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Implement unsize coercion using proper trait solving

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This commit is contained in:
Florian Diebold 2020-02-21 18:24:18 +01:00 committed by Florian Diebold
parent baf832d6d9
commit de39d221a1
5 changed files with 170 additions and 187 deletions
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7
crates/ra_hir_ty/src/infer.rs
View File

@ -206,12 +206,6 @@ struct InferenceContext<'a, D: HirDatabase> {
/// closures, but currently this is the only field that will change there,
/// so it doesn't make sense.
return_ty: Ty,
/// Impls of `CoerceUnsized` used in coercion.
/// (from_ty_ctor, to_ty_ctor) => coerce_generic_index
// FIXME: Use trait solver for this.
// Chalk seems unable to work well with builtin impl of `Unsize` now.
coerce_unsized_map: FxHashMap<(TypeCtor, TypeCtor), usize>,
}
impl<'a, D: HirDatabase> InferenceContext<'a, D> {
@ -222,7 +216,6 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
obligations: Vec::default(),
return_ty: Ty::Unknown, // set in collect_fn_signature
trait_env: TraitEnvironment::lower(db, &resolver),
coerce_unsized_map: Self::init_coerce_unsized_map(db, &resolver),
db,
owner,
body: db.body(owner),

205
crates/ra_hir_ty/src/infer/coerce.rs
View File

@ -4,11 +4,12 @@
//!
//! See: https://doc.rust-lang.org/nomicon/coercions.html
use hir_def::{lang_item::LangItemTarget, resolver::Resolver, type_ref::Mutability, AdtId};
use rustc_hash::FxHashMap;
use hir_def::{lang_item::LangItemTarget, type_ref::Mutability};
use test_utils::tested_by;
use crate::{autoderef, db::HirDatabase, Substs, Ty, TypeCtor, TypeWalk};
use crate::{
autoderef, db::HirDatabase, traits::Solution, Obligation, Substs, TraitRef, Ty, TypeCtor,
};
use super::{unify::TypeVarValue, InEnvironment, InferTy, InferenceContext};
@ -39,44 +40,6 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
}
}
pub(super) fn init_coerce_unsized_map(
db: &'a D,
resolver: &Resolver,
) -> FxHashMap<(TypeCtor, TypeCtor), usize> {
let krate = resolver.krate().unwrap();
let impls = match db.lang_item(krate, "coerce_unsized".into()) {
Some(LangItemTarget::TraitId(trait_)) => db.impls_for_trait(krate, trait_),
_ => return FxHashMap::default(),
};
impls
.iter()
.filter_map(|&impl_id| {
let trait_ref = db.impl_trait(impl_id)?;
// `CoerseUnsized` has one generic parameter for the target type.
let cur_from_ty = trait_ref.value.substs.0.get(0)?;
let cur_to_ty = trait_ref.value.substs.0.get(1)?;
match (&cur_from_ty, cur_to_ty) {
(ty_app!(ctor1, st1), ty_app!(ctor2, st2)) => {
// FIXME: We return the first non-equal bound as the type parameter to coerce to unsized type.
// This works for smart-pointer-like coercion, which covers all impls from std.
st1.iter().zip(st2.iter()).enumerate().find_map(|(i, (ty1, ty2))| {
match (ty1, ty2) {
(Ty::Bound(idx1), Ty::Bound(idx2)) if idx1 != idx2 => {
Some(((*ctor1, *ctor2), i))
}
_ => None,
}
})
}
_ => None,
}
})
.collect()
}
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.
@ -157,154 +120,38 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
///
/// 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<bool> {
let (ctor1, st1, ctor2, st2) = match (from_ty, to_ty) {
(ty_app!(ctor1, st1), ty_app!(ctor2, st2)) => (ctor1, st1, ctor2, st2),
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 coerce_generic_index = *self.coerce_unsized_map.get(&(*ctor1, *ctor2))?;
// Check `Unsize` first
match self.check_unsize_and_coerce(
st1.0.get(coerce_generic_index)?,
st2.0.get(coerce_generic_index)?,
0,
) {
Some(true) => {}
ret => return ret,
let generic_params = crate::utils::generics(self.db, coerce_unsized_trait.into());
if generic_params.len() != 2 {
// The CoerceUnsized trait should have two generic params: Self and T.
return None;
}
let ret = st1
.iter()
.zip(st2.iter())
.enumerate()
.filter(|&(idx, _)| idx != coerce_generic_index)
.all(|(_, (ty1, ty2))| self.unify(ty1, ty2));
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));
Some(ret)
}
let canonicalizer = self.canonicalizer();
let canonicalized = canonicalizer.canonicalize_obligation(goal);
/// Check if `from_ty: Unsize<to_ty>`, and coerce to `to_ty` if it holds.
///
/// It should not be directly called. It is only used by `try_coerce_unsized`.
///
/// See: https://doc.rust-lang.org/nightly/std/marker/trait.Unsize.html
fn check_unsize_and_coerce(&mut self, from_ty: &Ty, to_ty: &Ty, depth: usize) -> Option<bool> {
if depth > 1000 {
panic!("Infinite recursion in coercion");
}
let solution = self.db.trait_solve(krate, canonicalized.value.clone())?;
match (&from_ty, &to_ty) {
// `[T; N]` -> `[T]`
(ty_app!(TypeCtor::Array, st1), ty_app!(TypeCtor::Slice, st2)) => {
Some(self.unify(&st1[0], &st2[0]))
match solution {
Solution::Unique(v) => {
canonicalized.apply_solution(self, v.0);
}
_ => return None,
};
// `T` -> `dyn Trait` when `T: Trait`
(_, Ty::Dyn(_)) => {
// FIXME: Check predicates
Some(true)
}
// `(..., T)` -> `(..., U)` when `T: Unsize<U>`
(
ty_app!(TypeCtor::Tuple { cardinality: len1 }, st1),
ty_app!(TypeCtor::Tuple { cardinality: len2 }, st2),
) => {
if len1 != len2 || *len1 == 0 {
return None;
}
match self.check_unsize_and_coerce(
st1.last().unwrap(),
st2.last().unwrap(),
depth + 1,
) {
Some(true) => {}
ret => return ret,
}
let ret = st1[..st1.len() - 1]
.iter()
.zip(&st2[..st2.len() - 1])
.all(|(ty1, ty2)| self.unify(ty1, ty2));
Some(ret)
}
// Foo<..., T, ...> is Unsize<Foo<..., U, ...>> if:
// - T: Unsize<U>
// - Foo is a struct
// - Only the last field of Foo has a type involving T
// - T is not part of the type of any other fields
// - Bar<T>: Unsize<Bar<U>>, if the last field of Foo has type Bar<T>
(
ty_app!(TypeCtor::Adt(AdtId::StructId(struct1)), st1),
ty_app!(TypeCtor::Adt(AdtId::StructId(struct2)), st2),
) if struct1 == struct2 => {
let field_tys = self.db.field_types((*struct1).into());
let struct_data = self.db.struct_data(*struct1);
let mut fields = struct_data.variant_data.fields().iter();
let (last_field_id, _data) = fields.next_back()?;
// Get the generic parameter involved in the last field.
let unsize_generic_index = {
let mut index = None;
let mut multiple_param = false;
field_tys[last_field_id].value.walk(&mut |ty| {
if let &Ty::Bound(idx) = ty {
if index.is_none() {
index = Some(idx);
} else if Some(idx) != index {
multiple_param = true;
}
}
});
if multiple_param {
return None;
}
index?
};
// Check other fields do not involve it.
let mut multiple_used = false;
fields.for_each(|(field_id, _data)| {
field_tys[field_id].value.walk(&mut |ty| match ty {
&Ty::Bound(idx) if idx == unsize_generic_index => multiple_used = true,
_ => {}
})
});
if multiple_used {
return None;
}
let unsize_generic_index = unsize_generic_index as usize;
// Check `Unsize` first
match self.check_unsize_and_coerce(
st1.get(unsize_generic_index)?,
st2.get(unsize_generic_index)?,
depth + 1,
) {
Some(true) => {}
ret => return ret,
}
// Then unify other parameters
let ret = st1
.iter()
.zip(st2.iter())
.enumerate()
.filter(|&(idx, _)| idx != unsize_generic_index)
.all(|(_, (ty1, ty2))| self.unify(ty1, ty2));
Some(ret)
}
_ => None,
}
Some(true)
}
/// Unify `from_ty` to `to_ty` with optional auto Deref

82
crates/ra_hir_ty/src/tests/coercion.rs
View File

@ -548,3 +548,85 @@ impl<TT> S<TT> {
"###
);
}
#[test]
fn coerce_unsize_array() {
assert_snapshot!(
infer_with_mismatches(r#"
#[lang = "unsize"]
pub trait Unsize<T> {}
#[lang = "coerce_unsized"]
pub trait CoerceUnsized<T> {}
impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
fn test() {
let f: &[usize] = &[1, 2, 3];
}
"#, true),
@r###"
[162; 199) '{ ... 3]; }': ()
[172; 173) 'f': &[usize]
[186; 196) '&[1, 2, 3]': &[usize; _]
[187; 196) '[1, 2, 3]': [usize; _]
[188; 189) '1': usize
[191; 192) '2': usize
[194; 195) '3': usize
"###
);
}
#[ignore]
#[test]
fn coerce_unsize_trait_object() {
assert_snapshot!(
infer_with_mismatches(r#"
#[lang = "unsize"]
pub trait Unsize<T> {}
#[lang = "coerce_unsized"]
pub trait CoerceUnsized<T> {}
impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
trait Foo {}
trait Bar: Foo {}
struct S;
impl Foo for S {}
impl Bar for S {}
fn test() {
let obj: &dyn Bar = &S;
let obj: &dyn Foo = obj;
}
"#, true),
@r###"
"###
);
}
#[ignore]
#[test]
fn coerce_unsize_generic() {
// FIXME: Implement this
// https://doc.rust-lang.org/reference/type-coercions.html#unsized-coercions
assert_snapshot!(
infer_with_mismatches(r#"
#[lang = "unsize"]
pub trait Unsize<T> {}
#[lang = "coerce_unsized"]
pub trait CoerceUnsized<T> {}
impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
struct Foo<T> { t: T };
struct Bar<T>(Foo<T>);
fn test() {
let _: &Foo<[usize]> = &Foo { t: [1, 2, 3] };
let _: &Bar<[usize]> = &Bar(Foo { t: [1, 2, 3] });
}
"#, true),
@r###"
"###
);
}

2
crates/ra_hir_ty/src/traits.rs
View File

@ -343,6 +343,8 @@ pub enum Impl {
ImplBlock(ImplId),
/// Closure types implement the Fn traits synthetically.
ClosureFnTraitImpl(ClosureFnTraitImplData),
/// [T; n]: Unsize<[T]>
UnsizeArray,
}
/// This exists just for Chalk, because our ImplIds are only unique per module.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]

61
crates/ra_hir_ty/src/traits/builtin.rs
View File

@ -5,7 +5,7 @@ use hir_expand::name::name;
use ra_db::CrateId;
use super::{AssocTyValue, Impl};
use crate::{db::HirDatabase, ApplicationTy, Substs, TraitRef, Ty, TypeCtor};
use crate::{db::HirDatabase, utils::generics, ApplicationTy, Substs, TraitRef, Ty, TypeCtor};
pub(super) struct BuiltinImplData {
pub num_vars: usize,
@ -43,12 +43,22 @@ pub(super) fn get_builtin_impls(
}
}
}
if let Ty::Apply(ApplicationTy { ctor: TypeCtor::Array, .. }) = ty {
if let Some(actual_trait) = get_unsize_trait(db, krate) {
if trait_ == actual_trait {
if check_unsize_impl_prerequisites(db, krate) {
callback(Impl::UnsizeArray);
}
}
}
}
}
pub(super) fn impl_datum(db: &impl HirDatabase, krate: CrateId, impl_: Impl) -> BuiltinImplData {
match impl_ {
Impl::ImplBlock(_) => unreachable!(),
Impl::ClosureFnTraitImpl(data) => closure_fn_trait_impl_datum(db, krate, data),
Impl::UnsizeArray => array_unsize_impl_datum(db, krate),
}
}
@ -65,6 +75,8 @@ pub(super) fn associated_ty_value(
}
}
// Closure Fn trait impls
fn check_closure_fn_trait_impl_prerequisites(
db: &impl HirDatabase,
krate: CrateId,
@ -165,6 +177,45 @@ fn closure_fn_trait_output_assoc_ty_value(
}
}
// Array unsizing
fn check_unsize_impl_prerequisites(db: &impl HirDatabase, krate: CrateId) -> bool {
// the Unsize trait needs to exist and have two type parameters (Self and T)
let unsize_trait = match get_unsize_trait(db, krate) {
Some(t) => t,
None => return false,
};
let generic_params = generics(db, unsize_trait.into());
if generic_params.len() != 2 {
return false;
}
true
}
fn array_unsize_impl_datum(db: &impl HirDatabase, krate: CrateId) -> BuiltinImplData {
// impl<T> Unsize<[T]> for [T; _]
// (this can be a single impl because we don't distinguish array sizes currently)
let trait_ = get_unsize_trait(db, krate) // get unsize trait
// the existence of the Unsize trait has been checked before
.expect("Unsize trait missing");
let var = Ty::Bound(0);
let substs = Substs::builder(2)
.push(Ty::apply_one(TypeCtor::Array, var.clone()))
.push(Ty::apply_one(TypeCtor::Slice, var))
.build();
let trait_ref = TraitRef { trait_, substs };
BuiltinImplData {
num_vars: 1,
trait_ref,
where_clauses: Vec::new(),
assoc_ty_values: Vec::new(),
}
}
fn get_fn_trait(
db: &impl HirDatabase,
krate: CrateId,
@ -176,3 +227,11 @@ fn get_fn_trait(
_ => None,
}
}
fn get_unsize_trait(db: &impl HirDatabase, krate: CrateId) -> Option<TraitId> {
let target = db.lang_item(krate, "unsize".into())?;
match target {
LangItemTarget::TraitId(t) => Some(t),
_ => None,
}
}