Treat read of COpy types via refs as not move in move-closure

compiler/rustc_typeck/src/check/upvar.rs

@@ -1116,14 +1116,21 @@ impl<'a, 'tcx> InferBorrowKind<'a, 'tcx> {
             place_with_id, diag_expr_id, mode
         );
 
-        let place = truncate_capture_for_move(place_with_id.place.clone());
         match (self.capture_clause, mode) {
             // In non-move closures, we only care about moves
             (hir::CaptureBy::Ref, euv::Copy) => return,
 
+            // We want to capture Copy types that read through a ref via a reborrow
+            (hir::CaptureBy::Value, euv::Copy)
+                if place_with_id.place.deref_tys().any(ty::TyS::is_ref) =>
+            {
+                return;
+            }
+
             (hir::CaptureBy::Ref, euv::Move) | (hir::CaptureBy::Value, euv::Move | euv::Copy) => {}
         };
 
+        let place = truncate_capture_for_move(place_with_id.place.clone());
         let place_with_id = PlaceWithHirId { place: place.clone(), hir_id: place_with_id.hir_id };
 
         if !self.capture_information.contains_key(&place) {

src/test/ui/closures/2229_closure_analysis/move_closure.rs

@@ -6,7 +6,25 @@
 //~| NOTE: see issue #53488 <https://github.com/rust-lang/rust/issues/53488>
 #![feature(rustc_attrs)]
 
-// Test we truncate derefs properly
+fn simple_move_closure() {
+    struct S(String);
+    struct T(S);
+
+    let t = T(S("s".into()));
+    let mut c = #[rustc_capture_analysis]
+    //~^ ERROR: attributes on expressions are experimental
+    //~| NOTE: see issue #15701 <https://github.com/rust-lang/rust/issues/15701>
+    move || {
+    //~^ ERROR: First Pass analysis includes:
+    //~| ERROR: Min Capture analysis includes:
+        t.0.0 = "new S".into();
+        //~^ NOTE: Capturing t[(0, 0),(0, 0)] -> ByValue
+        //~| NOTE: Min Capture t[(0, 0),(0, 0)] -> ByValue
+    };
+    c();
+}
+
+// Test move closure use reborrows when using references
 fn simple_ref() {
     let mut s = 10;
     let ref_s = &mut s;
@@ -24,8 +42,8 @@ fn simple_ref() {
     c();
 }
 
-// Test we truncate derefs properly
-fn struct_contains_ref_to_another_struct() {
+// Test move closure use reborrows when using references
+fn struct_contains_ref_to_another_struct_1() {
     struct S(String);
     struct T<'a>(&'a mut S);
 
@@ -46,27 +64,78 @@ fn struct_contains_ref_to_another_struct() {
     c();
 }
 
-// Test that we don't reduce precision when there is nothing deref.
-fn no_ref() {
+// Test that we can use reborrows to read data of Copy types
+// i.e. without truncating derefs
+fn struct_contains_ref_to_another_struct_2() {
+    struct S(i32);
+    struct T<'a>(&'a S);
+
+    let s = S(0);
+    let t = T(&s);
+
+    let mut c = #[rustc_capture_analysis]
+    //~^ ERROR: attributes on expressions are experimental
+    //~| NOTE: see issue #15701 <https://github.com/rust-lang/rust/issues/15701>
+    move || {
+    //~^ ERROR: First Pass analysis includes:
+    //~| ERROR: Min Capture analysis includes:
+        let _t = t.0.0;
+        //~^ NOTE: Capturing t[(0, 0),Deref,(0, 0)] -> ImmBorrow
+        //~| NOTE: Min Capture t[(0, 0),Deref,(0, 0)] -> ImmBorrow
+    };
+
+    c();
+}
+
+// Test that we can use truncate to move out of !Copy types
+fn struct_contains_ref_to_another_struct_3() {
     struct S(String);
-    struct T(S);
+    struct T<'a>(&'a S);
+
+    let s = S("s".into());
+    let t = T(&s);
 
-    let t = T(S("s".into()));
     let mut c = #[rustc_capture_analysis]
     //~^ ERROR: attributes on expressions are experimental
     //~| NOTE: see issue #15701 <https://github.com/rust-lang/rust/issues/15701>
     move || {
     //~^ ERROR: First Pass analysis includes:
     //~| ERROR: Min Capture analysis includes:
-        t.0.0 = "new S".into();
-        //~^ NOTE: Capturing t[(0, 0),(0, 0)] -> ByValue
-        //~| NOTE: Min Capture t[(0, 0),(0, 0)] -> ByValue
+        let _t = t.0.0;
+        //~^ NOTE: Capturing t[(0, 0),Deref,(0, 0)] -> ImmBorrow
+        //~| NOTE: Capturing t[(0, 0)] -> ByValue
+        //~| NOTE: Min Capture t[(0, 0)] -> ByValue
+    };
+
+    c();
+}
+
+// Test that derefs of box are truncated in move closures
+fn truncate_box_derefs() {
+    struct S(i32);
+
+    let b = Box::new(S(10));
+
+    let c = #[rustc_capture_analysis]
+    //~^ ERROR: attributes on expressions are experimental
+    //~| NOTE: see issue #15701 <https://github.com/rust-lang/rust/issues/15701>
+    move || {
+    //~^ ERROR: First Pass analysis includes:
+    //~| ERROR: Min Capture analysis includes:
+        let _t = b.0;
+        //~^ NOTE: Capturing b[Deref,(0, 0)] -> ByValue
+        //~| NOTE: Capturing b[] -> ByValue
+        //~| NOTE: Min Capture b[] -> ByValue
     };
+
     c();
 }
 
 fn main() {
+    simple_move_closure();
     simple_ref();
-    struct_contains_ref_to_another_struct();
-    no_ref();
+    struct_contains_ref_to_another_struct_1();
+    struct_contains_ref_to_another_struct_2();
+    struct_contains_ref_to_another_struct_3();
+    truncate_box_derefs();
 }