Check lazy type aliases for well-formedness

tests/ui/lazy-type-alias/enum-variant.rs

@@ -0,0 +1,18 @@
+// Regression test for issue #113736.
+// check-pass
+
+#![feature(lazy_type_alias)]
+//~^ WARN the feature `lazy_type_alias` is incomplete and may not be safe to use
+
+enum Enum {
+    Unit,
+    Tuple(),
+    Struct {},
+}
+
+fn main() {
+    type Alias = Enum;
+    let _ = Alias::Unit;
+    let _ = Alias::Tuple();
+    let _ = Alias::Struct {};
+}

tests/ui/lazy-type-alias/enum-variant.stderr

@@ -0,0 +1,11 @@
+warning: the feature `lazy_type_alias` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/enum-variant.rs:4:12
+   |
+LL | #![feature(lazy_type_alias)]
+   |            ^^^^^^^^^^^^^^^
+   |
+   = note: see issue #112792 <https://github.com/rust-lang/rust/issues/112792> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/lazy-type-alias/type-alias-bounds-are-enforced.rs

@@ -0,0 +1,14 @@
+// Check that we don't issue the lint `type_alias_bounds` for
+// lazy type aliases since the bounds are indeed enforced.
+
+// check-pass
+
+#![feature(lazy_type_alias)]
+#![allow(incomplete_features)]
+#![deny(type_alias_bounds)]
+
+use std::ops::Mul;
+
+type Alias<T: Mul> = <T as Mul>::Output;
+
+fn main() {}

tests/ui/lazy-type-alias/unsatisfied-bounds-type-alias-body.rs

@@ -0,0 +1,8 @@
+// Test that we check lazy type aliases for well-formedness.
+
+#![feature(lazy_type_alias)]
+#![allow(incomplete_features)]
+
+type Alias<T> = <T as std::ops::Mul>::Output; //~ ERROR cannot multiply `T` by `T`
+
+fn main() {}

tests/ui/lazy-type-alias/unsatisfied-bounds-type-alias-body.stderr

@@ -0,0 +1,14 @@
+error[E0277]: cannot multiply `T` by `T`
+  --> $DIR/unsatisfied-bounds-type-alias-body.rs:6:17
+   |
+LL | type Alias<T> = <T as std::ops::Mul>::Output;
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no implementation for `T * T`
+   |
+help: consider restricting type parameter `T`
+   |
+LL | type Alias<T: std::ops::Mul> = <T as std::ops::Mul>::Output;
+   |             +++++++++++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.