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Commit | Line | Data |
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9fa01778 | 1 | use crate::infer::at::At; |
9fa01778 | 2 | use crate::infer::canonical::OriginalQueryValues; |
dfeec247 | 3 | use crate::infer::InferOk; |
74b04a01 XL |
4 | |
5 | use rustc::ty::subst::GenericArg; | |
6 | use rustc::ty::{self, Ty, TyCtxt}; | |
7 | ||
8 | pub use rustc::traits::query::{DropckOutlivesResult, DtorckConstraint}; | |
0531ce1d | 9 | |
dc9dc135 | 10 | impl<'cx, 'tcx> At<'cx, 'tcx> { |
0531ce1d XL |
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 | |
16 | /// within. | |
17 | /// | |
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]`). | |
25 | /// | |
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 | |
e74abb32 | 28 | pub fn dropck_outlives(&self, ty: Ty<'tcx>) -> InferOk<'tcx, Vec<GenericArg<'tcx>>> { |
dfeec247 | 29 | debug!("dropck_outlives(ty={:?}, param_env={:?})", ty, self.param_env,); |
0531ce1d XL |
30 | |
31 | // Quick check: there are a number of cases that we know do not require | |
32 | // any destructor. | |
33 | let tcx = self.infcx.tcx; | |
60c5eb7d | 34 | if trivial_dropck_outlives(tcx, ty) { |
dfeec247 | 35 | return InferOk { value: vec![], obligations: vec![] }; |
0531ce1d XL |
36 | } |
37 | ||
0bf4aa26 | 38 | let mut orig_values = OriginalQueryValues::default(); |
8faf50e0 | 39 | let c_ty = self.infcx.canonicalize_query(&self.param_env.and(ty), &mut orig_values); |
0531ce1d XL |
40 | let span = self.cause.span; |
41 | debug!("c_ty = {:?}", c_ty); | |
e74abb32 | 42 | if let Ok(result) = &tcx.dropck_outlives(c_ty) { |
0731742a | 43 | if result.is_proven() { |
0bf4aa26 XL |
44 | if let Ok(InferOk { value, obligations }) = |
45 | self.infcx.instantiate_query_response_and_region_obligations( | |
dfeec247 XL |
46 | self.cause, |
47 | self.param_env, | |
48 | &orig_values, | |
49 | result, | |
50 | ) | |
0bf4aa26 | 51 | { |
dc9dc135 | 52 | let ty = self.infcx.resolve_vars_if_possible(&ty); |
0bf4aa26 | 53 | let kinds = value.into_kinds_reporting_overflows(tcx, span, ty); |
dfeec247 | 54 | return InferOk { value: kinds, obligations }; |
0531ce1d XL |
55 | } |
56 | } | |
0531ce1d XL |
57 | } |
58 | ||
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 | |
b7449926 | 62 | // Either of these should have created an error before. |
dfeec247 | 63 | tcx.sess.delay_span_bug(span, "dtorck encountered internal error"); |
0731742a | 64 | |
dfeec247 | 65 | InferOk { value: vec![], obligations: vec![] } |
0531ce1d XL |
66 | } |
67 | } | |
68 | ||
0531ce1d XL |
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 | |
9fa01778 | 74 | /// return `false`. But the reverse does not hold: in particular, |
0531ce1d XL |
75 | /// `needs_drop` returns false for `PhantomData`, but it is not |
76 | /// trivial for dropck-outlives. | |
77 | /// | |
78 | /// Note also that `needs_drop` requires a "global" type (i.e., one | |
a1dfa0c6 | 79 | /// with erased regions), but this function does not. |
dc9dc135 | 80 | pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool { |
e74abb32 | 81 | match ty.kind { |
0531ce1d XL |
82 | // None of these types have a destructor and hence they do not |
83 | // require anything in particular to outlive the dtor's | |
84 | // execution. | |
b7449926 XL |
85 | ty::Infer(ty::FreshIntTy(_)) |
86 | | ty::Infer(ty::FreshFloatTy(_)) | |
87 | | ty::Bool | |
88 | | ty::Int(_) | |
89 | | ty::Uint(_) | |
90 | | ty::Float(_) | |
91 | | ty::Never | |
92 | | ty::FnDef(..) | |
93 | | ty::FnPtr(_) | |
94 | | ty::Char | |
95 | | ty::GeneratorWitness(..) | |
96 | | ty::RawPtr(_) | |
97 | | ty::Ref(..) | |
98 | | ty::Str | |
99 | | ty::Foreign(..) | |
100 | | ty::Error => true, | |
0531ce1d XL |
101 | |
102 | // [T; N] and [T] have same properties as T. | |
60c5eb7d | 103 | ty::Array(ty, _) | ty::Slice(ty) => trivial_dropck_outlives(tcx, ty), |
0531ce1d XL |
104 | |
105 | // (T1..Tn) and closures have same properties as T1..Tn -- | |
106 | // check if *any* of those are trivial. | |
60c5eb7d | 107 | ty::Tuple(ref tys) => tys.iter().all(|t| trivial_dropck_outlives(tcx, t.expect_ty())), |
dfeec247 XL |
108 | ty::Closure(def_id, ref substs) => { |
109 | substs.as_closure().upvar_tys(def_id, tcx).all(|t| trivial_dropck_outlives(tcx, t)) | |
110 | } | |
0531ce1d | 111 | |
b7449926 XL |
112 | ty::Adt(def, _) => { |
113 | if Some(def.did) == tcx.lang_items().manually_drop() { | |
8faf50e0 | 114 | // `ManuallyDrop` never has a dtor. |
0531ce1d XL |
115 | true |
116 | } else { | |
117 | // Other types might. Moreover, PhantomData doesn't | |
118 | // have a dtor, but it is considered to own its | |
b7449926 XL |
119 | // content, so it is non-trivial. Unions can have `impl Drop`, |
120 | // and hence are non-trivial as well. | |
0531ce1d XL |
121 | false |
122 | } | |
123 | } | |
124 | ||
0bf4aa26 | 125 | // The following *might* require a destructor: needs deeper inspection. |
b7449926 XL |
126 | ty::Dynamic(..) |
127 | | ty::Projection(..) | |
128 | | ty::Param(_) | |
129 | | ty::Opaque(..) | |
a1dfa0c6 | 130 | | ty::Placeholder(..) |
b7449926 | 131 | | ty::Infer(_) |
a1dfa0c6 | 132 | | ty::Bound(..) |
b7449926 | 133 | | ty::Generator(..) => false, |
0bf4aa26 XL |
134 | |
135 | ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"), | |
0531ce1d XL |
136 | } |
137 | } |