Rollup merge of #89441 - Nadrieril:fix-89393, r=tmandry

Normalize after substituting via `field.ty()`

Back in https://github.com/rust-lang/rust/issues/72476 I hadn't understood where the problem was coming from, and only worked around the issue. What happens is that calling `field.ty()` on a field of a generic struct substitutes the appropriate generics but doesn't normalize the resulting type.
As a consumer of types I'm surprised that one would substitute without normalizing, feels like a footgun, so I added a comment.

Fixes https://github.com/rust-lang/rust/issues/89393.

src/test/ui/pattern/usefulness/issue-72476-and-89393-associated-type.rs

@@ -0,0 +1,56 @@
+// check-pass
+
+// From https://github.com/rust-lang/rust/issues/72476
+// and https://github.com/rust-lang/rust/issues/89393
+
+trait Trait {
+    type Projection;
+}
+
+struct A;
+impl Trait for A {
+    type Projection = bool;
+}
+
+struct B;
+impl Trait for B {
+    type Projection = (u32, u32);
+}
+
+struct Next<T: Trait>(T::Projection);
+
+fn foo1(item: Next<A>) {
+    match item {
+        Next(true) => {}
+        Next(false) => {}
+    }
+}
+
+fn foo2(x: <A as Trait>::Projection) {
+    match x {
+        true => {}
+        false => {}
+    }
+}
+
+fn foo3(x: Next<B>) {
+    let Next((_, _)) = x;
+    match x {
+        Next((_, _)) => {}
+    }
+}
+
+fn foo4(x: <B as Trait>::Projection) {
+    let (_, _) = x;
+    match x {
+        (_, _) => {}
+    }
+}
+
+fn foo5<T: Trait>(x: <T as Trait>::Projection) {
+    match x {
+        _ => {}
+    }
+}
+
+fn main() {}

src/test/ui/pattern/usefulness/issue-72476-associated-type.rs

@@ -1,22 +0,0 @@
-// check-pass
-
-// From https://github.com/rust-lang/rust/issues/72476
-
-trait A {
-    type Projection;
-}
-
-impl A for () {
-    type Projection = bool;
-}
-
-struct Next<T: A>(T::Projection);
-
-fn f(item: Next<()>) {
-    match item {
-        Next(true) => {}
-        Next(false) => {}
-    }
-}
-
-fn main() {}