implement creating generics for impl traits in associated types

crates/hir-def/src/generics.rs

@@ -339,6 +339,7 @@ impl GenericParamsCollector {
         target: Either<TypeRef, LifetimeRef>,
     ) {
         let bound = TypeBound::from_ast(lower_ctx, bound);
+        self.fill_impl_trait_bounds(lower_ctx.take_impl_traits_bounds());
         let predicate = match (target, bound) {
             (Either::Left(type_ref), bound) => match hrtb_lifetimes {
                 Some(hrtb_lifetimes) => WherePredicate::ForLifetime {
@@ -359,6 +360,23 @@ impl GenericParamsCollector {
         self.where_predicates.push(predicate);
     }
 
+    fn fill_impl_trait_bounds(&mut self, impl_bounds: Vec<Vec<Interned<TypeBound>>>) {
+        for bounds in impl_bounds {
+            let param = TypeParamData {
+                name: None,
+                default: None,
+                provenance: TypeParamProvenance::ArgumentImplTrait,
+            };
+            let param_id = self.type_or_consts.alloc(param.into());
+            for bound in bounds {
+                self.where_predicates.push(WherePredicate::TypeBound {
+                    target: WherePredicateTypeTarget::TypeOrConstParam(param_id),
+                    bound,
+                });
+            }
+        }
+    }
+
     pub(crate) fn fill_implicit_impl_trait_args(
         &mut self,
         db: &dyn DefDatabase,

crates/hir-def/src/lower.rs

@@ -1,26 +1,34 @@
 //! Context for lowering paths.
-use std::cell::OnceCell;
+use std::cell::{OnceCell, RefCell};
 
 use hir_expand::{
     span_map::{SpanMap, SpanMapRef},
     AstId, HirFileId, InFile,
 };
+use intern::Interned;
 use span::{AstIdMap, AstIdNode};
 use syntax::ast;
 use triomphe::Arc;
 
-use crate::{db::DefDatabase, path::Path};
+use crate::{db::DefDatabase, path::Path, type_ref::TypeBound};
 
 pub struct LowerCtx<'a> {
     pub db: &'a dyn DefDatabase,
     file_id: HirFileId,
     span_map: OnceCell<SpanMap>,
     ast_id_map: OnceCell<Arc<AstIdMap>>,
+    impl_trait_bounds: RefCell<Vec<Vec<Interned<TypeBound>>>>,
 }
 
 impl<'a> LowerCtx<'a> {
     pub fn new(db: &'a dyn DefDatabase, file_id: HirFileId) -> Self {
-        LowerCtx { db, file_id, span_map: OnceCell::new(), ast_id_map: OnceCell::new() }
+        LowerCtx {
+            db,
+            file_id,
+            span_map: OnceCell::new(),
+            ast_id_map: OnceCell::new(),
+            impl_trait_bounds: RefCell::new(Vec::new()),
+        }
     }
 
     pub fn with_span_map_cell(
@@ -28,7 +36,13 @@ impl<'a> LowerCtx<'a> {
         file_id: HirFileId,
         span_map: OnceCell<SpanMap>,
     ) -> Self {
-        LowerCtx { db, file_id, span_map, ast_id_map: OnceCell::new() }
+        LowerCtx {
+            db,
+            file_id,
+            span_map,
+            ast_id_map: OnceCell::new(),
+            impl_trait_bounds: RefCell::new(Vec::new()),
+        }
     }
 
     pub(crate) fn span_map(&self) -> SpanMapRef<'_> {
@@ -45,4 +59,12 @@ impl<'a> LowerCtx<'a> {
             self.ast_id_map.get_or_init(|| self.db.ast_id_map(self.file_id)).ast_id(item),
         )
     }
+
+    pub fn update_impl_traits_bounds(&self, bounds: Vec<Interned<TypeBound>>) {
+        self.impl_trait_bounds.borrow_mut().push(bounds);
+    }
+
+    pub fn take_impl_traits_bounds(&self) -> Vec<Vec<Interned<TypeBound>>> {
+        self.impl_trait_bounds.borrow_mut().drain(..).collect()
+    }
 }

crates/hir-def/src/path/lower.rs

@@ -208,6 +208,13 @@ pub(super) fn lower_generic_args(
                         .and_then(|args| lower_generic_args(lower_ctx, args))
                         .map(Interned::new);
                     let type_ref = assoc_type_arg.ty().map(|it| TypeRef::from_ast(lower_ctx, it));
+                    let type_ref = type_ref.inspect(|tr| {
+                        tr.walk(&mut |tr| {
+                            if let TypeRef::ImplTrait(bounds) = tr {
+                                lower_ctx.update_impl_traits_bounds(bounds.clone());
+                            }
+                        });
+                    });
                     let bounds = if let Some(l) = assoc_type_arg.type_bound_list() {
                         l.bounds()
                             .map(|it| Interned::new(TypeBound::from_ast(lower_ctx, it)))

crates/hir-def/src/resolver.rs

@@ -1,5 +1,5 @@
 //! Name resolution façade.
-use std::{fmt, hash::BuildHasherDefault, mem};
+use std::{fmt, hash::BuildHasherDefault, iter, mem};
 
 use base_db::CrateId;
 use hir_expand::{
@@ -591,13 +591,13 @@ impl Resolver {
 
     pub fn where_predicates_in_scope(
         &self,
-    ) -> impl Iterator<Item = &crate::generics::WherePredicate> {
+    ) -> impl Iterator<Item = (&crate::generics::WherePredicate, &GenericDefId)> {
         self.scopes()
             .filter_map(|scope| match scope {
-                Scope::GenericParams { params, .. } => Some(params),
+                Scope::GenericParams { params, def } => Some((params, def)),
                 _ => None,
             })
-            .flat_map(|params| params.where_predicates.iter())
+            .flat_map(|(params, def)| params.where_predicates.iter().zip(iter::repeat(def)))
     }
 
     pub fn generic_def(&self) -> Option<GenericDefId> {