1 use rustc::hir::def_id::DefId;
2 use rustc::infer::canonical::{Canonical, QueryResponse};
3 use rustc::traits::query::dropck_outlives::{DropckOutlivesResult, DtorckConstraint};
4 use rustc::traits::query::{CanonicalTyGoal, NoSolution};
5 use rustc::traits::{TraitEngine, Normalized, ObligationCause, TraitEngineExt};
6 use rustc::ty::query::Providers;
7 use rustc::ty::subst::{Subst, InternalSubsts};
8 use rustc::ty::{self, ParamEnvAnd, Ty, TyCtxt};
9 use rustc::util::nodemap::FxHashSet;
10 use syntax::source_map::{Span, DUMMY_SP};
12 crate fn provide(p: &mut Providers<'_>) {
15 adt_dtorck_constraint,
20 fn dropck_outlives<'tcx>(
22 canonical_goal: CanonicalTyGoal<'tcx>,
23 ) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, DropckOutlivesResult<'tcx>>>, NoSolution> {
24 debug!("dropck_outlives(goal={:#?})", canonical_goal);
26 tcx.infer_ctxt().enter_with_canonical(
29 |ref infcx, goal, canonical_inference_vars| {
36 let mut result = DropckOutlivesResult {
41 // A stack of types left to process. Each round, we pop
42 // something from the stack and invoke
43 // `dtorck_constraint_for_ty`. This may produce new types that
44 // have to be pushed on the stack. This continues until we have explored
45 // all the reachable types from the type `for_ty`.
47 // Example: Imagine that we have the following code:
62 // } // here, `a` is dropped
65 // at the point where `a` is dropped, we need to figure out
66 // which types inside of `a` contain region data that may be
67 // accessed by any destructors in `a`. We begin by pushing `A`
68 // onto the stack, as that is the type of `a`. We will then
69 // invoke `dtorck_constraint_for_ty` which will expand `A`
70 // into the types of its fields `(B, Vec<A>)`. These will get
71 // pushed onto the stack. Eventually, expanding `Vec<A>` will
72 // lead to us trying to push `A` a second time -- to prevent
73 // infinite recursion, we notice that `A` was already pushed
75 let mut ty_stack = vec![(for_ty, 0)];
77 // Set used to detect infinite recursion.
78 let mut ty_set = FxHashSet::default();
80 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
82 let cause = ObligationCause::dummy();
83 let mut constraints = DtorckConstraint::empty();
84 while let Some((ty, depth)) = ty_stack.pop() {
85 info!("{} kinds, {} overflows, {} ty_stack",
86 result.kinds.len(), result.overflows.len(), ty_stack.len());
87 dtorck_constraint_for_ty(tcx, DUMMY_SP, for_ty, depth, ty, &mut constraints)?;
89 // "outlives" represent types/regions that may be touched
91 result.kinds.extend(constraints.outlives.drain(..));
92 result.overflows.extend(constraints.overflows.drain(..));
94 // If we have even one overflow, we should stop trying to evaluate further --
95 // chances are, the subsequent overflows for this evaluation won't provide useful
96 // information and will just decrease the speed at which we can emit these errors
97 // (since we'll be printing for just that much longer for the often enormous types
99 if result.overflows.len() >= 1 {
103 // dtorck types are "types that will get dropped but which
104 // do not themselves define a destructor", more or less. We have
105 // to push them onto the stack to be expanded.
106 for ty in constraints.dtorck_types.drain(..) {
107 match infcx.at(&cause, param_env).normalize(&ty) {
112 fulfill_cx.register_predicate_obligations(infcx, obligations);
114 debug!("dropck_outlives: ty from dtorck_types = {:?}", ty);
117 // All parameters live for the duration of the
121 // A projection that we couldn't resolve - it
122 // might have a destructor.
123 ty::Projection(..) | ty::Opaque(..) => {
124 result.kinds.push(ty.into());
128 if ty_set.insert(ty) {
129 ty_stack.push((ty, depth + 1));
135 // We don't actually expect to fail to normalize.
136 // That implies a WF error somewhere else.
138 return Err(NoSolution);
144 debug!("dropck_outlives: result = {:#?}", result);
146 infcx.make_canonicalized_query_response(
147 canonical_inference_vars,
155 /// Returns a set of constraints that needs to be satisfied in
156 /// order for `ty` to be valid for destruction.
157 fn dtorck_constraint_for_ty<'tcx>(
163 constraints: &mut DtorckConstraint<'tcx>,
164 ) -> Result<(), NoSolution> {
166 "dtorck_constraint_for_ty({:?}, {:?}, {:?}, {:?})",
167 span, for_ty, depth, ty
170 if depth >= *tcx.sess.recursion_limit.get() {
171 constraints.overflows.push(ty);
175 if tcx.trivial_dropck_outlives(ty) {
192 | ty::GeneratorWitness(..) => {
193 // these types never have a destructor
196 ty::Array(ety, _) | ty::Slice(ety) => {
197 // single-element containers, behave like their element
198 dtorck_constraint_for_ty(tcx, span, for_ty, depth + 1, ety, constraints)?;
201 ty::Tuple(tys) => for ty in tys.iter() {
202 dtorck_constraint_for_ty(tcx, span, for_ty, depth + 1, ty.expect_ty(), constraints)?;
205 ty::Closure(def_id, substs) => for ty in substs.as_closure().upvar_tys(def_id, tcx) {
206 dtorck_constraint_for_ty(tcx, span, for_ty, depth + 1, ty, constraints)?;
209 ty::Generator(def_id, substs, _movability) => {
210 // rust-lang/rust#49918: types can be constructed, stored
211 // in the interior, and sit idle when generator yields
212 // (and is subsequently dropped).
214 // It would be nice to descend into interior of a
215 // generator to determine what effects dropping it might
216 // have (by looking at any drop effects associated with
219 // However, the interior's representation uses things like
220 // GeneratorWitness that explicitly assume they are not
221 // traversed in such a manner. So instead, we will
222 // simplify things for now by treating all generators as
223 // if they were like trait objects, where its upvars must
224 // all be alive for the generator's (potential)
227 // In particular, skipping over `_interior` is safe
228 // because any side-effects from dropping `_interior` can
229 // only take place through references with lifetimes
230 // derived from lifetimes attached to the upvars, and we
231 // *do* incorporate the upvars here.
233 constraints.outlives.extend(substs.as_generator().upvar_tys(def_id, tcx)
234 .map(|t| -> ty::subst::GenericArg<'tcx> { t.into() }));
237 ty::Adt(def, substs) => {
238 let DtorckConstraint {
242 } = tcx.at(span).adt_dtorck_constraint(def.did)?;
243 // FIXME: we can try to recursively `dtorck_constraint_on_ty`
244 // there, but that needs some way to handle cycles.
245 constraints.dtorck_types.extend(dtorck_types.subst(tcx, substs));
246 constraints.outlives.extend(outlives.subst(tcx, substs));
247 constraints.overflows.extend(overflows.subst(tcx, substs));
250 // Objects must be alive in order for their destructor
253 constraints.outlives.push(ty.into());
256 // Types that can't be resolved. Pass them forward.
257 ty::Projection(..) | ty::Opaque(..) | ty::Param(..) => {
258 constraints.dtorck_types.push(ty);
261 ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
263 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error => {
264 // By the time this code runs, all type variables ought to
265 // be fully resolved.
266 return Err(NoSolution)
273 /// Calculates the dtorck constraint for a type.
274 crate fn adt_dtorck_constraint(
277 ) -> Result<DtorckConstraint<'_>, NoSolution> {
278 let def = tcx.adt_def(def_id);
279 let span = tcx.def_span(def_id);
280 debug!("dtorck_constraint: {:?}", def);
282 if def.is_phantom_data() {
283 // The first generic parameter here is guaranteed to be a type because it's
285 let substs = InternalSubsts::identity_for_item(tcx, def_id);
286 assert_eq!(substs.len(), 1);
287 let result = DtorckConstraint {
289 dtorck_types: vec![substs.type_at(0)],
292 debug!("dtorck_constraint: {:?} => {:?}", def, result);
296 let mut result = DtorckConstraint::empty();
297 for field in def.all_fields() {
298 let fty = tcx.type_of(field.did);
299 dtorck_constraint_for_ty(tcx, span, fty, 0, fty, &mut result)?;
301 result.outlives.extend(tcx.destructor_constraints(def));
302 dedup_dtorck_constraint(&mut result);
304 debug!("dtorck_constraint: {:?} => {:?}", def, result);
309 fn dedup_dtorck_constraint(c: &mut DtorckConstraint<'_>) {
310 let mut outlives = FxHashSet::default();
311 let mut dtorck_types = FxHashSet::default();
313 c.outlives.retain(|&val| outlives.replace(val).is_none());
315 .retain(|&val| dtorck_types.replace(val).is_none());