add a TrivialClone implementation when deriving both Clone and Copy

Author: joboet

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem, Safety};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::Span;
 
@@ -23,6 +23,7 @@ pub(crate) fn expand_deriving_copy(
         methods: Vec::new(),
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
 
     trait_def.expand(cx, mitem, item, push);
@@ -46,6 +47,7 @@ pub(crate) fn expand_deriving_const_param_ty(
         methods: Vec::new(),
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
 
     trait_def.expand(cx, mitem, item, push);
@@ -60,6 +62,7 @@ pub(crate) fn expand_deriving_const_param_ty(
         methods: Vec::new(),
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
 
     trait_def.expand(cx, mitem, item, push);
@@ -83,6 +86,7 @@ pub(crate) fn expand_deriving_unsized_const_param_ty(
         methods: Vec::new(),
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
 
     trait_def.expand(cx, mitem, item, push);

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -1,7 +1,7 @@
-use rustc_ast::{self as ast, Generics, ItemKind, MetaItem, VariantData};
+use rustc_ast::{self as ast, Generics, ItemKind, MetaItem, Safety, VariantData};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable, ExtCtxt};
-use rustc_span::{Ident, Span, kw, sym};
+use rustc_span::{DUMMY_SP, Ident, Span, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
 use crate::deriving::generic::ty::*;
@@ -68,6 +68,25 @@ pub(crate) fn expand_deriving_clone(
         _ => cx.dcx().span_bug(span, "`#[derive(Clone)]` on trait item or impl item"),
     }
 
+    // If the clone method is just copying the value, also mark the type as
+    // `TrivialClone` to allow some library optimizations.
+    if is_simple {
+        let trivial_def = TraitDef {
+            span,
+            path: path_std!(clone::TrivialClone),
+            skip_path_as_bound: false,
+            needs_copy_as_bound_if_packed: true,
+            additional_bounds: bounds.clone(),
+            supports_unions: true,
+            methods: Vec::new(),
+            associated_types: Vec::new(),
+            is_const,
+            safety: Safety::Unsafe(DUMMY_SP),
+        };
+
+        trivial_def.expand_ext(cx, mitem, item, push, true);
+    }
+
     let trait_def = TraitDef {
         span,
         path: path_std!(clone::Clone),
@@ -87,6 +106,7 @@ pub(crate) fn expand_deriving_clone(
         }],
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
 
     trait_def.expand_ext(cx, mitem, item, push, is_simple)

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

@@ -1,4 +1,4 @@
-use rustc_ast::{self as ast, MetaItem};
+use rustc_ast::{self as ast, MetaItem, Safety};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::{Span, sym};
@@ -43,6 +43,7 @@ pub(crate) fn expand_deriving_eq(
         }],
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
     trait_def.expand_ext(cx, mitem, item, push, true)
 }

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

@@ -1,4 +1,4 @@
-use rustc_ast::MetaItem;
+use rustc_ast::{MetaItem, Safety};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::{Ident, Span, sym};
 use thin_vec::thin_vec;
@@ -34,6 +34,7 @@ pub(crate) fn expand_deriving_ord(
         }],
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
 
     trait_def.expand(cx, mitem, item, push)

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

@@ -1,5 +1,5 @@
 use rustc_ast::ptr::P;
-use rustc_ast::{BinOpKind, BorrowKind, Expr, ExprKind, MetaItem, Mutability};
+use rustc_ast::{BinOpKind, BorrowKind, Expr, ExprKind, MetaItem, Mutability, Safety};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::{Span, sym};
 use thin_vec::thin_vec;
@@ -84,6 +84,7 @@ pub(crate) fn expand_deriving_partial_eq(
         methods: Vec::new(),
         associated_types: Vec::new(),
         is_const: false,
+        safety: Safety::Default,
     };
     structural_trait_def.expand(cx, mitem, item, push);
 
@@ -110,6 +111,7 @@ pub(crate) fn expand_deriving_partial_eq(
         methods,
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
     trait_def.expand(cx, mitem, item, push)
 }

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

@@ -1,4 +1,4 @@
-use rustc_ast::{ExprKind, ItemKind, MetaItem, PatKind};
+use rustc_ast::{ExprKind, ItemKind, MetaItem, PatKind, Safety};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::{Ident, Span, sym};
 use thin_vec::thin_vec;
@@ -64,6 +64,7 @@ pub(crate) fn expand_deriving_partial_ord(
         methods: vec![partial_cmp_def],
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
     trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{self as ast, EnumDef, MetaItem};
+use rustc_ast::{self as ast, EnumDef, MetaItem, Safety};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_session::config::FmtDebug;
 use rustc_span::{Ident, Span, Symbol, sym};
@@ -41,6 +41,7 @@ pub(crate) fn expand_deriving_debug(
         }],
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
     trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -1,8 +1,7 @@
 use core::ops::ControlFlow;
 
-use rustc_ast as ast;
 use rustc_ast::visit::visit_opt;
-use rustc_ast::{EnumDef, VariantData, attr};
+use rustc_ast::{self as ast, EnumDef, Safety, VariantData, attr};
 use rustc_expand::base::{Annotatable, DummyResult, ExtCtxt};
 use rustc_span::{ErrorGuaranteed, Ident, Span, kw, sym};
 use smallvec::SmallVec;
@@ -51,6 +50,7 @@ pub(crate) fn expand_deriving_default(
         }],
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
     trait_def.expand(cx, mitem, item, push)
 }

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -183,7 +183,7 @@ pub(crate) use SubstructureFields::*;
 use rustc_ast::ptr::P;
 use rustc_ast::{
     self as ast, AnonConst, BindingMode, ByRef, EnumDef, Expr, GenericArg, GenericParamKind,
-    Generics, Mutability, PatKind, VariantData,
+    Generics, Mutability, PatKind, Safety, VariantData,
 };
 use rustc_attr_parsing::{AttributeKind, AttributeParser, ReprPacked};
 use rustc_expand::base::{Annotatable, ExtCtxt};
@@ -221,6 +221,9 @@ pub(crate) struct TraitDef<'a> {
     pub associated_types: Vec<(Ident, Ty)>,
 
     pub is_const: bool,
+
+    /// The safety of the `impl`.
+    pub safety: Safety,
 }
 
 pub(crate) struct MethodDef<'a> {
@@ -792,7 +795,7 @@ impl<'a> TraitDef<'a> {
             Ident::empty(),
             attrs,
             ast::ItemKind::Impl(Box::new(ast::Impl {
-                safety: ast::Safety::Default,
+                safety: self.safety,
                 polarity: ast::ImplPolarity::Positive,
                 defaultness: ast::Defaultness::Final,
                 constness: if self.is_const { ast::Const::Yes(DUMMY_SP) } else { ast::Const::No },

compiler/rustc_builtin_macros/src/deriving/hash.rs

@@ -1,4 +1,4 @@
-use rustc_ast::{MetaItem, Mutability};
+use rustc_ast::{MetaItem, Mutability, Safety};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::{Span, sym};
 use thin_vec::thin_vec;
@@ -41,6 +41,7 @@ pub(crate) fn expand_deriving_hash(
         }],
         associated_types: Vec::new(),
         is_const,
+        safety: Safety::Default,
     };
 
     hash_trait_def.expand(cx, mitem, item, push);

compiler/rustc_span/src/symbol.rs

@@ -364,6 +364,7 @@ symbols! {
         ToString,
         TokenStream,
         Trait,
+        TrivialClone,
         Try,
         TryCaptureGeneric,
         TryCapturePrintable,

library/core/src/clone.rs

@@ -205,7 +205,7 @@ pub unsafe trait TrivialClone: Clone {}
 /// Derive macro generating an impl of the trait `Clone`.
 #[rustc_builtin_macro]
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow_internal_unstable(core_intrinsics, derive_clone_copy)]
+#[allow_internal_unstable(core_intrinsics, derive_clone_copy, trivial_clone)]
 pub macro Clone($item:item) {
     /* compiler built-in */
 }

tests/ui/derives/duplicate-derive-copy-clone-diagnostics.rs

@@ -6,6 +6,7 @@
 #[derive(Copy, Clone)]
 //~^ ERROR conflicting implementations of trait `Clone` for type `E`
 //~| ERROR conflicting implementations of trait `Copy` for type `E`
+//~| ERROR conflicting implementations of trait `TrivialClone` for type `E`
 enum E {}
 
 fn main() {}

tests/ui/derives/duplicate-derive-copy-clone-diagnostics.stderr

@@ -6,6 +6,16 @@ LL | #[derive(Copy, Clone)]
 LL | #[derive(Copy, Clone)]
    |          ^^^^ conflicting implementation for `E`
 
+error[E0119]: conflicting implementations of trait `TrivialClone` for type `E`
+  --> $DIR/duplicate-derive-copy-clone-diagnostics.rs:6:16
+   |
+LL | #[derive(Copy, Clone)]
+   |                ----- first implementation here
+LL | #[derive(Copy, Clone)]
+   |                ^^^^^ conflicting implementation for `E`
+   |
+   = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+
 error[E0119]: conflicting implementations of trait `Clone` for type `E`
   --> $DIR/duplicate-derive-copy-clone-diagnostics.rs:6:16
    |
@@ -14,6 +24,6 @@ LL | #[derive(Copy, Clone)]
 LL | #[derive(Copy, Clone)]
    |                ^^^^^ conflicting implementation for `E`
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0119`.

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

@@ -25,6 +25,8 @@ extern crate std;
 // Empty struct.
 struct Empty;
 #[automatically_derived]
+unsafe impl ::core::clone::TrivialClone for Empty { }
+#[automatically_derived]
 impl ::core::clone::Clone for Empty {
     #[inline]
     fn clone(&self) -> Empty { *self }
@@ -85,6 +87,8 @@ struct Point {
     y: u32,
 }
 #[automatically_derived]
+unsafe impl ::core::clone::TrivialClone for Point { }
+#[automatically_derived]
 impl ::core::clone::Clone for Point {
     #[inline]
     fn clone(&self) -> Point {
@@ -170,6 +174,8 @@ struct PackedPoint {
     y: u32,
 }
 #[automatically_derived]
+unsafe impl ::core::clone::TrivialClone for PackedPoint { }
+#[automatically_derived]
 impl ::core::clone::Clone for PackedPoint {
     #[inline]
     fn clone(&self) -> PackedPoint {
@@ -262,6 +268,8 @@ struct Big {
     b8: u32,
 }
 #[automatically_derived]
+unsafe impl ::core::clone::TrivialClone for Big { }
+#[automatically_derived]
 impl ::core::clone::Clone for Big {
     #[inline]
     fn clone(&self) -> Big {
@@ -763,6 +771,8 @@ impl<T: ::core::cmp::Ord + ::core::marker::Copy + Trait, U: ::core::cmp::Ord +
 // An empty enum.
 enum Enum0 {}
 #[automatically_derived]
+unsafe impl ::core::clone::TrivialClone for Enum0 { }
+#[automatically_derived]
 impl ::core::clone::Clone for Enum0 {
     #[inline]
     fn clone(&self) -> Enum0 { *self }
@@ -958,6 +968,8 @@ enum Fieldless {
     C,
 }
 #[automatically_derived]
+unsafe impl ::core::clone::TrivialClone for Fieldless { }
+#[automatically_derived]
 impl ::core::clone::Clone for Fieldless {
     #[inline]
     fn clone(&self) -> Fieldless { *self }
@@ -1040,6 +1052,8 @@ enum Mixed {
     },
 }
 #[automatically_derived]
+unsafe impl ::core::clone::TrivialClone for Mixed { }
+#[automatically_derived]
 impl ::core::clone::Clone for Mixed {
     #[inline]
     fn clone(&self) -> Mixed {
@@ -1437,6 +1451,8 @@ pub union Union {
     pub i: i32,
 }
 #[automatically_derived]
+unsafe impl ::core::clone::TrivialClone for Union { }
+#[automatically_derived]
 impl ::core::clone::Clone for Union {
     #[inline]
     fn clone(&self) -> Union {