Do not add leading asterisk in the PartialEq

Adding leading asterisk can cause compilation failure for
the _types_ that don't implement the `Copy`.

Author: wutchzone

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

@@ -31,7 +31,7 @@ pub 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 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(

tests/ui/derives/derive-PartialEq-on-non-copy-type.rs

@@ -0,0 +1,18 @@
+//@ check-pass
+
+trait Animal {
+    fn noise(&self) -> String;
+}
+
+impl PartialEq for dyn Animal {
+    fn eq(&self, other: &Self) -> bool {
+        self.noise() == other.noise()
+    }
+}
+
+#[derive(PartialEq)]
+enum Monkey {
+    Baboon(Box<dyn Animal>),
+}
+
+fn main() {}

tests/ui/derives/derives-span-PartialEq-enum-struct-variant.stderr

@@ -1,4 +1,4 @@
-error[E0369]: binary operation `==` cannot be applied to type `Error`
+error[E0369]: binary operation `==` cannot be applied to type `&Error`
   --> $DIR/derives-span-PartialEq-enum-struct-variant.rs:9:6
    |
 LL | #[derive(PartialEq)]

tests/ui/derives/derives-span-PartialEq-enum.stderr

@@ -1,4 +1,4 @@
-error[E0369]: binary operation `==` cannot be applied to type `Error`
+error[E0369]: binary operation `==` cannot be applied to type `&Error`
   --> $DIR/derives-span-PartialEq-enum.rs:9:6
    |
 LL | #[derive(PartialEq)]

tests/ui/deriving/deriving-all-codegen.stdout

@@ -876,7 +876,7 @@ impl ::core::cmp::PartialEq for Enum1 {
     fn eq(&self, other: &Enum1) -> bool {
         match (self, other) {
             (Enum1::Single { x: __self_0 }, Enum1::Single { x: __arg1_0 }) =>
-                *__self_0 == *__arg1_0,
+                __self_0 == __arg1_0,
         }
     }
 }
@@ -1119,10 +1119,10 @@ impl ::core::cmp::PartialEq for Mixed {
         __self_discr == __arg1_discr &&
             match (self, other) {
                 (Mixed::R(__self_0), Mixed::R(__arg1_0)) =>
-                    *__self_0 == *__arg1_0,
+                    __self_0 == __arg1_0,
                 (Mixed::S { d1: __self_0, d2: __self_1 }, Mixed::S {
                     d1: __arg1_0, d2: __arg1_1 }) =>
-                    *__self_0 == *__arg1_0 && *__self_1 == *__arg1_1,
+                    __self_0 == __arg1_0 && __self_1 == __arg1_1,
                 _ => true,
             }
     }
@@ -1245,11 +1245,11 @@ impl ::core::cmp::PartialEq for Fielded {
         __self_discr == __arg1_discr &&
             match (self, other) {
                 (Fielded::X(__self_0), Fielded::X(__arg1_0)) =>
-                    *__self_0 == *__arg1_0,
+                    __self_0 == __arg1_0,
                 (Fielded::Y(__self_0), Fielded::Y(__arg1_0)) =>
-                    *__self_0 == *__arg1_0,
+                    __self_0 == __arg1_0,
                 (Fielded::Z(__self_0), Fielded::Z(__arg1_0)) =>
-                    *__self_0 == *__arg1_0,
+                    __self_0 == __arg1_0,
                 _ => unsafe { ::core::intrinsics::unreachable() }
             }
     }
@@ -1368,9 +1368,9 @@ impl<T: ::core::cmp::PartialEq, U: ::core::cmp::PartialEq>
         __self_discr == __arg1_discr &&
             match (self, other) {
                 (EnumGeneric::One(__self_0), EnumGeneric::One(__arg1_0)) =>
-                    *__self_0 == *__arg1_0,
+                    __self_0 == __arg1_0,
                 (EnumGeneric::Two(__self_0), EnumGeneric::Two(__arg1_0)) =>
-                    *__self_0 == *__arg1_0,
+                    __self_0 == __arg1_0,
                 _ => unsafe { ::core::intrinsics::unreachable() }
             }
     }