[experiment] Add MustClone and impl Copy+MustClone on Range{,From,Inclusive}.

compiler/rustc_hir/src/lang_items.rs

@@ -196,6 +196,7 @@ language_item_table! {
     StructuralTeq,           sym::structural_teq,      structural_teq_trait,       Target::Trait;
     Copy,                    sym::copy,                copy_trait,                 Target::Trait;
     Clone,                   sym::clone,               clone_trait,                Target::Trait;
+    MustClone,               sym::must_clone,          must_clone_trait,           Target::Trait;
     Sync,                    sym::sync,                sync_trait,                 Target::Trait;
     DiscriminantKind,        sym::discriminant_kind,   discriminant_kind_trait,    Target::Trait;
     // The associated item of `trait DiscriminantKind`.

compiler/rustc_middle/src/query/mod.rs

@@ -912,6 +912,10 @@ rustc_queries! {
         query is_copy_raw(env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
             desc { "computing whether `{}` is `Copy`", env.value }
         }
+        /// Query backing `TyS::is_must_clone`.
+        query is_must_clone_raw(env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
+            desc { "computing whether `{}` is `MustClone`", env.value }
+        }
         /// Query backing `TyS::is_sized`.
         query is_sized_raw(env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
             desc { "computing whether `{}` is `Sized`", env.value }

compiler/rustc_middle/src/ty/util.rs

@@ -688,6 +688,21 @@ impl<'tcx> ty::TyS<'tcx> {
         tcx_at.is_copy_raw(param_env.and(self))
     }
 
+    /// Checks whether values of type `T` are discouraged to be copied,
+    /// despite being `Copy` (i.e. whether `T: MustClone`).
+    /// This is only relevant when deciding whether to to forbid/lint
+    /// direct copies of `T`, but *not* e.g. whether a `struct`/`enum`
+    /// with fields of type `T` can implement `Copy`, or whether some
+    /// `Copy`-specific optimization (such as assuming `!needs_drop`)
+    /// can be applied.
+    pub fn is_must_clone(
+        &'tcx self,
+        tcx_at: TyCtxtAt<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+    ) -> bool {
+        tcx_at.is_must_clone_raw(param_env.and(self))
+    }
+
     /// Checks whether values of this type `T` have a size known at
     /// compile time (i.e., whether `T: Sized`). Lifetimes are ignored
     /// for the purposes of this check, so it can be an
@@ -705,7 +720,6 @@ impl<'tcx> ty::TyS<'tcx> {
     /// optimization as well as the rules around static values. Note
     /// that the `Freeze` trait is not exposed to end users and is
     /// effectively an implementation detail.
-    // FIXME: use `TyCtxtAt` instead of separate `Span`.
     pub fn is_freeze(&'tcx self, tcx_at: TyCtxtAt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> bool {
         self.is_trivially_freeze() || tcx_at.is_freeze_raw(param_env.and(self))
     }

compiler/rustc_mir/src/borrow_check/type_check/mod.rs

@@ -2000,6 +2000,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         // a required check to make sure that repeated elements implement `Copy`.
                         let span = body.source_info(location).span;
                         let ty = operand.ty(body, tcx);
+                        // FIXME(eddyb) add `|| type_is_must_clone(ty)` (or handle separately).
                         if !self.infcx.type_is_copy_modulo_regions(self.param_env, ty, span) {
                             let ccx = ConstCx::new_with_param_env(
                                 tcx,

compiler/rustc_mir_build/src/build/misc.rs

@@ -66,7 +66,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     crate fn consume_by_copy_or_move(&self, place: Place<'tcx>) -> Operand<'tcx> {
         let tcx = self.hir.tcx();
         let ty = place.ty(&self.local_decls, tcx).ty;
-        if !self.hir.type_is_copy_modulo_regions(ty, DUMMY_SP) {
+        if !self.hir.type_is_copy_modulo_regions(ty, DUMMY_SP)
+            || self.hir.type_is_must_clone(ty, DUMMY_SP)
+        {
             Operand::Move(place)
         } else {
             Operand::Copy(place)

compiler/rustc_mir_build/src/thir/cx/mod.rs

@@ -201,6 +201,10 @@ impl<'a, 'tcx> Cx<'a, 'tcx> {
     crate fn type_is_copy_modulo_regions(&self, ty: Ty<'tcx>, span: Span) -> bool {
         self.infcx.type_is_copy_modulo_regions(self.param_env, ty, span)
     }
+
+    crate fn type_is_must_clone(&self, ty: Ty<'tcx>, span: Span) -> bool {
+        self.infcx.type_is_must_clone(self.param_env, ty, span)
+    }
 }
 
 impl<'tcx> UserAnnotatedTyHelpers<'tcx> for Cx<'_, 'tcx> {

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -598,6 +598,7 @@ fn maybe_point_at_variant(ty: Ty<'_>, patterns: &[super::Pat<'_>]) -> Vec<Span>
 
 /// Check if a by-value binding is by-value. That is, check if the binding's type is not `Copy`.
 fn is_binding_by_move(cx: &MatchVisitor<'_, '_>, hir_id: HirId, span: Span) -> bool {
+    // FIXME(eddyb) add `|| type_is_must_clone(ty)` (or make sure it's unnecessary).
     !cx.typeck_results.node_type(hir_id).is_copy_modulo_regions(cx.tcx.at(span), cx.param_env)
 }
 

compiler/rustc_span/src/symbol.rs

@@ -688,6 +688,7 @@ symbols! {
         mul,
         mul_assign,
         mul_with_overflow,
+        must_clone,
         must_use,
         mut_ptr,
         mut_slice_ptr,

compiler/rustc_trait_selection/src/infer.rs

@@ -23,6 +23,8 @@ pub trait InferCtxtExt<'tcx> {
         span: Span,
     ) -> bool;
 
+    fn type_is_must_clone(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>, span: Span) -> bool;
+
     fn partially_normalize_associated_types_in<T>(
         &self,
         span: Span,
@@ -49,13 +51,35 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'tcx> {
 
         let copy_def_id = self.tcx.require_lang_item(LangItem::Copy, None);
 
-        // This can get called from typeck (by euv), and `moves_by_default`
+        // This can get called from typeck (by euv), and `is_copy_modulo_regions`
         // rightly refuses to work with inference variables, but
-        // moves_by_default has a cache, which we want to use in other
+        // `is_copy_modulo_regions` has a cache, which we want to use in other
         // cases.
         traits::type_known_to_meet_bound_modulo_regions(self, param_env, ty, copy_def_id, span)
     }
 
+    fn type_is_must_clone(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>, span: Span) -> bool {
+        let ty = self.resolve_vars_if_possible(&ty);
+
+        if !(param_env, ty).needs_infer() {
+            return ty.is_must_clone(self.tcx.at(span), param_env);
+        }
+
+        let must_clone_def_id = self.tcx.require_lang_item(LangItem::MustClone, None);
+
+        // This can get called from typeck (by euv), and `is_must_clone`
+        // rightly refuses to work with inference variables, but
+        // `is_must_clone` has a cache, which we want to use in other
+        // cases.
+        traits::type_known_to_meet_bound_modulo_regions(
+            self,
+            param_env,
+            ty,
+            must_clone_def_id,
+            span,
+        )
+    }
+
     /// Normalizes associated types in `value`, potentially returning
     /// new obligations that must further be processed.
     fn partially_normalize_associated_types_in<T>(

compiler/rustc_ty/src/common_traits.rs

@@ -10,6 +10,10 @@ fn is_copy_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
     is_item_raw(tcx, query, LangItem::Copy)
 }
 
+fn is_must_clone_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
+    is_item_raw(tcx, query, LangItem::MustClone)
+}
+
 fn is_sized_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
     is_item_raw(tcx, query, LangItem::Sized)
 }
@@ -37,5 +41,11 @@ fn is_item_raw<'tcx>(
 }
 
 pub(crate) fn provide(providers: &mut ty::query::Providers) {
-    *providers = ty::query::Providers { is_copy_raw, is_sized_raw, is_freeze_raw, ..*providers };
+    *providers = ty::query::Providers {
+        is_copy_raw,
+        is_must_clone_raw,
+        is_sized_raw,
+        is_freeze_raw,
+        ..*providers
+    };
 }

compiler/rustc_typeck/src/expr_use_visitor.rs

@@ -588,10 +588,9 @@ fn copy_or_move<'a, 'tcx>(
     mc: &mc::MemCategorizationContext<'a, 'tcx>,
     place_with_id: &PlaceWithHirId<'tcx>,
 ) -> ConsumeMode {
-    if !mc.type_is_copy_modulo_regions(
-        place_with_id.place.ty(),
-        mc.tcx().hir().span(place_with_id.hir_id),
-    ) {
+    let ty = place_with_id.place.ty();
+    let span = mc.tcx().hir().span(place_with_id.hir_id);
+    if !mc.type_is_copy_modulo_regions(ty, span) || mc.type_is_must_clone(ty, span) {
         Move
     } else {
         Copy

compiler/rustc_typeck/src/mem_categorization.rs

@@ -124,6 +124,10 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
         self.infcx.type_is_copy_modulo_regions(self.param_env, ty, span)
     }
 
+    crate fn type_is_must_clone(&self, ty: Ty<'tcx>, span: Span) -> bool {
+        self.infcx.type_is_must_clone(self.param_env, ty, span)
+    }
+
     fn resolve_vars_if_possible<T>(&self, value: &T) -> T
     where
         T: TypeFoldable<'tcx>,

library/core/src/marker.rs

@@ -391,6 +391,21 @@ pub macro Copy($item:item) {
     /* compiler built-in */
 }
 
+/// Types that are `Copy` but which require `.clone()` for copying,
+/// in order to indicate that some state is being duplicated, such
+/// as iterators (where implicit copies may appear misleading).
+///
+/// This doesn't propagate to aggregate types containing `MustClone`
+/// fields, unless they themselves also implement `MustClone`.
+/// Generics are also not affected, i.e. a `MustClone` type can still
+/// be used with a generic expecting a type that implements `Copy`.
+#[unstable(feature = "must_clone", issue = "none")]
+#[lang = "must_clone"]
+#[cfg(not(bootstrap))]
+pub trait MustClone: Copy {
+    // Empty.
+}
+
 /// Types for which it is safe to share references between threads.
 ///
 /// This trait is automatically implemented when the compiler determines

library/core/src/ops/range.rs

@@ -71,7 +71,8 @@ impl fmt::Debug for RangeFull {
 /// ```
 #[lang = "Range"]
 #[doc(alias = "..")]
-#[derive(Clone, Default, PartialEq, Eq, Hash)] // not Copy -- see #27186
+#[derive(Clone, Default, PartialEq, Eq, Hash)]
+#[cfg_attr(not(bootstrap), derive(Copy))]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Range<Idx> {
     /// The lower bound of the range (inclusive).
@@ -82,6 +83,10 @@ pub struct Range<Idx> {
     pub end: Idx,
 }
 
+#[unstable(feature = "must_clone", issue = "none")]
+#[cfg(not(bootstrap))]
+impl<Idx: Copy> crate::marker::MustClone for Range<Idx> {}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<Idx: fmt::Debug> fmt::Debug for Range<Idx> {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -174,14 +179,19 @@ impl<Idx: PartialOrd<Idx>> Range<Idx> {
 /// ```
 #[lang = "RangeFrom"]
 #[doc(alias = "..")]
-#[derive(Clone, PartialEq, Eq, Hash)] // not Copy -- see #27186
+#[derive(Clone, PartialEq, Eq, Hash)]
+#[cfg_attr(not(bootstrap), derive(Copy))]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct RangeFrom<Idx> {
     /// The lower bound of the range (inclusive).
     #[stable(feature = "rust1", since = "1.0.0")]
     pub start: Idx,
 }
 
+#[unstable(feature = "must_clone", issue = "none")]
+#[cfg(not(bootstrap))]
+impl<Idx: Copy> crate::marker::MustClone for RangeFrom<Idx> {}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<Idx: fmt::Debug> fmt::Debug for RangeFrom<Idx> {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -324,7 +334,8 @@ impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
 /// ```
 #[lang = "RangeInclusive"]
 #[doc(alias = "..=")]
-#[derive(Clone, PartialEq, Eq, Hash)] // not Copy -- see #27186
+#[derive(Clone, PartialEq, Eq, Hash)]
+#[cfg_attr(not(bootstrap), derive(Copy))]
 #[stable(feature = "inclusive_range", since = "1.26.0")]
 pub struct RangeInclusive<Idx> {
     // Note that the fields here are not public to allow changing the
@@ -344,6 +355,10 @@ pub struct RangeInclusive<Idx> {
     pub(crate) exhausted: bool,
 }
 
+#[unstable(feature = "must_clone", issue = "none")]
+#[cfg(not(bootstrap))]
+impl<Idx: Copy> crate::marker::MustClone for RangeInclusive<Idx> {}
+
 impl<Idx> RangeInclusive<Idx> {
     /// Creates a new inclusive range. Equivalent to writing `start..=end`.
     ///

src/test/codegen/avr/avr-func-addrspace.rs

@@ -17,6 +17,8 @@
 pub trait Sized { }
 #[lang = "copy"]
 pub trait Copy { }
+#[lang = "must_clone"]
+pub trait MustClone { }
 #[lang = "receiver"]
 pub trait Receiver { }
 

src/test/ui/range/range_traits-2.rs

@@ -1,6 +1,8 @@
+// run-pass
+
 use std::ops::*;
 
-#[derive(Copy, Clone)] //~ ERROR Copy
+#[derive(Copy, Clone)]
 struct R(Range<usize>);
 
 fn main() {}

src/test/ui/range/range_traits-3.rs

@@ -1,6 +1,8 @@
+// run-pass
+
 use std::ops::*;
 
-#[derive(Copy, Clone)] //~ ERROR Copy
+#[derive(Copy, Clone)]
 struct R(RangeFrom<usize>);
 
 fn main() {}

src/test/ui/range/range_traits-6.rs

@@ -1,6 +1,8 @@
+// run-pass
+
 use std::ops::*;
 
-#[derive(Copy, Clone)] //~ ERROR Copy
+#[derive(Copy, Clone)]
 struct R(RangeInclusive<usize>);
 
 fn main() {}