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

Diff for: 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(

Diff for: 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)]

Diff for: 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)]

Diff for: tests/ui/deriving/deriving-all-codegen.rs

@@ -156,6 +156,20 @@ enum EnumGeneric<T, U> {
     Two(U),
 }
 
+// An enum that has variant, which does't implement `Copy`.
+#[derive(PartialEq)]
+enum NonCopyEnum {
+    // The `dyn NonCopyTrait` implements `PartialEq`, but it doesn't require `Copy`.
+    // So we cannot generate `PartialEq` with dereference.
+    NonCopyField(Box<dyn NonCopyTrait>),
+}
+trait NonCopyTrait {}
+impl PartialEq for dyn NonCopyTrait {
+    fn eq(&self, _other: &Self) -> bool {
+        true
+    }
+}
+
 // A union. Most builtin traits are not derivable for unions.
 #[derive(Clone, Copy)]
 pub union Union {

Diff for: 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() }
             }
     }
@@ -1426,6 +1426,30 @@ impl<T: ::core::cmp::Ord, U: ::core::cmp::Ord> ::core::cmp::Ord for
     }
 }
 
+// An enum that has variant, which does't implement `Copy`.
+enum NonCopyEnum {
+
+    // The `dyn NonCopyTrait` implements `PartialEq`, but it doesn't require `Copy`.
+    // So we cannot generate `PartialEq` with dereference.
+    NonCopyField(Box<dyn NonCopyTrait>),
+}
+#[automatically_derived]
+impl ::core::marker::StructuralPartialEq for NonCopyEnum { }
+#[automatically_derived]
+impl ::core::cmp::PartialEq for NonCopyEnum {
+    #[inline]
+    fn eq(&self, other: &NonCopyEnum) -> bool {
+        match (self, other) {
+            (NonCopyEnum::NonCopyField(__self_0),
+                NonCopyEnum::NonCopyField(__arg1_0)) => __self_0 == __arg1_0,
+        }
+    }
+}
+trait NonCopyTrait {}
+impl PartialEq for dyn NonCopyTrait {
+    fn eq(&self, _other: &Self) -> bool { true }
+}
+
 // A union. Most builtin traits are not derivable for unions.
 pub union Union {
     pub b: bool,