1 // Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 use check::regionck::{self, Rcx};
13 use middle::def_id::DefId;
14 use middle::free_region::FreeRegionMap;
17 use middle::subst::{self, Subst};
19 use middle::ty::{self, Ty};
20 use util::nodemap::FnvHashSet;
23 use syntax::codemap::{self, Span};
24 use syntax::parse::token::special_idents;
26 /// check_drop_impl confirms that the Drop implementation identfied by
27 /// `drop_impl_did` is not any more specialized than the type it is
28 /// attached to (Issue #8142).
32 /// 1. The self type must be nominal (this is already checked during
35 /// 2. The generic region/type parameters of the impl's self-type must
36 /// all be parameters of the Drop impl itself (i.e. no
37 /// specialization like `impl Drop for Foo<i32>`), and,
39 /// 3. Any bounds on the generic parameters must be reflected in the
40 /// struct/enum definition for the nominal type itself (i.e.
41 /// cannot do `struct S<T>; impl<T:Clone> Drop for S<T> { ... }`).
43 pub fn check_drop_impl(tcx: &ty::ctxt, drop_impl_did: DefId) -> Result<(), ()> {
44 let ty::TypeScheme { generics: ref dtor_generics,
45 ty: dtor_self_type } = tcx.lookup_item_type(drop_impl_did);
46 let dtor_predicates = tcx.lookup_predicates(drop_impl_did);
47 match dtor_self_type.sty {
48 ty::TyEnum(adt_def, self_to_impl_substs) |
49 ty::TyStruct(adt_def, self_to_impl_substs) => {
50 try!(ensure_drop_params_and_item_params_correspond(tcx,
56 ensure_drop_predicates_are_implied_by_item_defn(tcx,
63 // Destructors only work on nominal types. This was
64 // already checked by coherence, so we can panic here.
65 let span = tcx.map.def_id_span(drop_impl_did, codemap::DUMMY_SP);
67 span, &format!("should have been rejected by coherence check: {}",
73 fn ensure_drop_params_and_item_params_correspond<'tcx>(
76 drop_impl_generics: &ty::Generics<'tcx>,
77 drop_impl_ty: &ty::Ty<'tcx>,
78 self_type_did: DefId) -> Result<(), ()>
80 let drop_impl_node_id = tcx.map.as_local_node_id(drop_impl_did).unwrap();
81 let self_type_node_id = tcx.map.as_local_node_id(self_type_did).unwrap();
83 // check that the impl type can be made to match the trait type.
85 let impl_param_env = ty::ParameterEnvironment::for_item(tcx, self_type_node_id);
86 let infcx = infer::new_infer_ctxt(tcx, &tcx.tables, Some(impl_param_env), true);
88 let named_type = tcx.lookup_item_type(self_type_did).ty;
89 let named_type = named_type.subst(tcx, &infcx.parameter_environment.free_substs);
91 let drop_impl_span = tcx.map.def_id_span(drop_impl_did, codemap::DUMMY_SP);
92 let fresh_impl_substs =
93 infcx.fresh_substs_for_generics(drop_impl_span, drop_impl_generics);
94 let fresh_impl_self_ty = drop_impl_ty.subst(tcx, &fresh_impl_substs);
96 if let Err(_) = infer::mk_eqty(&infcx, true, infer::TypeOrigin::Misc(drop_impl_span),
97 named_type, fresh_impl_self_ty) {
98 span_err!(tcx.sess, drop_impl_span, E0366,
99 "Implementations of Drop cannot be specialized");
100 let item_span = tcx.map.span(self_type_node_id);
101 tcx.sess.span_note(item_span,
102 "Use same sequence of generic type and region \
103 parameters that is on the struct/enum definition");
107 if let Err(ref errors) = infcx.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
108 // this could be reached when we get lazy normalization
109 traits::report_fulfillment_errors(&infcx, errors);
113 let free_regions = FreeRegionMap::new();
114 infcx.resolve_regions_and_report_errors(&free_regions, drop_impl_node_id);
118 /// Confirms that every predicate imposed by dtor_predicates is
119 /// implied by assuming the predicates attached to self_type_did.
120 fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
121 tcx: &ty::ctxt<'tcx>,
122 drop_impl_did: DefId,
123 dtor_predicates: &ty::GenericPredicates<'tcx>,
124 self_type_did: DefId,
125 self_to_impl_substs: &subst::Substs<'tcx>) -> Result<(), ()> {
127 // Here is an example, analogous to that from
128 // `compare_impl_method`.
130 // Consider a struct type:
132 // struct Type<'c, 'b:'c, 'a> {
133 // x: &'a Contents // (contents are irrelevant;
134 // y: &'c Cell<&'b Contents>, // only the bounds matter for our purposes.)
139 // impl<'z, 'y:'z, 'x:'y> Drop for P<'z, 'y, 'x> {
140 // fn drop(&mut self) { self.y.set(self.x); } // (only legal if 'x: 'y)
143 // We start out with self_to_impl_substs, that maps the generic
144 // parameters of Type to that of the Drop impl.
146 // self_to_impl_substs = {'c => 'z, 'b => 'y, 'a => 'x}
148 // Applying this to the predicates (i.e. assumptions) provided by the item
149 // definition yields the instantiated assumptions:
153 // We then check all of the predicates of the Drop impl:
157 // and ensure each is in the list of instantiated
158 // assumptions. Here, `'y:'z` is present, but `'x:'y` is
159 // absent. So we report an error that the Drop impl injected a
160 // predicate that is not present on the struct definition.
162 let self_type_node_id = tcx.map.as_local_node_id(self_type_did).unwrap();
164 let drop_impl_span = tcx.map.def_id_span(drop_impl_did, codemap::DUMMY_SP);
166 // We can assume the predicates attached to struct/enum definition
168 let generic_assumptions = tcx.lookup_predicates(self_type_did);
170 let assumptions_in_impl_context = generic_assumptions.instantiate(tcx, &self_to_impl_substs);
171 assert!(assumptions_in_impl_context.predicates.is_empty_in(subst::SelfSpace));
172 assert!(assumptions_in_impl_context.predicates.is_empty_in(subst::FnSpace));
173 let assumptions_in_impl_context =
174 assumptions_in_impl_context.predicates.get_slice(subst::TypeSpace);
176 // An earlier version of this code attempted to do this checking
177 // via the traits::fulfill machinery. However, it ran into trouble
178 // since the fulfill machinery merely turns outlives-predicates
179 // 'a:'b and T:'b into region inference constraints. It is simpler
180 // just to look for all the predicates directly.
182 assert!(dtor_predicates.predicates.is_empty_in(subst::SelfSpace));
183 assert!(dtor_predicates.predicates.is_empty_in(subst::FnSpace));
184 let predicates = dtor_predicates.predicates.get_slice(subst::TypeSpace);
185 for predicate in predicates {
186 // (We do not need to worry about deep analysis of type
187 // expressions etc because the Drop impls are already forced
188 // to take on a structure that is roughly a alpha-renaming of
189 // the generic parameters of the item definition.)
191 // This path now just checks *all* predicates via the direct
192 // lookup, rather than using fulfill machinery.
194 // However, it may be more efficient in the future to batch
195 // the analysis together via the fulfill , rather than the
196 // repeated `contains` calls.
198 if !assumptions_in_impl_context.contains(&predicate) {
199 let item_span = tcx.map.span(self_type_node_id);
200 span_err!(tcx.sess, drop_impl_span, E0367,
201 "The requirement `{}` is added only by the Drop impl.", predicate);
202 tcx.sess.span_note(item_span,
203 "The same requirement must be part of \
204 the struct/enum definition");
208 if tcx.sess.has_errors() {
214 /// check_safety_of_destructor_if_necessary confirms that the type
215 /// expression `typ` conforms to the "Drop Check Rule" from the Sound
216 /// Generic Drop (RFC 769).
220 /// The Drop Check Rule is the following:
222 /// Let `v` be some value (either temporary or named) and 'a be some
223 /// lifetime (scope). If the type of `v` owns data of type `D`, where
225 /// * (1.) `D` has a lifetime- or type-parametric Drop implementation, and
226 /// * (2.) the structure of `D` can reach a reference of type `&'a _`, and
228 /// * (A.) the Drop impl for `D` instantiates `D` at 'a directly,
229 /// i.e. `D<'a>`, or,
230 /// * (B.) the Drop impl for `D` has some type parameter with a
231 /// trait bound `T` where `T` is a trait that has at least
234 /// then 'a must strictly outlive the scope of v.
238 /// This function is meant to by applied to the type for every
239 /// expression in the program.
240 pub fn check_safety_of_destructor_if_necessary<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
243 scope: region::CodeExtent) {
244 debug!("check_safety_of_destructor_if_necessary typ: {:?} scope: {:?}",
247 let parent_scope = rcx.tcx().region_maps.opt_encl_scope(scope).unwrap_or_else(|| {
248 rcx.tcx().sess.span_bug(
249 span, &format!("no enclosing scope found for scope: {:?}", scope))
252 let result = iterate_over_potentially_unsafe_regions_in_type(
256 parent_scope: parent_scope,
257 breadcrumbs: FnvHashSet()
264 Err(Error::Overflow(ref ctxt, ref detected_on_typ)) => {
266 span_err!(tcx.sess, span, E0320,
267 "overflow while adding drop-check rules for {}", typ);
269 TypeContext::Root => {
270 // no need for an additional note if the overflow
271 // was somehow on the root.
273 TypeContext::ADT { def_id, variant, field, field_index } => {
274 let adt = tcx.lookup_adt_def(def_id);
275 let variant_name = match adt.adt_kind() {
276 ty::AdtKind::Enum => format!("enum {} variant {}",
277 tcx.item_path_str(def_id),
279 ty::AdtKind::Struct => format!("struct {}",
280 tcx.item_path_str(def_id))
282 let field_name = if field == special_idents::unnamed_field.name {
283 format!("#{}", field_index)
285 format!("`{}`", field)
290 "overflowed on {} field {} type: {}",
301 Overflow(TypeContext, ty::Ty<'tcx>),
304 #[derive(Copy, Clone)]
315 struct DropckContext<'a, 'b: 'a, 'tcx: 'b> {
316 rcx: &'a mut Rcx<'b, 'tcx>,
317 /// types that have already been traversed
318 breadcrumbs: FnvHashSet<Ty<'tcx>>,
319 /// span for error reporting
321 /// the scope reachable dtorck types must outlive
322 parent_scope: region::CodeExtent
325 // `context` is used for reporting overflow errors
326 fn iterate_over_potentially_unsafe_regions_in_type<'a, 'b, 'tcx>(
327 cx: &mut DropckContext<'a, 'b, 'tcx>,
328 context: TypeContext,
330 depth: usize) -> Result<(), Error<'tcx>>
332 let tcx = cx.rcx.tcx();
333 // Issue #22443: Watch out for overflow. While we are careful to
334 // handle regular types properly, non-regular ones cause problems.
335 let recursion_limit = tcx.sess.recursion_limit.get();
336 if depth / 4 >= recursion_limit {
337 // This can get into rather deep recursion, especially in the
338 // presence of things like Vec<T> -> Unique<T> -> PhantomData<T> -> T.
339 // use a higher recursion limit to avoid errors.
340 return Err(Error::Overflow(context, ty))
343 if !cx.breadcrumbs.insert(ty) {
344 debug!("iterate_over_potentially_unsafe_regions_in_type \
345 {}ty: {} scope: {:?} - cached",
346 (0..depth).map(|_| ' ').collect::<String>(),
347 ty, cx.parent_scope);
348 return Ok(()); // we already visited this type
350 debug!("iterate_over_potentially_unsafe_regions_in_type \
351 {}ty: {} scope: {:?}",
352 (0..depth).map(|_| ' ').collect::<String>(),
353 ty, cx.parent_scope);
355 // If `typ` has a destructor, then we must ensure that all
356 // borrowed data reachable via `typ` must outlive the parent
357 // of `scope`. This is handled below.
359 // However, there is an important special case: by
360 // parametricity, any generic type parameters have *no* trait
361 // bounds in the Drop impl can not be used in any way (apart
362 // from being dropped), and thus we can treat data borrowed
363 // via such type parameters remains unreachable.
365 // For example, consider `impl<T> Drop for Vec<T> { ... }`,
366 // which does have to be able to drop instances of `T`, but
367 // otherwise cannot read data from `T`.
369 // Of course, for the type expression passed in for any such
370 // unbounded type parameter `T`, we must resume the recursive
371 // analysis on `T` (since it would be ignored by
372 // type_must_outlive).
374 // FIXME (pnkfelix): Long term, we could be smart and actually
375 // feed which generic parameters can be ignored *into* `fn
376 // type_must_outlive` (or some generalization thereof). But
377 // for the short term, it probably covers most cases of
378 // interest to just special case Drop impls where: (1.) there
379 // are no generic lifetime parameters and (2.) *all* generic
380 // type parameters are unbounded. If both conditions hold, we
381 // simply skip the `type_must_outlive` call entirely (but
382 // resume the recursive checking of the type-substructure).
383 if has_dtor_of_interest(tcx, ty) {
384 debug!("iterate_over_potentially_unsafe_regions_in_type \
385 {}ty: {} - is a dtorck type!",
386 (0..depth).map(|_| ' ').collect::<String>(),
389 regionck::type_must_outlive(cx.rcx,
390 infer::SubregionOrigin::SafeDestructor(cx.span),
392 ty::ReScope(cx.parent_scope));
397 debug!("iterate_over_potentially_unsafe_regions_in_type \
398 {}ty: {} scope: {:?} - checking interior",
399 (0..depth).map(|_| ' ').collect::<String>(),
400 ty, cx.parent_scope);
402 // We still need to ensure all referenced data is safe.
404 ty::TyBool | ty::TyChar | ty::TyInt(_) | ty::TyUint(_) |
405 ty::TyFloat(_) | ty::TyStr => {
406 // primitive - definitely safe
410 ty::TyBox(ity) | ty::TyArray(ity, _) | ty::TySlice(ity) => {
411 // single-element containers, behave like their element
412 iterate_over_potentially_unsafe_regions_in_type(
413 cx, context, ity, depth+1)
416 ty::TyStruct(def, substs) if def.is_phantom_data() => {
417 // PhantomData<T> - behaves identically to T
418 let ity = *substs.types.get(subst::TypeSpace, 0);
419 iterate_over_potentially_unsafe_regions_in_type(
420 cx, context, ity, depth+1)
423 ty::TyStruct(def, substs) | ty::TyEnum(def, substs) => {
425 for variant in &def.variants {
426 for (i, field) in variant.fields.iter().enumerate() {
427 let fty = field.ty(tcx, substs);
428 let fty = cx.rcx.fcx.resolve_type_vars_if_possible(
429 cx.rcx.fcx.normalize_associated_types_in(cx.span, &fty));
430 try!(iterate_over_potentially_unsafe_regions_in_type(
435 variant: variant.name,
445 ty::TyTuple(ref tys) |
446 ty::TyClosure(_, box ty::ClosureSubsts { upvar_tys: ref tys, .. }) => {
448 try!(iterate_over_potentially_unsafe_regions_in_type(
449 cx, context, ty, depth+1))
454 ty::TyRawPtr(..) | ty::TyRef(..) | ty::TyParam(..) => {
455 // these always come with a witness of liveness (references
456 // explicitly, pointers implicitly, parameters by the
461 ty::TyBareFn(..) => {
462 // FIXME(#26656): this type is always destruction-safe, but
463 // it implicitly witnesses Self: Fn, which can be false.
467 ty::TyInfer(..) | ty::TyError => {
468 tcx.sess.delay_span_bug(cx.span, "unresolved type in regionck");
472 // these are always dtorck
473 ty::TyTrait(..) | ty::TyProjection(_) => unreachable!(),
477 fn has_dtor_of_interest<'tcx>(tcx: &ty::ctxt<'tcx>,
478 ty: ty::Ty<'tcx>) -> bool {
480 ty::TyEnum(def, _) | ty::TyStruct(def, _) => {
483 ty::TyTrait(..) | ty::TyProjection(..) => {
484 debug!("ty: {:?} isn't known, and therefore is a dropck type", ty);