automatically implement TrivialClone for closures and tuples

If each of the component types is `TrivialClone`, the closure/tuple itself can be trivially cloned.

Author: joboet

compiler/rustc_hir/src/lang_items.rs

@@ -176,6 +176,7 @@ language_item_table! {
     Clone,                   sym::clone,               clone_trait,                Target::Trait,          GenericRequirement::None;
     CloneFn,                 sym::clone_fn,            clone_fn,                   Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
     UseCloned,               sym::use_cloned,          use_cloned_trait,           Target::Trait,          GenericRequirement::None;
+    TrivialClone,            sym::trivial_clone,       trivial_clone_trait,        Target::Trait,          GenericRequirement::None;
     Sync,                    sym::sync,                sync_trait,                 Target::Trait,          GenericRequirement::Exact(0);
     DiscriminantKind,        sym::discriminant_kind,   discriminant_kind_trait,    Target::Trait,          GenericRequirement::None;
     /// The associated item of the `DiscriminantKind` trait.

compiler/rustc_middle/src/ty/context.rs

@@ -856,6 +856,7 @@ bidirectional_lang_item_map! {
     PointeeTrait,
     Sized,
     TransmuteTrait,
+    TrivialClone,
     Tuple,
     Unpin,
     Unsize,

compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs

@@ -547,9 +547,11 @@ where
                 Some(SolverTraitLangItem::PointeeSized) => {
                     unreachable!("`PointeeSized` is removed during lowering");
                 }
-                Some(SolverTraitLangItem::Copy | SolverTraitLangItem::Clone) => {
-                    G::consider_builtin_copy_clone_candidate(self, goal)
-                }
+                Some(
+                    SolverTraitLangItem::Copy
+                    | SolverTraitLangItem::Clone
+                    | SolverTraitLangItem::TrivialClone,
+                ) => G::consider_builtin_copy_clone_candidate(self, goal),
                 Some(SolverTraitLangItem::Fn) => {
                     G::consider_builtin_fn_trait_candidates(self, goal, ty::ClosureKind::Fn)
                 }

compiler/rustc_span/src/symbol.rs

@@ -2271,6 +2271,7 @@ symbols! {
         transparent_enums,
         transparent_unions,
         trivial_bounds,
+        trivial_clone,
         truncf16,
         truncf32,
         truncf64,

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -67,7 +67,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
             let lang_item = tcx.as_lang_item(def_id);
             match lang_item {
-                Some(LangItem::Copy | LangItem::Clone) => {
+                Some(LangItem::Copy | LangItem::Clone | LangItem::TrivialClone) => {
                     debug!(obligation_self_ty = ?obligation.predicate.skip_binder().self_ty());
 
                     // User-defined copy impls are permitted, but only for

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -249,7 +249,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             Some(LangItem::PointeeSized) => {
                 bug!("`PointeeSized` is removing during lowering");
             }
-            Some(LangItem::Copy | LangItem::Clone) => self.copy_clone_conditions(self_ty),
+            Some(LangItem::Copy | LangItem::Clone | LangItem::TrivialClone) => {
+                self.copy_clone_conditions(self_ty)
+            }
             Some(LangItem::FusedIterator) => {
                 if self.coroutine_is_gen(self_ty) {
                     ty::Binder::dummy(vec![])

compiler/rustc_type_ir/src/lang_items.rs

@@ -48,6 +48,7 @@ pub enum SolverTraitLangItem {
     PointeeTrait,
     Sized,
     TransmuteTrait,
+    TrivialClone,
     Tuple,
     Unpin,
     Unsize,

library/core/src/clone.rs

@@ -269,6 +269,7 @@ pub const trait Clone: Sized {
     issue = "none"
 )]
 #[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+#[lang = "trivial_clone"]
 // SAFETY:
 // It is sound to specialize on this because the `clone` implementation cannot be
 // lifetime-dependent. Therefore, if `TrivialClone` is implemented for any lifetime,

tests/ui/functions-closures/trivial-clone-closure.rs

@@ -0,0 +1,13 @@
+//@ run-pass
+// Check that closures implement `TrivialClone`.
+
+#![feature(trivial_clone)]
+
+use std::clone::TrivialClone;
+
+fn require_trivial_clone<T: TrivialClone>(_t: T) {}
+
+fn main() {
+    let some_trivial_clone_value = 42i32;
+    require_trivial_clone(move || some_trivial_clone_value);
+}