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|
//! This module provides the built-in trait implementations, e.g. to make
//! closures implement `Fn`.
use hir_def::{expr::Expr, lang_item::LangItemTarget, TraitId, TypeAliasId};
use hir_expand::name::name;
use ra_db::CrateId;
use super::{AssocTyValue, Impl};
use crate::{db::HirDatabase, ApplicationTy, Substs, TraitRef, Ty, TypeCtor};
pub(super) struct BuiltinImplData {
pub num_vars: usize,
pub trait_ref: TraitRef,
pub where_clauses: Vec<super::GenericPredicate>,
pub assoc_ty_values: Vec<AssocTyValue>,
}
pub(super) struct BuiltinImplAssocTyValueData {
pub impl_: Impl,
pub assoc_ty_id: TypeAliasId,
pub num_vars: usize,
pub value: Ty,
}
pub(super) fn get_builtin_impls(
db: &impl HirDatabase,
krate: CrateId,
ty: &Ty,
trait_: TraitId,
mut callback: impl FnMut(Impl),
) {
// Note: since impl_datum needs to be infallible, we need to make sure here
// that we have all prerequisites to build the respective impls.
if let Ty::Apply(ApplicationTy { ctor: TypeCtor::Closure { def, expr }, .. }) = ty {
for &fn_trait in [super::FnTrait::FnOnce, super::FnTrait::FnMut, super::FnTrait::Fn].iter()
{
if let Some(actual_trait) = get_fn_trait(db, krate, fn_trait) {
if trait_ == actual_trait {
let impl_ = super::ClosureFnTraitImplData { def: *def, expr: *expr, fn_trait };
if check_closure_fn_trait_impl_prerequisites(db, krate, impl_) {
callback(Impl::ClosureFnTraitImpl(impl_));
}
}
}
}
}
}
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),
}
}
pub(super) fn associated_ty_value(
db: &impl HirDatabase,
krate: CrateId,
data: AssocTyValue,
) -> BuiltinImplAssocTyValueData {
match data {
AssocTyValue::TypeAlias(_) => unreachable!(),
AssocTyValue::ClosureFnTraitImplOutput(data) => {
closure_fn_trait_output_assoc_ty_value(db, krate, data)
}
}
}
fn check_closure_fn_trait_impl_prerequisites(
db: &impl HirDatabase,
krate: CrateId,
data: super::ClosureFnTraitImplData,
) -> bool {
// the respective Fn/FnOnce/FnMut trait needs to exist
if get_fn_trait(db, krate, data.fn_trait).is_none() {
return false;
}
// FIXME: there are more assumptions that we should probably check here:
// the traits having no type params, FnOnce being a supertrait
// the FnOnce trait needs to exist and have an assoc type named Output
let fn_once_trait = match get_fn_trait(db, krate, super::FnTrait::FnOnce) {
Some(t) => t,
None => return false,
};
db.trait_data(fn_once_trait).associated_type_by_name(&name![Output]).is_some()
}
fn closure_fn_trait_impl_datum(
db: &impl HirDatabase,
krate: CrateId,
data: super::ClosureFnTraitImplData,
) -> BuiltinImplData {
// for some closure |X, Y| -> Z:
// impl<T, U, V> Fn<(T, U)> for closure<fn(T, U) -> V> { Output = V }
let trait_ = get_fn_trait(db, krate, data.fn_trait) // get corresponding fn trait
// the existence of the Fn trait has been checked before
.expect("fn trait for closure impl missing");
let num_args: u16 = match &db.body(data.def)[data.expr] {
Expr::Lambda { args, .. } => args.len() as u16,
_ => {
log::warn!("closure for closure type {:?} not found", data);
0
}
};
let arg_ty = Ty::apply(
TypeCtor::Tuple { cardinality: num_args },
Substs::builder(num_args as usize).fill_with_bound_vars(0).build(),
);
let sig_ty = Ty::apply(
TypeCtor::FnPtr { num_args },
Substs::builder(num_args as usize + 1).fill_with_bound_vars(0).build(),
);
let self_ty = Ty::apply_one(TypeCtor::Closure { def: data.def, expr: data.expr }, sig_ty);
let trait_ref = TraitRef {
trait_,
substs: Substs::build_for_def(db, trait_).push(self_ty).push(arg_ty).build(),
};
let output_ty_id = AssocTyValue::ClosureFnTraitImplOutput(data);
BuiltinImplData {
num_vars: num_args as usize + 1,
trait_ref,
where_clauses: Vec::new(),
assoc_ty_values: vec![output_ty_id],
}
}
fn closure_fn_trait_output_assoc_ty_value(
db: &impl HirDatabase,
krate: CrateId,
data: super::ClosureFnTraitImplData,
) -> BuiltinImplAssocTyValueData {
let impl_ = Impl::ClosureFnTraitImpl(data);
let num_args: u16 = match &db.body(data.def)[data.expr] {
Expr::Lambda { args, .. } => args.len() as u16,
_ => {
log::warn!("closure for closure type {:?} not found", data);
0
}
};
let output_ty = Ty::Bound(num_args.into());
let fn_once_trait =
get_fn_trait(db, krate, super::FnTrait::FnOnce).expect("assoc ty value should not exist");
let output_ty_id = db
.trait_data(fn_once_trait)
.associated_type_by_name(&name![Output])
.expect("assoc ty value should not exist");
BuiltinImplAssocTyValueData {
impl_,
assoc_ty_id: output_ty_id,
num_vars: num_args as usize + 1,
value: output_ty,
}
}
fn get_fn_trait(
db: &impl HirDatabase,
krate: CrateId,
fn_trait: super::FnTrait,
) -> Option<TraitId> {
let target = db.lang_item(krate, fn_trait.lang_item_name().into())?;
match target {
LangItemTarget::TraitId(t) => Some(t),
_ => None,
}
}
|
