Add UI tests for empty items

Author: daxpedda

non-msrv-tests/tests/ui/use_case.rs

@@ -1,5 +1,21 @@
 use derive_where::DeriveWhere;
 
+#[derive(DeriveWhere)]
+#[derive_where(Clone)]
+struct StructEmpty {}
+
+#[derive(DeriveWhere)]
+#[derive_where(Clone)]
+struct TupleEmpty();
+
+#[derive(DeriveWhere)]
+#[derive_where(Clone)]
+struct Unit;
+
+#[derive(DeriveWhere)]
+#[derive_where(Clone)]
+struct UnionEmpty {}
+
 #[derive(DeriveWhere)]
 #[derive_where(Clone)]
 struct StructNone(u8);

non-msrv-tests/tests/ui/use_case.stderr

@@ -1,15 +1,43 @@
-error: derive-where doesn't support items without generics, `skip` attributes or `enum`s implementing `Default`, as this can already be handled by standard `#[derive(..)]`
+error: derive-where doesn't support empty items, as this can already be handled by standard `#[derive(..)]`
  --> tests/ui/use_case.rs:4:1
   |
 4 | / #[derive_where(Clone)]
-5 | | struct StructNone(u8);
-  | |______________________^
+5 | | struct StructEmpty {}
+  | |_____________________^
+
+error: derive-where doesn't support empty items, as this can already be handled by standard `#[derive(..)]`
+ --> tests/ui/use_case.rs:8:1
+  |
+8 | / #[derive_where(Clone)]
+9 | | struct TupleEmpty();
+  | |____________________^
+
+error: derive-where doesn't support empty items, as this can already be handled by standard `#[derive(..)]`
+  --> tests/ui/use_case.rs:12:1
+   |
+12 | / #[derive_where(Clone)]
+13 | | struct Unit;
+   | |____________^
+
+error: derive-where doesn't support empty items, as this can already be handled by standard `#[derive(..)]`
+  --> tests/ui/use_case.rs:16:1
+   |
+16 | / #[derive_where(Clone)]
+17 | | struct UnionEmpty {}
+   | |____________________^
+
+error: derive-where doesn't support items without generics, `skip` attributes or `enum`s implementing `Default`, as this can already be handled by standard `#[derive(..)]`
+  --> tests/ui/use_case.rs:20:1
+   |
+20 | / #[derive_where(Clone)]
+21 | | struct StructNone(u8);
+   | |______________________^
 
 error: derive-where doesn't support items without generics, `skip` attributes or `enum`s implementing `Default`, as this can already be handled by standard `#[derive(..)]`
-  --> tests/ui/use_case.rs:8:1
+  --> tests/ui/use_case.rs:24:1
    |
-8  | / #[derive_where(Clone)]
-9  | | enum EnumNone {
-10 | |     A(u8),
-11 | | }
+24 | / #[derive_where(Clone)]
+25 | | enum EnumNone {
+26 | |     A(u8),
+27 | | }
    | |_^