Add note pointing to where a closure and it's captured variables are dropped

Author: roxelo

compiler/rustc_typeck/src/check/upvar.rs

@@ -511,15 +511,30 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         .as_str(),
                     );
                     for (var_hir_id, diagnostics_info) in need_migrations.iter() {
+                        let mut captured_names = format!("");
                         for (captured_hir_id, captured_name) in diagnostics_info.iter() {
                             if let Some(captured_hir_id) = captured_hir_id {
                                 let cause_span = self.tcx.hir().span(*captured_hir_id);
                                 diagnostics_builder.span_label(cause_span, format!("in Rust 2018, closure captures all of `{}`, but in Rust 2021, it only captures `{}`",
                                     self.tcx.hir().name(*var_hir_id),
                                     captured_name,
                                 ));
+                                if captured_names == "" {
+                                    captured_names = format!("`{}`", captured_name);
+                                } else {
+                                    captured_names = format!("{}, `{}`", captured_names, captured_name);
+                                }
                             }
                         }
+
+                        if reasons.contains("drop order") {
+                            let drop_location_span = drop_location_span(self.tcx, &closure_hir_id);
+
+                            diagnostics_builder.span_label(drop_location_span, format!("in Rust 2018, `{}` would be dropped here, but in Rust 2021, only {} would be dropped here alongside the closure",
+                                self.tcx.hir().name(*var_hir_id),
+                                captured_names,
+                            ));
+                        }
                     }
                     diagnostics_builder.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>");
                     let closure_body_span = self.tcx.hir().span(body_id.hir_id);
@@ -1350,6 +1365,31 @@ fn apply_capture_kind_on_capture_ty(
     }
 }
 
+/// Returns the Span of where the value with the provided HirId would be dropped
+fn drop_location_span(tcx: TyCtxt<'tcx>, hir_id: &hir::HirId) -> Span {
+    let owner_id = tcx.hir().get_enclosing_scope(*hir_id).unwrap();
+
+    let owner_node = tcx.hir().get(owner_id);
+    match owner_node {
+        hir::Node::Item(item) => match item.kind {
+            hir::ItemKind::Fn(_, _, owner_id) => {
+                let owner_span = tcx.hir().span(owner_id.hir_id);
+                tcx.sess.source_map().end_point(owner_span)
+            }
+            _ => {
+                bug!("Drop location span error: need to handle more ItemKind {:?}", item.kind);
+            }
+        },
+        hir::Node::Block(block) => {
+            let owner_span = tcx.hir().span(block.hir_id);
+            tcx.sess.source_map().end_point(owner_span)
+        }
+        _ => {
+            bug!("Drop location span error: need to handle more Node {:?}", owner_node);
+        }
+    }
+}
+
 struct InferBorrowKind<'a, 'tcx> {
     fcx: &'a FnCtxt<'a, 'tcx>,
 

src/test/ui/closures/2229_closure_analysis/migrations/auto_traits.fixed

@@ -1,5 +1,6 @@
 // run-rustfix
 #![deny(rust_2021_incompatible_closure_captures)]
+//~^ NOTE: the lint level is defined here
 
 use std::thread;
 
@@ -12,8 +13,10 @@ fn test_send_trait() {
     let fptr = SendPointer(&mut f as *mut i32);
     thread::spawn(move || { let _ = &fptr; unsafe {
         //~^ ERROR: `Send` closure trait implementation
+        //~| NOTE: for more information, see
         //~| HELP: add a dummy let to cause `fptr` to be fully captured
         *fptr.0 = 20;
+        //~^ NOTE: in Rust 2018, closure captures all of `fptr`, but in Rust 2021, it only captures `fptr.0`
     } });
 }
 
@@ -29,8 +32,10 @@ fn test_sync_trait() {
     let fptr = SyncPointer(f);
     thread::spawn(move || { let _ = &fptr; unsafe {
         //~^ ERROR: `Sync`, `Send` closure trait implementation
+        //~| NOTE: for more information, see
         //~| HELP: add a dummy let to cause `fptr` to be fully captured
         *fptr.0.0 = 20;
+        //~^ NOTE: in Rust 2018, closure captures all of `fptr`, but in Rust 2021, it only captures `fptr.0.0`
     } });
 }
 
@@ -50,15 +55,18 @@ fn test_clone_trait() {
     let f = U(S(String::from("Hello World")), T(0));
     let c = || { let _ = &f; 
         //~^ ERROR: `Clone` closure trait implementation, and drop order
+        //~| NOTE: for more information, see
         //~| HELP: add a dummy let to cause `f` to be fully captured
         let f_1 = f.1;
+        //~^ NOTE: in Rust 2018, closure captures all of `f`, but in Rust 2021, it only captures `f.1`
         println!("{:?}", f_1.0);
     };
 
     let c_clone = c.clone();
 
     c_clone();
 }
+//~^ NOTE: in Rust 2018, `f` would be dropped here, but in Rust 2021, only `f.1` would be dropped here alongside the closure
 
 fn main() {
     test_send_trait();

src/test/ui/closures/2229_closure_analysis/migrations/auto_traits.rs

@@ -1,5 +1,6 @@
 // run-rustfix
 #![deny(rust_2021_incompatible_closure_captures)]
+//~^ NOTE: the lint level is defined here
 
 use std::thread;
 
@@ -12,8 +13,10 @@ fn test_send_trait() {
     let fptr = SendPointer(&mut f as *mut i32);
     thread::spawn(move || unsafe {
         //~^ ERROR: `Send` closure trait implementation
+        //~| NOTE: for more information, see
         //~| HELP: add a dummy let to cause `fptr` to be fully captured
         *fptr.0 = 20;
+        //~^ NOTE: in Rust 2018, closure captures all of `fptr`, but in Rust 2021, it only captures `fptr.0`
     });
 }
 
@@ -29,8 +32,10 @@ fn test_sync_trait() {
     let fptr = SyncPointer(f);
     thread::spawn(move || unsafe {
         //~^ ERROR: `Sync`, `Send` closure trait implementation
+        //~| NOTE: for more information, see
         //~| HELP: add a dummy let to cause `fptr` to be fully captured
         *fptr.0.0 = 20;
+        //~^ NOTE: in Rust 2018, closure captures all of `fptr`, but in Rust 2021, it only captures `fptr.0.0`
     });
 }
 
@@ -50,15 +55,18 @@ fn test_clone_trait() {
     let f = U(S(String::from("Hello World")), T(0));
     let c = || {
         //~^ ERROR: `Clone` closure trait implementation, and drop order
+        //~| NOTE: for more information, see
         //~| HELP: add a dummy let to cause `f` to be fully captured
         let f_1 = f.1;
+        //~^ NOTE: in Rust 2018, closure captures all of `f`, but in Rust 2021, it only captures `f.1`
         println!("{:?}", f_1.0);
     };
 
     let c_clone = c.clone();
 
     c_clone();
 }
+//~^ NOTE: in Rust 2018, `f` would be dropped here, but in Rust 2021, only `f.1` would be dropped here alongside the closure
 
 fn main() {
     test_send_trait();

src/test/ui/closures/2229_closure_analysis/migrations/auto_traits.stderr

@@ -1,12 +1,14 @@
 error: changes to closure capture in Rust 2021 will affect `Send` closure trait implementation
-  --> $DIR/auto_traits.rs:13:19
+  --> $DIR/auto_traits.rs:14:19
    |
 LL |       thread::spawn(move || unsafe {
    |  ___________________^
 LL | |
 LL | |
+LL | |
 LL | |         *fptr.0 = 20;
    | |         ------- in Rust 2018, closure captures all of `fptr`, but in Rust 2021, it only captures `fptr.0`
+LL | |
 LL | |     });
    | |_____^
    |
@@ -21,19 +23,22 @@ help: add a dummy let to cause `fptr` to be fully captured
 LL |     thread::spawn(move || { let _ = &fptr; unsafe {
 LL |
 LL |
+LL |
 LL |         *fptr.0 = 20;
-LL |     } });
-   |
+LL |
+ ...
 
 error: changes to closure capture in Rust 2021 will affect `Sync`, `Send` closure trait implementation
-  --> $DIR/auto_traits.rs:30:19
+  --> $DIR/auto_traits.rs:33:19
    |
 LL |       thread::spawn(move || unsafe {
    |  ___________________^
 LL | |
 LL | |
+LL | |
 LL | |         *fptr.0.0 = 20;
    | |         --------- in Rust 2018, closure captures all of `fptr`, but in Rust 2021, it only captures `fptr.0.0`
+LL | |
 LL | |     });
    | |_____^
    |
@@ -43,33 +48,39 @@ help: add a dummy let to cause `fptr` to be fully captured
 LL |     thread::spawn(move || { let _ = &fptr; unsafe {
 LL |
 LL |
+LL |
 LL |         *fptr.0.0 = 20;
-LL |     } });
-   |
+LL |
+ ...
 
 error: changes to closure capture in Rust 2021 will affect `Clone` closure trait implementation, and drop order
-  --> $DIR/auto_traits.rs:51:13
+  --> $DIR/auto_traits.rs:56:13
    |
 LL |       let c = || {
    |  _____________^
 LL | |
 LL | |
+LL | |
 LL | |         let f_1 = f.1;
    | |                   --- in Rust 2018, closure captures all of `f`, but in Rust 2021, it only captures `f.1`
+LL | |
 LL | |         println!("{:?}", f_1.0);
 LL | |     };
    | |_____^
+...
+LL |   }
+   |   - in Rust 2018, `f` would be dropped here, but in Rust 2021, only `f.1` would be dropped here alongside the closure
    |
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>
 help: add a dummy let to cause `f` to be fully captured
    |
 LL |     let c = || { let _ = &f; 
 LL |
 LL |
+LL |
 LL |         let f_1 = f.1;
-LL |         println!("{:?}", f_1.0);
-LL |     };
-   |
+LL |
+ ...
 
 error: aborting due to 3 previous errors
 

src/test/ui/closures/2229_closure_analysis/migrations/insignificant_drop.fixed

@@ -27,6 +27,9 @@ fn test1_all_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
+//~| in Rust 2018, `t1` would be dropped here, but in Rust 2021, only `t1.0` would be dropped here alongside the closure
+//~| in Rust 2018, `t2` would be dropped here, but in Rust 2021, only `t2.0` would be dropped here alongside the closure
 
 // String implements drop and therefore should be migrated.
 // But in this test cases, `t2` is completely captured and when it is dropped won't be affected
@@ -48,6 +51,8 @@ fn test2_only_precise_paths_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
+//~| in Rust 2018, `t1` would be dropped here, but in Rust 2021, only `t1.0` would be dropped here alongside the closure
 
 // If a variable would've not been captured by value then it would've not been
 // dropped with the closure and therefore doesn't need migration.
@@ -65,6 +70,7 @@ fn test3_only_by_value_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
 
 // Copy types get copied into the closure instead of move. Therefore we don't need to
 // migrate then as their drop order isn't tied to the closure.
@@ -85,6 +91,7 @@ fn test4_only_non_copy_types_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
 
 fn test5_only_drop_types_need_migration() {
     struct S(i32, i32);
@@ -105,6 +112,7 @@ fn test5_only_drop_types_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
 
 // Since we are using a move closure here, both `t` and `t1` get moved
 // even though they are being used by ref inside the closure.
@@ -122,6 +130,8 @@ fn test6_move_closures_non_copy_types_might_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.1` would be dropped here alongside the closure
+//~| in Rust 2018, `t1` would be dropped here, but in Rust 2021, only `t1.1` would be dropped here alongside the closure
 
 // Test migration analysis in case of Drop + Non Drop aggregates.
 // Note we need migration here only because the non-copy (because Drop type) is captured,
@@ -139,6 +149,7 @@ fn test7_drop_non_drop_aggregate_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
 
 fn main() {
     test1_all_need_migration();

src/test/ui/closures/2229_closure_analysis/migrations/insignificant_drop.rs

@@ -27,6 +27,9 @@ fn test1_all_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
+//~| in Rust 2018, `t1` would be dropped here, but in Rust 2021, only `t1.0` would be dropped here alongside the closure
+//~| in Rust 2018, `t2` would be dropped here, but in Rust 2021, only `t2.0` would be dropped here alongside the closure
 
 // String implements drop and therefore should be migrated.
 // But in this test cases, `t2` is completely captured and when it is dropped won't be affected
@@ -48,6 +51,8 @@ fn test2_only_precise_paths_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
+//~| in Rust 2018, `t1` would be dropped here, but in Rust 2021, only `t1.0` would be dropped here alongside the closure
 
 // If a variable would've not been captured by value then it would've not been
 // dropped with the closure and therefore doesn't need migration.
@@ -65,6 +70,7 @@ fn test3_only_by_value_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
 
 // Copy types get copied into the closure instead of move. Therefore we don't need to
 // migrate then as their drop order isn't tied to the closure.
@@ -85,6 +91,7 @@ fn test4_only_non_copy_types_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
 
 fn test5_only_drop_types_need_migration() {
     struct S(i32, i32);
@@ -105,6 +112,7 @@ fn test5_only_drop_types_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
 
 // Since we are using a move closure here, both `t` and `t1` get moved
 // even though they are being used by ref inside the closure.
@@ -122,6 +130,8 @@ fn test6_move_closures_non_copy_types_might_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.1` would be dropped here alongside the closure
+//~| in Rust 2018, `t1` would be dropped here, but in Rust 2021, only `t1.1` would be dropped here alongside the closure
 
 // Test migration analysis in case of Drop + Non Drop aggregates.
 // Note we need migration here only because the non-copy (because Drop type) is captured,
@@ -139,6 +149,7 @@ fn test7_drop_non_drop_aggregate_need_migration() {
 
     c();
 }
+//~^ in Rust 2018, `t` would be dropped here, but in Rust 2021, only `t.0` would be dropped here alongside the closure
 
 fn main() {
     test1_all_need_migration();