Rollup merge of #122027 - compiler-errors:rpitit-cycle, r=spastorino

Uplift some feeding out of `associated_type_for_impl_trait_in_impl` and into queries

This PR moves the `type_of` and `generics_of` query feeding out of `associated_type_for_impl_trait_in_impl`, since eagerly feeding results in query cycles due to a subtle interaction with `resolve_bound_vars`.

Fixes #122019

r? spastorino

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -14,6 +14,43 @@ use rustc_span::Span;
 pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
     use rustc_hir::*;
 
+    // For an RPITIT, synthesize generics which are equal to the opaque's generics
+    // and parent fn's generics compressed into one list.
+    if let Some(ty::ImplTraitInTraitData::Trait { fn_def_id, opaque_def_id }) =
+        tcx.opt_rpitit_info(def_id.to_def_id())
+    {
+        let trait_def_id = tcx.parent(fn_def_id);
+        let opaque_ty_generics = tcx.generics_of(opaque_def_id);
+        let opaque_ty_parent_count = opaque_ty_generics.parent_count;
+        let mut params = opaque_ty_generics.params.clone();
+
+        let parent_generics = tcx.generics_of(trait_def_id);
+        let parent_count = parent_generics.parent_count + parent_generics.params.len();
+
+        let mut trait_fn_params = tcx.generics_of(fn_def_id).params.clone();
+
+        for param in &mut params {
+            param.index = param.index + parent_count as u32 + trait_fn_params.len() as u32
+                - opaque_ty_parent_count as u32;
+        }
+
+        trait_fn_params.extend(params);
+        params = trait_fn_params;
+
+        let param_def_id_to_index =
+            params.iter().map(|param| (param.def_id, param.index)).collect();
+
+        return ty::Generics {
+            parent: Some(trait_def_id),
+            parent_count,
+            params,
+            param_def_id_to_index,
+            has_self: opaque_ty_generics.has_self,
+            has_late_bound_regions: opaque_ty_generics.has_late_bound_regions,
+            host_effect_index: parent_generics.host_effect_index,
+        };
+    }
+
     let hir_id = tcx.local_def_id_to_hir_id(def_id);
 
     let node = tcx.hir_node(hir_id);

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -5,7 +5,7 @@ use rustc_hir::HirId;
 use rustc_middle::query::plumbing::CyclePlaceholder;
 use rustc_middle::ty::print::with_forced_trimmed_paths;
 use rustc_middle::ty::util::IntTypeExt;
-use rustc_middle::ty::{self, ImplTraitInTraitData, IsSuggestable, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{self, IsSuggestable, Ty, TyCtxt, TypeVisitableExt};
 use rustc_span::symbol::Ident;
 use rustc_span::{Span, DUMMY_SP};
 
@@ -350,22 +350,31 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
     // If we are computing `type_of` the synthesized associated type for an RPITIT in the impl
     // side, use `collect_return_position_impl_trait_in_trait_tys` to infer the value of the
     // associated type in the impl.
-    if let Some(ImplTraitInTraitData::Impl { fn_def_id, .. }) =
-        tcx.opt_rpitit_info(def_id.to_def_id())
-    {
-        match tcx.collect_return_position_impl_trait_in_trait_tys(fn_def_id) {
-            Ok(map) => {
-                let assoc_item = tcx.associated_item(def_id);
-                return map[&assoc_item.trait_item_def_id.unwrap()];
-            }
-            Err(_) => {
-                return ty::EarlyBinder::bind(Ty::new_error_with_message(
-                    tcx,
-                    DUMMY_SP,
-                    "Could not collect return position impl trait in trait tys",
-                ));
+    match tcx.opt_rpitit_info(def_id.to_def_id()) {
+        Some(ty::ImplTraitInTraitData::Impl { fn_def_id }) => {
+            match tcx.collect_return_position_impl_trait_in_trait_tys(fn_def_id) {
+                Ok(map) => {
+                    let assoc_item = tcx.associated_item(def_id);
+                    return map[&assoc_item.trait_item_def_id.unwrap()];
+                }
+                Err(_) => {
+                    return ty::EarlyBinder::bind(Ty::new_error_with_message(
+                        tcx,
+                        DUMMY_SP,
+                        "Could not collect return position impl trait in trait tys",
+                    ));
+                }
             }
         }
+        // For an RPITIT in a trait, just return the corresponding opaque.
+        Some(ty::ImplTraitInTraitData::Trait { opaque_def_id, .. }) => {
+            return ty::EarlyBinder::bind(Ty::new_opaque(
+                tcx,
+                opaque_def_id,
+                ty::GenericArgs::identity_for_item(tcx, opaque_def_id),
+            ));
+        }
+        None => {}
     }
 
     let hir_id = tcx.local_def_id_to_hir_id(def_id);

compiler/rustc_middle/src/query/mod.rs

@@ -826,15 +826,15 @@ rustc_queries! {
     /// creates and returns the associated items that correspond to each impl trait in return position
     /// of the implemented trait.
     query associated_types_for_impl_traits_in_associated_fn(fn_def_id: DefId) -> &'tcx [DefId] {
-        desc { |tcx| "creating associated items for impl trait in trait returned by `{}`", tcx.def_path_str(fn_def_id) }
+        desc { |tcx| "creating associated items for opaque types returned by `{}`", tcx.def_path_str(fn_def_id) }
         cache_on_disk_if { fn_def_id.is_local() }
         separate_provide_extern
     }
 
     /// Given an impl trait in trait `opaque_ty_def_id`, create and return the corresponding
     /// associated item.
     query associated_type_for_impl_trait_in_trait(opaque_ty_def_id: LocalDefId) -> LocalDefId {
-        desc { |tcx| "creates the associated item corresponding to the opaque type `{}`", tcx.def_path_str(opaque_ty_def_id.to_def_id()) }
+        desc { |tcx| "creating the associated item corresponding to the opaque type `{}`", tcx.def_path_str(opaque_ty_def_id.to_def_id()) }
         cache_on_disk_if { true }
     }
 

compiler/rustc_ty_utils/src/assoc.rs

@@ -4,7 +4,7 @@ use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId};
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, GenericArgs, ImplTraitInTraitData, Ty, TyCtxt};
+use rustc_middle::ty::{self, ImplTraitInTraitData, TyCtxt};
 use rustc_span::symbol::kw;
 
 pub(crate) fn provide(providers: &mut Providers) {
@@ -284,48 +284,8 @@ fn associated_type_for_impl_trait_in_trait(
     // Copy defaultness of the containing function.
     trait_assoc_ty.defaultness(tcx.defaultness(fn_def_id));
 
-    // Copy type_of of the opaque.
-    trait_assoc_ty.type_of(ty::EarlyBinder::bind(Ty::new_opaque(
-        tcx,
-        opaque_ty_def_id.to_def_id(),
-        GenericArgs::identity_for_item(tcx, opaque_ty_def_id),
-    )));
-
     trait_assoc_ty.is_type_alias_impl_trait(false);
 
-    // Copy generics_of of the opaque type item but the trait is the parent.
-    trait_assoc_ty.generics_of({
-        let opaque_ty_generics = tcx.generics_of(opaque_ty_def_id);
-        let opaque_ty_parent_count = opaque_ty_generics.parent_count;
-        let mut params = opaque_ty_generics.params.clone();
-
-        let parent_generics = tcx.generics_of(trait_def_id);
-        let parent_count = parent_generics.parent_count + parent_generics.params.len();
-
-        let mut trait_fn_params = tcx.generics_of(fn_def_id).params.clone();
-
-        for param in &mut params {
-            param.index = param.index + parent_count as u32 + trait_fn_params.len() as u32
-                - opaque_ty_parent_count as u32;
-        }
-
-        trait_fn_params.extend(params);
-        params = trait_fn_params;
-
-        let param_def_id_to_index =
-            params.iter().map(|param| (param.def_id, param.index)).collect();
-
-        ty::Generics {
-            parent: Some(trait_def_id.to_def_id()),
-            parent_count,
-            params,
-            param_def_id_to_index,
-            has_self: opaque_ty_generics.has_self,
-            has_late_bound_regions: opaque_ty_generics.has_late_bound_regions,
-            host_effect_index: parent_generics.host_effect_index,
-        }
-    });
-
     // There are no inferred outlives for the synthesized associated type.
     trait_assoc_ty.inferred_outlives_of(&[]);
 
@@ -382,8 +342,9 @@ fn associated_type_for_impl_trait_in_impl(
     impl_assoc_ty.defaultness(tcx.defaultness(impl_fn_def_id));
 
     // Copy generics_of the trait's associated item but the impl as the parent.
-    // FIXME(-Zlower-impl-trait-in-trait-to-assoc-ty) resolves to the trait instead of the impl
-    // generics.
+    // FIXME: This may be detrimental to diagnostics, as we resolve the early-bound vars
+    // here to paramswhose parent are items in the trait. We could synthesize new params
+    // here, but it seems overkill.
     impl_assoc_ty.generics_of({
         let trait_assoc_generics = tcx.generics_of(trait_assoc_def_id);
         let trait_assoc_parent_count = trait_assoc_generics.parent_count;

tests/ui/impl-trait/in-trait/rpitit-cycle-in-generics-of.rs

@@ -0,0 +1,18 @@
+//@ check-pass
+
+// Check that we don't hit a query cycle when:
+// 1. Computing generics_of, which requires...
+// 2. Calling resolve_bound_vars, which requires...
+// 3. Calling associated_items, which requires...
+// 4. Calling associated_type_for_impl_trait_in_trait, which requires...
+// 5. Computing generics_of, which cycles.
+
+pub trait Foo<'a> {
+    type Assoc;
+
+    fn demo<T>(other: T) -> impl Foo<'a, Assoc = Self::Assoc>
+    where
+        T: Foo<'a, Assoc = ()>;
+}
+
+fn main() {}