From 6a77ec7bbe6ddbf663dce9529d11d1bb56c5489a Mon Sep 17 00:00:00 2001 From: Aleksey Kladov Date: Thu, 13 Aug 2020 16:35:29 +0200 Subject: Rename ra_hir_ty -> hir_ty --- crates/hir_ty/src/infer/coerce.rs | 197 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 197 insertions(+) create mode 100644 crates/hir_ty/src/infer/coerce.rs (limited to 'crates/hir_ty/src/infer/coerce.rs') diff --git a/crates/hir_ty/src/infer/coerce.rs b/crates/hir_ty/src/infer/coerce.rs new file mode 100644 index 000000000..32c7c57cd --- /dev/null +++ b/crates/hir_ty/src/infer/coerce.rs @@ -0,0 +1,197 @@ +//! Coercion logic. Coercions are certain type conversions that can implicitly +//! happen in certain places, e.g. weakening `&mut` to `&` or deref coercions +//! like going from `&Vec` to `&[T]`. +//! +//! See: https://doc.rust-lang.org/nomicon/coercions.html + +use hir_def::{lang_item::LangItemTarget, type_ref::Mutability}; +use test_utils::mark; + +use crate::{autoderef, traits::Solution, Obligation, Substs, TraitRef, Ty, TypeCtor}; + +use super::{unify::TypeVarValue, InEnvironment, InferTy, InferenceContext}; + +impl<'a> InferenceContext<'a> { + /// Unify two types, but may coerce the first one to the second one + /// using "implicit coercion rules" if needed. + pub(super) fn coerce(&mut self, from_ty: &Ty, to_ty: &Ty) -> bool { + let from_ty = self.resolve_ty_shallow(from_ty).into_owned(); + let to_ty = self.resolve_ty_shallow(to_ty); + self.coerce_inner(from_ty, &to_ty) + } + + /// Merge two types from different branches, with possible coercion. + /// + /// Mostly this means trying to coerce one to the other, but + /// - if we have two function types for different functions, we need to + /// coerce both to function pointers; + /// - if we were concerned with lifetime subtyping, we'd need to look for a + /// least upper bound. + pub(super) fn coerce_merge_branch(&mut self, ty1: &Ty, ty2: &Ty) -> Ty { + if self.coerce(ty1, ty2) { + ty2.clone() + } else if self.coerce(ty2, ty1) { + ty1.clone() + } else { + if let (ty_app!(TypeCtor::FnDef(_)), ty_app!(TypeCtor::FnDef(_))) = (ty1, ty2) { + mark::hit!(coerce_fn_reification); + // Special case: two function types. Try to coerce both to + // pointers to have a chance at getting a match. See + // https://github.com/rust-lang/rust/blob/7b805396bf46dce972692a6846ce2ad8481c5f85/src/librustc_typeck/check/coercion.rs#L877-L916 + let sig1 = ty1.callable_sig(self.db).expect("FnDef without callable sig"); + let sig2 = ty2.callable_sig(self.db).expect("FnDef without callable sig"); + let ptr_ty1 = Ty::fn_ptr(sig1); + let ptr_ty2 = Ty::fn_ptr(sig2); + self.coerce_merge_branch(&ptr_ty1, &ptr_ty2) + } else { + mark::hit!(coerce_merge_fail_fallback); + ty1.clone() + } + } + } + + fn coerce_inner(&mut self, mut from_ty: Ty, to_ty: &Ty) -> bool { + match (&from_ty, to_ty) { + // Never type will make type variable to fallback to Never Type instead of Unknown. + (ty_app!(TypeCtor::Never), Ty::Infer(InferTy::TypeVar(tv))) => { + let var = self.table.new_maybe_never_type_var(); + self.table.var_unification_table.union_value(*tv, TypeVarValue::Known(var)); + return true; + } + (ty_app!(TypeCtor::Never), _) => return true, + + // Trivial cases, this should go after `never` check to + // avoid infer result type to be never + _ => { + if self.table.unify_inner_trivial(&from_ty, &to_ty, 0) { + return true; + } + } + } + + // Pointer weakening and function to pointer + match (&mut from_ty, to_ty) { + // `*mut T`, `&mut T, `&T`` -> `*const T` + // `&mut T` -> `&T` + // `&mut T` -> `*mut T` + (ty_app!(c1@TypeCtor::RawPtr(_)), ty_app!(c2@TypeCtor::RawPtr(Mutability::Shared))) + | (ty_app!(c1@TypeCtor::Ref(_)), ty_app!(c2@TypeCtor::RawPtr(Mutability::Shared))) + | (ty_app!(c1@TypeCtor::Ref(_)), ty_app!(c2@TypeCtor::Ref(Mutability::Shared))) + | (ty_app!(c1@TypeCtor::Ref(Mutability::Mut)), ty_app!(c2@TypeCtor::RawPtr(_))) => { + *c1 = *c2; + } + + // Illegal mutablity conversion + ( + ty_app!(TypeCtor::RawPtr(Mutability::Shared)), + ty_app!(TypeCtor::RawPtr(Mutability::Mut)), + ) + | ( + ty_app!(TypeCtor::Ref(Mutability::Shared)), + ty_app!(TypeCtor::Ref(Mutability::Mut)), + ) => return false, + + // `{function_type}` -> `fn()` + (ty_app!(TypeCtor::FnDef(_)), ty_app!(TypeCtor::FnPtr { .. })) => { + match from_ty.callable_sig(self.db) { + None => return false, + Some(sig) => { + from_ty = Ty::fn_ptr(sig); + } + } + } + + (ty_app!(TypeCtor::Closure { .. }, params), ty_app!(TypeCtor::FnPtr { .. })) => { + from_ty = params[0].clone(); + } + + _ => {} + } + + if let Some(ret) = self.try_coerce_unsized(&from_ty, &to_ty) { + return ret; + } + + // Auto Deref if cannot coerce + match (&from_ty, to_ty) { + // FIXME: DerefMut + (ty_app!(TypeCtor::Ref(_), st1), ty_app!(TypeCtor::Ref(_), st2)) => { + self.unify_autoderef_behind_ref(&st1[0], &st2[0]) + } + + // Otherwise, normal unify + _ => self.unify(&from_ty, to_ty), + } + } + + /// Coerce a type using `from_ty: CoerceUnsized` + /// + /// See: https://doc.rust-lang.org/nightly/std/marker/trait.CoerceUnsized.html + fn try_coerce_unsized(&mut self, from_ty: &Ty, to_ty: &Ty) -> Option { + let krate = self.resolver.krate().unwrap(); + let coerce_unsized_trait = match self.db.lang_item(krate, "coerce_unsized".into()) { + Some(LangItemTarget::TraitId(trait_)) => trait_, + _ => return None, + }; + + let generic_params = crate::utils::generics(self.db.upcast(), coerce_unsized_trait.into()); + if generic_params.len() != 2 { + // The CoerceUnsized trait should have two generic params: Self and T. + return None; + } + + let substs = Substs::build_for_generics(&generic_params) + .push(from_ty.clone()) + .push(to_ty.clone()) + .build(); + let trait_ref = TraitRef { trait_: coerce_unsized_trait, substs }; + let goal = InEnvironment::new(self.trait_env.clone(), Obligation::Trait(trait_ref)); + + let canonicalizer = self.canonicalizer(); + let canonicalized = canonicalizer.canonicalize_obligation(goal); + + let solution = self.db.trait_solve(krate, canonicalized.value.clone())?; + + match solution { + Solution::Unique(v) => { + canonicalized.apply_solution(self, v.0); + } + _ => return None, + }; + + Some(true) + } + + /// Unify `from_ty` to `to_ty` with optional auto Deref + /// + /// Note that the parameters are already stripped the outer reference. + fn unify_autoderef_behind_ref(&mut self, from_ty: &Ty, to_ty: &Ty) -> bool { + let canonicalized = self.canonicalizer().canonicalize_ty(from_ty.clone()); + let to_ty = self.resolve_ty_shallow(&to_ty); + // FIXME: Auto DerefMut + for derefed_ty in autoderef::autoderef( + self.db, + self.resolver.krate(), + InEnvironment { + value: canonicalized.value.clone(), + environment: self.trait_env.clone(), + }, + ) { + let derefed_ty = canonicalized.decanonicalize_ty(derefed_ty.value); + match (&*self.resolve_ty_shallow(&derefed_ty), &*to_ty) { + // Stop when constructor matches. + (ty_app!(from_ctor, st1), ty_app!(to_ctor, st2)) if from_ctor == to_ctor => { + // It will not recurse to `coerce`. + return self.table.unify_substs(st1, st2, 0); + } + _ => { + if self.table.unify_inner_trivial(&derefed_ty, &to_ty, 0) { + return true; + } + } + } + } + + false + } +} -- cgit v1.2.3