Handle type params in insig dtors

Author: arora-aman

Diff for: compiler/rustc_ty_utils/src/needs_drop.rs

@@ -3,6 +3,7 @@
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::subst::Subst;
+use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::util::{needs_drop_components, AlwaysRequiresDrop};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_session::Limit;
@@ -12,7 +13,7 @@ type NeedsDropResult<T> = Result<T, AlwaysRequiresDrop>;
 
 fn needs_drop_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
     let adt_components =
-        move |adt_def: &ty::AdtDef| tcx.adt_drop_tys(adt_def.did).map(|tys| tys.iter());
+        move |adt_def: &ty::AdtDef, _| tcx.adt_drop_tys(adt_def.did).map(|tys| tys.iter());
 
     // If we don't know a type doesn't need drop, for example if it's a type
     // parameter without a `Copy` bound, then we conservatively return that it
@@ -28,8 +29,9 @@ fn has_significant_drop_raw<'tcx>(
     tcx: TyCtxt<'tcx>,
     query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
 ) -> bool {
-    let significant_drop_fields =
-        move |adt_def: &ty::AdtDef| tcx.adt_significant_drop_tys(adt_def.did).map(|tys| tys.iter());
+    let significant_drop_fields = move |adt_def: &ty::AdtDef, _| {
+        tcx.adt_significant_drop_tys(adt_def.did).map(|tys| tys.iter())
+    };
     let res = NeedsDropTypes::new(tcx, query.param_env, query.value, significant_drop_fields)
         .next()
         .is_some();
@@ -74,7 +76,7 @@ impl<'tcx, F> NeedsDropTypes<'tcx, F> {
 
 impl<'tcx, F, I> Iterator for NeedsDropTypes<'tcx, F>
 where
-    F: Fn(&ty::AdtDef) -> NeedsDropResult<I>,
+    F: Fn(&ty::AdtDef, SubstsRef<'tcx>) -> NeedsDropResult<I>,
     I: Iterator<Item = Ty<'tcx>>,
 {
     type Item = NeedsDropResult<Ty<'tcx>>;
@@ -138,7 +140,7 @@ where
                     // `ManuallyDrop`. If it's a struct or enum without a `Drop`
                     // impl then check whether the field types need `Drop`.
                     ty::Adt(adt_def, substs) => {
-                        let tys = match (self.adt_components)(adt_def) {
+                        let tys = match (self.adt_components)(adt_def, substs) {
                             Err(e) => return Some(Err(e)),
                             Ok(tys) => tys,
                         };
@@ -185,12 +187,12 @@ enum DtorType {
 // Depending on the implentation of `adt_has_dtor`, it is used to check if the
 // ADT has a destructor or if the ADT only has a significant destructor. For
 // understanding significant destructor look at `adt_significant_drop_tys`.
-fn adt_drop_tys_helper(
-    tcx: TyCtxt<'_>,
+fn adt_drop_tys_helper<'tcx>(
+    tcx: TyCtxt<'tcx>,
     def_id: DefId,
     adt_has_dtor: impl Fn(&ty::AdtDef) -> Option<DtorType>,
-) -> Result<&ty::List<Ty<'_>>, AlwaysRequiresDrop> {
-    let adt_components = move |adt_def: &ty::AdtDef| {
+) -> Result<&ty::List<Ty<'tcx>>, AlwaysRequiresDrop> {
+    let adt_components = move |adt_def: &ty::AdtDef, substs: SubstsRef<'tcx>| {
         if adt_def.is_manually_drop() {
             debug!("adt_drop_tys: `{:?}` is manually drop", adt_def);
             return Ok(Vec::new().into_iter());
@@ -202,7 +204,11 @@ fn adt_drop_tys_helper(
                 }
                 DtorType::Insignificant => {
                     debug!("adt_drop_tys: `{:?}` drop is insignificant", adt_def);
-                    return Ok(Vec::new().into_iter());
+
+                    // Since the destructor is insignificant, we just want to make sure all of
+                    // the passed in type parameters are also insignificant.
+                    // Eg: Vec<T> dtor is insignificant when T=i32 but significant when T=Mutex.
+                    return Ok(substs.types().collect::<Vec<Ty<'_>>>().into_iter());
                 }
             }
         } else if adt_def.is_union() {

Diff for: src/test/ui/closures/2229_closure_analysis/migrations/insignificant_drop_attr_migrations.fixed

@@ -9,15 +9,15 @@
 
 struct InsignificantDropPoint {
     x: i32,
-    y: Mutex<T>,
+    y: Mutex<i32>,
 }
 
 impl Drop for InsignificantDropPoint {
     #[rustc_insignificant_dtor]
     fn drop(&mut self) {}
 }
 
-struct SigDrop { x: () }
+struct SigDrop;
 
 impl Drop for SigDrop {
     fn drop(&mut self) {}
@@ -45,9 +45,10 @@ fn insign_dtor() {
 
 // `SigDrop` implements drop and therefore needs to be migrated.
 fn significant_drop_needs_migration() {
-    let t = (SigDrop { x: () }, SigDrop { x: () });
+    let t = (SigDrop {}, SigDrop {});
 
     let c = || {
+        let _ = &t;
         //~^ ERROR: drop order
         //~| NOTE: for more information, see
         //~| HELP: add a dummy let to cause `t` to be fully captured
@@ -64,10 +65,11 @@ fn significant_drop_needs_migration() {
 // consdered to have an significant drop. Since the elements
 // of `GenericStruct` implement drop, migration is required.
 fn generic_struct_with_significant_drop_needs_migration() {
-    let t = Wrapper(GenericStruct(SigDrop { x: () }, SigDrop { x: () }), 5);
+    let t = Wrapper(GenericStruct(SigDrop {}, SigDrop {}), 5);
 
     // move is used to force i32 to be copied instead of being a ref
     let c = move || {
+        let _ = &t;
         //~^ ERROR: drop order
         //~| NOTE: for more information, see
         //~| HELP: add a dummy let to cause `t` to be fully captured

Diff for: src/test/ui/closures/2229_closure_analysis/migrations/insignificant_drop_attr_migrations.stderr

@@ -1,19 +1,45 @@
-error[E0107]: missing generics for struct `Mutex`
-  --> $DIR/insignificant_drop_attr_migrations.rs:12:8
+error: changes to closure capture in Rust 2021 will affect drop order
+  --> $DIR/insignificant_drop_attr_migrations.rs:50:13
    |
-LL |     y: Mutex,
-   |        ^^^^^ expected 1 generic argument
+LL |     let c = || {
+   |             ^^
+...
+LL |         let _t = t.0;
+   |                  --- in Rust 2018, this closure captures all of `t`, but in Rust 2021, it will only capture `t.0`
+...
+LL | }
+   | - in Rust 2018, `t` is dropped here, but in Rust 2021, only `t.0` will be dropped here as part of the closure
    |
-note: struct defined here, with 1 generic parameter: `T`
-  --> $SRC_DIR/std/src/sync/mutex.rs:LL:COL
+note: the lint level is defined here
+  --> $DIR/insignificant_drop_attr_migrations.rs:3:9
    |
-LL | pub struct Mutex<T: ?Sized> {
-   |            ^^^^^ -
-help: add missing generic argument
+LL | #![deny(rust_2021_incompatible_closure_captures)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = 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 `t` to be fully captured
+   |
+LL ~     let c = || {
+LL +         let _ = &t;
+   |
+
+error: changes to closure capture in Rust 2021 will affect drop order
+  --> $DIR/insignificant_drop_attr_migrations.rs:70:13
+   |
+LL |     let c = move || {
+   |             ^^^^^^^
+...
+LL |         let _t = t.1;
+   |                  --- in Rust 2018, this closure captures all of `t`, but in Rust 2021, it will only capture `t.1`
+...
+LL | }
+   | - in Rust 2018, `t` is dropped here, but in Rust 2021, only `t.1` will be dropped here as part of 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 `t` to be fully captured
+   |
+LL ~     let c = move || {
+LL +         let _ = &t;
    |
-LL |     y: Mutex<T>,
-   |        ~~~~~~~~
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0107`.