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, LOCAL_CRATE};
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 assert!(drop_impl_did.is_local() && self_type_did.is_local());
82 // check that the impl type can be made to match the trait type.
84 let impl_param_env = ty::ParameterEnvironment::for_item(tcx, self_type_did.node);
85 let infcx = infer::new_infer_ctxt(tcx, &tcx.tables, Some(impl_param_env), true);
87 let named_type = tcx.lookup_item_type(self_type_did).ty;
88 let named_type = named_type.subst(tcx, &infcx.parameter_environment.free_substs);
90 let drop_impl_span = tcx.map.def_id_span(drop_impl_did, codemap::DUMMY_SP);
91 let fresh_impl_substs =
92 infcx.fresh_substs_for_generics(drop_impl_span, drop_impl_generics);
93 let fresh_impl_self_ty = drop_impl_ty.subst(tcx, &fresh_impl_substs);
95 if let Err(_) = infer::mk_eqty(&infcx, true, infer::TypeOrigin::Misc(drop_impl_span),
96 named_type, fresh_impl_self_ty) {
97 span_err!(tcx.sess, drop_impl_span, E0366,
98 "Implementations of Drop cannot be specialized");
99 let item_span = tcx.map.span(self_type_did.node);
100 tcx.sess.span_note(item_span,
101 "Use same sequence of generic type and region \
102 parameters that is on the struct/enum definition");
106 if let Err(ref errors) = infcx.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
107 // this could be reached when we get lazy normalization
108 traits::report_fulfillment_errors(&infcx, errors);
112 let free_regions = FreeRegionMap::new();
113 infcx.resolve_regions_and_report_errors(&free_regions, drop_impl_did.node);
117 /// Confirms that every predicate imposed by dtor_predicates is
118 /// implied by assuming the predicates attached to self_type_did.
119 fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
120 tcx: &ty::ctxt<'tcx>,
121 drop_impl_did: DefId,
122 dtor_predicates: &ty::GenericPredicates<'tcx>,
123 self_type_did: DefId,
124 self_to_impl_substs: &subst::Substs<'tcx>) -> Result<(), ()> {
126 // Here is an example, analogous to that from
127 // `compare_impl_method`.
129 // Consider a struct type:
131 // struct Type<'c, 'b:'c, 'a> {
132 // x: &'a Contents // (contents are irrelevant;
133 // y: &'c Cell<&'b Contents>, // only the bounds matter for our purposes.)
138 // impl<'z, 'y:'z, 'x:'y> Drop for P<'z, 'y, 'x> {
139 // fn drop(&mut self) { self.y.set(self.x); } // (only legal if 'x: 'y)
142 // We start out with self_to_impl_substs, that maps the generic
143 // parameters of Type to that of the Drop impl.
145 // self_to_impl_substs = {'c => 'z, 'b => 'y, 'a => 'x}
147 // Applying this to the predicates (i.e. assumptions) provided by the item
148 // definition yields the instantiated assumptions:
152 // We then check all of the predicates of the Drop impl:
156 // and ensure each is in the list of instantiated
157 // assumptions. Here, `'y:'z` is present, but `'x:'y` is
158 // absent. So we report an error that the Drop impl injected a
159 // predicate that is not present on the struct definition.
161 assert_eq!(self_type_did.krate, LOCAL_CRATE);
163 let drop_impl_span = tcx.map.def_id_span(drop_impl_did, codemap::DUMMY_SP);
165 // We can assume the predicates attached to struct/enum definition
167 let generic_assumptions = tcx.lookup_predicates(self_type_did);
169 let assumptions_in_impl_context = generic_assumptions.instantiate(tcx, &self_to_impl_substs);
170 assert!(assumptions_in_impl_context.predicates.is_empty_in(subst::SelfSpace));
171 assert!(assumptions_in_impl_context.predicates.is_empty_in(subst::FnSpace));
172 let assumptions_in_impl_context =
173 assumptions_in_impl_context.predicates.get_slice(subst::TypeSpace);
175 // An earlier version of this code attempted to do this checking
176 // via the traits::fulfill machinery. However, it ran into trouble
177 // since the fulfill machinery merely turns outlives-predicates
178 // 'a:'b and T:'b into region inference constraints. It is simpler
179 // just to look for all the predicates directly.
181 assert!(dtor_predicates.predicates.is_empty_in(subst::SelfSpace));
182 assert!(dtor_predicates.predicates.is_empty_in(subst::FnSpace));
183 let predicates = dtor_predicates.predicates.get_slice(subst::TypeSpace);
184 for predicate in predicates {
185 // (We do not need to worry about deep analysis of type
186 // expressions etc because the Drop impls are already forced
187 // to take on a structure that is roughly a alpha-renaming of
188 // the generic parameters of the item definition.)
190 // This path now just checks *all* predicates via the direct
191 // lookup, rather than using fulfill machinery.
193 // However, it may be more efficient in the future to batch
194 // the analysis together via the fulfill , rather than the
195 // repeated `contains` calls.
197 if !assumptions_in_impl_context.contains(&predicate) {
198 let item_span = tcx.map.span(self_type_did.node);
199 span_err!(tcx.sess, drop_impl_span, E0367,
200 "The requirement `{}` is added only by the Drop impl.", predicate);
201 tcx.sess.span_note(item_span,
202 "The same requirement must be part of \
203 the struct/enum definition");
207 if tcx.sess.has_errors() {
213 /// check_safety_of_destructor_if_necessary confirms that the type
214 /// expression `typ` conforms to the "Drop Check Rule" from the Sound
215 /// Generic Drop (RFC 769).
219 /// The Drop Check Rule is the following:
221 /// Let `v` be some value (either temporary or named) and 'a be some
222 /// lifetime (scope). If the type of `v` owns data of type `D`, where
224 /// * (1.) `D` has a lifetime- or type-parametric Drop implementation, and
225 /// * (2.) the structure of `D` can reach a reference of type `&'a _`, and
227 /// * (A.) the Drop impl for `D` instantiates `D` at 'a directly,
228 /// i.e. `D<'a>`, or,
229 /// * (B.) the Drop impl for `D` has some type parameter with a
230 /// trait bound `T` where `T` is a trait that has at least
233 /// then 'a must strictly outlive the scope of v.
237 /// This function is meant to by applied to the type for every
238 /// expression in the program.
239 pub fn check_safety_of_destructor_if_necessary<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
242 scope: region::CodeExtent) {
243 debug!("check_safety_of_destructor_if_necessary typ: {:?} scope: {:?}",
246 let parent_scope = rcx.tcx().region_maps.opt_encl_scope(scope).unwrap_or_else(|| {
247 rcx.tcx().sess.span_bug(
248 span, &format!("no enclosing scope found for scope: {:?}", scope))
251 let result = iterate_over_potentially_unsafe_regions_in_type(
255 parent_scope: parent_scope,
256 breadcrumbs: FnvHashSet()
263 Err(Error::Overflow(ref ctxt, ref detected_on_typ)) => {
265 span_err!(tcx.sess, span, E0320,
266 "overflow while adding drop-check rules for {}", typ);
268 TypeContext::Root => {
269 // no need for an additional note if the overflow
270 // was somehow on the root.
272 TypeContext::ADT { def_id, variant, field, field_index } => {
273 let adt = tcx.lookup_adt_def(def_id);
274 let variant_name = match adt.adt_kind() {
275 ty::AdtKind::Enum => format!("enum {} variant {}",
276 tcx.item_path_str(def_id),
278 ty::AdtKind::Struct => format!("struct {}",
279 tcx.item_path_str(def_id))
281 let field_name = if field == special_idents::unnamed_field.name {
282 format!("#{}", field_index)
284 format!("`{}`", field)
289 "overflowed on {} field {} type: {}",
300 Overflow(TypeContext, ty::Ty<'tcx>),
303 #[derive(Copy, Clone)]
314 struct DropckContext<'a, 'b: 'a, 'tcx: 'b> {
315 rcx: &'a mut Rcx<'b, 'tcx>,
316 /// types that have already been traversed
317 breadcrumbs: FnvHashSet<Ty<'tcx>>,
318 /// span for error reporting
320 /// the scope reachable dtorck types must outlive
321 parent_scope: region::CodeExtent
324 // `context` is used for reporting overflow errors
325 fn iterate_over_potentially_unsafe_regions_in_type<'a, 'b, 'tcx>(
326 cx: &mut DropckContext<'a, 'b, 'tcx>,
327 context: TypeContext,
329 depth: usize) -> Result<(), Error<'tcx>>
331 let tcx = cx.rcx.tcx();
332 // Issue #22443: Watch out for overflow. While we are careful to
333 // handle regular types properly, non-regular ones cause problems.
334 let recursion_limit = tcx.sess.recursion_limit.get();
335 if depth / 4 >= recursion_limit {
336 // This can get into rather deep recursion, especially in the
337 // presence of things like Vec<T> -> Unique<T> -> PhantomData<T> -> T.
338 // use a higher recursion limit to avoid errors.
339 return Err(Error::Overflow(context, ty))
342 if !cx.breadcrumbs.insert(ty) {
343 debug!("iterate_over_potentially_unsafe_regions_in_type \
344 {}ty: {} scope: {:?} - cached",
345 (0..depth).map(|_| ' ').collect::<String>(),
346 ty, cx.parent_scope);
347 return Ok(()); // we already visited this type
349 debug!("iterate_over_potentially_unsafe_regions_in_type \
350 {}ty: {} scope: {:?}",
351 (0..depth).map(|_| ' ').collect::<String>(),
352 ty, cx.parent_scope);
354 // If `typ` has a destructor, then we must ensure that all
355 // borrowed data reachable via `typ` must outlive the parent
356 // of `scope`. This is handled below.
358 // However, there is an important special case: by
359 // parametricity, any generic type parameters have *no* trait
360 // bounds in the Drop impl can not be used in any way (apart
361 // from being dropped), and thus we can treat data borrowed
362 // via such type parameters remains unreachable.
364 // For example, consider `impl<T> Drop for Vec<T> { ... }`,
365 // which does have to be able to drop instances of `T`, but
366 // otherwise cannot read data from `T`.
368 // Of course, for the type expression passed in for any such
369 // unbounded type parameter `T`, we must resume the recursive
370 // analysis on `T` (since it would be ignored by
371 // type_must_outlive).
373 // FIXME (pnkfelix): Long term, we could be smart and actually
374 // feed which generic parameters can be ignored *into* `fn
375 // type_must_outlive` (or some generalization thereof). But
376 // for the short term, it probably covers most cases of
377 // interest to just special case Drop impls where: (1.) there
378 // are no generic lifetime parameters and (2.) *all* generic
379 // type parameters are unbounded. If both conditions hold, we
380 // simply skip the `type_must_outlive` call entirely (but
381 // resume the recursive checking of the type-substructure).
382 if has_dtor_of_interest(tcx, ty) {
383 debug!("iterate_over_potentially_unsafe_regions_in_type \
384 {}ty: {} - is a dtorck type!",
385 (0..depth).map(|_| ' ').collect::<String>(),
388 regionck::type_must_outlive(cx.rcx,
389 infer::SubregionOrigin::SafeDestructor(cx.span),
391 ty::ReScope(cx.parent_scope));
396 debug!("iterate_over_potentially_unsafe_regions_in_type \
397 {}ty: {} scope: {:?} - checking interior",
398 (0..depth).map(|_| ' ').collect::<String>(),
399 ty, cx.parent_scope);
401 // We still need to ensure all referenced data is safe.
403 ty::TyBool | ty::TyChar | ty::TyInt(_) | ty::TyUint(_) |
404 ty::TyFloat(_) | ty::TyStr => {
405 // primitive - definitely safe
409 ty::TyBox(ity) | ty::TyArray(ity, _) | ty::TySlice(ity) => {
410 // single-element containers, behave like their element
411 iterate_over_potentially_unsafe_regions_in_type(
412 cx, context, ity, depth+1)
415 ty::TyStruct(def, substs) if def.is_phantom_data() => {
416 // PhantomData<T> - behaves identically to T
417 let ity = *substs.types.get(subst::TypeSpace, 0);
418 iterate_over_potentially_unsafe_regions_in_type(
419 cx, context, ity, depth+1)
422 ty::TyStruct(def, substs) | ty::TyEnum(def, substs) => {
424 for variant in &def.variants {
425 for (i, field) in variant.fields.iter().enumerate() {
426 let fty = field.ty(tcx, substs);
427 let fty = cx.rcx.fcx.resolve_type_vars_if_possible(
428 cx.rcx.fcx.normalize_associated_types_in(cx.span, &fty));
429 try!(iterate_over_potentially_unsafe_regions_in_type(
434 variant: variant.name,
444 ty::TyTuple(ref tys) |
445 ty::TyClosure(_, box ty::ClosureSubsts { upvar_tys: ref tys, .. }) => {
447 try!(iterate_over_potentially_unsafe_regions_in_type(
448 cx, context, ty, depth+1))
453 ty::TyRawPtr(..) | ty::TyRef(..) | ty::TyParam(..) => {
454 // these always come with a witness of liveness (references
455 // explicitly, pointers implicitly, parameters by the
460 ty::TyBareFn(..) => {
461 // FIXME(#26656): this type is always destruction-safe, but
462 // it implicitly witnesses Self: Fn, which can be false.
466 ty::TyInfer(..) | ty::TyError => {
467 tcx.sess.delay_span_bug(cx.span, "unresolved type in regionck");
471 // these are always dtorck
472 ty::TyTrait(..) | ty::TyProjection(_) => unreachable!(),
476 fn has_dtor_of_interest<'tcx>(tcx: &ty::ctxt<'tcx>,
477 ty: ty::Ty<'tcx>) -> bool {
479 ty::TyEnum(def, _) | ty::TyStruct(def, _) => {
482 ty::TyTrait(..) | ty::TyProjection(..) => {
483 debug!("ty: {:?} isn't known, and therefore is a dropck type", ty);