feature-gate member constraints outside of async-await

Minimizes risk.

src/test/ui/feature-gates/feature-gate-member-constraints.rs

@@ -0,0 +1,9 @@
+trait Trait<'a, 'b> { }
+impl<T> Trait<'_, '_> for T {}
+
+fn foo<'a, 'b>(x: &'a u32, y: &'b u32) -> impl Trait<'a, 'b> {
+    //~^ ERROR ambiguous lifetime bound
+    (x, y)
+}
+
+fn main() { }

src/test/ui/feature-gates/feature-gate-member-constraints.stderr

@@ -0,0 +1,10 @@
+error: ambiguous lifetime bound in `impl Trait`
+  --> $DIR/feature-gate-member-constraints.rs:4:43
+   |
+LL | fn foo<'a, 'b>(x: &'a u32, y: &'b u32) -> impl Trait<'a, 'b> {
+   |                                           ^^^^^^^^^^^^^^^^^^ neither `'a` nor `'b` outlives the other
+   |
+   = help: add #![feature(member_constraints)] to the crate attributes to enable
+
+error: aborting due to previous error
+

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

@@ -1,5 +1,6 @@
 // compile-flags:-Zborrowck=mir
 
+#![feature(member_constraints)]
 #![feature(existential_type)]
 
 #[derive(Clone)]

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

@@ -1,5 +1,5 @@
 error: lifetime may not live long enough
-  --> $DIR/error-handling.rs:12:56
+  --> $DIR/error-handling.rs:13:56
    |
 LL | fn foo<'a, 'b, 'c>(x: &'static i32, mut y: &'a i32) -> E<'b, 'c> {
    |        -- lifetime `'a` defined here                   ^^^^^^^^^ opaque type requires that `'a` must outlive `'static`

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

@@ -3,6 +3,8 @@
 // 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

@@ -3,6 +3,8 @@
 // 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-existential.rs

@@ -3,6 +3,7 @@
 // revisions: migrate mir
 //[mir]compile-flags: -Z borrowck=mir
 
+#![feature(member_constraints)]
 #![feature(existential_type)]
 
 trait Trait<'a, 'b> { }

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

@@ -3,6 +3,8 @@
 // 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-other.rs

@@ -3,6 +3,8 @@
 // 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.rs

@@ -1,5 +1,7 @@
 // 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:16:74
+  --> $DIR/ordinary-bounds-unrelated.rs:18:74
    |
 LL | fn upper_bounds<'a, 'b, 'c, 'd, 'e>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'d, 'e>
    |                                                                          ^^^^^^^^^^^^^^^^^^
    |
-note: hidden type `Ordinary<'_>` captures the scope of call-site for function at 21:1
-  --> $DIR/ordinary-bounds-unrelated.rs:21:1
+note: hidden type `Ordinary<'_>` captures the scope of call-site for function at 23:1
+  --> $DIR/ordinary-bounds-unrelated.rs:23:1
    |
 LL | / {
 LL | |     // Hidden type `Ordinary<'0>` with constraints:

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

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

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:18:62
+  --> $DIR/ordinary-bounds-unsuited.rs:20:62
    |
 LL | fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b>
    |                                                              ^^^^^^^^^^^^^^^^^^
    |
-note: hidden type `Ordinary<'_>` captures the scope of call-site for function at 20:1
-  --> $DIR/ordinary-bounds-unsuited.rs:20:1
+note: hidden type `Ordinary<'_>` captures the scope of call-site for function at 22:1
+  --> $DIR/ordinary-bounds-unsuited.rs:22:1
    |
 LL | / {
 LL | |     // We return a value:

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

@@ -1,5 +1,7 @@
 // run-pass
 
+#![feature(member_constraints)]
+
 use std::fmt::Debug;
 
 trait MultiRegionTrait<'a, 'b> {}