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fix: infer from RPIT bounds of _this_ function #12086

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Merged
merged 1 commit into from
May 3, 2022
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fix: infer from RPIT bounds of _this_ function #12086

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52 changes: 44 additions & 8 deletions crates/hir-ty/src/infer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ use std::sync::Arc;
use chalk_ir::{cast::Cast, ConstValue, DebruijnIndex, Mutability, Safety, Scalar, TypeFlags};
use hir_def::{
body::Body,
data::{ConstData, FunctionData, StaticData},
data::{ConstData, StaticData},
expr::{BindingAnnotation, ExprId, PatId},
lang_item::LangItemTarget,
path::{path, Path},
Expand All @@ -32,12 +32,13 @@ use hir_expand::name::{name, Name};
use itertools::Either;
use la_arena::ArenaMap;
use rustc_hash::FxHashMap;
use stdx::impl_from;
use stdx::{always, impl_from};

use crate::{
db::HirDatabase, fold_tys_and_consts, infer::coerce::CoerceMany, lower::ImplTraitLoweringMode,
to_assoc_type_id, AliasEq, AliasTy, Const, DomainGoal, GenericArg, Goal, InEnvironment,
Interner, ProjectionTy, Substitution, TraitEnvironment, TraitRef, Ty, TyBuilder, TyExt, TyKind,
db::HirDatabase, fold_tys, fold_tys_and_consts, infer::coerce::CoerceMany,
lower::ImplTraitLoweringMode, to_assoc_type_id, AliasEq, AliasTy, Const, DomainGoal,
GenericArg, Goal, ImplTraitId, InEnvironment, Interner, ProjectionTy, Substitution,
TraitEnvironment, TraitRef, Ty, TyBuilder, TyExt, TyKind,
};

// This lint has a false positive here. See the link below for details.
Expand All @@ -64,7 +65,7 @@ pub(crate) fn infer_query(db: &dyn HirDatabase, def: DefWithBodyId) -> Arc<Infer

match def {
DefWithBodyId::ConstId(c) => ctx.collect_const(&db.const_data(c)),
DefWithBodyId::FunctionId(f) => ctx.collect_fn(&db.function_data(f)),
DefWithBodyId::FunctionId(f) => ctx.collect_fn(f),
DefWithBodyId::StaticId(s) => ctx.collect_static(&db.static_data(s)),
}

Expand Down Expand Up @@ -457,7 +458,8 @@ impl<'a> InferenceContext<'a> {
self.return_ty = self.make_ty(&data.type_ref);
}

fn collect_fn(&mut self, data: &FunctionData) {
fn collect_fn(&mut self, func: FunctionId) {
let data = self.db.function_data(func);
let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver)
.with_impl_trait_mode(ImplTraitLoweringMode::Param);
let param_tys =
Expand All @@ -474,8 +476,42 @@ impl<'a> InferenceContext<'a> {
} else {
&*data.ret_type
};
let return_ty = self.make_ty_with_mode(return_ty, ImplTraitLoweringMode::Disallowed); // FIXME implement RPIT
let return_ty = self.make_ty_with_mode(return_ty, ImplTraitLoweringMode::Opaque);
self.return_ty = return_ty;

if let Some(rpits) = self.db.return_type_impl_traits(func) {
// RPIT opaque types use substitution of their parent function.
let fn_placeholders = TyBuilder::placeholder_subst(self.db, func);
self.return_ty = fold_tys(
self.return_ty.clone(),
|ty, _| {
let opaque_ty_id = match ty.kind(Interner) {
TyKind::OpaqueType(opaque_ty_id, _) => *opaque_ty_id,
_ => return ty,
};
let idx = match self.db.lookup_intern_impl_trait_id(opaque_ty_id.into()) {
ImplTraitId::ReturnTypeImplTrait(_, idx) => idx,
_ => unreachable!(),
};
let bounds = (*rpits).map_ref(|rpits| {
rpits.impl_traits[idx as usize].bounds.map_ref(|it| it.into_iter())
});
let var = self.table.new_type_var();
let var_subst = Substitution::from1(Interner, var.clone());
for bound in bounds {
let predicate =
bound.map(|it| it.cloned()).substitute(Interner, &fn_placeholders);
let (var_predicate, binders) = predicate
.substitute(Interner, &var_subst)
.into_value_and_skipped_binders();
always!(binders.len(Interner) == 0); // quantified where clauses not yet handled
self.push_obligation(var_predicate.cast(Interner));
}
var
},
DebruijnIndex::INNERMOST,
);
}
}

fn infer_body(&mut self) {
Expand Down
36 changes: 31 additions & 5 deletions crates/hir-ty/src/tests/traits.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1255,6 +1255,32 @@ fn test() {
);
}

#[test]
fn infer_from_return_pos_impl_trait() {
check_infer_with_mismatches(
r#"
//- minicore: fn, sized
trait Trait<T> {}
struct Bar<T>(T);
impl<T> Trait<T> for Bar<T> {}
fn foo<const C: u8, T>() -> (impl FnOnce(&str, T), impl Trait<u8>) {
(|input, t| {}, Bar(C))
}
"#,
expect![[r#"
134..165 '{ ...(C)) }': (|&str, T| -> (), Bar<u8>)
140..163 '(|inpu...ar(C))': (|&str, T| -> (), Bar<u8>)
141..154 '|input, t| {}': |&str, T| -> ()
142..147 'input': &str
149..150 't': T
152..154 '{}': ()
156..159 'Bar': Bar<u8>(u8) -> Bar<u8>
156..162 'Bar(C)': Bar<u8>
160..161 'C': u8
"#]],
);
}

#[test]
fn dyn_trait() {
check_infer(
Expand Down Expand Up @@ -2392,7 +2418,7 @@ fn test() -> impl Trait<i32> {
171..182 '{ loop {} }': T
173..180 'loop {}': !
178..180 '{}': ()
213..309 '{ ...t()) }': S<{unknown}>
213..309 '{ ...t()) }': S<i32>
223..225 's1': S<u32>
228..229 'S': S<u32>(u32) -> S<u32>
228..240 'S(default())': S<u32>
Expand All @@ -2408,10 +2434,10 @@ fn test() -> impl Trait<i32> {
276..288 'S(default())': S<i32>
278..285 'default': fn default<i32>() -> i32
278..287 'default()': i32
295..296 'S': S<{unknown}>({unknown}) -> S<{unknown}>
295..307 'S(default())': S<{unknown}>
297..304 'default': fn default<{unknown}>() -> {unknown}
297..306 'default()': {unknown}
295..296 'S': S<i32>(i32) -> S<i32>
295..307 'S(default())': S<i32>
297..304 'default': fn default<i32>() -> i32
297..306 'default()': i32
"#]],
);
}
Expand Down