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1 | // Copyright 2012 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. | |
4 | // | |
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. | |
10 | ||
11 | //! # Type Coercion | |
12 | //! | |
13 | //! Under certain circumstances we will coerce from one type to another, | |
14 | //! for example by auto-borrowing. This occurs in situations where the | |
15 | //! compiler has a firm 'expected type' that was supplied from the user, | |
16 | //! and where the actual type is similar to that expected type in purpose | |
17 | //! but not in representation (so actual subtyping is inappropriate). | |
18 | //! | |
19 | //! ## Reborrowing | |
20 | //! | |
21 | //! Note that if we are expecting a reference, we will *reborrow* | |
22 | //! even if the argument provided was already a reference. This is | |
23 | //! useful for freezing mut/const things (that is, when the expected is &T | |
24 | //! but you have &const T or &mut T) and also for avoiding the linearity | |
25 | //! of mut things (when the expected is &mut T and you have &mut T). See | |
26 | //! the various `src/test/run-pass/coerce-reborrow-*.rs` tests for | |
27 | //! examples of where this is useful. | |
28 | //! | |
29 | //! ## Subtle note | |
30 | //! | |
31 | //! When deciding what type coercions to consider, we do not attempt to | |
32 | //! resolve any type variables we may encounter. This is because `b` | |
33 | //! represents the expected type "as the user wrote it", meaning that if | |
34 | //! the user defined a generic function like | |
35 | //! | |
36 | //! fn foo<A>(a: A, b: A) { ... } | |
37 | //! | |
38 | //! and then we wrote `foo(&1, @2)`, we will not auto-borrow | |
39 | //! either argument. In older code we went to some lengths to | |
40 | //! resolve the `b` variable, which could mean that we'd | |
41 | //! auto-borrow later arguments but not earlier ones, which | |
42 | //! seems very confusing. | |
43 | //! | |
44 | //! ## Subtler note | |
45 | //! | |
46 | //! However, right now, if the user manually specifies the | |
47 | //! values for the type variables, as so: | |
48 | //! | |
49 | //! foo::<&int>(@1, @2) | |
50 | //! | |
51 | //! then we *will* auto-borrow, because we can't distinguish this from a | |
52 | //! function that declared `&int`. This is inconsistent but it's easiest | |
53 | //! at the moment. The right thing to do, I think, is to consider the | |
54 | //! *unsubstituted* type when deciding whether to auto-borrow, but the | |
55 | //! *substituted* type when considering the bounds and so forth. But most | |
56 | //! of our methods don't give access to the unsubstituted type, and | |
57 | //! rightly so because they'd be error-prone. So maybe the thing to do is | |
58 | //! to actually determine the kind of coercions that should occur | |
59 | //! separately and pass them in. Or maybe it's ok as is. Anyway, it's | |
60 | //! sort of a minor point so I've opted to leave it for later---after all | |
61 | //! we may want to adjust precisely when coercions occur. | |
62 | ||
e9174d1e | 63 | use check::{autoderef, FnCtxt, UnresolvedTypeAction}; |
1a4d82fc | 64 | |
54a0048b SL |
65 | use rustc::infer::{Coercion, InferOk, TypeOrigin, TypeTrace}; |
66 | use rustc::traits::{self, ObligationCause}; | |
67 | use rustc::traits::{predicate_for_trait_def, report_selection_error}; | |
68 | use rustc::ty::adjustment::{AutoAdjustment, AutoDerefRef, AdjustDerefRef}; | |
69 | use rustc::ty::adjustment::{AutoPtr, AutoUnsafe, AdjustReifyFnPointer}; | |
70 | use rustc::ty::adjustment::{AdjustUnsafeFnPointer, AdjustMutToConstPointer}; | |
71 | use rustc::ty::{self, LvaluePreference, TypeAndMut, Ty, TyCtxt}; | |
72 | use rustc::ty::fold::TypeFoldable; | |
73 | use rustc::ty::error::TypeError; | |
74 | use rustc::ty::relate::{RelateResult, TypeRelation}; | |
85aaf69f | 75 | use util::common::indent; |
1a4d82fc | 76 | |
d9579d0f AL |
77 | use std::cell::RefCell; |
78 | use std::collections::VecDeque; | |
54a0048b | 79 | use rustc::hir; |
1a4d82fc | 80 | |
85aaf69f SL |
81 | struct Coerce<'a, 'tcx: 'a> { |
82 | fcx: &'a FnCtxt<'a, 'tcx>, | |
54a0048b SL |
83 | origin: TypeOrigin, |
84 | use_lub: bool, | |
d9579d0f | 85 | unsizing_obligations: RefCell<Vec<traits::PredicateObligation<'tcx>>>, |
85aaf69f SL |
86 | } |
87 | ||
54a0048b SL |
88 | type CoerceResult<'tcx> = RelateResult<'tcx, (Ty<'tcx>, AutoAdjustment<'tcx>)>; |
89 | ||
90 | fn coerce_mutbls<'tcx>(from_mutbl: hir::Mutability, | |
91 | to_mutbl: hir::Mutability) | |
92 | -> RelateResult<'tcx, ()> { | |
93 | match (from_mutbl, to_mutbl) { | |
94 | (hir::MutMutable, hir::MutMutable) | | |
95 | (hir::MutImmutable, hir::MutImmutable) | | |
96 | (hir::MutMutable, hir::MutImmutable) => Ok(()), | |
97 | (hir::MutImmutable, hir::MutMutable) => Err(TypeError::Mutability) | |
98 | } | |
99 | } | |
1a4d82fc JJ |
100 | |
101 | impl<'f, 'tcx> Coerce<'f, 'tcx> { | |
54a0048b SL |
102 | fn new(fcx: &'f FnCtxt<'f, 'tcx>, origin: TypeOrigin) -> Self { |
103 | Coerce { | |
104 | fcx: fcx, | |
105 | origin: origin, | |
106 | use_lub: false, | |
107 | unsizing_obligations: RefCell::new(vec![]) | |
108 | } | |
109 | } | |
110 | ||
111 | fn tcx(&self) -> &TyCtxt<'tcx> { | |
85aaf69f | 112 | self.fcx.tcx() |
1a4d82fc JJ |
113 | } |
114 | ||
54a0048b SL |
115 | fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { |
116 | let infcx = self.fcx.infcx(); | |
117 | infcx.commit_if_ok(|_| { | |
118 | let trace = TypeTrace::types(self.origin, false, a, b); | |
119 | if self.use_lub { | |
120 | infcx.lub(false, trace, &a, &b) | |
121 | .map(|InferOk { value, obligations }| { | |
122 | // FIXME(#32730) propagate obligations | |
123 | assert!(obligations.is_empty()); | |
124 | value | |
125 | }) | |
126 | } else { | |
127 | infcx.sub(false, trace, &a, &b) | |
128 | .map(|InferOk { value, obligations }| { | |
129 | // FIXME(#32730) propagate obligations | |
130 | assert!(obligations.is_empty()); | |
131 | value | |
132 | }) | |
133 | } | |
134 | }) | |
85aaf69f SL |
135 | } |
136 | ||
54a0048b SL |
137 | /// Unify two types (using sub or lub) and produce a noop coercion. |
138 | fn unify_and_identity(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> { | |
139 | self.unify(&a, &b).and_then(|ty| self.identity(ty)) | |
1a4d82fc JJ |
140 | } |
141 | ||
54a0048b SL |
142 | /// Synthesize an identity adjustment. |
143 | fn identity(&self, ty: Ty<'tcx>) -> CoerceResult<'tcx> { | |
144 | Ok((ty, AdjustDerefRef(AutoDerefRef { | |
145 | autoderefs: 0, | |
146 | autoref: None, | |
147 | unsize: None | |
148 | }))) | |
149 | } | |
150 | ||
151 | fn coerce<'a, E, I>(&self, | |
152 | exprs: &E, | |
153 | a: Ty<'tcx>, | |
154 | b: Ty<'tcx>) | |
155 | -> CoerceResult<'tcx> | |
156 | // FIXME(eddyb) use copyable iterators when that becomes ergonomic. | |
157 | where E: Fn() -> I, | |
158 | I: IntoIterator<Item=&'a hir::Expr> { | |
1a4d82fc | 159 | |
92a42be0 | 160 | let a = self.fcx.infcx().shallow_resolve(a); |
54a0048b | 161 | debug!("Coerce.tys({:?} => {:?})", a, b); |
92a42be0 SL |
162 | |
163 | // Just ignore error types. | |
164 | if a.references_error() || b.references_error() { | |
54a0048b | 165 | return self.identity(b); |
92a42be0 SL |
166 | } |
167 | ||
1a4d82fc | 168 | // Consider coercing the subtype to a DST |
92a42be0 | 169 | let unsize = self.coerce_unsized(a, b); |
1a4d82fc JJ |
170 | if unsize.is_ok() { |
171 | return unsize; | |
172 | } | |
173 | ||
174 | // Examine the supertype and consider auto-borrowing. | |
175 | // | |
176 | // Note: does not attempt to resolve type variables we encounter. | |
177 | // See above for details. | |
178 | match b.sty { | |
62682a34 | 179 | ty::TyRawPtr(mt_b) => { |
92a42be0 | 180 | return self.coerce_unsafe_ptr(a, b, mt_b.mutbl); |
1a4d82fc JJ |
181 | } |
182 | ||
54a0048b SL |
183 | ty::TyRef(r_b, mt_b) => { |
184 | return self.coerce_borrowed_pointer(exprs, a, b, r_b, mt_b); | |
1a4d82fc JJ |
185 | } |
186 | ||
187 | _ => {} | |
188 | } | |
189 | ||
92a42be0 | 190 | match a.sty { |
54a0048b | 191 | ty::TyFnDef(_, _, a_f) => { |
92a42be0 SL |
192 | // Function items are coercible to any closure |
193 | // type; function pointers are not (that would | |
194 | // require double indirection). | |
195 | self.coerce_from_fn_item(a, a_f, b) | |
1a4d82fc | 196 | } |
54a0048b | 197 | ty::TyFnPtr(a_f) => { |
92a42be0 SL |
198 | // We permit coercion of fn pointers to drop the |
199 | // unsafe qualifier. | |
200 | self.coerce_from_fn_pointer(a, a_f, b) | |
201 | } | |
202 | _ => { | |
54a0048b SL |
203 | // Otherwise, just use unification rules. |
204 | self.unify_and_identity(a, b) | |
92a42be0 SL |
205 | } |
206 | } | |
1a4d82fc JJ |
207 | } |
208 | ||
85aaf69f SL |
209 | /// Reborrows `&mut A` to `&mut B` and `&(mut) A` to `&B`. |
210 | /// To match `A` with `B`, autoderef will be performed, | |
211 | /// calling `deref`/`deref_mut` where necessary. | |
54a0048b SL |
212 | fn coerce_borrowed_pointer<'a, E, I>(&self, |
213 | exprs: &E, | |
214 | a: Ty<'tcx>, | |
215 | b: Ty<'tcx>, | |
216 | r_b: &'tcx ty::Region, | |
217 | mt_b: TypeAndMut<'tcx>) | |
218 | -> CoerceResult<'tcx> | |
219 | // FIXME(eddyb) use copyable iterators when that becomes ergonomic. | |
220 | where E: Fn() -> I, | |
221 | I: IntoIterator<Item=&'a hir::Expr> { | |
222 | ||
223 | debug!("coerce_borrowed_pointer(a={:?}, b={:?})", a, b); | |
1a4d82fc JJ |
224 | |
225 | // If we have a parameter of type `&M T_a` and the value | |
226 | // provided is `expr`, we will be adding an implicit borrow, | |
227 | // meaning that we convert `f(expr)` to `f(&M *expr)`. Therefore, | |
228 | // to type check, we will construct the type that `&M*expr` would | |
229 | // yield. | |
230 | ||
54a0048b SL |
231 | let (r_a, mt_a) = match a.sty { |
232 | ty::TyRef(r_a, mt_a) => { | |
233 | coerce_mutbls(mt_a.mutbl, mt_b.mutbl)?; | |
234 | (r_a, mt_a) | |
1a4d82fc | 235 | } |
54a0048b SL |
236 | _ => return self.unify_and_identity(a, b) |
237 | }; | |
1a4d82fc | 238 | |
54a0048b | 239 | let span = self.origin.span(); |
9346a6ac | 240 | |
54a0048b | 241 | let lvalue_pref = LvaluePreference::from_mutbl(mt_b.mutbl); |
85aaf69f | 242 | let mut first_error = None; |
54a0048b SL |
243 | let mut r_borrow_var = None; |
244 | let (_, autoderefs, success) = autoderef(self.fcx, span, a, exprs, | |
85aaf69f SL |
245 | UnresolvedTypeAction::Ignore, |
246 | lvalue_pref, | |
54a0048b SL |
247 | |referent_ty, autoderef| |
248 | { | |
85aaf69f SL |
249 | if autoderef == 0 { |
250 | // Don't let this pass, otherwise it would cause | |
251 | // &T to autoref to &&T. | |
252 | return None; | |
253 | } | |
54a0048b SL |
254 | |
255 | // At this point, we have deref'd `a` to `referent_ty`. So | |
256 | // imagine we are coercing from `&'a mut Vec<T>` to `&'b mut [T]`. | |
257 | // In the autoderef loop for `&'a mut Vec<T>`, we would get | |
258 | // three callbacks: | |
259 | // | |
260 | // - `&'a mut Vec<T>` -- 0 derefs, just ignore it | |
261 | // - `Vec<T>` -- 1 deref | |
262 | // - `[T]` -- 2 deref | |
263 | // | |
264 | // At each point after the first callback, we want to | |
265 | // check to see whether this would match out target type | |
266 | // (`&'b mut [T]`) if we autoref'd it. We can't just | |
267 | // compare the referent types, though, because we still | |
268 | // have to consider the mutability. E.g., in the case | |
269 | // we've been considering, we have an `&mut` reference, so | |
270 | // the `T` in `[T]` needs to be unified with equality. | |
271 | // | |
272 | // Therefore, we construct reference types reflecting what | |
273 | // the types will be after we do the final auto-ref and | |
274 | // compare those. Note that this means we use the target | |
275 | // mutability [1], since it may be that we are coercing | |
276 | // from `&mut T` to `&U`. | |
277 | // | |
278 | // One fine point concerns the region that we use. We | |
279 | // choose the region such that the region of the final | |
280 | // type that results from `unify` will be the region we | |
281 | // want for the autoref: | |
282 | // | |
283 | // - if in sub mode, that means we want to use `'b` (the | |
284 | // region from the target reference) for both | |
285 | // pointers [2]. This is because sub mode (somewhat | |
286 | // arbitrarily) returns the subtype region. In the case | |
287 | // where we are coercing to a target type, we know we | |
288 | // want to use that target type region (`'b`) because -- | |
289 | // for the program to type-check -- it must be the | |
290 | // smaller of the two. | |
291 | // - One fine point. It may be surprising that we can | |
292 | // use `'b` without relating `'a` and `'b`. The reason | |
293 | // that this is ok is that what we produce is | |
294 | // effectively a `&'b *x` expression (if you could | |
295 | // annotate the region of a borrow), and regionck has | |
296 | // code that adds edges from the region of a borrow | |
297 | // (`'b`, here) into the regions in the borrowed | |
298 | // expression (`*x`, here). (Search for "link".) | |
299 | // - if in lub mode, things can get fairly complicated. The | |
300 | // easiest thing is just to make a fresh | |
301 | // region variable [4], which effectively means we defer | |
302 | // the decision to region inference (and regionck, which will add | |
303 | // some more edges to this variable). However, this can wind up | |
304 | // creating a crippling number of variables in some cases -- | |
305 | // e.g. #32278 -- so we optimize one particular case [3]. | |
306 | // Let me try to explain with some examples: | |
307 | // - The "running example" above represents the simple case, | |
308 | // where we have one `&` reference at the outer level and | |
309 | // ownership all the rest of the way down. In this case, | |
310 | // we want `LUB('a, 'b)` as the resulting region. | |
311 | // - However, if there are nested borrows, that region is | |
312 | // too strong. Consider a coercion from `&'a &'x Rc<T>` to | |
313 | // `&'b T`. In this case, `'a` is actually irrelevant. | |
314 | // The pointer we want is `LUB('x, 'b`). If we choose `LUB('a,'b)` | |
315 | // we get spurious errors (`run-pass/regions-lub-ref-ref-rc.rs`). | |
316 | // (The errors actually show up in borrowck, typically, because | |
317 | // this extra edge causes the region `'a` to be inferred to something | |
318 | // too big, which then results in borrowck errors.) | |
319 | // - We could track the innermost shared reference, but there is already | |
320 | // code in regionck that has the job of creating links between | |
321 | // the region of a borrow and the regions in the thing being | |
322 | // borrowed (here, `'a` and `'x`), and it knows how to handle | |
323 | // all the various cases. So instead we just make a region variable | |
324 | // and let regionck figure it out. | |
325 | let r = if !self.use_lub { | |
326 | r_b // [2] above | |
327 | } else if autoderef == 1 { | |
328 | r_a // [3] above | |
85aaf69f | 329 | } else { |
54a0048b SL |
330 | if r_borrow_var.is_none() { // create var lazilly, at most once |
331 | let coercion = Coercion(span); | |
332 | let r = self.fcx.infcx().next_region_var(coercion); | |
333 | r_borrow_var = Some(self.tcx().mk_region(r)); // [4] above | |
334 | } | |
335 | r_borrow_var.unwrap() | |
336 | }; | |
337 | let derefd_ty_a = self.tcx().mk_ref(r, TypeAndMut { | |
338 | ty: referent_ty, | |
339 | mutbl: mt_b.mutbl // [1] above | |
340 | }); | |
341 | match self.unify(derefd_ty_a, b) { | |
342 | Ok(ty) => Some(ty), | |
343 | Err(err) => { | |
344 | if first_error.is_none() { | |
345 | first_error = Some(err); | |
346 | } | |
347 | None | |
348 | } | |
85aaf69f SL |
349 | } |
350 | }); | |
351 | ||
54a0048b SL |
352 | // Extract type or return an error. We return the first error |
353 | // we got, which should be from relating the "base" type | |
354 | // (e.g., in example above, the failure from relating `Vec<T>` | |
355 | // to the target type), since that should be the least | |
356 | // confusing. | |
357 | let ty = match success { | |
358 | Some(ty) => ty, | |
85aaf69f | 359 | None => { |
54a0048b SL |
360 | let err = first_error.expect("coerce_borrowed_pointer had no error"); |
361 | debug!("coerce_borrowed_pointer: failed with err = {:?}", err); | |
362 | return Err(err); | |
85aaf69f | 363 | } |
54a0048b SL |
364 | }; |
365 | ||
366 | // Now apply the autoref. We have to extract the region out of | |
367 | // the final ref type we got. | |
368 | if ty == a && mt_a.mutbl == hir::MutImmutable && autoderefs == 1 { | |
369 | // As a special case, if we would produce `&'a *x`, that's | |
370 | // a total no-op. We end up with the type `&'a T` just as | |
371 | // we started with. In that case, just skip it | |
372 | // altogether. This is just an optimization. | |
373 | // | |
374 | // Note that for `&mut`, we DO want to reborrow -- | |
375 | // otherwise, this would be a move, which might be an | |
376 | // error. For example `foo(self.x)` where `self` and | |
377 | // `self.x` both have `&mut `type would be a move of | |
378 | // `self.x`, but we auto-coerce it to `foo(&mut *self.x)`, | |
379 | // which is a borrow. | |
380 | assert_eq!(mt_b.mutbl, hir::MutImmutable); // can only coerce &T -> &U | |
381 | return self.identity(ty); | |
85aaf69f | 382 | } |
54a0048b SL |
383 | let r_borrow = match ty.sty { |
384 | ty::TyRef(r_borrow, _) => r_borrow, | |
385 | _ => span_bug!(span, "expected a ref type, got {:?}", ty) | |
386 | }; | |
387 | let autoref = Some(AutoPtr(r_borrow, mt_b.mutbl)); | |
388 | debug!("coerce_borrowed_pointer: succeeded ty={:?} autoderefs={:?} autoref={:?}", | |
389 | ty, autoderefs, autoref); | |
390 | Ok((ty, AdjustDerefRef(AutoDerefRef { | |
391 | autoderefs: autoderefs, | |
392 | autoref: autoref, | |
393 | unsize: None | |
394 | }))) | |
1a4d82fc JJ |
395 | } |
396 | ||
397 | ||
62682a34 SL |
398 | // &[T; n] or &mut [T; n] -> &[T] |
399 | // or &mut [T; n] -> &mut [T] | |
1a4d82fc JJ |
400 | // or &Concrete -> &Trait, etc. |
401 | fn coerce_unsized(&self, | |
d9579d0f AL |
402 | source: Ty<'tcx>, |
403 | target: Ty<'tcx>) | |
1a4d82fc | 404 | -> CoerceResult<'tcx> { |
62682a34 SL |
405 | debug!("coerce_unsized(source={:?}, target={:?})", |
406 | source, | |
407 | target); | |
d9579d0f AL |
408 | |
409 | let traits = (self.tcx().lang_items.unsize_trait(), | |
410 | self.tcx().lang_items.coerce_unsized_trait()); | |
411 | let (unsize_did, coerce_unsized_did) = if let (Some(u), Some(cu)) = traits { | |
412 | (u, cu) | |
413 | } else { | |
414 | debug!("Missing Unsize or CoerceUnsized traits"); | |
c1a9b12d | 415 | return Err(TypeError::Mismatch); |
d9579d0f | 416 | }; |
1a4d82fc JJ |
417 | |
418 | // Note, we want to avoid unnecessary unsizing. We don't want to coerce to | |
419 | // a DST unless we have to. This currently comes out in the wash since | |
420 | // we can't unify [T] with U. But to properly support DST, we need to allow | |
d9579d0f | 421 | // that, at which point we will need extra checks on the target here. |
1a4d82fc | 422 | |
d9579d0f AL |
423 | // Handle reborrows before selecting `Source: CoerceUnsized<Target>`. |
424 | let (source, reborrow) = match (&source.sty, &target.sty) { | |
62682a34 | 425 | (&ty::TyRef(_, mt_a), &ty::TyRef(_, mt_b)) => { |
54a0048b | 426 | coerce_mutbls(mt_a.mutbl, mt_b.mutbl)?; |
d9579d0f AL |
427 | |
428 | let coercion = Coercion(self.origin.span()); | |
429 | let r_borrow = self.fcx.infcx().next_region_var(coercion); | |
430 | let region = self.tcx().mk_region(r_borrow); | |
e9174d1e | 431 | (mt_a.ty, Some(AutoPtr(region, mt_b.mutbl))) |
1a4d82fc | 432 | } |
62682a34 | 433 | (&ty::TyRef(_, mt_a), &ty::TyRawPtr(mt_b)) => { |
54a0048b | 434 | coerce_mutbls(mt_a.mutbl, mt_b.mutbl)?; |
e9174d1e | 435 | (mt_a.ty, Some(AutoUnsafe(mt_b.mutbl))) |
1a4d82fc | 436 | } |
d9579d0f AL |
437 | _ => (source, None) |
438 | }; | |
c1a9b12d | 439 | let source = source.adjust_for_autoref(self.tcx(), reborrow); |
d9579d0f | 440 | |
c1a9b12d | 441 | let mut selcx = traits::SelectionContext::new(self.fcx.infcx()); |
d9579d0f AL |
442 | |
443 | // Use a FIFO queue for this custom fulfillment procedure. | |
444 | let mut queue = VecDeque::new(); | |
445 | let mut leftover_predicates = vec![]; | |
446 | ||
447 | // Create an obligation for `Source: CoerceUnsized<Target>`. | |
448 | let cause = ObligationCause::misc(self.origin.span(), self.fcx.body_id); | |
449 | queue.push_back(predicate_for_trait_def(self.tcx(), | |
450 | cause, | |
451 | coerce_unsized_did, | |
452 | 0, | |
453 | source, | |
454 | vec![target])); | |
455 | ||
456 | // Keep resolving `CoerceUnsized` and `Unsize` predicates to avoid | |
457 | // emitting a coercion in cases like `Foo<$1>` -> `Foo<$2>`, where | |
458 | // inference might unify those two inner type variables later. | |
459 | let traits = [coerce_unsized_did, unsize_did]; | |
460 | while let Some(obligation) = queue.pop_front() { | |
62682a34 | 461 | debug!("coerce_unsized resolve step: {:?}", obligation); |
d9579d0f AL |
462 | let trait_ref = match obligation.predicate { |
463 | ty::Predicate::Trait(ref tr) if traits.contains(&tr.def_id()) => { | |
464 | tr.clone() | |
465 | } | |
466 | _ => { | |
467 | leftover_predicates.push(obligation); | |
468 | continue; | |
469 | } | |
470 | }; | |
471 | match selcx.select(&obligation.with(trait_ref)) { | |
472 | // Uncertain or unimplemented. | |
473 | Ok(None) | Err(traits::Unimplemented) => { | |
474 | debug!("coerce_unsized: early return - can't prove obligation"); | |
c1a9b12d | 475 | return Err(TypeError::Mismatch); |
c34b1796 | 476 | } |
d9579d0f AL |
477 | |
478 | // Object safety violations or miscellaneous. | |
479 | Err(err) => { | |
480 | report_selection_error(self.fcx.infcx(), &obligation, &err); | |
481 | // Treat this like an obligation and follow through | |
482 | // with the unsizing - the lack of a coercion should | |
483 | // be silent, as it causes a type mismatch later. | |
484 | } | |
485 | ||
486 | Ok(Some(vtable)) => { | |
62682a34 SL |
487 | for obligation in vtable.nested_obligations() { |
488 | queue.push_back(obligation); | |
489 | } | |
d9579d0f | 490 | } |
1a4d82fc | 491 | } |
d9579d0f AL |
492 | } |
493 | ||
54a0048b | 494 | *self.unsizing_obligations.borrow_mut() = leftover_predicates; |
9346a6ac | 495 | |
9346a6ac AL |
496 | let adjustment = AutoDerefRef { |
497 | autoderefs: if reborrow.is_some() { 1 } else { 0 }, | |
498 | autoref: reborrow, | |
499 | unsize: Some(target) | |
500 | }; | |
62682a34 | 501 | debug!("Success, coerced with {:?}", adjustment); |
54a0048b | 502 | Ok((target, AdjustDerefRef(adjustment))) |
1a4d82fc JJ |
503 | } |
504 | ||
c34b1796 AL |
505 | fn coerce_from_fn_pointer(&self, |
506 | a: Ty<'tcx>, | |
507 | fn_ty_a: &'tcx ty::BareFnTy<'tcx>, | |
508 | b: Ty<'tcx>) | |
509 | -> CoerceResult<'tcx> | |
510 | { | |
511 | /*! | |
512 | * Attempts to coerce from the type of a Rust function item | |
513 | * into a closure or a `proc`. | |
514 | */ | |
515 | ||
54a0048b SL |
516 | let b = self.fcx.infcx().shallow_resolve(b); |
517 | debug!("coerce_from_fn_pointer(a={:?}, b={:?})", a, b); | |
c34b1796 | 518 | |
54a0048b SL |
519 | if let ty::TyFnPtr(fn_ty_b) = b.sty { |
520 | match (fn_ty_a.unsafety, fn_ty_b.unsafety) { | |
521 | (hir::Unsafety::Normal, hir::Unsafety::Unsafe) => { | |
522 | let unsafe_a = self.tcx().safe_to_unsafe_fn_ty(fn_ty_a); | |
523 | return self.unify_and_identity(unsafe_a, b).map(|(ty, _)| { | |
524 | (ty, AdjustUnsafeFnPointer) | |
525 | }); | |
1a4d82fc | 526 | } |
54a0048b | 527 | _ => {} |
1a4d82fc | 528 | } |
54a0048b SL |
529 | } |
530 | self.unify_and_identity(a, b) | |
1a4d82fc JJ |
531 | } |
532 | ||
1a4d82fc JJ |
533 | fn coerce_from_fn_item(&self, |
534 | a: Ty<'tcx>, | |
1a4d82fc JJ |
535 | fn_ty_a: &'tcx ty::BareFnTy<'tcx>, |
536 | b: Ty<'tcx>) | |
537 | -> CoerceResult<'tcx> { | |
538 | /*! | |
539 | * Attempts to coerce from the type of a Rust function item | |
540 | * into a closure or a `proc`. | |
541 | */ | |
542 | ||
54a0048b SL |
543 | let b = self.fcx.infcx().shallow_resolve(b); |
544 | debug!("coerce_from_fn_item(a={:?}, b={:?})", a, b); | |
1a4d82fc | 545 | |
54a0048b SL |
546 | match b.sty { |
547 | ty::TyFnPtr(_) => { | |
548 | let a_fn_pointer = self.tcx().mk_ty(ty::TyFnPtr(fn_ty_a)); | |
549 | self.unify_and_identity(a_fn_pointer, b).map(|(ty, _)| { | |
550 | (ty, AdjustReifyFnPointer) | |
551 | }) | |
1a4d82fc | 552 | } |
54a0048b SL |
553 | _ => self.unify_and_identity(a, b) |
554 | } | |
1a4d82fc JJ |
555 | } |
556 | ||
85aaf69f SL |
557 | fn coerce_unsafe_ptr(&self, |
558 | a: Ty<'tcx>, | |
559 | b: Ty<'tcx>, | |
e9174d1e | 560 | mutbl_b: hir::Mutability) |
85aaf69f | 561 | -> CoerceResult<'tcx> { |
62682a34 SL |
562 | debug!("coerce_unsafe_ptr(a={:?}, b={:?})", |
563 | a, | |
564 | b); | |
1a4d82fc | 565 | |
62682a34 SL |
566 | let (is_ref, mt_a) = match a.sty { |
567 | ty::TyRef(_, mt) => (true, mt), | |
568 | ty::TyRawPtr(mt) => (false, mt), | |
1a4d82fc | 569 | _ => { |
54a0048b | 570 | return self.unify_and_identity(a, b); |
1a4d82fc JJ |
571 | } |
572 | }; | |
573 | ||
574 | // Check that the types which they point at are compatible. | |
c1a9b12d | 575 | let a_unsafe = self.tcx().mk_ptr(ty::TypeAndMut{ mutbl: mutbl_b, ty: mt_a.ty }); |
54a0048b SL |
576 | let (ty, noop) = self.unify_and_identity(a_unsafe, b)?; |
577 | coerce_mutbls(mt_a.mutbl, mutbl_b)?; | |
1a4d82fc JJ |
578 | |
579 | // Although references and unsafe ptrs have the same | |
580 | // representation, we still register an AutoDerefRef so that | |
581 | // regionck knows that the region for `a` must be valid here. | |
54a0048b SL |
582 | Ok((ty, if is_ref { |
583 | AdjustDerefRef(AutoDerefRef { | |
62682a34 | 584 | autoderefs: 1, |
e9174d1e | 585 | autoref: Some(AutoUnsafe(mutbl_b)), |
62682a34 | 586 | unsize: None |
54a0048b | 587 | }) |
7453a54e | 588 | } else if mt_a.mutbl != mutbl_b { |
54a0048b | 589 | AdjustMutToConstPointer |
62682a34 | 590 | } else { |
54a0048b SL |
591 | noop |
592 | })) | |
1a4d82fc JJ |
593 | } |
594 | } | |
595 | ||
54a0048b SL |
596 | fn apply<'a, 'b, 'tcx, E, I>(coerce: &mut Coerce<'a, 'tcx>, |
597 | exprs: &E, | |
85aaf69f SL |
598 | a: Ty<'tcx>, |
599 | b: Ty<'tcx>) | |
54a0048b SL |
600 | -> CoerceResult<'tcx> |
601 | where E: Fn() -> I, | |
602 | I: IntoIterator<Item=&'b hir::Expr> { | |
9346a6ac | 603 | |
54a0048b SL |
604 | let (ty, adjustment) = indent(|| coerce.coerce(exprs, a, b))?; |
605 | ||
606 | let fcx = coerce.fcx; | |
607 | if let AdjustDerefRef(auto) = adjustment { | |
d9579d0f | 608 | if auto.unsize.is_some() { |
54a0048b SL |
609 | let mut obligations = coerce.unsizing_obligations.borrow_mut(); |
610 | for obligation in obligations.drain(..) { | |
d9579d0f | 611 | fcx.register_predicate(obligation); |
9346a6ac AL |
612 | } |
613 | } | |
614 | } | |
615 | ||
54a0048b | 616 | Ok((ty, adjustment)) |
85aaf69f SL |
617 | } |
618 | ||
54a0048b SL |
619 | /// Attempt to coerce an expression to a type, and return the |
620 | /// adjusted type of the expression, if successful. | |
621 | /// Adjustments are only recorded if the coercion succeeded. | |
622 | /// The expressions *must not* have any pre-existing adjustments. | |
623 | pub fn try<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>, | |
624 | expr: &hir::Expr, | |
625 | target: Ty<'tcx>) | |
626 | -> RelateResult<'tcx, Ty<'tcx>> { | |
627 | let source = fcx.resolve_type_vars_if_possible(fcx.expr_ty(expr)); | |
628 | debug!("coercion::try({:?}: {:?} -> {:?})", expr, source, target); | |
629 | ||
630 | let mut coerce = Coerce::new(fcx, TypeOrigin::ExprAssignable(expr.span)); | |
631 | fcx.infcx().commit_if_ok(|_| { | |
632 | let (ty, adjustment) = | |
633 | apply(&mut coerce, &|| Some(expr), source, target)?; | |
634 | if !adjustment.is_identity() { | |
635 | debug!("Success, coerced with {:?}", adjustment); | |
636 | assert!(!fcx.inh.tables.borrow().adjustments.contains_key(&expr.id)); | |
637 | fcx.write_adjustment(expr.id, adjustment); | |
638 | } | |
639 | Ok(ty) | |
640 | }) | |
641 | } | |
642 | ||
643 | /// Given some expressions, their known unified type and another expression, | |
644 | /// tries to unify the types, potentially inserting coercions on any of the | |
645 | /// provided expressions and returns their LUB (aka "common supertype"). | |
646 | pub fn try_find_lub<'a, 'b, 'tcx, E, I>(fcx: &FnCtxt<'a, 'tcx>, | |
647 | origin: TypeOrigin, | |
648 | exprs: E, | |
649 | prev_ty: Ty<'tcx>, | |
650 | new: &'b hir::Expr) | |
651 | -> RelateResult<'tcx, Ty<'tcx>> | |
652 | // FIXME(eddyb) use copyable iterators when that becomes ergonomic. | |
653 | where E: Fn() -> I, | |
654 | I: IntoIterator<Item=&'b hir::Expr> { | |
655 | ||
656 | let prev_ty = fcx.resolve_type_vars_if_possible(prev_ty); | |
657 | let new_ty = fcx.resolve_type_vars_if_possible(fcx.expr_ty(new)); | |
658 | debug!("coercion::try_find_lub({:?}, {:?})", prev_ty, new_ty); | |
659 | ||
660 | let trace = TypeTrace::types(origin, true, prev_ty, new_ty); | |
661 | ||
662 | // Special-case that coercion alone cannot handle: | |
663 | // Two function item types of differing IDs or Substs. | |
664 | match (&prev_ty.sty, &new_ty.sty) { | |
665 | (&ty::TyFnDef(a_def_id, a_substs, a_fty), | |
666 | &ty::TyFnDef(b_def_id, b_substs, b_fty)) => { | |
667 | // The signature must always match. | |
668 | let fty = fcx.infcx().lub(true, trace.clone(), a_fty, b_fty) | |
669 | .map(|InferOk { value, obligations }| { | |
670 | // FIXME(#32730) propagate obligations | |
671 | assert!(obligations.is_empty()); | |
672 | value | |
673 | })?; | |
674 | ||
675 | if a_def_id == b_def_id { | |
676 | // Same function, maybe the parameters match. | |
677 | let substs = fcx.infcx().commit_if_ok(|_| { | |
678 | fcx.infcx().lub(true, trace.clone(), a_substs, b_substs) | |
679 | .map(|InferOk { value, obligations }| { | |
680 | // FIXME(#32730) propagate obligations | |
681 | assert!(obligations.is_empty()); | |
682 | value | |
683 | }) | |
684 | }).map(|s| fcx.tcx().mk_substs(s)); | |
685 | ||
686 | if let Ok(substs) = substs { | |
687 | // We have a LUB of prev_ty and new_ty, just return it. | |
688 | return Ok(fcx.tcx().mk_fn_def(a_def_id, substs, fty)); | |
689 | } | |
690 | } | |
691 | ||
692 | // Reify both sides and return the reified fn pointer type. | |
693 | for expr in exprs().into_iter().chain(Some(new)) { | |
694 | // No adjustments can produce a fn item, so this should never trip. | |
695 | assert!(!fcx.inh.tables.borrow().adjustments.contains_key(&expr.id)); | |
696 | fcx.write_adjustment(expr.id, AdjustReifyFnPointer); | |
697 | } | |
698 | return Ok(fcx.tcx().mk_fn_ptr(fty)); | |
699 | } | |
700 | _ => {} | |
701 | } | |
702 | ||
703 | let mut coerce = Coerce::new(fcx, origin); | |
704 | coerce.use_lub = true; | |
705 | ||
706 | // First try to coerce the new expression to the type of the previous ones, | |
707 | // but only if the new expression has no coercion already applied to it. | |
708 | let mut first_error = None; | |
709 | if !fcx.inh.tables.borrow().adjustments.contains_key(&new.id) { | |
710 | let result = fcx.infcx().commit_if_ok(|_| { | |
711 | apply(&mut coerce, &|| Some(new), new_ty, prev_ty) | |
712 | }); | |
713 | match result { | |
714 | Ok((ty, adjustment)) => { | |
715 | if !adjustment.is_identity() { | |
716 | fcx.write_adjustment(new.id, adjustment); | |
717 | } | |
718 | return Ok(ty); | |
719 | } | |
720 | Err(e) => first_error = Some(e) | |
721 | } | |
722 | } | |
723 | ||
724 | // Then try to coerce the previous expressions to the type of the new one. | |
725 | // This requires ensuring there are no coercions applied to *any* of the | |
726 | // previous expressions, other than noop reborrows (ignoring lifetimes). | |
727 | for expr in exprs() { | |
728 | let noop = match fcx.inh.tables.borrow().adjustments.get(&expr.id) { | |
729 | Some(&AdjustDerefRef(AutoDerefRef { | |
730 | autoderefs: 1, | |
731 | autoref: Some(AutoPtr(_, mutbl_adj)), | |
732 | unsize: None | |
733 | })) => match fcx.expr_ty(expr).sty { | |
734 | ty::TyRef(_, mt_orig) => { | |
735 | // Reborrow that we can safely ignore. | |
736 | mutbl_adj == mt_orig.mutbl | |
737 | } | |
738 | _ => false | |
739 | }, | |
740 | Some(_) => false, | |
741 | None => true | |
742 | }; | |
743 | ||
744 | if !noop { | |
745 | return fcx.infcx().commit_if_ok(|_| { | |
746 | fcx.infcx().lub(true, trace.clone(), &prev_ty, &new_ty) | |
747 | .map(|InferOk { value, obligations }| { | |
748 | // FIXME(#32730) propagate obligations | |
749 | assert!(obligations.is_empty()); | |
750 | value | |
751 | }) | |
752 | }); | |
753 | } | |
754 | } | |
755 | ||
756 | match fcx.infcx().commit_if_ok(|_| apply(&mut coerce, &exprs, prev_ty, new_ty)) { | |
757 | Err(_) => { | |
758 | // Avoid giving strange errors on failed attempts. | |
759 | if let Some(e) = first_error { | |
760 | Err(e) | |
761 | } else { | |
762 | fcx.infcx().commit_if_ok(|_| { | |
763 | fcx.infcx().lub(true, trace, &prev_ty, &new_ty) | |
764 | .map(|InferOk { value, obligations }| { | |
765 | // FIXME(#32730) propagate obligations | |
766 | assert!(obligations.is_empty()); | |
767 | value | |
768 | }) | |
769 | }) | |
770 | } | |
771 | } | |
772 | Ok((ty, adjustment)) => { | |
773 | if !adjustment.is_identity() { | |
774 | for expr in exprs() { | |
775 | fcx.write_adjustment(expr.id, adjustment); | |
776 | } | |
777 | } | |
778 | Ok(ty) | |
779 | } | |
1a4d82fc JJ |
780 | } |
781 | } |