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Commit | Line | Data |
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ba9703b0 | 1 | use crate::infer::InferCtxtExt as _; |
9fa01778 | 2 | use crate::traits::{self, PredicateObligation}; |
dc9dc135 XL |
3 | use rustc_data_structures::fx::FxHashMap; |
4 | use rustc_data_structures::sync::Lrc; | |
dfeec247 | 5 | use rustc_hir as hir; |
f9f354fc | 6 | use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId}; |
dfeec247 | 7 | use rustc_hir::Node; |
ba9703b0 | 8 | use rustc_infer::infer::error_reporting::unexpected_hidden_region_diagnostic; |
f9f354fc | 9 | use rustc_infer::infer::free_regions::FreeRegionRelations; |
ba9703b0 XL |
10 | use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; |
11 | use rustc_infer::infer::{self, InferCtxt, InferOk}; | |
12 | use rustc_middle::ty::fold::{BottomUpFolder, TypeFoldable, TypeFolder, TypeVisitor}; | |
29967ef6 | 13 | use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst, SubstsRef}; |
f035d41b | 14 | use rustc_middle::ty::{self, Ty, TyCtxt}; |
dfeec247 | 15 | use rustc_span::Span; |
60c5eb7d | 16 | |
29967ef6 XL |
17 | use std::ops::ControlFlow; |
18 | ||
b7449926 | 19 | pub type OpaqueTypeMap<'tcx> = DefIdMap<OpaqueTypeDecl<'tcx>>; |
ff7c6d11 | 20 | |
416331ca | 21 | /// Information about the opaque types whose values we |
ff7c6d11 XL |
22 | /// are inferring in this function (these are the `impl Trait` that |
23 | /// appear in the return type). | |
24 | #[derive(Copy, Clone, Debug)] | |
b7449926 | 25 | pub struct OpaqueTypeDecl<'tcx> { |
60c5eb7d XL |
26 | /// The opaque type (`ty::Opaque`) for this declaration. |
27 | pub opaque_type: Ty<'tcx>, | |
28 | ||
416331ca | 29 | /// The substitutions that we apply to the opaque type that this |
ff7c6d11 XL |
30 | /// `impl Trait` desugars to. e.g., if: |
31 | /// | |
32 | /// fn foo<'a, 'b, T>() -> impl Trait<'a> | |
33 | /// | |
34 | /// winds up desugared to: | |
35 | /// | |
416331ca | 36 | /// type Foo<'x, X> = impl Trait<'x> |
ff7c6d11 XL |
37 | /// fn foo<'a, 'b, T>() -> Foo<'a, T> |
38 | /// | |
39 | /// then `substs` would be `['a, T]`. | |
532ac7d7 | 40 | pub substs: SubstsRef<'tcx>, |
ff7c6d11 | 41 | |
29967ef6 | 42 | /// The span of this particular definition of the opaque type. So |
dc9dc135 XL |
43 | /// for example: |
44 | /// | |
29967ef6 | 45 | /// ```ignore (incomplete snippet) |
416331ca | 46 | /// type Foo = impl Baz; |
dc9dc135 | 47 | /// fn bar() -> Foo { |
29967ef6 | 48 | /// // ^^^ This is the span we are looking for! |
dc9dc135 XL |
49 | /// ``` |
50 | /// | |
51 | /// In cases where the fn returns `(impl Trait, impl Trait)` or | |
52 | /// other such combinations, the result is currently | |
53 | /// over-approximated, but better than nothing. | |
54 | pub definition_span: Span, | |
55 | ||
416331ca | 56 | /// The type variable that represents the value of the opaque type |
ff7c6d11 XL |
57 | /// that we require. In other words, after we compile this function, |
58 | /// we will be created a constraint like: | |
59 | /// | |
60 | /// Foo<'a, T> = ?C | |
61 | /// | |
62 | /// where `?C` is the value of this type variable. =) It may | |
63 | /// naturally refer to the type and lifetime parameters in scope | |
64 | /// in this function, though ultimately it should only reference | |
65 | /// those that are arguments to `Foo` in the constraint above. (In | |
66 | /// other words, `?C` should not include `'b`, even though it's a | |
67 | /// lifetime parameter on `foo`.) | |
68 | pub concrete_ty: Ty<'tcx>, | |
69 | ||
9fa01778 | 70 | /// Returns `true` if the `impl Trait` bounds include region bounds. |
ff7c6d11 XL |
71 | /// For example, this would be true for: |
72 | /// | |
73 | /// fn foo<'a, 'b, 'c>() -> impl Trait<'c> + 'a + 'b | |
74 | /// | |
75 | /// but false for: | |
76 | /// | |
77 | /// fn foo<'c>() -> impl Trait<'c> | |
78 | /// | |
79 | /// unless `Trait` was declared like: | |
80 | /// | |
81 | /// trait Trait<'c>: 'c | |
82 | /// | |
83 | /// in which case it would be true. | |
84 | /// | |
85 | /// This is used during regionck to decide whether we need to | |
86 | /// impose any additional constraints to ensure that region | |
87 | /// variables in `concrete_ty` wind up being constrained to | |
88 | /// something from `substs` (or, at minimum, things that outlive | |
89 | /// the fn body). (Ultimately, writeback is responsible for this | |
90 | /// check.) | |
91 | pub has_required_region_bounds: bool, | |
532ac7d7 | 92 | |
416331ca XL |
93 | /// The origin of the opaque type. |
94 | pub origin: hir::OpaqueTyOrigin, | |
ff7c6d11 XL |
95 | } |
96 | ||
74b04a01 XL |
97 | /// Whether member constraints should be generated for all opaque types |
98 | pub enum GenerateMemberConstraints { | |
99 | /// The default, used by typeck | |
100 | WhenRequired, | |
101 | /// The borrow checker needs member constraints in any case where we don't | |
102 | /// have a `'static` bound. This is because the borrow checker has more | |
103 | /// flexibility in the values of regions. For example, given `f<'a, 'b>` | |
104 | /// the borrow checker can have an inference variable outlive `'a` and `'b`, | |
105 | /// but not be equal to `'static`. | |
106 | IfNoStaticBound, | |
107 | } | |
108 | ||
ba9703b0 XL |
109 | pub trait InferCtxtExt<'tcx> { |
110 | fn instantiate_opaque_types<T: TypeFoldable<'tcx>>( | |
111 | &self, | |
f035d41b | 112 | parent_def_id: LocalDefId, |
ba9703b0 XL |
113 | body_id: hir::HirId, |
114 | param_env: ty::ParamEnv<'tcx>, | |
fc512014 | 115 | value: T, |
ba9703b0 XL |
116 | value_span: Span, |
117 | ) -> InferOk<'tcx, (T, OpaqueTypeMap<'tcx>)>; | |
118 | ||
119 | fn constrain_opaque_types<FRR: FreeRegionRelations<'tcx>>( | |
120 | &self, | |
121 | opaque_types: &OpaqueTypeMap<'tcx>, | |
122 | free_region_relations: &FRR, | |
123 | ); | |
124 | ||
125 | fn constrain_opaque_type<FRR: FreeRegionRelations<'tcx>>( | |
126 | &self, | |
127 | def_id: DefId, | |
128 | opaque_defn: &OpaqueTypeDecl<'tcx>, | |
129 | mode: GenerateMemberConstraints, | |
130 | free_region_relations: &FRR, | |
131 | ); | |
132 | ||
133 | /*private*/ | |
134 | fn generate_member_constraint( | |
135 | &self, | |
136 | concrete_ty: Ty<'tcx>, | |
ba9703b0 XL |
137 | opaque_defn: &OpaqueTypeDecl<'tcx>, |
138 | opaque_type_def_id: DefId, | |
f035d41b | 139 | first_own_region_index: usize, |
ba9703b0 XL |
140 | ); |
141 | ||
142 | /*private*/ | |
143 | fn member_constraint_feature_gate( | |
144 | &self, | |
145 | opaque_defn: &OpaqueTypeDecl<'tcx>, | |
146 | opaque_type_def_id: DefId, | |
147 | conflict1: ty::Region<'tcx>, | |
148 | conflict2: ty::Region<'tcx>, | |
149 | ) -> bool; | |
150 | ||
151 | fn infer_opaque_definition_from_instantiation( | |
152 | &self, | |
153 | def_id: DefId, | |
154 | substs: SubstsRef<'tcx>, | |
155 | instantiated_ty: Ty<'tcx>, | |
156 | span: Span, | |
157 | ) -> Ty<'tcx>; | |
158 | } | |
159 | ||
160 | impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> { | |
9fa01778 | 161 | /// Replaces all opaque types in `value` with fresh inference variables |
ff7c6d11 XL |
162 | /// and creates appropriate obligations. For example, given the input: |
163 | /// | |
164 | /// impl Iterator<Item = impl Debug> | |
165 | /// | |
166 | /// this method would create two type variables, `?0` and `?1`. It would | |
167 | /// return the type `?0` but also the obligations: | |
168 | /// | |
169 | /// ?0: Iterator<Item = ?1> | |
170 | /// ?1: Debug | |
171 | /// | |
b7449926 | 172 | /// Moreover, it returns a `OpaqueTypeMap` that would map `?0` to |
ff7c6d11 XL |
173 | /// info about the `impl Iterator<..>` type and `?1` to info about |
174 | /// the `impl Debug` type. | |
175 | /// | |
176 | /// # Parameters | |
177 | /// | |
9fa01778 | 178 | /// - `parent_def_id` -- the `DefId` of the function in which the opaque type |
0bf4aa26 | 179 | /// is defined |
ff7c6d11 XL |
180 | /// - `body_id` -- the body-id with which the resulting obligations should |
181 | /// be associated | |
182 | /// - `param_env` -- the in-scope parameter environment to be used for | |
183 | /// obligations | |
b7449926 | 184 | /// - `value` -- the value within which we are instantiating opaque types |
dc9dc135 | 185 | /// - `value_span` -- the span where the value came from, used in error reporting |
ba9703b0 | 186 | fn instantiate_opaque_types<T: TypeFoldable<'tcx>>( |
ff7c6d11 | 187 | &self, |
f035d41b | 188 | parent_def_id: LocalDefId, |
9fa01778 | 189 | body_id: hir::HirId, |
ff7c6d11 | 190 | param_env: ty::ParamEnv<'tcx>, |
fc512014 | 191 | value: T, |
dc9dc135 | 192 | value_span: Span, |
b7449926 | 193 | ) -> InferOk<'tcx, (T, OpaqueTypeMap<'tcx>)> { |
dc9dc135 XL |
194 | debug!( |
195 | "instantiate_opaque_types(value={:?}, parent_def_id={:?}, body_id={:?}, \ | |
e1599b0c XL |
196 | param_env={:?}, value_span={:?})", |
197 | value, parent_def_id, body_id, param_env, value_span, | |
ff7c6d11 XL |
198 | ); |
199 | let mut instantiator = Instantiator { | |
200 | infcx: self, | |
201 | parent_def_id, | |
202 | body_id, | |
203 | param_env, | |
dc9dc135 | 204 | value_span, |
a1dfa0c6 | 205 | opaque_types: Default::default(), |
ff7c6d11 XL |
206 | obligations: vec![], |
207 | }; | |
b7449926 | 208 | let value = instantiator.instantiate_opaque_types_in_map(value); |
dc9dc135 | 209 | InferOk { value: (value, instantiator.opaque_types), obligations: instantiator.obligations } |
ff7c6d11 XL |
210 | } |
211 | ||
416331ca XL |
212 | /// Given the map `opaque_types` containing the opaque |
213 | /// `impl Trait` types whose underlying, hidden types are being | |
ff7c6d11 XL |
214 | /// inferred, this method adds constraints to the regions |
215 | /// appearing in those underlying hidden types to ensure that they | |
216 | /// at least do not refer to random scopes within the current | |
217 | /// function. These constraints are not (quite) sufficient to | |
218 | /// guarantee that the regions are actually legal values; that | |
219 | /// final condition is imposed after region inference is done. | |
220 | /// | |
221 | /// # The Problem | |
222 | /// | |
9fa01778 | 223 | /// Let's work through an example to explain how it works. Assume |
ff7c6d11 XL |
224 | /// the current function is as follows: |
225 | /// | |
226 | /// ```text | |
227 | /// fn foo<'a, 'b>(..) -> (impl Bar<'a>, impl Bar<'b>) | |
228 | /// ``` | |
229 | /// | |
230 | /// Here, we have two `impl Trait` types whose values are being | |
231 | /// inferred (the `impl Bar<'a>` and the `impl | |
232 | /// Bar<'b>`). Conceptually, this is sugar for a setup where we | |
416331ca | 233 | /// define underlying opaque types (`Foo1`, `Foo2`) and then, in |
ff7c6d11 XL |
234 | /// the return type of `foo`, we *reference* those definitions: |
235 | /// | |
236 | /// ```text | |
416331ca XL |
237 | /// type Foo1<'x> = impl Bar<'x>; |
238 | /// type Foo2<'x> = impl Bar<'x>; | |
ff7c6d11 XL |
239 | /// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. } |
240 | /// // ^^^^ ^^ | |
241 | /// // | | | |
242 | /// // | substs | |
243 | /// // def_id | |
244 | /// ``` | |
245 | /// | |
246 | /// As indicating in the comments above, each of those references | |
247 | /// is (in the compiler) basically a substitution (`substs`) | |
248 | /// applied to the type of a suitable `def_id` (which identifies | |
249 | /// `Foo1` or `Foo2`). | |
250 | /// | |
251 | /// Now, at this point in compilation, what we have done is to | |
252 | /// replace each of the references (`Foo1<'a>`, `Foo2<'b>`) with | |
253 | /// fresh inference variables C1 and C2. We wish to use the values | |
254 | /// of these variables to infer the underlying types of `Foo1` and | |
9fa01778 | 255 | /// `Foo2`. That is, this gives rise to higher-order (pattern) unification |
ff7c6d11 XL |
256 | /// constraints like: |
257 | /// | |
258 | /// ```text | |
259 | /// for<'a> (Foo1<'a> = C1) | |
260 | /// for<'b> (Foo1<'b> = C2) | |
261 | /// ``` | |
262 | /// | |
263 | /// For these equation to be satisfiable, the types `C1` and `C2` | |
264 | /// can only refer to a limited set of regions. For example, `C1` | |
265 | /// can only refer to `'static` and `'a`, and `C2` can only refer | |
266 | /// to `'static` and `'b`. The job of this function is to impose that | |
267 | /// constraint. | |
268 | /// | |
269 | /// Up to this point, C1 and C2 are basically just random type | |
270 | /// inference variables, and hence they may contain arbitrary | |
271 | /// regions. In fact, it is fairly likely that they do! Consider | |
272 | /// this possible definition of `foo`: | |
273 | /// | |
274 | /// ```text | |
275 | /// fn foo<'a, 'b>(x: &'a i32, y: &'b i32) -> (impl Bar<'a>, impl Bar<'b>) { | |
276 | /// (&*x, &*y) | |
277 | /// } | |
278 | /// ``` | |
279 | /// | |
280 | /// Here, the values for the concrete types of the two impl | |
281 | /// traits will include inference variables: | |
282 | /// | |
283 | /// ```text | |
284 | /// &'0 i32 | |
285 | /// &'1 i32 | |
286 | /// ``` | |
287 | /// | |
288 | /// Ordinarily, the subtyping rules would ensure that these are | |
289 | /// sufficiently large. But since `impl Bar<'a>` isn't a specific | |
9fa01778 | 290 | /// type per se, we don't get such constraints by default. This |
ff7c6d11 XL |
291 | /// is where this function comes into play. It adds extra |
292 | /// constraints to ensure that all the regions which appear in the | |
293 | /// inferred type are regions that could validly appear. | |
294 | /// | |
295 | /// This is actually a bit of a tricky constraint in general. We | |
296 | /// want to say that each variable (e.g., `'0`) can only take on | |
416331ca | 297 | /// values that were supplied as arguments to the opaque type |
ff7c6d11 XL |
298 | /// (e.g., `'a` for `Foo1<'a>`) or `'static`, which is always in |
299 | /// scope. We don't have a constraint quite of this kind in the current | |
300 | /// region checker. | |
301 | /// | |
302 | /// # The Solution | |
303 | /// | |
dc9dc135 XL |
304 | /// We generally prefer to make `<=` constraints, since they |
305 | /// integrate best into the region solver. To do that, we find the | |
306 | /// "minimum" of all the arguments that appear in the substs: that | |
307 | /// is, some region which is less than all the others. In the case | |
308 | /// of `Foo1<'a>`, that would be `'a` (it's the only choice, after | |
309 | /// all). Then we apply that as a least bound to the variables | |
310 | /// (e.g., `'a <= '0`). | |
ff7c6d11 XL |
311 | /// |
312 | /// In some cases, there is no minimum. Consider this example: | |
313 | /// | |
314 | /// ```text | |
315 | /// fn baz<'a, 'b>() -> impl Trait<'a, 'b> { ... } | |
316 | /// ``` | |
317 | /// | |
dc9dc135 | 318 | /// Here we would report a more complex "in constraint", like `'r |
74b04a01 | 319 | /// in ['a, 'b, 'static]` (where `'r` is some region appearing in |
dc9dc135 XL |
320 | /// the hidden type). |
321 | /// | |
322 | /// # Constrain regions, not the hidden concrete type | |
323 | /// | |
324 | /// Note that generating constraints on each region `Rc` is *not* | |
325 | /// the same as generating an outlives constraint on `Tc` iself. | |
326 | /// For example, if we had a function like this: | |
327 | /// | |
328 | /// ```rust | |
329 | /// fn foo<'a, T>(x: &'a u32, y: T) -> impl Foo<'a> { | |
330 | /// (x, y) | |
331 | /// } | |
332 | /// | |
333 | /// // Equivalent to: | |
416331ca | 334 | /// type FooReturn<'a, T> = impl Foo<'a>; |
dc9dc135 XL |
335 | /// fn foo<'a, T>(..) -> FooReturn<'a, T> { .. } |
336 | /// ``` | |
337 | /// | |
338 | /// then the hidden type `Tc` would be `(&'0 u32, T)` (where `'0` | |
339 | /// is an inference variable). If we generated a constraint that | |
340 | /// `Tc: 'a`, then this would incorrectly require that `T: 'a` -- | |
416331ca | 341 | /// but this is not necessary, because the opaque type we |
dc9dc135 XL |
342 | /// create will be allowed to reference `T`. So we only generate a |
343 | /// constraint that `'0: 'a`. | |
ff7c6d11 XL |
344 | /// |
345 | /// # The `free_region_relations` parameter | |
346 | /// | |
347 | /// The `free_region_relations` argument is used to find the | |
416331ca | 348 | /// "minimum" of the regions supplied to a given opaque type. |
ff7c6d11 XL |
349 | /// It must be a relation that can answer whether `'a <= 'b`, |
350 | /// where `'a` and `'b` are regions that appear in the "substs" | |
416331ca | 351 | /// for the opaque type references (the `<'a>` in `Foo1<'a>`). |
ff7c6d11 XL |
352 | /// |
353 | /// Note that we do not impose the constraints based on the | |
354 | /// generic regions from the `Foo1` definition (e.g., `'x`). This | |
355 | /// is because the constraints we are imposing here is basically | |
356 | /// the concern of the one generating the constraining type C1, | |
357 | /// which is the current function. It also means that we can | |
358 | /// take "implied bounds" into account in some cases: | |
359 | /// | |
360 | /// ```text | |
361 | /// trait SomeTrait<'a, 'b> { } | |
362 | /// fn foo<'a, 'b>(_: &'a &'b u32) -> impl SomeTrait<'a, 'b> { .. } | |
363 | /// ``` | |
364 | /// | |
365 | /// Here, the fact that `'b: 'a` is known only because of the | |
366 | /// implied bounds from the `&'a &'b u32` parameter, and is not | |
416331ca | 367 | /// "inherent" to the opaque type definition. |
ff7c6d11 XL |
368 | /// |
369 | /// # Parameters | |
370 | /// | |
b7449926 | 371 | /// - `opaque_types` -- the map produced by `instantiate_opaque_types` |
ff7c6d11 XL |
372 | /// - `free_region_relations` -- something that can be used to relate |
373 | /// the free regions (`'a`) that appear in the impl trait. | |
ba9703b0 | 374 | fn constrain_opaque_types<FRR: FreeRegionRelations<'tcx>>( |
ff7c6d11 | 375 | &self, |
b7449926 | 376 | opaque_types: &OpaqueTypeMap<'tcx>, |
ff7c6d11 XL |
377 | free_region_relations: &FRR, |
378 | ) { | |
b7449926 | 379 | debug!("constrain_opaque_types()"); |
ff7c6d11 | 380 | |
b7449926 | 381 | for (&def_id, opaque_defn) in opaque_types { |
74b04a01 XL |
382 | self.constrain_opaque_type( |
383 | def_id, | |
384 | opaque_defn, | |
385 | GenerateMemberConstraints::WhenRequired, | |
386 | free_region_relations, | |
387 | ); | |
ff7c6d11 XL |
388 | } |
389 | } | |
390 | ||
dc9dc135 | 391 | /// See `constrain_opaque_types` for documentation. |
ba9703b0 | 392 | fn constrain_opaque_type<FRR: FreeRegionRelations<'tcx>>( |
ff7c6d11 XL |
393 | &self, |
394 | def_id: DefId, | |
b7449926 | 395 | opaque_defn: &OpaqueTypeDecl<'tcx>, |
74b04a01 | 396 | mode: GenerateMemberConstraints, |
ff7c6d11 XL |
397 | free_region_relations: &FRR, |
398 | ) { | |
b7449926 XL |
399 | debug!("constrain_opaque_type()"); |
400 | debug!("constrain_opaque_type: def_id={:?}", def_id); | |
401 | debug!("constrain_opaque_type: opaque_defn={:#?}", opaque_defn); | |
ff7c6d11 | 402 | |
48663c56 XL |
403 | let tcx = self.tcx; |
404 | ||
fc512014 | 405 | let concrete_ty = self.resolve_vars_if_possible(opaque_defn.concrete_ty); |
ff7c6d11 | 406 | |
b7449926 | 407 | debug!("constrain_opaque_type: concrete_ty={:?}", concrete_ty); |
ff7c6d11 | 408 | |
f035d41b XL |
409 | let first_own_region = match opaque_defn.origin { |
410 | hir::OpaqueTyOrigin::FnReturn | hir::OpaqueTyOrigin::AsyncFn => { | |
411 | // We lower | |
412 | // | |
413 | // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm> | |
414 | // | |
415 | // into | |
416 | // | |
417 | // type foo::<'p0..'pn>::Foo<'q0..'qm> | |
418 | // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>. | |
419 | // | |
420 | // For these types we onlt iterate over `'l0..lm` below. | |
421 | tcx.generics_of(def_id).parent_count | |
422 | } | |
423 | // These opaque type inherit all lifetime parameters from their | |
424 | // parent, so we have to check them all. | |
6a06907d XL |
425 | hir::OpaqueTyOrigin::Binding |
426 | | hir::OpaqueTyOrigin::TyAlias | |
427 | | hir::OpaqueTyOrigin::Misc => 0, | |
f035d41b | 428 | }; |
ff7c6d11 | 429 | |
48663c56 | 430 | let span = tcx.def_span(def_id); |
ff7c6d11 | 431 | |
48663c56 | 432 | // If there are required region bounds, we can use them. |
b7449926 | 433 | if opaque_defn.has_required_region_bounds { |
29967ef6 XL |
434 | let bounds = tcx.explicit_item_bounds(def_id); |
435 | debug!("constrain_opaque_type: predicates: {:#?}", bounds); | |
436 | let bounds: Vec<_> = | |
437 | bounds.iter().map(|(bound, _)| bound.subst(tcx, opaque_defn.substs)).collect(); | |
48663c56 XL |
438 | debug!("constrain_opaque_type: bounds={:#?}", bounds); |
439 | let opaque_type = tcx.mk_opaque(def_id, opaque_defn.substs); | |
440 | ||
dfeec247 | 441 | let required_region_bounds = |
29967ef6 | 442 | required_region_bounds(tcx, opaque_type, bounds.into_iter()); |
48663c56 XL |
443 | debug_assert!(!required_region_bounds.is_empty()); |
444 | ||
dc9dc135 XL |
445 | for required_region in required_region_bounds { |
446 | concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor { | |
dc9dc135 | 447 | op: |r| self.sub_regions(infer::CallReturn(span), required_region, r), |
48663c56 XL |
448 | }); |
449 | } | |
74b04a01 | 450 | if let GenerateMemberConstraints::IfNoStaticBound = mode { |
f035d41b | 451 | self.generate_member_constraint(concrete_ty, opaque_defn, def_id, first_own_region); |
74b04a01 | 452 | } |
ff7c6d11 XL |
453 | return; |
454 | } | |
455 | ||
456 | // There were no `required_region_bounds`, | |
457 | // so we have to search for a `least_region`. | |
458 | // Go through all the regions used as arguments to the | |
416331ca | 459 | // opaque type. These are the parameters to the opaque |
ff7c6d11 XL |
460 | // type; so in our example above, `substs` would contain |
461 | // `['a]` for the first impl trait and `'b` for the | |
462 | // second. | |
463 | let mut least_region = None; | |
dc9dc135 | 464 | |
f035d41b XL |
465 | for subst_arg in &opaque_defn.substs[first_own_region..] { |
466 | let subst_region = match subst_arg.unpack() { | |
467 | GenericArgKind::Lifetime(r) => r, | |
468 | GenericArgKind::Type(_) | GenericArgKind::Const(_) => continue, | |
469 | }; | |
ff7c6d11 XL |
470 | |
471 | // Compute the least upper bound of it with the other regions. | |
b7449926 | 472 | debug!("constrain_opaque_types: least_region={:?}", least_region); |
f035d41b | 473 | debug!("constrain_opaque_types: subst_region={:?}", subst_region); |
ff7c6d11 | 474 | match least_region { |
f035d41b | 475 | None => least_region = Some(subst_region), |
ff7c6d11 | 476 | Some(lr) => { |
f035d41b | 477 | if free_region_relations.sub_free_regions(self.tcx, lr, subst_region) { |
ff7c6d11 | 478 | // keep the current least region |
f035d41b XL |
479 | } else if free_region_relations.sub_free_regions(self.tcx, subst_region, lr) { |
480 | // switch to `subst_region` | |
481 | least_region = Some(subst_region); | |
ff7c6d11 XL |
482 | } else { |
483 | // There are two regions (`lr` and | |
f035d41b | 484 | // `subst_region`) which are not relatable. We |
dc9dc135 XL |
485 | // can't find a best choice. Therefore, |
486 | // instead of creating a single bound like | |
487 | // `'r: 'a` (which is our preferred choice), | |
488 | // we will create a "in bound" like `'r in | |
489 | // ['a, 'b, 'c]`, where `'a..'c` are the | |
490 | // regions that appear in the impl trait. | |
74b04a01 XL |
491 | |
492 | // For now, enforce a feature gate outside of async functions. | |
f035d41b | 493 | self.member_constraint_feature_gate(opaque_defn, def_id, lr, subst_region); |
74b04a01 | 494 | |
dc9dc135 XL |
495 | return self.generate_member_constraint( |
496 | concrete_ty, | |
dc9dc135 XL |
497 | opaque_defn, |
498 | def_id, | |
f035d41b | 499 | first_own_region, |
dc9dc135 | 500 | ); |
ff7c6d11 XL |
501 | } |
502 | } | |
503 | } | |
504 | } | |
505 | ||
48663c56 | 506 | let least_region = least_region.unwrap_or(tcx.lifetimes.re_static); |
b7449926 | 507 | debug!("constrain_opaque_types: least_region={:?}", least_region); |
ff7c6d11 | 508 | |
74b04a01 XL |
509 | if let GenerateMemberConstraints::IfNoStaticBound = mode { |
510 | if least_region != tcx.lifetimes.re_static { | |
f035d41b | 511 | self.generate_member_constraint(concrete_ty, opaque_defn, def_id, first_own_region); |
74b04a01 XL |
512 | } |
513 | } | |
dc9dc135 | 514 | concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor { |
dc9dc135 | 515 | op: |r| self.sub_regions(infer::CallReturn(span), least_region, r), |
48663c56 | 516 | }); |
ff7c6d11 XL |
517 | } |
518 | ||
dc9dc135 XL |
519 | /// As a fallback, we sometimes generate an "in constraint". For |
520 | /// a case like `impl Foo<'a, 'b>`, where `'a` and `'b` cannot be | |
521 | /// related, we would generate a constraint `'r in ['a, 'b, | |
522 | /// 'static]` for each region `'r` that appears in the hidden type | |
523 | /// (i.e., it must be equal to `'a`, `'b`, or `'static`). | |
524 | /// | |
525 | /// `conflict1` and `conflict2` are the two region bounds that we | |
526 | /// detected which were unrelated. They are used for diagnostics. | |
527 | fn generate_member_constraint( | |
528 | &self, | |
529 | concrete_ty: Ty<'tcx>, | |
dc9dc135 XL |
530 | opaque_defn: &OpaqueTypeDecl<'tcx>, |
531 | opaque_type_def_id: DefId, | |
f035d41b | 532 | first_own_region: usize, |
dc9dc135 | 533 | ) { |
dc9dc135 XL |
534 | // Create the set of choice regions: each region in the hidden |
535 | // type can be equal to any of the region parameters of the | |
536 | // opaque type definition. | |
537 | let choice_regions: Lrc<Vec<ty::Region<'tcx>>> = Lrc::new( | |
f035d41b | 538 | opaque_defn.substs[first_own_region..] |
dc9dc135 | 539 | .iter() |
f035d41b XL |
540 | .filter_map(|arg| match arg.unpack() { |
541 | GenericArgKind::Lifetime(r) => Some(r), | |
542 | GenericArgKind::Type(_) | GenericArgKind::Const(_) => None, | |
dc9dc135 | 543 | }) |
dc9dc135 XL |
544 | .chain(std::iter::once(self.tcx.lifetimes.re_static)) |
545 | .collect(), | |
546 | ); | |
547 | ||
548 | concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor { | |
dfeec247 XL |
549 | op: |r| { |
550 | self.member_constraint( | |
551 | opaque_type_def_id, | |
552 | opaque_defn.definition_span, | |
553 | concrete_ty, | |
554 | r, | |
555 | &choice_regions, | |
556 | ) | |
557 | }, | |
dc9dc135 XL |
558 | }); |
559 | } | |
560 | ||
561 | /// Member constraints are presently feature-gated except for | |
562 | /// async-await. We expect to lift this once we've had a bit more | |
563 | /// time. | |
564 | fn member_constraint_feature_gate( | |
565 | &self, | |
566 | opaque_defn: &OpaqueTypeDecl<'tcx>, | |
567 | opaque_type_def_id: DefId, | |
568 | conflict1: ty::Region<'tcx>, | |
569 | conflict2: ty::Region<'tcx>, | |
570 | ) -> bool { | |
571 | // If we have `#![feature(member_constraints)]`, no problems. | |
572 | if self.tcx.features().member_constraints { | |
573 | return false; | |
574 | } | |
575 | ||
576 | let span = self.tcx.def_span(opaque_type_def_id); | |
577 | ||
578 | // Without a feature-gate, we only generate member-constraints for async-await. | |
579 | let context_name = match opaque_defn.origin { | |
580 | // No feature-gate required for `async fn`. | |
416331ca | 581 | hir::OpaqueTyOrigin::AsyncFn => return false, |
dc9dc135 XL |
582 | |
583 | // Otherwise, generate the label we'll use in the error message. | |
f035d41b | 584 | hir::OpaqueTyOrigin::Binding |
74b04a01 | 585 | | hir::OpaqueTyOrigin::FnReturn |
6a06907d | 586 | | hir::OpaqueTyOrigin::TyAlias |
74b04a01 | 587 | | hir::OpaqueTyOrigin::Misc => "impl Trait", |
dc9dc135 XL |
588 | }; |
589 | let msg = format!("ambiguous lifetime bound in `{}`", context_name); | |
590 | let mut err = self.tcx.sess.struct_span_err(span, &msg); | |
591 | ||
592 | let conflict1_name = conflict1.to_string(); | |
593 | let conflict2_name = conflict2.to_string(); | |
594 | let label_owned; | |
595 | let label = match (&*conflict1_name, &*conflict2_name) { | |
596 | ("'_", "'_") => "the elided lifetimes here do not outlive one another", | |
597 | _ => { | |
598 | label_owned = format!( | |
599 | "neither `{}` nor `{}` outlives the other", | |
600 | conflict1_name, conflict2_name, | |
601 | ); | |
602 | &label_owned | |
603 | } | |
604 | }; | |
605 | err.span_label(span, label); | |
606 | ||
fc512014 | 607 | if self.tcx.sess.is_nightly_build() { |
dfeec247 | 608 | err.help("add #![feature(member_constraints)] to the crate attributes to enable"); |
dc9dc135 XL |
609 | } |
610 | ||
611 | err.emit(); | |
612 | true | |
613 | } | |
614 | ||
b7449926 | 615 | /// Given the fully resolved, instantiated type for an opaque |
ff7c6d11 | 616 | /// type, i.e., the value of an inference variable like C1 or C2 |
416331ca | 617 | /// (*), computes the "definition type" for an opaque type |
ff7c6d11 XL |
618 | /// definition -- that is, the inferred value of `Foo1<'x>` or |
619 | /// `Foo2<'x>` that we would conceptually use in its definition: | |
620 | /// | |
416331ca XL |
621 | /// type Foo1<'x> = impl Bar<'x> = AAA; <-- this type AAA |
622 | /// type Foo2<'x> = impl Bar<'x> = BBB; <-- or this type BBB | |
ff7c6d11 XL |
623 | /// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. } |
624 | /// | |
625 | /// Note that these values are defined in terms of a distinct set of | |
626 | /// generic parameters (`'x` instead of `'a`) from C1 or C2. The main | |
627 | /// purpose of this function is to do that translation. | |
628 | /// | |
629 | /// (*) C1 and C2 were introduced in the comments on | |
b7449926 | 630 | /// `constrain_opaque_types`. Read that comment for more context. |
ff7c6d11 XL |
631 | /// |
632 | /// # Parameters | |
633 | /// | |
634 | /// - `def_id`, the `impl Trait` type | |
74b04a01 | 635 | /// - `substs`, the substs used to instantiate this opaque type |
ff7c6d11 | 636 | /// - `instantiated_ty`, the inferred type C1 -- fully resolved, lifted version of |
b7449926 | 637 | /// `opaque_defn.concrete_ty` |
ba9703b0 | 638 | fn infer_opaque_definition_from_instantiation( |
ff7c6d11 XL |
639 | &self, |
640 | def_id: DefId, | |
74b04a01 | 641 | substs: SubstsRef<'tcx>, |
dc9dc135 | 642 | instantiated_ty: Ty<'tcx>, |
416331ca | 643 | span: Span, |
dc9dc135 | 644 | ) -> Ty<'tcx> { |
ff7c6d11 | 645 | debug!( |
b7449926 | 646 | "infer_opaque_definition_from_instantiation(def_id={:?}, instantiated_ty={:?})", |
8faf50e0 | 647 | def_id, instantiated_ty |
ff7c6d11 XL |
648 | ); |
649 | ||
ff7c6d11 XL |
650 | // Use substs to build up a reverse map from regions to their |
651 | // identity mappings. This is necessary because of `impl | |
652 | // Trait` lifetimes are computed by replacing existing | |
653 | // lifetimes with 'static and remapping only those used in the | |
654 | // `impl Trait` return type, resulting in the parameters | |
655 | // shifting. | |
e74abb32 | 656 | let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id); |
74b04a01 | 657 | let map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>> = |
f9f354fc | 658 | substs.iter().enumerate().map(|(index, subst)| (subst, id_substs[index])).collect(); |
ff7c6d11 XL |
659 | |
660 | // Convert the type from the function into a type valid outside | |
661 | // the function, by replacing invalid regions with 'static, | |
662 | // after producing an error for each of them. | |
dc9dc135 XL |
663 | let definition_ty = instantiated_ty.fold_with(&mut ReverseMapper::new( |
664 | self.tcx, | |
665 | self.is_tainted_by_errors(), | |
666 | def_id, | |
667 | map, | |
668 | instantiated_ty, | |
416331ca | 669 | span, |
dc9dc135 XL |
670 | )); |
671 | debug!("infer_opaque_definition_from_instantiation: definition_ty={:?}", definition_ty); | |
0531ce1d | 672 | |
ff7c6d11 XL |
673 | definition_ty |
674 | } | |
675 | } | |
676 | ||
48663c56 XL |
677 | // Visitor that requires that (almost) all regions in the type visited outlive |
678 | // `least_region`. We cannot use `push_outlives_components` because regions in | |
679 | // closure signatures are not included in their outlives components. We need to | |
680 | // ensure all regions outlive the given bound so that we don't end up with, | |
f9f354fc | 681 | // say, `ReVar` appearing in a return type and causing ICEs when other |
48663c56 XL |
682 | // functions end up with region constraints involving regions from other |
683 | // functions. | |
684 | // | |
685 | // We also cannot use `for_each_free_region` because for closures it includes | |
686 | // the regions parameters from the enclosing item. | |
687 | // | |
688 | // We ignore any type parameters because impl trait values are assumed to | |
689 | // capture all the in-scope type parameters. | |
ba9703b0 | 690 | struct ConstrainOpaqueTypeRegionVisitor<OP> { |
dc9dc135 | 691 | op: OP, |
48663c56 XL |
692 | } |
693 | ||
ba9703b0 | 694 | impl<'tcx, OP> TypeVisitor<'tcx> for ConstrainOpaqueTypeRegionVisitor<OP> |
dc9dc135 XL |
695 | where |
696 | OP: FnMut(ty::Region<'tcx>), | |
48663c56 | 697 | { |
fc512014 XL |
698 | fn visit_binder<T: TypeFoldable<'tcx>>( |
699 | &mut self, | |
cdc7bbd5 | 700 | t: &ty::Binder<'tcx, T>, |
fc512014 | 701 | ) -> ControlFlow<Self::BreakTy> { |
f035d41b | 702 | t.as_ref().skip_binder().visit_with(self); |
29967ef6 | 703 | ControlFlow::CONTINUE |
48663c56 XL |
704 | } |
705 | ||
fc512014 | 706 | fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> { |
48663c56 XL |
707 | match *r { |
708 | // ignore bound regions, keep visiting | |
29967ef6 | 709 | ty::ReLateBound(_, _) => ControlFlow::CONTINUE, |
48663c56 | 710 | _ => { |
dc9dc135 | 711 | (self.op)(r); |
29967ef6 | 712 | ControlFlow::CONTINUE |
48663c56 XL |
713 | } |
714 | } | |
715 | } | |
716 | ||
fc512014 | 717 | fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { |
48663c56 | 718 | // We're only interested in types involving regions |
1b1a35ee | 719 | if !ty.flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS) { |
29967ef6 | 720 | return ControlFlow::CONTINUE; |
48663c56 XL |
721 | } |
722 | ||
1b1a35ee | 723 | match ty.kind() { |
ba9703b0 | 724 | ty::Closure(_, ref substs) => { |
48663c56 XL |
725 | // Skip lifetime parameters of the enclosing item(s) |
726 | ||
29967ef6 | 727 | substs.as_closure().tupled_upvars_ty().visit_with(self); |
ba9703b0 | 728 | substs.as_closure().sig_as_fn_ptr_ty().visit_with(self); |
48663c56 XL |
729 | } |
730 | ||
ba9703b0 | 731 | ty::Generator(_, ref substs, _) => { |
48663c56 XL |
732 | // Skip lifetime parameters of the enclosing item(s) |
733 | // Also skip the witness type, because that has no free regions. | |
734 | ||
29967ef6 | 735 | substs.as_generator().tupled_upvars_ty().visit_with(self); |
ba9703b0 XL |
736 | substs.as_generator().return_ty().visit_with(self); |
737 | substs.as_generator().yield_ty().visit_with(self); | |
738 | substs.as_generator().resume_ty().visit_with(self); | |
48663c56 XL |
739 | } |
740 | _ => { | |
741 | ty.super_visit_with(self); | |
742 | } | |
743 | } | |
744 | ||
29967ef6 | 745 | ControlFlow::CONTINUE |
48663c56 XL |
746 | } |
747 | } | |
748 | ||
dc9dc135 XL |
749 | struct ReverseMapper<'tcx> { |
750 | tcx: TyCtxt<'tcx>, | |
0531ce1d XL |
751 | |
752 | /// If errors have already been reported in this fn, we suppress | |
753 | /// our own errors because they are sometimes derivative. | |
754 | tainted_by_errors: bool, | |
755 | ||
b7449926 | 756 | opaque_type_def_id: DefId, |
e74abb32 | 757 | map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>, |
0531ce1d XL |
758 | map_missing_regions_to_empty: bool, |
759 | ||
760 | /// initially `Some`, set to `None` once error has been reported | |
761 | hidden_ty: Option<Ty<'tcx>>, | |
416331ca XL |
762 | |
763 | /// Span of function being checked. | |
764 | span: Span, | |
0531ce1d XL |
765 | } |
766 | ||
dc9dc135 | 767 | impl ReverseMapper<'tcx> { |
0531ce1d | 768 | fn new( |
dc9dc135 | 769 | tcx: TyCtxt<'tcx>, |
0531ce1d | 770 | tainted_by_errors: bool, |
b7449926 | 771 | opaque_type_def_id: DefId, |
e74abb32 | 772 | map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>, |
0531ce1d | 773 | hidden_ty: Ty<'tcx>, |
416331ca | 774 | span: Span, |
0531ce1d XL |
775 | ) -> Self { |
776 | Self { | |
777 | tcx, | |
778 | tainted_by_errors, | |
b7449926 | 779 | opaque_type_def_id, |
0531ce1d XL |
780 | map, |
781 | map_missing_regions_to_empty: false, | |
782 | hidden_ty: Some(hidden_ty), | |
416331ca | 783 | span, |
0531ce1d XL |
784 | } |
785 | } | |
786 | ||
e74abb32 XL |
787 | fn fold_kind_mapping_missing_regions_to_empty( |
788 | &mut self, | |
789 | kind: GenericArg<'tcx>, | |
790 | ) -> GenericArg<'tcx> { | |
0531ce1d XL |
791 | assert!(!self.map_missing_regions_to_empty); |
792 | self.map_missing_regions_to_empty = true; | |
793 | let kind = kind.fold_with(self); | |
794 | self.map_missing_regions_to_empty = false; | |
795 | kind | |
796 | } | |
797 | ||
e74abb32 | 798 | fn fold_kind_normally(&mut self, kind: GenericArg<'tcx>) -> GenericArg<'tcx> { |
0531ce1d XL |
799 | assert!(!self.map_missing_regions_to_empty); |
800 | kind.fold_with(self) | |
801 | } | |
802 | } | |
803 | ||
dc9dc135 XL |
804 | impl TypeFolder<'tcx> for ReverseMapper<'tcx> { |
805 | fn tcx(&self) -> TyCtxt<'tcx> { | |
0531ce1d XL |
806 | self.tcx |
807 | } | |
808 | ||
809 | fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { | |
810 | match r { | |
74b04a01 XL |
811 | // Ignore bound regions and `'static` regions that appear in the |
812 | // type, we only need to remap regions that reference lifetimes | |
813 | // from the function declaraion. | |
814 | // This would ignore `'r` in a type like `for<'r> fn(&'r u32)`. | |
815 | ty::ReLateBound(..) | ty::ReStatic => return r, | |
816 | ||
817 | // If regions have been erased (by writeback), don't try to unerase | |
818 | // them. | |
819 | ty::ReErased => return r, | |
820 | ||
821 | // The regions that we expect from borrow checking. | |
822 | ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReEmpty(ty::UniverseIndex::ROOT) => {} | |
823 | ||
f9f354fc | 824 | ty::ReEmpty(_) | ty::RePlaceholder(_) | ty::ReVar(_) => { |
74b04a01 XL |
825 | // All of the regions in the type should either have been |
826 | // erased by writeback, or mapped back to named regions by | |
827 | // borrow checking. | |
828 | bug!("unexpected region kind in opaque type: {:?}", r); | |
829 | } | |
0531ce1d XL |
830 | } |
831 | ||
416331ca | 832 | let generics = self.tcx().generics_of(self.opaque_type_def_id); |
0531ce1d | 833 | match self.map.get(&r.into()).map(|k| k.unpack()) { |
e74abb32 | 834 | Some(GenericArgKind::Lifetime(r1)) => r1, |
0531ce1d | 835 | Some(u) => panic!("region mapped to unexpected kind: {:?}", u), |
74b04a01 XL |
836 | None if self.map_missing_regions_to_empty || self.tainted_by_errors => { |
837 | self.tcx.lifetimes.re_root_empty | |
838 | } | |
416331ca | 839 | None if generics.parent.is_some() => { |
74b04a01 XL |
840 | if let Some(hidden_ty) = self.hidden_ty.take() { |
841 | unexpected_hidden_region_diagnostic( | |
842 | self.tcx, | |
74b04a01 XL |
843 | self.tcx.def_span(self.opaque_type_def_id), |
844 | hidden_ty, | |
845 | r, | |
846 | ) | |
847 | .emit(); | |
0531ce1d | 848 | } |
74b04a01 | 849 | self.tcx.lifetimes.re_root_empty |
dc9dc135 | 850 | } |
416331ca | 851 | None => { |
dfeec247 XL |
852 | self.tcx |
853 | .sess | |
854 | .struct_span_err(self.span, "non-defining opaque type use in defining scope") | |
416331ca XL |
855 | .span_label( |
856 | self.span, | |
dfeec247 XL |
857 | format!( |
858 | "lifetime `{}` is part of concrete type but not used in \ | |
859 | parameter list of the `impl Trait` type alias", | |
860 | r | |
861 | ), | |
416331ca XL |
862 | ) |
863 | .emit(); | |
864 | ||
74b04a01 | 865 | self.tcx().lifetimes.re_static |
dfeec247 | 866 | } |
0531ce1d XL |
867 | } |
868 | } | |
869 | ||
870 | fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { | |
1b1a35ee | 871 | match *ty.kind() { |
b7449926 | 872 | ty::Closure(def_id, substs) => { |
0531ce1d XL |
873 | // I am a horrible monster and I pray for death. When |
874 | // we encounter a closure here, it is always a closure | |
875 | // from within the function that we are currently | |
876 | // type-checking -- one that is now being encapsulated | |
416331ca | 877 | // in an opaque type. Ideally, we would |
0531ce1d XL |
878 | // go through the types/lifetimes that it references |
879 | // and treat them just like we would any other type, | |
880 | // which means we would error out if we find any | |
881 | // reference to a type/region that is not in the | |
882 | // "reverse map". | |
883 | // | |
884 | // **However,** in the case of closures, there is a | |
885 | // somewhat subtle (read: hacky) consideration. The | |
886 | // problem is that our closure types currently include | |
887 | // all the lifetime parameters declared on the | |
888 | // enclosing function, even if they are unused by the | |
889 | // closure itself. We can't readily filter them out, | |
890 | // so here we replace those values with `'empty`. This | |
891 | // can't really make a difference to the rest of the | |
892 | // compiler; those regions are ignored for the | |
893 | // outlives relation, and hence don't affect trait | |
894 | // selection or auto traits, and they are erased | |
94b46f34 | 895 | // during codegen. |
0531ce1d XL |
896 | |
897 | let generics = self.tcx.generics_of(def_id); | |
f9f354fc | 898 | let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| { |
dfeec247 XL |
899 | if index < generics.parent_count { |
900 | // Accommodate missing regions in the parent kinds... | |
901 | self.fold_kind_mapping_missing_regions_to_empty(kind) | |
902 | } else { | |
903 | // ...but not elsewhere. | |
904 | self.fold_kind_normally(kind) | |
905 | } | |
906 | })); | |
0531ce1d | 907 | |
e74abb32 | 908 | self.tcx.mk_closure(def_id, substs) |
0531ce1d XL |
909 | } |
910 | ||
48663c56 XL |
911 | ty::Generator(def_id, substs, movability) => { |
912 | let generics = self.tcx.generics_of(def_id); | |
f9f354fc | 913 | let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| { |
dfeec247 XL |
914 | if index < generics.parent_count { |
915 | // Accommodate missing regions in the parent kinds... | |
916 | self.fold_kind_mapping_missing_regions_to_empty(kind) | |
917 | } else { | |
918 | // ...but not elsewhere. | |
919 | self.fold_kind_normally(kind) | |
920 | } | |
921 | })); | |
48663c56 | 922 | |
e74abb32 | 923 | self.tcx.mk_generator(def_id, substs, movability) |
48663c56 XL |
924 | } |
925 | ||
416331ca XL |
926 | ty::Param(..) => { |
927 | // Look it up in the substitution list. | |
928 | match self.map.get(&ty.into()).map(|k| k.unpack()) { | |
929 | // Found it in the substitution list; replace with the parameter from the | |
930 | // opaque type. | |
e74abb32 | 931 | Some(GenericArgKind::Type(t1)) => t1, |
416331ca XL |
932 | Some(u) => panic!("type mapped to unexpected kind: {:?}", u), |
933 | None => { | |
dfeec247 XL |
934 | self.tcx |
935 | .sess | |
416331ca XL |
936 | .struct_span_err( |
937 | self.span, | |
dfeec247 XL |
938 | &format!( |
939 | "type parameter `{}` is part of concrete type but not \ | |
416331ca | 940 | used in parameter list for the `impl Trait` type alias", |
dfeec247 XL |
941 | ty |
942 | ), | |
416331ca XL |
943 | ) |
944 | .emit(); | |
945 | ||
f035d41b | 946 | self.tcx().ty_error() |
416331ca XL |
947 | } |
948 | } | |
949 | } | |
950 | ||
0531ce1d XL |
951 | _ => ty.super_fold_with(self), |
952 | } | |
953 | } | |
416331ca XL |
954 | |
955 | fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> { | |
956 | trace!("checking const {:?}", ct); | |
957 | // Find a const parameter | |
958 | match ct.val { | |
60c5eb7d | 959 | ty::ConstKind::Param(..) => { |
416331ca XL |
960 | // Look it up in the substitution list. |
961 | match self.map.get(&ct.into()).map(|k| k.unpack()) { | |
962 | // Found it in the substitution list, replace with the parameter from the | |
963 | // opaque type. | |
e74abb32 | 964 | Some(GenericArgKind::Const(c1)) => c1, |
416331ca XL |
965 | Some(u) => panic!("const mapped to unexpected kind: {:?}", u), |
966 | None => { | |
dfeec247 XL |
967 | self.tcx |
968 | .sess | |
416331ca XL |
969 | .struct_span_err( |
970 | self.span, | |
dfeec247 XL |
971 | &format!( |
972 | "const parameter `{}` is part of concrete type but not \ | |
416331ca | 973 | used in parameter list for the `impl Trait` type alias", |
dfeec247 XL |
974 | ct |
975 | ), | |
416331ca XL |
976 | ) |
977 | .emit(); | |
978 | ||
f035d41b | 979 | self.tcx().const_error(ct.ty) |
416331ca XL |
980 | } |
981 | } | |
982 | } | |
983 | ||
984 | _ => ct, | |
985 | } | |
986 | } | |
0531ce1d XL |
987 | } |
988 | ||
dc9dc135 XL |
989 | struct Instantiator<'a, 'tcx> { |
990 | infcx: &'a InferCtxt<'a, 'tcx>, | |
f035d41b | 991 | parent_def_id: LocalDefId, |
9fa01778 | 992 | body_id: hir::HirId, |
ff7c6d11 | 993 | param_env: ty::ParamEnv<'tcx>, |
dc9dc135 | 994 | value_span: Span, |
b7449926 | 995 | opaque_types: OpaqueTypeMap<'tcx>, |
ff7c6d11 XL |
996 | obligations: Vec<PredicateObligation<'tcx>>, |
997 | } | |
998 | ||
dc9dc135 | 999 | impl<'a, 'tcx> Instantiator<'a, 'tcx> { |
fc512014 | 1000 | fn instantiate_opaque_types_in_map<T: TypeFoldable<'tcx>>(&mut self, value: T) -> T { |
b7449926 | 1001 | debug!("instantiate_opaque_types_in_map(value={:?})", value); |
ff7c6d11 XL |
1002 | let tcx = self.infcx.tcx; |
1003 | value.fold_with(&mut BottomUpFolder { | |
1004 | tcx, | |
48663c56 | 1005 | ty_op: |ty| { |
e74abb32 | 1006 | if ty.references_error() { |
f035d41b | 1007 | return tcx.ty_error(); |
1b1a35ee | 1008 | } else if let ty::Opaque(def_id, substs) = ty.kind() { |
ff7c6d11 XL |
1009 | // Check that this is `impl Trait` type is |
1010 | // declared by `parent_def_id` -- i.e., one whose | |
1011 | // value we are inferring. At present, this is | |
1012 | // always true during the first phase of | |
1013 | // type-check, but not always true later on during | |
416331ca | 1014 | // NLL. Once we support named opaque types more fully, |
ff7c6d11 XL |
1015 | // this same scenario will be able to arise during all phases. |
1016 | // | |
416331ca XL |
1017 | // Here is an example using type alias `impl Trait` |
1018 | // that indicates the distinction we are checking for: | |
ff7c6d11 XL |
1019 | // |
1020 | // ```rust | |
1021 | // mod a { | |
416331ca | 1022 | // pub type Foo = impl Iterator; |
ff7c6d11 XL |
1023 | // pub fn make_foo() -> Foo { .. } |
1024 | // } | |
1025 | // | |
1026 | // mod b { | |
1027 | // fn foo() -> a::Foo { a::make_foo() } | |
1028 | // } | |
1029 | // ``` | |
1030 | // | |
1031 | // Here, the return type of `foo` references a | |
b7449926 | 1032 | // `Opaque` indeed, but not one whose value is |
ff7c6d11 XL |
1033 | // presently being inferred. You can get into a |
1034 | // similar situation with closure return types | |
1035 | // today: | |
1036 | // | |
1037 | // ```rust | |
1038 | // fn foo() -> impl Iterator { .. } | |
1039 | // fn bar() { | |
b7449926 | 1040 | // let x = || foo(); // returns the Opaque assoc with `foo` |
ff7c6d11 XL |
1041 | // } |
1042 | // ``` | |
f9f354fc | 1043 | if let Some(def_id) = def_id.as_local() { |
3dfed10e | 1044 | let opaque_hir_id = tcx.hir().local_def_id_to_hir_id(def_id); |
8faf50e0 XL |
1045 | let parent_def_id = self.parent_def_id; |
1046 | let def_scope_default = || { | |
532ac7d7 | 1047 | let opaque_parent_hir_id = tcx.hir().get_parent_item(opaque_hir_id); |
f035d41b | 1048 | parent_def_id == tcx.hir().local_def_id(opaque_parent_hir_id) |
8faf50e0 | 1049 | }; |
dc9dc135 | 1050 | let (in_definition_scope, origin) = match tcx.hir().find(opaque_hir_id) { |
e74abb32 | 1051 | Some(Node::Item(item)) => match item.kind { |
dc9dc135 | 1052 | // Anonymous `impl Trait` |
416331ca | 1053 | hir::ItemKind::OpaqueTy(hir::OpaqueTy { |
8faf50e0 | 1054 | impl_trait_fn: Some(parent), |
532ac7d7 | 1055 | origin, |
8faf50e0 | 1056 | .. |
f035d41b | 1057 | }) => (parent == self.parent_def_id.to_def_id(), origin), |
416331ca XL |
1058 | // Named `type Foo = impl Bar;` |
1059 | hir::ItemKind::OpaqueTy(hir::OpaqueTy { | |
8faf50e0 | 1060 | impl_trait_fn: None, |
532ac7d7 | 1061 | origin, |
8faf50e0 | 1062 | .. |
532ac7d7 | 1063 | }) => ( |
f035d41b | 1064 | may_define_opaque_type(tcx, self.parent_def_id, opaque_hir_id), |
532ac7d7 | 1065 | origin, |
8faf50e0 | 1066 | ), |
f035d41b | 1067 | _ => (def_scope_default(), hir::OpaqueTyOrigin::Misc), |
94b46f34 | 1068 | }, |
8faf50e0 | 1069 | _ => bug!( |
f035d41b | 1070 | "expected item, found {}", |
dc9dc135 | 1071 | tcx.hir().node_to_string(opaque_hir_id), |
8faf50e0 | 1072 | ), |
94b46f34 | 1073 | }; |
8faf50e0 | 1074 | if in_definition_scope { |
f9f354fc | 1075 | return self.fold_opaque_ty(ty, def_id.to_def_id(), substs, origin); |
ff7c6d11 XL |
1076 | } |
1077 | ||
0531ce1d | 1078 | debug!( |
b7449926 | 1079 | "instantiate_opaque_types_in_map: \ |
0bf4aa26 | 1080 | encountered opaque outside its definition scope \ |
8faf50e0 XL |
1081 | def_id={:?}", |
1082 | def_id, | |
0531ce1d | 1083 | ); |
ff7c6d11 XL |
1084 | } |
1085 | } | |
1086 | ||
1087 | ty | |
1088 | }, | |
48663c56 XL |
1089 | lt_op: |lt| lt, |
1090 | ct_op: |ct| ct, | |
ff7c6d11 XL |
1091 | }) |
1092 | } | |
1093 | ||
b7449926 | 1094 | fn fold_opaque_ty( |
ff7c6d11 XL |
1095 | &mut self, |
1096 | ty: Ty<'tcx>, | |
1097 | def_id: DefId, | |
532ac7d7 | 1098 | substs: SubstsRef<'tcx>, |
416331ca | 1099 | origin: hir::OpaqueTyOrigin, |
ff7c6d11 XL |
1100 | ) -> Ty<'tcx> { |
1101 | let infcx = self.infcx; | |
1102 | let tcx = infcx.tcx; | |
1103 | ||
dc9dc135 | 1104 | debug!("instantiate_opaque_types: Opaque(def_id={:?}, substs={:?})", def_id, substs); |
ff7c6d11 | 1105 | |
dc9dc135 | 1106 | // Use the same type variable if the exact same opaque type appears more |
0731742a | 1107 | // than once in the return type (e.g., if it's passed to a type alias). |
b7449926 | 1108 | if let Some(opaque_defn) = self.opaque_types.get(&def_id) { |
e1599b0c | 1109 | debug!("instantiate_opaque_types: returning concrete ty {:?}", opaque_defn.concrete_ty); |
b7449926 | 1110 | return opaque_defn.concrete_ty; |
ff7c6d11 XL |
1111 | } |
1112 | let span = tcx.def_span(def_id); | |
e1599b0c | 1113 | debug!("fold_opaque_ty {:?} {:?}", self.value_span, span); |
dc9dc135 XL |
1114 | let ty_var = infcx |
1115 | .next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span }); | |
ff7c6d11 | 1116 | |
29967ef6 XL |
1117 | let item_bounds = tcx.explicit_item_bounds(def_id); |
1118 | debug!("instantiate_opaque_types: bounds={:#?}", item_bounds); | |
1119 | let bounds: Vec<_> = | |
1120 | item_bounds.iter().map(|(bound, _)| bound.subst(tcx, substs)).collect(); | |
416331ca XL |
1121 | |
1122 | let param_env = tcx.param_env(def_id); | |
1123 | let InferOk { value: bounds, obligations } = | |
fc512014 | 1124 | infcx.partially_normalize_associated_types_in(span, self.body_id, param_env, bounds); |
416331ca XL |
1125 | self.obligations.extend(obligations); |
1126 | ||
b7449926 | 1127 | debug!("instantiate_opaque_types: bounds={:?}", bounds); |
ff7c6d11 | 1128 | |
29967ef6 | 1129 | let required_region_bounds = required_region_bounds(tcx, ty, bounds.iter().copied()); |
dc9dc135 | 1130 | debug!("instantiate_opaque_types: required_region_bounds={:?}", required_region_bounds); |
ff7c6d11 | 1131 | |
dc9dc135 | 1132 | // Make sure that we are in fact defining the *entire* type |
416331ca | 1133 | // (e.g., `type Foo<T: Bound> = impl Bar;` needs to be |
dc9dc135 XL |
1134 | // defined by a function like `fn foo<T: Bound>() -> Foo<T>`). |
1135 | debug!("instantiate_opaque_types: param_env={:#?}", self.param_env,); | |
1136 | debug!("instantiate_opaque_types: generics={:#?}", tcx.generics_of(def_id),); | |
1137 | ||
1138 | // Ideally, we'd get the span where *this specific `ty` came | |
1139 | // from*, but right now we just use the span from the overall | |
1140 | // value being folded. In simple cases like `-> impl Foo`, | |
1141 | // these are the same span, but not in cases like `-> (impl | |
1142 | // Foo, impl Bar)`. | |
1143 | let definition_span = self.value_span; | |
8faf50e0 | 1144 | |
b7449926 | 1145 | self.opaque_types.insert( |
ff7c6d11 | 1146 | def_id, |
b7449926 | 1147 | OpaqueTypeDecl { |
60c5eb7d | 1148 | opaque_type: ty, |
ff7c6d11 | 1149 | substs, |
dc9dc135 | 1150 | definition_span, |
ff7c6d11 XL |
1151 | concrete_ty: ty_var, |
1152 | has_required_region_bounds: !required_region_bounds.is_empty(), | |
532ac7d7 | 1153 | origin, |
ff7c6d11 XL |
1154 | }, |
1155 | ); | |
b7449926 | 1156 | debug!("instantiate_opaque_types: ty_var={:?}", ty_var); |
ff7c6d11 | 1157 | |
29967ef6 | 1158 | for predicate in &bounds { |
5869c6ff | 1159 | if let ty::PredicateKind::Projection(projection) = predicate.kind().skip_binder() { |
3dfed10e | 1160 | if projection.ty.references_error() { |
e74abb32 XL |
1161 | // No point on adding these obligations since there's a type error involved. |
1162 | return ty_var; | |
1163 | } | |
1164 | } | |
1165 | } | |
1166 | ||
29967ef6 XL |
1167 | self.obligations.reserve(bounds.len()); |
1168 | for predicate in bounds { | |
ff7c6d11 | 1169 | // Change the predicate to refer to the type variable, |
0bf4aa26 XL |
1170 | // which will be the concrete type instead of the opaque type. |
1171 | // This also instantiates nested instances of `impl Trait`. | |
fc512014 | 1172 | let predicate = self.instantiate_opaque_types_in_map(predicate); |
ff7c6d11 | 1173 | |
cdc7bbd5 | 1174 | let cause = traits::ObligationCause::new(span, self.body_id, traits::OpaqueType); |
ff7c6d11 XL |
1175 | |
1176 | // Require that the predicate holds for the concrete type. | |
b7449926 | 1177 | debug!("instantiate_opaque_types: predicate={:?}", predicate); |
dc9dc135 | 1178 | self.obligations.push(traits::Obligation::new(cause, self.param_env, predicate)); |
ff7c6d11 XL |
1179 | } |
1180 | ||
1181 | ty_var | |
1182 | } | |
1183 | } | |
8faf50e0 | 1184 | |
dc9dc135 | 1185 | /// Returns `true` if `opaque_hir_id` is a sibling or a child of a sibling of `def_id`. |
8faf50e0 | 1186 | /// |
dc9dc135 | 1187 | /// Example: |
8faf50e0 XL |
1188 | /// ```rust |
1189 | /// pub mod foo { | |
1190 | /// pub mod bar { | |
416331ca XL |
1191 | /// pub trait Bar { .. } |
1192 | /// | |
1193 | /// pub type Baz = impl Bar; | |
8faf50e0 XL |
1194 | /// |
1195 | /// fn f1() -> Baz { .. } | |
1196 | /// } | |
1197 | /// | |
1198 | /// fn f2() -> bar::Baz { .. } | |
1199 | /// } | |
1200 | /// ``` | |
1201 | /// | |
f9f354fc | 1202 | /// Here, `def_id` is the `LocalDefId` of the defining use of the opaque type (e.g., `f1` or `f2`), |
416331ca | 1203 | /// and `opaque_hir_id` is the `HirId` of the definition of the opaque type `Baz`. |
dc9dc135 | 1204 | /// For the above example, this function returns `true` for `f1` and `false` for `f2`. |
f9f354fc XL |
1205 | pub fn may_define_opaque_type( |
1206 | tcx: TyCtxt<'_>, | |
1207 | def_id: LocalDefId, | |
1208 | opaque_hir_id: hir::HirId, | |
1209 | ) -> bool { | |
3dfed10e | 1210 | let mut hir_id = tcx.hir().local_def_id_to_hir_id(def_id); |
dc9dc135 | 1211 | |
416331ca | 1212 | // Named opaque types can be defined by any siblings or children of siblings. |
e74abb32 | 1213 | let scope = tcx.hir().get_defining_scope(opaque_hir_id); |
dc9dc135 XL |
1214 | // We walk up the node tree until we hit the root or the scope of the opaque type. |
1215 | while hir_id != scope && hir_id != hir::CRATE_HIR_ID { | |
532ac7d7 | 1216 | hir_id = tcx.hir().get_parent_item(hir_id); |
8faf50e0 | 1217 | } |
dc9dc135 | 1218 | // Syntactically, we are allowed to define the concrete type if: |
416331ca XL |
1219 | let res = hir_id == scope; |
1220 | trace!( | |
1221 | "may_define_opaque_type(def={:?}, opaque_node={:?}) = {}", | |
dfeec247 | 1222 | tcx.hir().find(hir_id), |
416331ca XL |
1223 | tcx.hir().get(opaque_hir_id), |
1224 | res | |
1225 | ); | |
1226 | res | |
8faf50e0 | 1227 | } |
dfeec247 XL |
1228 | |
1229 | /// Given a set of predicates that apply to an object type, returns | |
1230 | /// the region bounds that the (erased) `Self` type must | |
1231 | /// outlive. Precisely *because* the `Self` type is erased, the | |
1232 | /// parameter `erased_self_ty` must be supplied to indicate what type | |
1233 | /// has been used to represent `Self` in the predicates | |
1234 | /// themselves. This should really be a unique type; `FreshTy(0)` is a | |
1235 | /// popular choice. | |
1236 | /// | |
1237 | /// N.B., in some cases, particularly around higher-ranked bounds, | |
1238 | /// this function returns a kind of conservative approximation. | |
1239 | /// That is, all regions returned by this function are definitely | |
1240 | /// required, but there may be other region bounds that are not | |
1241 | /// returned, as well as requirements like `for<'a> T: 'a`. | |
1242 | /// | |
1243 | /// Requires that trait definitions have been processed so that we can | |
1244 | /// elaborate predicates and walk supertraits. | |
dfeec247 XL |
1245 | crate fn required_region_bounds( |
1246 | tcx: TyCtxt<'tcx>, | |
1247 | erased_self_ty: Ty<'tcx>, | |
ba9703b0 | 1248 | predicates: impl Iterator<Item = ty::Predicate<'tcx>>, |
dfeec247 | 1249 | ) -> Vec<ty::Region<'tcx>> { |
ba9703b0 | 1250 | debug!("required_region_bounds(erased_self_ty={:?})", erased_self_ty); |
dfeec247 XL |
1251 | |
1252 | assert!(!erased_self_ty.has_escaping_bound_vars()); | |
1253 | ||
1254 | traits::elaborate_predicates(tcx, predicates) | |
ba9703b0 XL |
1255 | .filter_map(|obligation| { |
1256 | debug!("required_region_bounds(obligation={:?})", obligation); | |
5869c6ff XL |
1257 | match obligation.predicate.kind().skip_binder() { |
1258 | ty::PredicateKind::Projection(..) | |
1259 | | ty::PredicateKind::Trait(..) | |
1260 | | ty::PredicateKind::Subtype(..) | |
1261 | | ty::PredicateKind::WellFormed(..) | |
1262 | | ty::PredicateKind::ObjectSafe(..) | |
1263 | | ty::PredicateKind::ClosureKind(..) | |
1264 | | ty::PredicateKind::RegionOutlives(..) | |
1265 | | ty::PredicateKind::ConstEvaluatable(..) | |
1266 | | ty::PredicateKind::ConstEquate(..) | |
1267 | | ty::PredicateKind::TypeWellFormedFromEnv(..) => None, | |
1268 | ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ref t, ref r)) => { | |
dfeec247 XL |
1269 | // Search for a bound of the form `erased_self_ty |
1270 | // : 'a`, but be wary of something like `for<'a> | |
1271 | // erased_self_ty : 'a` (we interpret a | |
1272 | // higher-ranked bound like that as 'static, | |
1273 | // though at present the code in `fulfill.rs` | |
1274 | // considers such bounds to be unsatisfiable, so | |
1275 | // it's kind of a moot point since you could never | |
1276 | // construct such an object, but this seems | |
1277 | // correct even if that code changes). | |
dfeec247 XL |
1278 | if t == &erased_self_ty && !r.has_escaping_bound_vars() { |
1279 | Some(*r) | |
1280 | } else { | |
1281 | None | |
1282 | } | |
1283 | } | |
1284 | } | |
1285 | }) | |
1286 | .collect() | |
1287 | } |