Allow ~const bounds on trait assoc functions

src/test/ui/rfc-2632-const-trait-impl/trait-where-clause-run.rs

@@ -0,0 +1,41 @@
+// run-pass
+
+#![feature(const_trait_impl)]
+#![feature(const_fn_trait_bound)]
+
+trait Bar {
+    fn bar() -> u8;
+}
+
+trait Foo {
+    #[default_method_body_is_const]
+    fn foo() -> u8 where Self: ~const Bar {
+        <Self as Bar>::bar() * 6
+    }
+}
+
+struct NonConst;
+struct Const;
+
+impl Bar for NonConst {
+    fn bar() -> u8 {
+        3
+    }
+}
+
+impl Foo for NonConst {}
+
+impl const Bar for Const {
+    fn bar() -> u8 {
+        4
+    }
+}
+
+impl const Foo for Const {}
+
+fn main() {
+    const ANS1: u8 = Const::foo();
+    let ans2 = NonConst::foo();
+
+    assert_eq!(ANS1 + ans2, 42);
+}

src/test/ui/rfc-2632-const-trait-impl/trait-where-clause-self-referential.rs

@@ -0,0 +1,24 @@
+// check-pass
+
+#![feature(const_trait_impl)]
+#![feature(const_fn_trait_bound)]
+
+trait Foo {
+    fn bar() where Self: ~const Foo;
+}
+
+struct S;
+
+impl Foo for S {
+    fn bar() {}
+}
+
+fn baz<T: Foo>() {
+    T::bar();
+}
+
+const fn qux<T: ~const Foo>() {
+    T::bar();
+}
+
+fn main() {}

src/test/ui/rfc-2632-const-trait-impl/trait-where-clause.rs

@@ -6,28 +6,35 @@ trait Bar {}
 trait Foo {
     fn a();
     fn b() where Self: ~const Bar;
+    fn c<T: ~const Bar>();
 }
 
 const fn test1<T: ~const Foo + Bar>() {
     T::a();
     T::b();
     //~^ ERROR the trait bound
+    T::c::<T>();
+    //~^ ERROR the trait bound
 }
 
 const fn test2<T: ~const Foo + ~const Bar>() {
     T::a();
     T::b();
+    T::c::<T>();
 }
 
 fn test3<T: Foo>() {
     T::a();
     T::b();
     //~^ ERROR the trait bound
+    T::c::<T>();
+    //~^ ERROR the trait bound
 }
 
 fn test4<T: Foo + Bar>() {
     T::a();
     T::b();
+    T::c::<T>();
 }
 
 fn main() {}

src/test/ui/rfc-2632-const-trait-impl/trait-where-clause.stderr

@@ -1,5 +1,5 @@
 error[E0277]: the trait bound `T: Bar` is not satisfied
-  --> $DIR/trait-where-clause.rs:13:5
+  --> $DIR/trait-where-clause.rs:14:5
    |
 LL |     T::b();
    |     ^^^^ the trait `Bar` is not implemented for `T`
@@ -15,7 +15,23 @@ LL | const fn test1<T: ~const Foo + Bar + Bar>() {
    |                                    +++++
 
 error[E0277]: the trait bound `T: Bar` is not satisfied
-  --> $DIR/trait-where-clause.rs:24:5
+  --> $DIR/trait-where-clause.rs:16:5
+   |
+LL |     T::c::<T>();
+   |     ^^^^^^^^^ the trait `Bar` is not implemented for `T`
+   |
+note: required by `Foo::c`
+  --> $DIR/trait-where-clause.rs:9:5
+   |
+LL |     fn c<T: ~const Bar>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+help: consider further restricting this bound
+   |
+LL | const fn test1<T: ~const Foo + Bar + Bar>() {
+   |                                    +++++
+
+error[E0277]: the trait bound `T: Bar` is not satisfied
+  --> $DIR/trait-where-clause.rs:28:5
    |
 LL |     T::b();
    |     ^^^^ the trait `Bar` is not implemented for `T`
@@ -30,6 +46,22 @@ help: consider further restricting this bound
 LL | fn test3<T: Foo + Bar>() {
    |                 +++++
 
-error: aborting due to 2 previous errors
+error[E0277]: the trait bound `T: Bar` is not satisfied
+  --> $DIR/trait-where-clause.rs:30:5
+   |
+LL |     T::c::<T>();
+   |     ^^^^^^^^^ the trait `Bar` is not implemented for `T`
+   |
+note: required by `Foo::c`
+  --> $DIR/trait-where-clause.rs:9:5
+   |
+LL |     fn c<T: ~const Bar>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+help: consider further restricting this bound
+   |
+LL | fn test3<T: Foo + Bar>() {
+   |                 +++++
+
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0277`.