avoid clone path prefix when lowering to hir

Signed-off-by: SparrowLii <liyuan179@huawei.com>

Author: SparrowLii

compiler/rustc_ast_lowering/src/item.rs

@@ -551,17 +551,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 for &(ref use_tree, id) in trees {
                     let new_hir_id = self.local_def_id(id);
 
-                    let mut prefix = prefix.clone();
-
-                    // Give the segments new node-ids since they are being cloned.
-                    for seg in &mut prefix.segments {
-                        // Give the cloned segment the same resolution information
-                        // as the old one (this is needed for stability checking).
-                        let new_id = self.next_node_id();
-                        self.resolver.clone_res(seg.id, new_id);
-                        seg.id = new_id;
-                    }
-
                     // Each `use` import is an item and thus are owners of the
                     // names in the path. Up to this point the nested import is
                     // the current owner, since we want each desugared import to

compiler/rustc_ast_lowering/src/lib.rs

@@ -148,10 +148,6 @@ trait ResolverAstLoweringExt {
     fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>>;
     fn get_partial_res(&self, id: NodeId) -> Option<PartialRes>;
     fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
-    // Clones the resolution (if any) on 'source' and applies it
-    // to 'target'. Used when desugaring a `UseTreeKind::Nested` to
-    // multiple `UseTreeKind::Simple`s
-    fn clone_res(&mut self, source: NodeId, target: NodeId);
     fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
     fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
     fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
@@ -184,12 +180,6 @@ impl ResolverAstLoweringExt for ResolverAstLowering {
         None
     }
 
-    fn clone_res(&mut self, source: NodeId, target: NodeId) {
-        if let Some(res) = self.partial_res_map.get(&source) {
-            self.partial_res_map.insert(target, *res);
-        }
-    }
-
     /// Obtains resolution for a `NodeId` with a single resolution.
     fn get_partial_res(&self, id: NodeId) -> Option<PartialRes> {
         self.partial_res_map.get(&id).copied()