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|
//! In certain situations, rust automatically inserts derefs as necessary: for
//! example, field accesses `foo.bar` still work when `foo` is actually a
//! reference to a type with the field `bar`. This is an approximation of the
//! logic in rustc (which lives in librustc_typeck/check/autoderef.rs).
use std::iter::successors;
use hir_def::lang_item::LangItemTarget;
use hir_expand::name;
use log::{info, warn};
use ra_db::CrateId;
use crate::{db::HirDatabase, Trait};
use super::{
traits::{InEnvironment, Solution},
Canonical, Substs, Ty, TypeWalk,
};
const AUTODEREF_RECURSION_LIMIT: usize = 10;
pub(crate) fn autoderef<'a>(
db: &'a impl HirDatabase,
krate: Option<CrateId>,
ty: InEnvironment<Canonical<Ty>>,
) -> impl Iterator<Item = Canonical<Ty>> + 'a {
let InEnvironment { value: ty, environment } = ty;
successors(Some(ty), move |ty| {
deref(db, krate?, InEnvironment { value: ty, environment: environment.clone() })
})
.take(AUTODEREF_RECURSION_LIMIT)
}
pub(crate) fn deref(
db: &impl HirDatabase,
krate: CrateId,
ty: InEnvironment<&Canonical<Ty>>,
) -> Option<Canonical<Ty>> {
if let Some(derefed) = ty.value.value.builtin_deref() {
Some(Canonical { value: derefed, num_vars: ty.value.num_vars })
} else {
deref_by_trait(db, krate, ty)
}
}
fn deref_by_trait(
db: &impl HirDatabase,
krate: CrateId,
ty: InEnvironment<&Canonical<Ty>>,
) -> Option<Canonical<Ty>> {
let deref_trait = match db.lang_item(krate.into(), "deref".into())? {
LangItemTarget::TraitId(t) => Trait::from(t),
_ => return None,
};
let target = deref_trait.associated_type_by_name(db, &name::TARGET_TYPE)?;
let generic_params = db.generic_params(target.id.into());
if generic_params.count_params_including_parent() != 1 {
// the Target type + Deref trait should only have one generic parameter,
// namely Deref's Self type
return None;
}
// FIXME make the Canonical handling nicer
let parameters = Substs::build_for_generics(&generic_params)
.push(ty.value.value.clone().shift_bound_vars(1))
.build();
let projection = super::traits::ProjectionPredicate {
ty: Ty::Bound(0),
projection_ty: super::ProjectionTy { associated_ty: target.id, parameters },
};
let obligation = super::Obligation::Projection(projection);
let in_env = InEnvironment { value: obligation, environment: ty.environment };
let canonical = super::Canonical { num_vars: 1 + ty.value.num_vars, value: in_env };
let solution = db.trait_solve(krate.into(), canonical)?;
match &solution {
Solution::Unique(vars) => {
// FIXME: vars may contain solutions for any inference variables
// that happened to be inside ty. To correctly handle these, we
// would have to pass the solution up to the inference context, but
// that requires a larger refactoring (especially if the deref
// happens during method resolution). So for the moment, we just
// check that we're not in the situation we're we would actually
// need to handle the values of the additional variables, i.e.
// they're just being 'passed through'. In the 'standard' case where
// we have `impl<T> Deref for Foo<T> { Target = T }`, that should be
// the case.
for i in 1..vars.0.num_vars {
if vars.0.value[i] != Ty::Bound((i - 1) as u32) {
warn!("complex solution for derefing {:?}: {:?}, ignoring", ty.value, solution);
return None;
}
}
Some(Canonical { value: vars.0.value[0].clone(), num_vars: vars.0.num_vars })
}
Solution::Ambig(_) => {
info!("Ambiguous solution for derefing {:?}: {:?}", ty.value, solution);
None
}
}
}
|
