1 use crate::infer::at::At;
2 use crate::infer::canonical::OriginalQueryValues;
3 use crate::infer::InferOk;
5 use rustc::ty::subst::GenericArg;
6 use rustc::ty::{self, Ty, TyCtxt};
8 pub use rustc::traits::query::{DropckOutlivesResult, DtorckConstraint};
10 impl<'cx, 'tcx> At<'cx, 'tcx> {
11 /// Given a type `ty` of some value being dropped, computes a set
12 /// of "kinds" (types, regions) that must be outlive the execution
13 /// of the destructor. These basically correspond to data that the
14 /// destructor might access. This is used during regionck to
15 /// impose "outlives" constraints on any lifetimes referenced
18 /// The rules here are given by the "dropck" RFCs, notably [#1238]
19 /// and [#1327]. This is a fixed-point computation, where we
20 /// explore all the data that will be dropped (transitively) when
21 /// a value of type `ty` is dropped. For each type T that will be
22 /// dropped and which has a destructor, we must assume that all
23 /// the types/regions of T are live during the destructor, unless
24 /// they are marked with a special attribute (`#[may_dangle]`).
26 /// [#1238]: https://github.com/rust-lang/rfcs/blob/master/text/1238-nonparametric-dropck.md
27 /// [#1327]: https://github.com/rust-lang/rfcs/blob/master/text/1327-dropck-param-eyepatch.md
28 pub fn dropck_outlives(&self, ty: Ty<'tcx>) -> InferOk<'tcx, Vec<GenericArg<'tcx>>> {
29 debug!("dropck_outlives(ty={:?}, param_env={:?})", ty, self.param_env,);
31 // Quick check: there are a number of cases that we know do not require
33 let tcx = self.infcx.tcx;
34 if trivial_dropck_outlives(tcx, ty) {
35 return InferOk { value: vec![], obligations: vec![] };
38 let mut orig_values = OriginalQueryValues::default();
39 let c_ty = self.infcx.canonicalize_query(&self.param_env.and(ty), &mut orig_values);
40 let span = self.cause.span;
41 debug!("c_ty = {:?}", c_ty);
42 if let Ok(result) = &tcx.dropck_outlives(c_ty) {
43 if result.is_proven() {
44 if let Ok(InferOk { value, obligations }) =
45 self.infcx.instantiate_query_response_and_region_obligations(
52 let ty = self.infcx.resolve_vars_if_possible(&ty);
53 let kinds = value.into_kinds_reporting_overflows(tcx, span, ty);
54 return InferOk { value: kinds, obligations };
59 // Errors and ambiuity in dropck occur in two cases:
60 // - unresolved inference variables at the end of typeck
61 // - non well-formed types where projections cannot be resolved
62 // Either of these should have created an error before.
63 tcx.sess.delay_span_bug(span, "dtorck encountered internal error");
65 InferOk { value: vec![], obligations: vec![] }
69 /// This returns true if the type `ty` is "trivial" for
70 /// dropck-outlives -- that is, if it doesn't require any types to
71 /// outlive. This is similar but not *quite* the same as the
72 /// `needs_drop` test in the compiler already -- that is, for every
73 /// type T for which this function return true, needs-drop would
74 /// return `false`. But the reverse does not hold: in particular,
75 /// `needs_drop` returns false for `PhantomData`, but it is not
76 /// trivial for dropck-outlives.
78 /// Note also that `needs_drop` requires a "global" type (i.e., one
79 /// with erased regions), but this function does not.
80 pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
82 // None of these types have a destructor and hence they do not
83 // require anything in particular to outlive the dtor's
85 ty::Infer(ty::FreshIntTy(_))
86 | ty::Infer(ty::FreshFloatTy(_))
95 | ty::GeneratorWitness(..)
102 // [T; N] and [T] have same properties as T.
103 ty::Array(ty, _) | ty::Slice(ty) => trivial_dropck_outlives(tcx, ty),
105 // (T1..Tn) and closures have same properties as T1..Tn --
106 // check if *any* of those are trivial.
107 ty::Tuple(ref tys) => tys.iter().all(|t| trivial_dropck_outlives(tcx, t.expect_ty())),
108 ty::Closure(def_id, ref substs) => {
109 substs.as_closure().upvar_tys(def_id, tcx).all(|t| trivial_dropck_outlives(tcx, t))
113 if Some(def.did) == tcx.lang_items().manually_drop() {
114 // `ManuallyDrop` never has a dtor.
117 // Other types might. Moreover, PhantomData doesn't
118 // have a dtor, but it is considered to own its
119 // content, so it is non-trivial. Unions can have `impl Drop`,
120 // and hence are non-trivial as well.
125 // The following *might* require a destructor: needs deeper inspection.
130 | ty::Placeholder(..)
133 | ty::Generator(..) => false,
135 ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),