fix: Yet another false positive invalid cast diagnostic

crates/ide-diagnostics/src/handlers/invalid_cast.rs

@@ -440,8 +440,9 @@ fn main() {
     q as *const [i32];
   //^^^^^^^^^^^^^^^^^ error: cannot cast thin pointer `*const i32` to fat pointer `*const [i32]`
 
+    // FIXME: This should emit diagnostics but disabled to prevent many false positives
     let t: *mut (dyn Trait + 'static) = 0 as *mut _;
-                                      //^^^^^^^^^^^ error: cannot cast `usize` to a fat pointer `*mut _`
+
     let mut fail: *const str = 0 as *const str;
                              //^^^^^^^^^^^^^^^ error: cannot cast `usize` to a fat pointer `*const str`
     let mut fail2: *const str = 0isize as *const str;
@@ -1161,6 +1162,49 @@ struct ZerocopyKnownLayoutMaybeUninit(<<Flexible as Field>::Type as KnownLayout>
 fn test(ptr: *mut [u8]) -> *mut ZerocopyKnownLayoutMaybeUninit {
     ptr as *mut _
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn regression_19431() {
+        check_diagnostics(
+            r#"
+//- minicore: coerce_unsized
+struct Dst([u8]);
+
+struct Struct {
+    body: Dst,
+}
+
+trait Field {
+    type Type: ?Sized;
+}
+
+impl Field for Struct {
+    type Type = Dst;
+}
+
+trait KnownLayout {
+    type MaybeUninit: ?Sized;
+    type PointerMetadata;
+}
+
+impl<T> KnownLayout for [T] {
+    type MaybeUninit = [T];
+    type PointerMetadata = usize;
+}
+
+impl KnownLayout for Dst {
+    type MaybeUninit = Dst;
+    type PointerMetadata = <[u8] as KnownLayout>::PointerMetadata;
+}
+
+struct ZerocopyKnownLayoutMaybeUninit(<<Struct as Field>::Type as KnownLayout>::MaybeUninit);
+
+fn test(ptr: *mut ZerocopyKnownLayoutMaybeUninit) -> *mut <<Struct as Field>::Type as KnownLayout>::MaybeUninit {
+    ptr as *mut _
+}
 "#,
         );
     }