Auto merge of rust-lang#126161 - Bryanskiy:delegation-generics-4, r=<try>

Delegation: support generics in associated delegation items

This is a continuation of rust-lang#125929.

[design](https://github.com/Bryanskiy/posts/blob/master/delegation%20in%20generic%20contexts.md)

Generic parameters inheritance was implemented in all contexts. Generic arguments are not yet supported.

r? `@petrochenkov`

Author: bors

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -59,6 +59,12 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
     let hir_id = tcx.local_def_id_to_hir_id(def_id);
 
     let node = tcx.hir_node(hir_id);
+    if let Some(sig) = node.fn_sig()
+        && let Some(sig_id) = sig.decl.opt_delegation_sig_id()
+    {
+        return inherit_generics_for_delegation_item(tcx, def_id, sig_id);
+    }
+
     let parent_def_id = match node {
         Node::ImplItem(_)
         | Node::TraitItem(_)
@@ -229,16 +235,6 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                 // inherit the generics of the item.
                 Some(parent.to_def_id())
             }
-            ItemKind::Fn(sig, _, _) => {
-                // For a delegation item inherit generics from callee.
-                if let Some(sig_id) = sig.decl.opt_delegation_sig_id()
-                    && let Some(generics) =
-                        inherit_generics_for_delegation_item(tcx, def_id, sig_id)
-                {
-                    return generics;
-                }
-                None
-            }
             _ => None,
         },
         _ => None,

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -138,6 +138,12 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     let hir_id = tcx.local_def_id_to_hir_id(def_id);
     let node = tcx.hir_node(hir_id);
 
+    if let Some(sig) = node.fn_sig()
+        && let Some(sig_id) = sig.decl.opt_delegation_sig_id()
+    {
+        return inherit_predicates_for_delegation_item(tcx, def_id, sig_id);
+    }
+
     let mut is_trait = None;
     let mut is_default_impl_trait = None;
 
@@ -164,16 +170,6 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
             ItemKind::Trait(_, _, _, self_bounds, ..) | ItemKind::TraitAlias(_, self_bounds) => {
                 is_trait = Some(self_bounds);
             }
-
-            ItemKind::Fn(sig, _, _) => {
-                // For a delegation item inherit predicates from callee.
-                if let Some(sig_id) = sig.decl.opt_delegation_sig_id()
-                    && let Some(predicates) =
-                        inherit_predicates_for_delegation_item(tcx, def_id, sig_id)
-                {
-                    return predicates;
-                }
-            }
             _ => {}
         }
     };