Rollup merge of #75554 - jumbatm:fix-clashing-extern-decl-overflow, r=lcnr

Fix clashing_extern_declarations stack overflow for recursive types.

Fixes #75512.

Adds a seen set to `structurally_same_type` to avoid recursing indefinitely for types which contain values of the same type through a pointer or reference.

src/test/ui/lint/clashing-extern-fn-recursion.rs

@@ -0,0 +1,119 @@
+// check-pass
+//
+// This tests checks that clashing_extern_declarations handles types that are recursive through a
+// pointer or ref argument. See #75512.
+
+#![crate_type = "lib"]
+
+mod raw_ptr_recursion {
+    mod a {
+        #[repr(C)]
+        struct Pointy {
+            pointy: *const Pointy,
+        }
+
+        extern "C" {
+            fn run_pointy(pointy: Pointy);
+        }
+    }
+    mod b {
+        #[repr(C)]
+        struct Pointy {
+            pointy: *const Pointy,
+        }
+
+        extern "C" {
+            fn run_pointy(pointy: Pointy);
+        }
+    }
+}
+
+mod raw_ptr_recursion_once_removed {
+    mod a {
+        #[repr(C)]
+        struct Pointy1 {
+            pointy_two: *const Pointy2,
+        }
+
+        #[repr(C)]
+        struct Pointy2 {
+            pointy_one: *const Pointy1,
+        }
+
+        extern "C" {
+            fn run_pointy2(pointy: Pointy2);
+        }
+    }
+
+    mod b {
+        #[repr(C)]
+        struct Pointy1 {
+            pointy_two: *const Pointy2,
+        }
+
+        #[repr(C)]
+        struct Pointy2 {
+            pointy_one: *const Pointy1,
+        }
+
+        extern "C" {
+            fn run_pointy2(pointy: Pointy2);
+        }
+    }
+}
+
+mod ref_recursion {
+    mod a {
+        #[repr(C)]
+        struct Reffy<'a> {
+            reffy: &'a Reffy<'a>,
+        }
+
+        extern "C" {
+            fn reffy_recursion(reffy: Reffy);
+        }
+    }
+    mod b {
+        #[repr(C)]
+        struct Reffy<'a> {
+            reffy: &'a Reffy<'a>,
+        }
+
+        extern "C" {
+            fn reffy_recursion(reffy: Reffy);
+        }
+    }
+}
+
+mod ref_recursion_once_removed {
+    mod a {
+        #[repr(C)]
+        struct Reffy1<'a> {
+            reffy: &'a Reffy2<'a>,
+        }
+
+        struct Reffy2<'a> {
+            reffy: &'a Reffy1<'a>,
+        }
+
+        extern "C" {
+            #[allow(improper_ctypes)]
+            fn reffy_once_removed(reffy: Reffy1);
+        }
+    }
+    mod b {
+        #[repr(C)]
+        struct Reffy1<'a> {
+            reffy: &'a Reffy2<'a>,
+        }
+
+        struct Reffy2<'a> {
+            reffy: &'a Reffy1<'a>,
+        }
+
+        extern "C" {
+            #[allow(improper_ctypes)]
+            fn reffy_once_removed(reffy: Reffy1);
+        }
+    }
+}