diff options
Diffstat (limited to 'crates/ra_hir/src/ty/infer/coerce.rs')
-rw-r--r-- | crates/ra_hir/src/ty/infer/coerce.rs | 336 |
1 files changed, 336 insertions, 0 deletions
diff --git a/crates/ra_hir/src/ty/infer/coerce.rs b/crates/ra_hir/src/ty/infer/coerce.rs new file mode 100644 index 000000000..0429a9866 --- /dev/null +++ b/crates/ra_hir/src/ty/infer/coerce.rs | |||
@@ -0,0 +1,336 @@ | |||
1 | //! Coercion logic. Coercions are certain type conversions that can implicitly | ||
2 | //! happen in certain places, e.g. weakening `&mut` to `&` or deref coercions | ||
3 | //! like going from `&Vec<T>` to `&[T]`. | ||
4 | //! | ||
5 | //! See: https://doc.rust-lang.org/nomicon/coercions.html | ||
6 | |||
7 | use rustc_hash::FxHashMap; | ||
8 | |||
9 | use test_utils::tested_by; | ||
10 | |||
11 | use super::{InferTy, InferenceContext, TypeVarValue}; | ||
12 | use crate::{ | ||
13 | db::HirDatabase, | ||
14 | lang_item::LangItemTarget, | ||
15 | resolve::Resolver, | ||
16 | ty::{autoderef, Substs, Ty, TypeCtor, TypeWalk}, | ||
17 | type_ref::Mutability, | ||
18 | Adt, | ||
19 | }; | ||
20 | |||
21 | impl<'a, D: HirDatabase> InferenceContext<'a, D> { | ||
22 | /// Unify two types, but may coerce the first one to the second one | ||
23 | /// using "implicit coercion rules" if needed. | ||
24 | pub(super) fn coerce(&mut self, from_ty: &Ty, to_ty: &Ty) -> bool { | ||
25 | let from_ty = self.resolve_ty_shallow(from_ty).into_owned(); | ||
26 | let to_ty = self.resolve_ty_shallow(to_ty); | ||
27 | self.coerce_inner(from_ty, &to_ty) | ||
28 | } | ||
29 | |||
30 | /// Merge two types from different branches, with possible implicit coerce. | ||
31 | /// | ||
32 | /// Note that it is only possible that one type are coerced to another. | ||
33 | /// Coercing both types to another least upper bound type is not possible in rustc, | ||
34 | /// which will simply result in "incompatible types" error. | ||
35 | pub(super) fn coerce_merge_branch<'t>(&mut self, ty1: &Ty, ty2: &Ty) -> Ty { | ||
36 | if self.coerce(ty1, ty2) { | ||
37 | ty2.clone() | ||
38 | } else if self.coerce(ty2, ty1) { | ||
39 | ty1.clone() | ||
40 | } else { | ||
41 | tested_by!(coerce_merge_fail_fallback); | ||
42 | // For incompatible types, we use the latter one as result | ||
43 | // to be better recovery for `if` without `else`. | ||
44 | ty2.clone() | ||
45 | } | ||
46 | } | ||
47 | |||
48 | pub(super) fn init_coerce_unsized_map( | ||
49 | db: &'a D, | ||
50 | resolver: &Resolver, | ||
51 | ) -> FxHashMap<(TypeCtor, TypeCtor), usize> { | ||
52 | let krate = resolver.krate().unwrap(); | ||
53 | let impls = match db.lang_item(krate, "coerce_unsized".into()) { | ||
54 | Some(LangItemTarget::Trait(trait_)) => db.impls_for_trait(krate, trait_), | ||
55 | _ => return FxHashMap::default(), | ||
56 | }; | ||
57 | |||
58 | impls | ||
59 | .iter() | ||
60 | .filter_map(|impl_block| { | ||
61 | // `CoerseUnsized` has one generic parameter for the target type. | ||
62 | let trait_ref = impl_block.target_trait_ref(db)?; | ||
63 | let cur_from_ty = trait_ref.substs.0.get(0)?; | ||
64 | let cur_to_ty = trait_ref.substs.0.get(1)?; | ||
65 | |||
66 | match (&cur_from_ty, cur_to_ty) { | ||
67 | (ty_app!(ctor1, st1), ty_app!(ctor2, st2)) => { | ||
68 | // FIXME: We return the first non-equal bound as the type parameter to coerce to unsized type. | ||
69 | // This works for smart-pointer-like coercion, which covers all impls from std. | ||
70 | st1.iter().zip(st2.iter()).enumerate().find_map(|(i, (ty1, ty2))| { | ||
71 | match (ty1, ty2) { | ||
72 | (Ty::Param { idx: p1, .. }, Ty::Param { idx: p2, .. }) | ||
73 | if p1 != p2 => | ||
74 | { | ||
75 | Some(((*ctor1, *ctor2), i)) | ||
76 | } | ||
77 | _ => None, | ||
78 | } | ||
79 | }) | ||
80 | } | ||
81 | _ => None, | ||
82 | } | ||
83 | }) | ||
84 | .collect() | ||
85 | } | ||
86 | |||
87 | fn coerce_inner(&mut self, mut from_ty: Ty, to_ty: &Ty) -> bool { | ||
88 | match (&from_ty, to_ty) { | ||
89 | // Never type will make type variable to fallback to Never Type instead of Unknown. | ||
90 | (ty_app!(TypeCtor::Never), Ty::Infer(InferTy::TypeVar(tv))) => { | ||
91 | let var = self.new_maybe_never_type_var(); | ||
92 | self.var_unification_table.union_value(*tv, TypeVarValue::Known(var)); | ||
93 | return true; | ||
94 | } | ||
95 | (ty_app!(TypeCtor::Never), _) => return true, | ||
96 | |||
97 | // Trivial cases, this should go after `never` check to | ||
98 | // avoid infer result type to be never | ||
99 | _ => { | ||
100 | if self.unify_inner_trivial(&from_ty, &to_ty) { | ||
101 | return true; | ||
102 | } | ||
103 | } | ||
104 | } | ||
105 | |||
106 | // Pointer weakening and function to pointer | ||
107 | match (&mut from_ty, to_ty) { | ||
108 | // `*mut T`, `&mut T, `&T`` -> `*const T` | ||
109 | // `&mut T` -> `&T` | ||
110 | // `&mut T` -> `*mut T` | ||
111 | (ty_app!(c1@TypeCtor::RawPtr(_)), ty_app!(c2@TypeCtor::RawPtr(Mutability::Shared))) | ||
112 | | (ty_app!(c1@TypeCtor::Ref(_)), ty_app!(c2@TypeCtor::RawPtr(Mutability::Shared))) | ||
113 | | (ty_app!(c1@TypeCtor::Ref(_)), ty_app!(c2@TypeCtor::Ref(Mutability::Shared))) | ||
114 | | (ty_app!(c1@TypeCtor::Ref(Mutability::Mut)), ty_app!(c2@TypeCtor::RawPtr(_))) => { | ||
115 | *c1 = *c2; | ||
116 | } | ||
117 | |||
118 | // Illegal mutablity conversion | ||
119 | ( | ||
120 | ty_app!(TypeCtor::RawPtr(Mutability::Shared)), | ||
121 | ty_app!(TypeCtor::RawPtr(Mutability::Mut)), | ||
122 | ) | ||
123 | | ( | ||
124 | ty_app!(TypeCtor::Ref(Mutability::Shared)), | ||
125 | ty_app!(TypeCtor::Ref(Mutability::Mut)), | ||
126 | ) => return false, | ||
127 | |||
128 | // `{function_type}` -> `fn()` | ||
129 | (ty_app!(TypeCtor::FnDef(_)), ty_app!(TypeCtor::FnPtr { .. })) => { | ||
130 | match from_ty.callable_sig(self.db) { | ||
131 | None => return false, | ||
132 | Some(sig) => { | ||
133 | let num_args = sig.params_and_return.len() as u16 - 1; | ||
134 | from_ty = | ||
135 | Ty::apply(TypeCtor::FnPtr { num_args }, Substs(sig.params_and_return)); | ||
136 | } | ||
137 | } | ||
138 | } | ||
139 | |||
140 | _ => {} | ||
141 | } | ||
142 | |||
143 | if let Some(ret) = self.try_coerce_unsized(&from_ty, &to_ty) { | ||
144 | return ret; | ||
145 | } | ||
146 | |||
147 | // Auto Deref if cannot coerce | ||
148 | match (&from_ty, to_ty) { | ||
149 | // FIXME: DerefMut | ||
150 | (ty_app!(TypeCtor::Ref(_), st1), ty_app!(TypeCtor::Ref(_), st2)) => { | ||
151 | self.unify_autoderef_behind_ref(&st1[0], &st2[0]) | ||
152 | } | ||
153 | |||
154 | // Otherwise, normal unify | ||
155 | _ => self.unify(&from_ty, to_ty), | ||
156 | } | ||
157 | } | ||
158 | |||
159 | /// Coerce a type using `from_ty: CoerceUnsized<ty_ty>` | ||
160 | /// | ||
161 | /// See: https://doc.rust-lang.org/nightly/std/marker/trait.CoerceUnsized.html | ||
162 | fn try_coerce_unsized(&mut self, from_ty: &Ty, to_ty: &Ty) -> Option<bool> { | ||
163 | let (ctor1, st1, ctor2, st2) = match (from_ty, to_ty) { | ||
164 | (ty_app!(ctor1, st1), ty_app!(ctor2, st2)) => (ctor1, st1, ctor2, st2), | ||
165 | _ => return None, | ||
166 | }; | ||
167 | |||
168 | let coerce_generic_index = *self.coerce_unsized_map.get(&(*ctor1, *ctor2))?; | ||
169 | |||
170 | // Check `Unsize` first | ||
171 | match self.check_unsize_and_coerce( | ||
172 | st1.0.get(coerce_generic_index)?, | ||
173 | st2.0.get(coerce_generic_index)?, | ||
174 | 0, | ||
175 | ) { | ||
176 | Some(true) => {} | ||
177 | ret => return ret, | ||
178 | } | ||
179 | |||
180 | let ret = st1 | ||
181 | .iter() | ||
182 | .zip(st2.iter()) | ||
183 | .enumerate() | ||
184 | .filter(|&(idx, _)| idx != coerce_generic_index) | ||
185 | .all(|(_, (ty1, ty2))| self.unify(ty1, ty2)); | ||
186 | |||
187 | Some(ret) | ||
188 | } | ||
189 | |||
190 | /// Check if `from_ty: Unsize<to_ty>`, and coerce to `to_ty` if it holds. | ||
191 | /// | ||
192 | /// It should not be directly called. It is only used by `try_coerce_unsized`. | ||
193 | /// | ||
194 | /// See: https://doc.rust-lang.org/nightly/std/marker/trait.Unsize.html | ||
195 | fn check_unsize_and_coerce(&mut self, from_ty: &Ty, to_ty: &Ty, depth: usize) -> Option<bool> { | ||
196 | if depth > 1000 { | ||
197 | panic!("Infinite recursion in coercion"); | ||
198 | } | ||
199 | |||
200 | match (&from_ty, &to_ty) { | ||
201 | // `[T; N]` -> `[T]` | ||
202 | (ty_app!(TypeCtor::Array, st1), ty_app!(TypeCtor::Slice, st2)) => { | ||
203 | Some(self.unify(&st1[0], &st2[0])) | ||
204 | } | ||
205 | |||
206 | // `T` -> `dyn Trait` when `T: Trait` | ||
207 | (_, Ty::Dyn(_)) => { | ||
208 | // FIXME: Check predicates | ||
209 | Some(true) | ||
210 | } | ||
211 | |||
212 | // `(..., T)` -> `(..., U)` when `T: Unsize<U>` | ||
213 | ( | ||
214 | ty_app!(TypeCtor::Tuple { cardinality: len1 }, st1), | ||
215 | ty_app!(TypeCtor::Tuple { cardinality: len2 }, st2), | ||
216 | ) => { | ||
217 | if len1 != len2 || *len1 == 0 { | ||
218 | return None; | ||
219 | } | ||
220 | |||
221 | match self.check_unsize_and_coerce( | ||
222 | st1.last().unwrap(), | ||
223 | st2.last().unwrap(), | ||
224 | depth + 1, | ||
225 | ) { | ||
226 | Some(true) => {} | ||
227 | ret => return ret, | ||
228 | } | ||
229 | |||
230 | let ret = st1[..st1.len() - 1] | ||
231 | .iter() | ||
232 | .zip(&st2[..st2.len() - 1]) | ||
233 | .all(|(ty1, ty2)| self.unify(ty1, ty2)); | ||
234 | |||
235 | Some(ret) | ||
236 | } | ||
237 | |||
238 | // Foo<..., T, ...> is Unsize<Foo<..., U, ...>> if: | ||
239 | // - T: Unsize<U> | ||
240 | // - Foo is a struct | ||
241 | // - Only the last field of Foo has a type involving T | ||
242 | // - T is not part of the type of any other fields | ||
243 | // - Bar<T>: Unsize<Bar<U>>, if the last field of Foo has type Bar<T> | ||
244 | ( | ||
245 | ty_app!(TypeCtor::Adt(Adt::Struct(struct1)), st1), | ||
246 | ty_app!(TypeCtor::Adt(Adt::Struct(struct2)), st2), | ||
247 | ) if struct1 == struct2 => { | ||
248 | let fields = struct1.fields(self.db); | ||
249 | let (last_field, prev_fields) = fields.split_last()?; | ||
250 | |||
251 | // Get the generic parameter involved in the last field. | ||
252 | let unsize_generic_index = { | ||
253 | let mut index = None; | ||
254 | let mut multiple_param = false; | ||
255 | last_field.ty(self.db).walk(&mut |ty| match ty { | ||
256 | &Ty::Param { idx, .. } => { | ||
257 | if index.is_none() { | ||
258 | index = Some(idx); | ||
259 | } else if Some(idx) != index { | ||
260 | multiple_param = true; | ||
261 | } | ||
262 | } | ||
263 | _ => {} | ||
264 | }); | ||
265 | |||
266 | if multiple_param { | ||
267 | return None; | ||
268 | } | ||
269 | index? | ||
270 | }; | ||
271 | |||
272 | // Check other fields do not involve it. | ||
273 | let mut multiple_used = false; | ||
274 | prev_fields.iter().for_each(|field| { | ||
275 | field.ty(self.db).walk(&mut |ty| match ty { | ||
276 | &Ty::Param { idx, .. } if idx == unsize_generic_index => { | ||
277 | multiple_used = true | ||
278 | } | ||
279 | _ => {} | ||
280 | }) | ||
281 | }); | ||
282 | if multiple_used { | ||
283 | return None; | ||
284 | } | ||
285 | |||
286 | let unsize_generic_index = unsize_generic_index as usize; | ||
287 | |||
288 | // Check `Unsize` first | ||
289 | match self.check_unsize_and_coerce( | ||
290 | st1.get(unsize_generic_index)?, | ||
291 | st2.get(unsize_generic_index)?, | ||
292 | depth + 1, | ||
293 | ) { | ||
294 | Some(true) => {} | ||
295 | ret => return ret, | ||
296 | } | ||
297 | |||
298 | // Then unify other parameters | ||
299 | let ret = st1 | ||
300 | .iter() | ||
301 | .zip(st2.iter()) | ||
302 | .enumerate() | ||
303 | .filter(|&(idx, _)| idx != unsize_generic_index) | ||
304 | .all(|(_, (ty1, ty2))| self.unify(ty1, ty2)); | ||
305 | |||
306 | Some(ret) | ||
307 | } | ||
308 | |||
309 | _ => None, | ||
310 | } | ||
311 | } | ||
312 | |||
313 | /// Unify `from_ty` to `to_ty` with optional auto Deref | ||
314 | /// | ||
315 | /// Note that the parameters are already stripped the outer reference. | ||
316 | fn unify_autoderef_behind_ref(&mut self, from_ty: &Ty, to_ty: &Ty) -> bool { | ||
317 | let canonicalized = self.canonicalizer().canonicalize_ty(from_ty.clone()); | ||
318 | let to_ty = self.resolve_ty_shallow(&to_ty); | ||
319 | // FIXME: Auto DerefMut | ||
320 | for derefed_ty in | ||
321 | autoderef::autoderef(self.db, &self.resolver.clone(), canonicalized.value.clone()) | ||
322 | { | ||
323 | let derefed_ty = canonicalized.decanonicalize_ty(derefed_ty.value); | ||
324 | match (&*self.resolve_ty_shallow(&derefed_ty), &*to_ty) { | ||
325 | // Stop when constructor matches. | ||
326 | (ty_app!(from_ctor, st1), ty_app!(to_ctor, st2)) if from_ctor == to_ctor => { | ||
327 | // It will not recurse to `coerce`. | ||
328 | return self.unify_substs(st1, st2, 0); | ||
329 | } | ||
330 | _ => {} | ||
331 | } | ||
332 | } | ||
333 | |||
334 | false | ||
335 | } | ||
336 | } | ||