Add regression test for #82830

Author: JohnTitor

src/test/ui/traits/issue-82830.rs

@@ -0,0 +1,16 @@
+trait A<Y, N> {
+    type B;
+}
+
+type MaybeBox<T> = <T as A<T, Box<T>>>::B;
+struct P {
+    t: MaybeBox<P>, //~ ERROR: overflow evaluating the requirement `P: Sized`
+}
+
+impl<Y, N> A<Y, N> for P {
+    type B = N;
+}
+
+fn main() {
+    let t: MaybeBox<P>;
+}

src/test/ui/traits/issue-82830.stderr

@@ -0,0 +1,15 @@
+error[E0275]: overflow evaluating the requirement `P: Sized`
+  --> $DIR/issue-82830.rs:7:8
+   |
+LL |     t: MaybeBox<P>,
+   |        ^^^^^^^^^^^
+   |
+note: required because of the requirements on the impl of `A<P, Box<P>>` for `P`
+  --> $DIR/issue-82830.rs:10:12
+   |
+LL | impl<Y, N> A<Y, N> for P {
+   |            ^^^^^^^     ^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0275`.