Make needs_drop
less pessimistic on generators
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parent
8d67f576b5
commit
50c1c295ee
4 changed files with 29 additions and 18 deletions
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@ -1047,10 +1047,7 @@ pub fn needs_drop_components(
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// Foreign types can never have destructors.
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ty::Foreign(..) => Ok(SmallVec::new()),
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// Pessimistically assume that all generators will require destructors
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// as we don't know if a destructor is a noop or not until after the MIR
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// state transformation pass.
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ty::Generator(..) | ty::Dynamic(..) | ty::Error => Err(AlwaysRequiresDrop),
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ty::Dynamic(..) | ty::Error => Err(AlwaysRequiresDrop),
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ty::Slice(ty) => needs_drop_components(ty, target_layout),
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ty::Array(elem_ty, size) => {
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@ -1083,7 +1080,8 @@ pub fn needs_drop_components(
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| ty::Placeholder(..)
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| ty::Opaque(..)
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| ty::Infer(_)
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| ty::Closure(..) => Ok(smallvec![ty]),
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| ty::Closure(..)
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| ty::Generator(..) => Ok(smallvec![ty]),
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}
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}
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@ -99,6 +99,23 @@ where
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}
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}
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ty::Generator(def_id, substs, _) => {
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let substs = substs.as_generator();
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for upvar_ty in substs.upvar_tys(def_id, tcx) {
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queue_type(self, upvar_ty);
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}
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let witness = substs.witness(def_id, tcx);
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let interior_tys = match &witness.kind {
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ty::GeneratorWitness(tys) => tcx.erase_late_bound_regions(tys),
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_ => bug!(),
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};
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for interior_ty in interior_tys {
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queue_type(self, interior_ty);
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}
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}
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// Check for a `Drop` impl and whether this is a union or
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// `ManuallyDrop`. If it's a struct or enum without a `Drop`
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// impl then check whether the field types need `Drop`.
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@ -1,19 +1,16 @@
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error[E0597]: `a` does not live long enough
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--> $DIR/borrowing.rs:9:33
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LL | let _b = {
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| -- borrow later stored here
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LL | let a = 3;
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LL | Pin::new(&mut || yield &a).resume(())
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| ----------^
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| | |
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| | borrowed value does not live long enough
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| -- ^ borrowed value does not live long enough
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| |
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| value captured here by generator
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| a temporary with access to the borrow is created here ...
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LL |
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LL | };
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| -- ... and the borrow might be used here, when that temporary is dropped and runs the destructor for generator
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| |
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| `a` dropped here while still borrowed
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= note: The temporary is part of an expression at the end of a block. Consider forcing this temporary to be dropped sooner, before the block's local variables are dropped. For example, you could save the expression's value in a new local variable `x` and then make `x` be the expression at the end of the block.
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| - `a` dropped here while still borrowed
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error[E0597]: `a` does not live long enough
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--> $DIR/borrowing.rs:16:20
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@ -4,10 +4,9 @@ error[E0499]: cannot borrow `thing` as mutable more than once at a time
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LL | gen.as_mut().resume(&mut thing);
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| ---------- first mutable borrow occurs here
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LL | gen.as_mut().resume(&mut thing);
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| ^^^^^^^^^^ second mutable borrow occurs here
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LL |
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LL | }
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| - first borrow might be used here, when `gen` is dropped and runs the destructor for generator
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| ------ ^^^^^^^^^^ second mutable borrow occurs here
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| |
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| first borrow later used by call
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error: aborting due to previous error
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