Rollup merge of #92248 - compiler-errors:normalize-type-for-pointee, r=jackh726

Normalize struct tail type when checking Pointee trait

Let's go ahead and implement the FIXMEs by properly normalizing the struct-tail type when satisfying a Pointee obligation. This should fix the ICE when we try to calculate a layout depending on `<Ty as Pointee>::Metadata` later.
Fixes #92128
Fixes #92577

Additionally, mark the obligation as ambiguous if there are any infer types in that struct-tail type. This has the effect of causing `<_ as Pointee>::Metadata` to be properly replaced with an infer variable ([here](https://github.com/rust-lang/rust/blob/master/compiler/rustc_trait_selection/src/traits/project.rs#L813)) and registered as an obligation... this turns out to be very important in unifying function parameters with formals that are assoc types.

Fixes #91446

1 files changed, 22 insertions, 0 deletions

diff --git a/src/test/ui/traits/pointee-deduction.rs b/src/test/ui/traits/pointee-deduction.rs
new file mode 100644
index 00000000000..f888246967d
--- /dev/null
+++ b/src/test/ui/traits/pointee-deduction.rs
@@ -0,0 +1,22 @@
+// run-pass
+
+#![feature(ptr_metadata)]
+
+use std::alloc::Layout;
+use std::ptr::Pointee;
+
+trait Foo {
+    type Bar;
+}
+
+impl Foo for () {
+    type Bar = ();
+}
+
+struct Wrapper1<T: Foo>(<T as Foo>::Bar);
+struct Wrapper2<T: Foo>(<Wrapper1<T> as Pointee>::Metadata);
+
+fn main() {
+    let _: Wrapper2<()> = Wrapper2(());
+    let _ = Layout::new::<Wrapper2<()>>();
+}