Add test cases for detecting structural recursion

src/test/ui/issues/issue-74224.rs

@@ -0,0 +1,11 @@
+struct A<T> {
+//~^ ERROR recursive type `A` has infinite size
+    x: T,
+    y: A<A<T>>,
+}
+
+struct B {
+    z: A<usize>
+}
+
+fn main() {}

src/test/ui/issues/issue-74224.stderr

@@ -0,0 +1,17 @@
+error[E0072]: recursive type `A` has infinite size
+  --> $DIR/issue-74224.rs:1:1
+   |
+LL | struct A<T> {
+   | ^^^^^^^^^^^ recursive type has infinite size
+...
+LL |     y: A<A<T>>,
+   |        ------- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `A` representable
+   |
+LL |     y: Box<A<A<T>>>,
+   |        ^^^^       ^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0072`.

src/test/ui/issues/issue-84611.rs

@@ -0,0 +1,11 @@
+struct Foo<T> {
+//~^ ERROR recursive type `Foo` has infinite size
+    x: Foo<[T; 1]>,
+    y: T,
+}
+
+struct Bar {
+    x: Foo<Bar>,
+}
+
+fn main() {}

src/test/ui/issues/issue-84611.stderr

@@ -0,0 +1,17 @@
+error[E0072]: recursive type `Foo` has infinite size
+  --> $DIR/issue-84611.rs:1:1
+   |
+LL | struct Foo<T> {
+   | ^^^^^^^^^^^^^ recursive type has infinite size
+LL |
+LL |     x: Foo<[T; 1]>,
+   |        ----------- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
+   |
+LL |     x: Box<Foo<[T; 1]>>,
+   |        ^^^^           ^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0072`.

src/test/ui/mutual-struct-recursion.rs

@@ -0,0 +1,23 @@
+struct A<T> {
+//~^ ERROR recursive type `A` has infinite size
+    x: T,
+    y: B<T>,
+}
+
+struct B<T> {
+//~^ ERROR recursive type `B` has infinite size
+    z: A<T>
+}
+
+struct C<T> {
+//~^ ERROR recursive type `C` has infinite size
+    x: T,
+    y: Option<Option<D<T>>>,
+}
+
+struct D<T> {
+//~^ ERROR recursive type `D` has infinite size
+    z: Option<Option<C<T>>>,
+}
+
+fn main() {}

src/test/ui/mutual-struct-recursion.stderr

@@ -0,0 +1,59 @@
+error[E0072]: recursive type `A` has infinite size
+  --> $DIR/mutual-struct-recursion.rs:1:1
+   |
+LL | struct A<T> {
+   | ^^^^^^^^^^^ recursive type has infinite size
+...
+LL |     y: B<T>,
+   |        ---- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `A` representable
+   |
+LL |     y: Box<B<T>>,
+   |        ^^^^    ^
+
+error[E0072]: recursive type `B` has infinite size
+  --> $DIR/mutual-struct-recursion.rs:7:1
+   |
+LL | struct B<T> {
+   | ^^^^^^^^^^^ recursive type has infinite size
+LL |
+LL |     z: A<T>
+   |        ---- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `B` representable
+   |
+LL |     z: Box<A<T>>
+   |        ^^^^    ^
+
+error[E0072]: recursive type `C` has infinite size
+  --> $DIR/mutual-struct-recursion.rs:12:1
+   |
+LL | struct C<T> {
+   | ^^^^^^^^^^^ recursive type has infinite size
+...
+LL |     y: Option<Option<D<T>>>,
+   |        -------------------- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `C` representable
+   |
+LL |     y: Box<Option<Option<D<T>>>>,
+   |        ^^^^                    ^
+
+error[E0072]: recursive type `D` has infinite size
+  --> $DIR/mutual-struct-recursion.rs:18:1
+   |
+LL | struct D<T> {
+   | ^^^^^^^^^^^ recursive type has infinite size
+LL |
+LL |     z: Option<Option<C<T>>>,
+   |        -------------------- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `D` representable
+   |
+LL |     z: Box<Option<Option<C<T>>>>,
+   |        ^^^^                    ^
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0072`.