add tests for the check and enhanced alias bound assembly

Author: adwinwhite

tests/ui/implied-bounds/item-bounds-from-projection-clause.rs

@@ -0,0 +1,40 @@
+//@ check-pass
+//@ compile-flags: -Znext-solver
+
+// If the rhs of a projection predicate is generic, then we imply item bounds of the associated
+// types on it.
+
+trait Trait {
+    type Assoc: Copy;
+}
+
+trait Explicit {}
+impl<T: Trait<Assoc = U>, U: Copy> Explicit for T {}
+
+fn assert_explicit<T: Explicit>() {}
+fn imply_copy<T: Trait<Assoc = U>, U>() {
+    assert_explicit::<T>();
+}
+
+
+trait BoundA {}
+
+trait HasBoundA {
+    type AssocA: BoundA;
+}
+
+trait BoundB {}
+trait HasBoundB {
+    type AssocB: BoundB;
+}
+
+fn imply_both<T, U>()
+where
+    T: HasBoundA<AssocA = U> + HasBoundB<AssocB = U>,
+{
+    assert_both::<U>();
+}
+
+fn assert_both<T: BoundA + BoundB>() {}
+
+fn main() {}

tests/ui/wf/wf-item-bounds-on-projection.rs

@@ -0,0 +1,31 @@
+// Projection predicate's WFedness requires that the rhs term satisfy all item bounds defined on the
+// associated type.
+// Generic types have those bounds implied.
+
+trait Required {}
+
+trait AssocHasBound {
+    type Assoc: Required;
+}
+
+trait Trait<T> {
+    type Assoc1: AssocHasBound<Assoc = i32>;
+    //~^ ERROR: the trait bound `i32: Required` is not satisfied [E0277]
+    type Assoc2: AssocHasBound<Assoc = T>;
+    type Assoc3: AssocHasBound<Assoc = Self::DummyAssoc>;
+    type DummyAssoc;
+}
+
+fn some_func<T1, T2, U>()
+where
+    T1: AssocHasBound<Assoc = i32>,
+    //~^ ERROR: type annotations needed [E0284]
+    T1: AssocHasBound<Assoc = U>,
+{}
+
+fn opaque_with_concrete_assoc(_: impl AssocHasBound<Assoc = i32>) {}
+//~^ ERROR: the trait bound `i32: Required` is not satisfied [E0277]
+
+fn opaque_with_generic_assoc<T>(_: impl AssocHasBound<Assoc = T>) {}
+
+fn main() {}

tests/ui/wf/wf-item-bounds-on-projection.stderr

@@ -0,0 +1,36 @@
+error[E0284]: type annotations needed
+  --> $DIR/wf-item-bounds-on-projection.rs:21:23
+   |
+LL |     T1: AssocHasBound<Assoc = i32>,
+   |                       ^^^^^^^^^^^ cannot infer type
+   |
+   = note: cannot satisfy `<T1 as AssocHasBound>::Assoc == _`
+
+error[E0277]: the trait bound `i32: Required` is not satisfied
+  --> $DIR/wf-item-bounds-on-projection.rs:26:53
+   |
+LL | fn opaque_with_concrete_assoc(_: impl AssocHasBound<Assoc = i32>) {}
+   |                                                     ^^^^^^^^^^^ the trait `Required` is not implemented for `i32`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/wf-item-bounds-on-projection.rs:5:1
+   |
+LL | trait Required {}
+   | ^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `i32: Required` is not satisfied
+  --> $DIR/wf-item-bounds-on-projection.rs:12:32
+   |
+LL |     type Assoc1: AssocHasBound<Assoc = i32>;
+   |                                ^^^^^^^^^^^ the trait `Required` is not implemented for `i32`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/wf-item-bounds-on-projection.rs:5:1
+   |
+LL | trait Required {}
+   | ^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0277, E0284.
+For more information about an error, try `rustc --explain E0277`.