moved renamed docs formatted stderr | invalid_dispatch_from_dyn_impls.rs

Author: Kivooeo

tests/ui/invalid_dispatch_from_dyn_impls.rs renamed to tests/ui/traits/dispatch-from-dyn-invalid-impls.rs

@@ -1,55 +1,71 @@
+//! Test various invalid implementations of DispatchFromDyn trait.
+//!
+//! DispatchFromDyn is a special trait used by the compiler for object-safe dynamic dispatch.
+//! This checks that the compiler correctly rejects invalid implementations:
+//! - Structs with extra non-coercible fields
+//! - Structs with multiple pointer fields
+//! - Structs with no coercible fields
+//! - Structs with repr(C) or other incompatible representations
+//! - Structs with over-aligned fields
+
 #![feature(unsize, dispatch_from_dyn)]
 
-use std::{
-    ops::DispatchFromDyn,
-    marker::{Unsize, PhantomData},
-};
+use std::marker::{PhantomData, Unsize};
+use std::ops::DispatchFromDyn;
 
+// Error: Extra field prevents DispatchFromDyn
 struct WrapperWithExtraField<T>(T, i32);
 
 impl<T, U> DispatchFromDyn<WrapperWithExtraField<U>> for WrapperWithExtraField<T>
 //~^ ERROR [E0378]
 where
-    T: DispatchFromDyn<U>,
-{}
-
+    T: DispatchFromDyn<U>
+{
+}
 
-struct MultiplePointers<T: ?Sized>{
+// Error: Multiple pointer fields create ambiguous coercion
+struct MultiplePointers<T: ?Sized> {
     ptr1: *const T,
     ptr2: *const T,
 }
 
 impl<T: ?Sized, U: ?Sized> DispatchFromDyn<MultiplePointers<U>> for MultiplePointers<T>
 //~^ ERROR implementing `DispatchFromDyn` does not allow multiple fields to be coerced
 where
-    T: Unsize<U>,
-{}
-
+    T: Unsize<U>
+{
+}
 
+// Error: No coercible fields (only PhantomData)
 struct NothingToCoerce<T: ?Sized> {
     data: PhantomData<T>,
 }
 
 impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NothingToCoerce<T>> for NothingToCoerce<U> {}
 //~^ ERROR implementing `DispatchFromDyn` requires a field to be coerced
 
+// Error: repr(C) is incompatible with DispatchFromDyn
 #[repr(C)]
 struct HasReprC<T: ?Sized>(Box<T>);
 
 impl<T: ?Sized, U: ?Sized> DispatchFromDyn<HasReprC<U>> for HasReprC<T>
 //~^ ERROR [E0378]
 where
-    T: Unsize<U>,
-{}
+    T: Unsize<U>
+{
+}
 
+// Error: Over-aligned fields are incompatible
 #[repr(align(64))]
 struct OverAlignedZst;
+
 struct OverAligned<T: ?Sized>(Box<T>, OverAlignedZst);
 
 impl<T: ?Sized, U: ?Sized> DispatchFromDyn<OverAligned<U>> for OverAligned<T>
 //~^ ERROR [E0378]
-    where
-        T: Unsize<U>,
-{}
+where
+    T: Unsize<U>
+{
+}
 
 fn main() {}

tests/ui/invalid_dispatch_from_dyn_impls.stderr renamed to tests/ui/traits/dispatch-from-dyn-invalid-impls.stderr

@@ -1,56 +1,56 @@
 error[E0378]: the trait `DispatchFromDyn` may only be implemented for structs containing the field being coerced, ZST fields with 1 byte alignment that don't mention type/const generics, and nothing else
-  --> $DIR/invalid_dispatch_from_dyn_impls.rs:10:1
+  --> $DIR/dispatch-from-dyn-invalid-impls.rs:19:1
    |
 LL | / impl<T, U> DispatchFromDyn<WrapperWithExtraField<U>> for WrapperWithExtraField<T>
 LL | |
 LL | | where
-LL | |     T: DispatchFromDyn<U>,
-   | |__________________________^
+LL | |     T: DispatchFromDyn<U>
+   | |_________________________^
    |
    = note: extra field `1` of type `i32` is not allowed
 
 error[E0375]: implementing `DispatchFromDyn` does not allow multiple fields to be coerced
-  --> $DIR/invalid_dispatch_from_dyn_impls.rs:22:1
+  --> $DIR/dispatch-from-dyn-invalid-impls.rs:32:1
    |
 LL | / impl<T: ?Sized, U: ?Sized> DispatchFromDyn<MultiplePointers<U>> for MultiplePointers<T>
 LL | |
 LL | | where
-LL | |     T: Unsize<U>,
-   | |_________________^
+LL | |     T: Unsize<U>
+   | |________________^
    |
 note: the trait `DispatchFromDyn` may only be implemented when a single field is being coerced
-  --> $DIR/invalid_dispatch_from_dyn_impls.rs:18:5
+  --> $DIR/dispatch-from-dyn-invalid-impls.rs:28:5
    |
 LL |     ptr1: *const T,
    |     ^^^^^^^^^^^^^^
 LL |     ptr2: *const T,
    |     ^^^^^^^^^^^^^^
 
 error[E0374]: implementing `DispatchFromDyn` requires a field to be coerced
-  --> $DIR/invalid_dispatch_from_dyn_impls.rs:33:1
+  --> $DIR/dispatch-from-dyn-invalid-impls.rs:44:1
    |
 LL | impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NothingToCoerce<T>> for NothingToCoerce<U> {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: expected a single field to be coerced, none found
 
 error[E0378]: structs implementing `DispatchFromDyn` may not have `#[repr(packed)]` or `#[repr(C)]`
-  --> $DIR/invalid_dispatch_from_dyn_impls.rs:39:1
+  --> $DIR/dispatch-from-dyn-invalid-impls.rs:51:1
    |
 LL | / impl<T: ?Sized, U: ?Sized> DispatchFromDyn<HasReprC<U>> for HasReprC<T>
 LL | |
 LL | | where
-LL | |     T: Unsize<U>,
-   | |_________________^
+LL | |     T: Unsize<U>
+   | |________________^
 
 error[E0378]: the trait `DispatchFromDyn` may only be implemented for structs containing the field being coerced, ZST fields with 1 byte alignment that don't mention type/const generics, and nothing else
-  --> $DIR/invalid_dispatch_from_dyn_impls.rs:49:1
+  --> $DIR/dispatch-from-dyn-invalid-impls.rs:64:1
    |
 LL | / impl<T: ?Sized, U: ?Sized> DispatchFromDyn<OverAligned<U>> for OverAligned<T>
 LL | |
-LL | |     where
-LL | |         T: Unsize<U>,
-   | |_____________________^
+LL | | where
+LL | |     T: Unsize<U>
+   | |________________^
    |
    = note: extra field `1` of type `OverAlignedZst` is not allowed