifetimes/error-handling.full_tait.stderr

@@ -1,5 +1,5 @@
 warning: the feature `type_alias_impl_trait` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/error-handling.rs:6:32
+  --> $DIR/error-handling.rs:5:32
    |
 LL | #![cfg_attr(full_tait, feature(type_alias_impl_trait))]
    |                                ^^^^^^^^^^^^^^^^^^^^^
@@ -8,7 +8,7 @@ LL | #![cfg_attr(full_tait, feature(type_alias_impl_trait))]
    = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
 
 error: lifetime may not live long enough
-  --> $DIR/error-handling.rs:26:16
+  --> $DIR/error-handling.rs:25:16
    |
 LL | fn foo<'a, 'b, 'c>(x: &'static i32, mut y: &'a i32) -> E<'b, 'c> {
    |        --  -- lifetime `'b` defined here

src/test/ui/impl-trait/multiple-lifetimes/error-handling.min_tait.stderr

@@ -1,5 +1,5 @@
 error: lifetime may not live long enough
-  --> $DIR/error-handling.rs:26:16
+  --> $DIR/error-handling.rs:25:16
    |
 LL | fn foo<'a, 'b, 'c>(x: &'static i32, mut y: &'a i32) -> E<'b, 'c> {
    |        --  -- lifetime `'b` defined here

src/test/ui/impl-trait/multiple-lifetimes/error-handling.rs

@@ -1,6 +1,5 @@
 // compile-flags:-Zborrowck=mir
 
-#![feature(member_constraints)]
 // revisions: min_tait full_tait
 #![feature(min_type_alias_impl_trait)]
 #![cfg_attr(full_tait, feature(type_alias_impl_trait))]

src/test/ui/impl-trait/multiple-lifetimes/inverse-bounds.rs

@@ -3,8 +3,6 @@
 // revisions: migrate mir
 //[mir]compile-flags: -Z borrowck=mir
 
-#![feature(member_constraints)]
-
 trait Trait<'a, 'b> {}
 impl<T> Trait<'_, '_> for T {}
 

src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-pick-original-elided.rs

@@ -3,10 +3,8 @@
 // revisions: migrate mir
 //[mir]compile-flags: -Z borrowck=mir
 
-#![feature(member_constraints)]
-
-trait Trait<'a, 'b> { }
-impl<T> Trait<'_, '_> for T { }
+trait Trait<'a, 'b> {}
+impl<T> Trait<'_, '_> for T {}
 
 // Test case where we have elision in the impl trait and we have to
 // pick the right region.
@@ -26,4 +24,4 @@ fn upper_bounds3<'b>(a: &u8) -> impl Trait<'_, 'b> {
     (a, a)
 }
 
-fn main() { }
+fn main() {}

src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-pick-original-type-alias-impl-trait.rs

@@ -3,10 +3,9 @@
 // revisions: migrate mir
 //[mir]compile-flags: -Z borrowck=mir
 
-#![feature(member_constraints)]
 #![feature(min_type_alias_impl_trait)]
-trait Trait<'a, 'b> { }
-impl<T> Trait<'_, '_> for T { }
+trait Trait<'a, 'b> {}
+impl<T> Trait<'_, '_> for T {}
 
 // Here we wind up selecting `'a` and `'b` in the hidden type because
 // those are the types that appear in the original values.
@@ -28,4 +27,4 @@ fn upper_bounds<'a, 'b>(a: &'a u8, b: &'b u8) -> Foo<'a, 'b> {
     (a, b)
 }
 
-fn main() { }
+fn main() {}

src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-pick-original.rs

@@ -3,10 +3,8 @@
 // revisions: migrate mir
 //[mir]compile-flags: -Z borrowck=mir
 
-#![feature(member_constraints)]
-
-trait Trait<'a, 'b> { }
-impl<T> Trait<'_, '_> for T { }
+trait Trait<'a, 'b> {}
+impl<T> Trait<'_, '_> for T {}
 
 // Here we wind up selecting `'a` and `'b` in the hidden type because
 // those are the types that appear in the original values.
@@ -26,4 +24,4 @@ fn upper_bounds<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a, 'b> {
     (a, b)
 }
 
-fn main() { }
+fn main() {}

src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-pick-other.rs

@@ -3,8 +3,6 @@
 // revisions: migrate mir
 //[mir]compile-flags: -Z borrowck=mir
 
-#![feature(member_constraints)]
-
 trait Trait<'a, 'b> {}
 impl<T> Trait<'_, '_> for T {}
 

src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-unrelated.nll.stderr

@@ -1,5 +1,5 @@
 error[E0700]: hidden type for `impl Trait` captures lifetime that does not appear in bounds
-  --> $DIR/ordinary-bounds-unrelated.rs:18:74
+  --> $DIR/ordinary-bounds-unrelated.rs:16:74
    |
 LL | fn upper_bounds<'a, 'b, 'c, 'd, 'e>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'d, 'e>
    |                                                                          ^^^^^^^^^^^^^^^^^^

src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-unrelated.rs

@@ -1,7 +1,5 @@
 // edition:2018
 
-#![feature(member_constraints)]
-
 trait Trait<'a, 'b> {}
 impl<T> Trait<'_, '_> for T {}
 

src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-unrelated.stderr

@@ -1,11 +1,11 @@
 error[E0700]: hidden type for `impl Trait` captures lifetime that does not appear in bounds
-  --> $DIR/ordinary-bounds-unrelated.rs:18:74
+  --> $DIR/ordinary-bounds-unrelated.rs:16:74
    |
 LL | fn upper_bounds<'a, 'b, 'c, 'd, 'e>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'d, 'e>
    |                                                                          ^^^^^^^^^^^^^^^^^^
    |
 note: hidden type `Ordinary<'_>` captures lifetime smaller than the function body
-  --> $DIR/ordinary-bounds-unrelated.rs:18:74
+  --> $DIR/ordinary-bounds-unrelated.rs:16:74
    |
 LL | fn upper_bounds<'a, 'b, 'c, 'd, 'e>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'d, 'e>
    |                                                                          ^^^^^^^^^^^^^^^^^^

src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-unsuited.nll.stderr

@@ -1,5 +1,5 @@
 error[E0700]: hidden type for `impl Trait` captures lifetime that does not appear in bounds
-  --> $DIR/ordinary-bounds-unsuited.rs:20:62
+  --> $DIR/ordinary-bounds-unsuited.rs:18:62
    |
 LL | fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b>
    |                                                              ^^^^^^^^^^^^^^^^^^

src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-unsuited.rs

@@ -1,7 +1,5 @@
 // edition:2018
 
-#![feature(member_constraints)]
-
 trait Trait<'a, 'b> {}
 impl<T> Trait<'_, '_> for T {}
 
@@ -18,7 +16,7 @@ struct Ordinary<'a>(&'a u8);
 // consider the loans for both `'a` and `'b` alive.
 
 fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b>
-    //~^ ERROR hidden type for `impl Trait` captures lifetime that does not appear in bounds
+//~^ ERROR hidden type for `impl Trait` captures lifetime that does not appear in bounds
 {
     // We return a value:
     //

src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-unsuited.stderr

@@ -1,11 +1,11 @@
 error[E0700]: hidden type for `impl Trait` captures lifetime that does not appear in bounds
-  --> $DIR/ordinary-bounds-unsuited.rs:20:62
+  --> $DIR/ordinary-bounds-unsuited.rs:18:62
    |
 LL | fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b>
    |                                                              ^^^^^^^^^^^^^^^^^^
    |
 note: hidden type `Ordinary<'_>` captures lifetime smaller than the function body
-  --> $DIR/ordinary-bounds-unsuited.rs:20:62
+  --> $DIR/ordinary-bounds-unsuited.rs:18:62
    |
 LL | fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b>
    |                                                              ^^^^^^^^^^^^^^^^^^

src/test/ui/impl-trait/needs_least_region_or_bound.rs

@@ -1,7 +1,5 @@
 // check-pass
 
-#![feature(member_constraints)]
-
 trait MultiRegionTrait<'a, 'b> {}
 impl<'a, 'b> MultiRegionTrait<'a, 'b> for (&'a u32, &'b u32) {}
 

src/test/ui/type-alias-impl-trait/issue-74761.full_tait.stderr

@@ -1,5 +1,5 @@
 warning: the feature `type_alias_impl_trait` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/issue-74761.rs:4:32
+  --> $DIR/issue-74761.rs:3:32
    |
 LL | #![cfg_attr(full_tait, feature(type_alias_impl_trait))]
    |                                ^^^^^^^^^^^^^^^^^^^^^
@@ -8,13 +8,13 @@ LL | #![cfg_attr(full_tait, feature(type_alias_impl_trait))]
    = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
 
 error[E0207]: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/issue-74761.rs:11:6
+  --> $DIR/issue-74761.rs:10:6
    |
 LL | impl<'a, 'b> A for () {
    |      ^^ unconstrained lifetime parameter
 
 error[E0207]: the lifetime parameter `'b` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/issue-74761.rs:11:10
+  --> $DIR/issue-74761.rs:10:10
    |
 LL | impl<'a, 'b> A for () {
    |          ^^ unconstrained lifetime parameter

src/test/ui/type-alias-impl-trait/issue-74761.min_tait.stderr

@@ -1,11 +1,11 @@
 error[E0207]: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/issue-74761.rs:11:6
+  --> $DIR/issue-74761.rs:10:6
    |
 LL | impl<'a, 'b> A for () {
    |      ^^ unconstrained lifetime parameter
 
 error[E0207]: the lifetime parameter `'b` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/issue-74761.rs:11:10
+  --> $DIR/issue-74761.rs:10:10
    |
 LL | impl<'a, 'b> A for () {
    |          ^^ unconstrained lifetime parameter

src/test/ui/type-alias-impl-trait/issue-74761.rs

@@ -1,4 +1,3 @@
-#![feature(member_constraints)]
 // revisions: min_tait full_tait
 #![feature(min_type_alias_impl_trait)]
 #![cfg_attr(full_tait, feature(type_alias_impl_trait))]