Generate the right MIR for by use closures

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -1071,7 +1071,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                     );
 
                     match capture_info.capture_kind {
-                        ty::UpvarCapture::ByValue => {
+                        ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => {
                             self.consume_or_copy(&place_with_id, place_with_id.hir_id);
                         }
                         ty::UpvarCapture::ByRef(upvar_borrow) => {

compiler/rustc_hir_typeck/src/upvar.rs

@@ -666,9 +666,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 origin = updated.1;
 
                 let (place, capture_kind) = match capture_clause {
-                    hir::CaptureBy::Value { .. } | hir::CaptureBy::Use { .. } => {
-                        adjust_for_move_closure(place, capture_kind)
-                    }
+                    hir::CaptureBy::Value { .. } => adjust_for_move_closure(place, capture_kind),
+                    hir::CaptureBy::Use { .. } => adjust_for_use_closure(place, capture_kind),
                     hir::CaptureBy::Ref => adjust_for_non_move_closure(place, capture_kind),
                 };
 
@@ -1303,7 +1302,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         for captured_place in root_var_min_capture_list.iter() {
             match captured_place.info.capture_kind {
                 // Only care about captures that are moved into the closure
-                ty::UpvarCapture::ByValue => {
+                ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => {
                     projections_list.push(captured_place.place.projections.as_slice());
                     diagnostics_info.insert(UpvarMigrationInfo::CapturingPrecise {
                         source_expr: captured_place.info.path_expr_id,
@@ -1927,7 +1926,7 @@ fn apply_capture_kind_on_capture_ty<'tcx>(
     region: ty::Region<'tcx>,
 ) -> Ty<'tcx> {
     match capture_kind {
-        ty::UpvarCapture::ByValue => ty,
+        ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => ty,
         ty::UpvarCapture::ByRef(kind) => Ty::new_ref(tcx, region, ty, kind.to_mutbl_lossy()),
     }
 }
@@ -2157,6 +2156,20 @@ fn adjust_for_move_closure(
     (place, ty::UpvarCapture::ByValue)
 }
 
+/// Truncate deref of any reference.
+fn adjust_for_use_closure(
+    mut place: Place<'_>,
+    mut kind: ty::UpvarCapture,
+) -> (Place<'_>, ty::UpvarCapture) {
+    let first_deref = place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
+
+    if let Some(idx) = first_deref {
+        truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
+    }
+
+    (place, ty::UpvarCapture::ByUse)
+}
+
 /// Adjust closure capture just that if taking ownership of data, only move data
 /// from enclosing stack frame.
 fn adjust_for_non_move_closure(
@@ -2167,7 +2180,7 @@ fn adjust_for_non_move_closure(
         place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
 
     match kind {
-        ty::UpvarCapture::ByValue => {
+        ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => {
             if let Some(idx) = contains_deref {
                 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
             }
@@ -2212,6 +2225,7 @@ fn construct_capture_kind_reason_string<'tcx>(
 
     let capture_kind_str = match capture_info.capture_kind {
         ty::UpvarCapture::ByValue => "ByValue".into(),
+        ty::UpvarCapture::ByUse => "ByUse".into(),
         ty::UpvarCapture::ByRef(kind) => format!("{kind:?}"),
     };
 
@@ -2233,6 +2247,7 @@ fn construct_capture_info_string<'tcx>(
 
     let capture_kind_str = match capture_info.capture_kind {
         ty::UpvarCapture::ByValue => "ByValue".into(),
+        ty::UpvarCapture::ByUse => "ByUse".into(),
         ty::UpvarCapture::ByRef(kind) => format!("{kind:?}"),
     };
     format!("{place_str} -> {capture_kind_str}")
@@ -2328,8 +2343,11 @@ fn determine_capture_info(
     // expressions.
     let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
         (ty::UpvarCapture::ByValue, ty::UpvarCapture::ByValue) => true,
+        (ty::UpvarCapture::ByUse, ty::UpvarCapture::ByUse) => true,
         (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => ref_a == ref_b,
-        (ty::UpvarCapture::ByValue, _) | (ty::UpvarCapture::ByRef(_), _) => false,
+        (ty::UpvarCapture::ByValue, _)
+        | (ty::UpvarCapture::ByUse, _)
+        | (ty::UpvarCapture::ByRef(_), _) => false,
     };
 
     if eq_capture_kind {
@@ -2339,8 +2357,10 @@ fn determine_capture_info(
         }
     } else {
         // We select the CaptureKind which ranks higher based the following priority order:
-        // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
+        // ByUse > ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
         match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
+            (ty::UpvarCapture::ByUse, _) => capture_info_a,
+            (_, ty::UpvarCapture::ByUse) => capture_info_b,
             (ty::UpvarCapture::ByValue, _) => capture_info_a,
             (_, ty::UpvarCapture::ByValue) => capture_info_b,
             (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
@@ -2394,7 +2414,7 @@ fn truncate_place_to_len_and_update_capture_kind<'tcx>(
         }
 
         ty::UpvarCapture::ByRef(..) => {}
-        ty::UpvarCapture::ByValue => {}
+        ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => {}
     }
 
     place.projections.truncate(len);

compiler/rustc_middle/src/ty/closure.rs

@@ -52,6 +52,9 @@ pub enum UpvarCapture {
     /// depending on inference.
     ByValue,
 
+    /// Upvar is captured by use. This is true when the closure is labeled `use`.
+    ByUse,
+
     /// Upvar is captured by reference.
     ByRef(BorrowKind),
 }
@@ -179,7 +182,7 @@ impl<'tcx> CapturedPlace<'tcx> {
 
     pub fn is_by_ref(&self) -> bool {
         match self.info.capture_kind {
-            ty::UpvarCapture::ByValue => false,
+            ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => false,
             ty::UpvarCapture::ByRef(..) => true,
         }
     }
@@ -215,7 +218,7 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn closure_captures(self, def_id: LocalDefId) -> &'tcx [&'tcx ty::CapturedPlace<'tcx>] {
         if !self.is_closure_like(def_id.to_def_id()) {
             return &[];
-        };
+        }
         self.closure_typeinfo(def_id).captures
     }
 }

compiler/rustc_mir_build/src/builder/mod.rs

@@ -39,7 +39,7 @@ pub(crate) fn closure_saved_names_of_captured_variables<'tcx>(
         .map(|captured_place| {
             let name = captured_place.to_symbol();
             match captured_place.info.capture_kind {
-                ty::UpvarCapture::ByValue => name,
+                ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => name,
                 ty::UpvarCapture::ByRef(..) => Symbol::intern(&format!("_ref__{name}")),
             }
         })
@@ -884,7 +884,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let mut projs = closure_env_projs.clone();
                 projs.push(ProjectionElem::Field(FieldIdx::new(i), ty));
                 match capture {
-                    ty::UpvarCapture::ByValue => {}
+                    ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => {}
                     ty::UpvarCapture::ByRef(..) => {
                         projs.push(ProjectionElem::Deref);
                     }

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

@@ -678,7 +678,7 @@ impl<'tcx> Cx<'tcx> {
                 }
             },
 
-            hir::ExprKind::Closure { .. } => {
+            hir::ExprKind::Closure(hir::Closure { .. }) => {
                 let closure_ty = self.typeck_results().expr_ty(expr);
                 let (def_id, args, movability) = match *closure_ty.kind() {
                     ty::Closure(def_id, args) => (def_id, UpvarArgs::Closure(args), None),
@@ -1269,6 +1269,17 @@ impl<'tcx> Cx<'tcx> {
 
         match upvar_capture {
             ty::UpvarCapture::ByValue => captured_place_expr,
+            ty::UpvarCapture::ByUse => {
+                let span = captured_place_expr.span;
+                let expr_id = self.thir.exprs.push(captured_place_expr);
+
+                Expr {
+                    temp_lifetime: TempLifetime { temp_lifetime, backwards_incompatible },
+                    ty: upvar_ty,
+                    span: closure_expr.span,
+                    kind: ExprKind::ByUse { expr: expr_id, span },
+                }
+            }
             ty::UpvarCapture::ByRef(upvar_borrow) => {
                 let borrow_kind = match upvar_borrow {
                     ty::BorrowKind::Immutable => BorrowKind::Shared,

compiler/rustc_mir_transform/src/coroutine/by_move_body.rs

@@ -170,7 +170,7 @@ pub(crate) fn coroutine_by_move_body_def_id<'tcx>(
             // this when building the field projection in the MIR body later on.
             let mut parent_capture_ty = parent_capture.place.ty();
             parent_capture_ty = match parent_capture.info.capture_kind {
-                ty::UpvarCapture::ByValue => parent_capture_ty,
+                ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => parent_capture_ty,
                 ty::UpvarCapture::ByRef(kind) => Ty::new_ref(
                     tcx,
                     tcx.lifetimes.re_erased,

compiler/rustc_passes/src/liveness.rs

@@ -706,7 +706,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                             );
                             self.acc(self.exit_ln, var, ACC_READ | ACC_USE);
                         }
-                        ty::UpvarCapture::ByValue => {}
+                        ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => {}
                     }
                 }
             }
@@ -1499,7 +1499,7 @@ impl<'tcx> Liveness<'_, 'tcx> {
         for (&var_hir_id, min_capture_list) in closure_min_captures {
             for captured_place in min_capture_list {
                 match captured_place.info.capture_kind {
-                    ty::UpvarCapture::ByValue => {}
+                    ty::UpvarCapture::ByValue | ty::UpvarCapture::ByUse => {}
                     ty::UpvarCapture::ByRef(..) => continue,
                 };
                 let span = captured_place.get_capture_kind_span(self.ir.tcx);

tests/ui/ergonomic-clones/closure.rs

@@ -2,11 +2,20 @@
 
 #![feature(ergonomic_clones)]
 
-fn ergonomic_clone_closure() -> i32 {
+fn ergonomic_clone_closure_no_captures() -> i32 {
     let cl = use || {
         1
     };
     cl()
 }
 
+fn ergonomic_clone_closure_with_captures() -> String {
+    let s = String::from("hi");
+
+    let cl = use || {
+        s
+    };
+    cl()
+}
+
 fn main() {}

tests/ui/feature-gates/feature-gate-ergonomic-clones.rs

@@ -13,7 +13,6 @@ fn ergonomic_closure_clone() {
 
     let s3 = use || {
         //~^ ERROR `.use` calls are experimental [E0658]
-        //~| ERROR use of moved value: `s1` [E0382]
         s1
     };
 }

tests/ui/feature-gates/feature-gate-ergonomic-clones.stderr

@@ -28,30 +28,6 @@ LL |     let s3 = use || {
    = help: add `#![feature(ergonomic_clones)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0382]: use of moved value: `s1`
-  --> $DIR/feature-gate-ergonomic-clones.rs:14:14
-   |
-LL |     let s1 = String::from("hi!");
-   |         -- move occurs because `s1` has type `String`, which does not implement the `Copy` trait
-LL |
-LL |     let s2 = use || {
-   |              ------ value moved into closure here
-LL |
-LL |         s1
-   |         -- variable moved due to use in closure
-...
-LL |     let s3 = use || {
-   |              ^^^^^^ value used here after move
-...
-LL |         s1
-   |         -- use occurs due to use in closure
-   |
-help: consider cloning the value if the performance cost is acceptable
-   |
-LL |         s1.clone()
-   |           ++++++++
-
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0382, E0658.
-For more information about an error, try `rustc --explain E0382`.
+For more information about this error, try `rustc --explain E0658`.