Auto merge of #124157 - wutchzone:partial_eq, r=estebank

Do not add leading asterisk in the `PartialEq`

I think we should address this issue, however I am not exactly sure, if this is the right way to do it. It is related to the #123056.

Imagine the simplified code:

```rust
trait MyTrait {}

impl PartialEq for dyn MyTrait {
    fn eq(&self, _other: &Self) -> bool {
        true
    }
}

#[derive(PartialEq)]
enum Bar {
    Foo(Box<dyn MyTrait>),
}
```

On the nightly compiler, the `derive` produces invalid code with the weird error message:
```
error[E0507]: cannot move out of `*__arg1_0` which is behind a shared reference
  --> src/main.rs:11:9
   |
9  | #[derive(PartialEq)]
   |          --------- in this derive macro expansion
10 | enum Things {
11 |     Foo(Box<dyn MyTrait>),
   |         ^^^^^^^^^^^^^^^^ move occurs because `*__arg1_0` has type `Box<dyn MyTrait>`, which does not implement the `Copy` trait
   |
   = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
```

It may be related to the perfect derive problem, although requiring the _type_ to be `Copy` seems unfortunate because it is not necessary. Besides, we are adding the extra dereference only for the diagnostics?

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -31,7 +31,7 @@ pub(crate) fn expand_deriving_partial_eq(
                     };
 
                     // We received arguments of type `&T`. Convert them to type `T` by stripping
-                    // any leading `&` or adding `*`. This isn't necessary for type checking, but
+                    // any leading `&`. This isn't necessary for type checking, but
                     // it results in better error messages if something goes wrong.
                     //
                     // Note: for arguments that look like `&{ x }`, which occur with packed
@@ -53,8 +53,7 @@ pub(crate) fn expand_deriving_partial_eq(
                                 inner.clone()
                             }
                         } else {
-                            // No leading `&`: add a leading `*`.
-                            cx.expr_deref(field.span, expr.clone())
+                            expr.clone()
                         }
                     };
                     cx.expr_binary(

compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -123,7 +123,7 @@ fn assert_ty_bounds(
     span: Span,
     assert_path: &[Symbol],
 ) {
-    // Deny anonymous structs or unions to avoid wierd errors.
+    // Deny anonymous structs or unions to avoid weird errors.
     assert!(!ty.kind.is_anon_adt(), "Anonymous structs or unions cannot be type parameters");
     // Generate statement `let _: assert_path<ty>;`.
     let span = cx.with_def_site_ctxt(span);

compiler/rustc_builtin_macros/src/format.rs

@@ -315,7 +315,7 @@ fn make_format_args(
 
     let mut used = vec![false; args.explicit_args().len()];
     let mut invalid_refs = Vec::new();
-    let mut numeric_refences_to_named_arg = Vec::new();
+    let mut numeric_references_to_named_arg = Vec::new();
 
     enum ArgRef<'a> {
         Index(usize),
@@ -336,7 +336,7 @@ fn make_format_args(
                     used[index] = true;
                     if arg.kind.ident().is_some() {
                         // This was a named argument, but it was used as a positional argument.
-                        numeric_refences_to_named_arg.push((index, span, used_as));
+                        numeric_references_to_named_arg.push((index, span, used_as));
                     }
                     Ok(index)
                 } else {
@@ -544,7 +544,7 @@ fn make_format_args(
     // Only check for unused named argument names if there are no other errors to avoid causing
     // too much noise in output errors, such as when a named argument is entirely unused.
     if invalid_refs.is_empty() && !has_unused && !unnamed_arg_after_named_arg {
-        for &(index, span, used_as) in &numeric_refences_to_named_arg {
+        for &(index, span, used_as) in &numeric_references_to_named_arg {
             let (position_sp_to_replace, position_sp_for_msg) = match used_as {
                 Placeholder(pspan) => (span, pspan),
                 Precision => {