rustc_ast_lowering: Stop lowering imports into multiple items

Lower them into a single item with multiple resolutions instead.
This also allows to remove additional `NodId`s and `DefId`s related to those additional items.

compiler/rustc_ast/src/ast.rs

@@ -2517,10 +2517,7 @@ pub struct Variant {
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum UseTreeKind {
     /// `use prefix` or `use prefix as rename`
-    ///
-    /// The extra `NodeId`s are for HIR lowering, when additional statements are created for each
-    /// namespace.
-    Simple(Option<Ident>, NodeId, NodeId),
+    Simple(Option<Ident>),
     /// `use prefix::{...}`
     Nested(Vec<(UseTree, NodeId)>),
     /// `use prefix::*`
@@ -2539,8 +2536,8 @@ pub struct UseTree {
 impl UseTree {
     pub fn ident(&self) -> Ident {
         match self.kind {
-            UseTreeKind::Simple(Some(rename), ..) => rename,
-            UseTreeKind::Simple(None, ..) => {
+            UseTreeKind::Simple(Some(rename)) => rename,
+            UseTreeKind::Simple(None) => {
                 self.prefix.segments.last().expect("empty prefix in a simple import").ident
             }
             _ => panic!("`UseTree::ident` can only be used on a simple import"),

compiler/rustc_ast/src/mut_visit.rs

@@ -410,11 +410,7 @@ pub fn noop_visit_use_tree<T: MutVisitor>(use_tree: &mut UseTree, vis: &mut T) {
     let UseTree { prefix, kind, span } = use_tree;
     vis.visit_path(prefix);
     match kind {
-        UseTreeKind::Simple(rename, id1, id2) => {
-            visit_opt(rename, |rename| vis.visit_ident(rename));
-            vis.visit_id(id1);
-            vis.visit_id(id2);
-        }
+        UseTreeKind::Simple(rename) => visit_opt(rename, |rename| vis.visit_ident(rename)),
         UseTreeKind::Nested(items) => {
             for (tree, id) in items {
                 vis.visit_use_tree(tree);

compiler/rustc_ast/src/visit.rs

@@ -439,7 +439,7 @@ pub fn walk_path<'a, V: Visitor<'a>>(visitor: &mut V, path: &'a Path) {
 pub fn walk_use_tree<'a, V: Visitor<'a>>(visitor: &mut V, use_tree: &'a UseTree, id: NodeId) {
     visitor.visit_path(&use_tree.prefix, id);
     match &use_tree.kind {
-        UseTreeKind::Simple(rename, ..) => {
+        UseTreeKind::Simple(rename) => {
             // The extra IDs are handled during HIR lowering.
             if let &Some(rename) = rename {
                 visitor.visit_ident(rename);

compiler/rustc_ast_lowering/src/item.rs

@@ -19,7 +19,6 @@ use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{Span, Symbol};
 use rustc_target::spec::abi;
 use smallvec::{smallvec, SmallVec};
-use std::iter;
 use thin_vec::ThinVec;
 
 pub(super) struct ItemLowerer<'a, 'hir> {
@@ -179,36 +178,22 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let mut node_ids =
             smallvec![hir::ItemId { owner_id: hir::OwnerId { def_id: self.local_def_id(i.id) } }];
         if let ItemKind::Use(use_tree) = &i.kind {
-            self.lower_item_id_use_tree(use_tree, i.id, &mut node_ids);
+            self.lower_item_id_use_tree(use_tree, &mut node_ids);
         }
         node_ids
     }
 
-    fn lower_item_id_use_tree(
-        &mut self,
-        tree: &UseTree,
-        base_id: NodeId,
-        vec: &mut SmallVec<[hir::ItemId; 1]>,
-    ) {
+    fn lower_item_id_use_tree(&mut self, tree: &UseTree, vec: &mut SmallVec<[hir::ItemId; 1]>) {
         match &tree.kind {
             UseTreeKind::Nested(nested_vec) => {
                 for &(ref nested, id) in nested_vec {
                     vec.push(hir::ItemId {
                         owner_id: hir::OwnerId { def_id: self.local_def_id(id) },
                     });
-                    self.lower_item_id_use_tree(nested, id, vec);
-                }
-            }
-            UseTreeKind::Glob => {}
-            UseTreeKind::Simple(_, id1, id2) => {
-                for (_, id) in
-                    iter::zip(self.expect_full_res_from_use(base_id).skip(1), [*id1, *id2])
-                {
-                    vec.push(hir::ItemId {
-                        owner_id: hir::OwnerId { def_id: self.local_def_id(id) },
-                    });
+                    self.lower_item_id_use_tree(nested, vec);
                 }
             }
+            UseTreeKind::Simple(..) | UseTreeKind::Glob => {}
         }
     }
 
@@ -489,7 +474,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let segments = prefix.segments.iter().chain(path.segments.iter()).cloned().collect();
 
         match tree.kind {
-            UseTreeKind::Simple(rename, id1, id2) => {
+            UseTreeKind::Simple(rename) => {
                 *ident = tree.ident();
 
                 // First, apply the prefix to the path.
@@ -505,58 +490,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     }
                 }
 
-                let mut resolutions = self.expect_full_res_from_use(id).fuse();
-                // We want to return *something* from this function, so hold onto the first item
-                // for later.
-                let ret_res = smallvec![self.lower_res(resolutions.next().unwrap_or(Res::Err))];
-
-                // Here, we are looping over namespaces, if they exist for the definition
-                // being imported. We only handle type and value namespaces because we
-                // won't be dealing with macros in the rest of the compiler.
-                // Essentially a single `use` which imports two names is desugared into
-                // two imports.
-                for new_node_id in [id1, id2] {
-                    let new_id = self.local_def_id(new_node_id);
-                    let Some(res) = resolutions.next() else {
-                        debug_assert!(self.children.iter().find(|(id, _)| id == &new_id).is_none());
-                        // Associate an HirId to both ids even if there is no resolution.
-                        self.children.push((
-                            new_id,
-                            hir::MaybeOwner::NonOwner(hir::HirId::make_owner(new_id))),
-                        );
-                        continue;
-                    };
-                    let ident = *ident;
-                    let mut path = path.clone();
-                    for seg in &mut path.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;
-                    }
-                    let span = path.span;
-
-                    self.with_hir_id_owner(new_node_id, |this| {
-                        let res = smallvec![this.lower_res(res)];
-                        let path = this.lower_use_path(res, &path, ParamMode::Explicit);
-                        let kind = hir::ItemKind::Use(path, hir::UseKind::Single);
-                        if let Some(attrs) = attrs {
-                            this.attrs.insert(hir::ItemLocalId::new(0), attrs);
-                        }
-
-                        let item = hir::Item {
-                            owner_id: hir::OwnerId { def_id: new_id },
-                            ident: this.lower_ident(ident),
-                            kind,
-                            vis_span,
-                            span: this.lower_span(span),
-                        };
-                        hir::OwnerNode::Item(this.arena.alloc(item))
-                    });
-                }
-
-                let path = self.lower_use_path(ret_res, &path, ParamMode::Explicit);
+                let res =
+                    self.expect_full_res_from_use(id).map(|res| self.lower_res(res)).collect();
+                let path = self.lower_use_path(res, &path, ParamMode::Explicit);
                 hir::ItemKind::Use(path, hir::UseKind::Single)
             }
             UseTreeKind::Glob => {
@@ -633,8 +569,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     });
                 }
 
-                let res = self.expect_full_res_from_use(id).next().unwrap_or(Res::Err);
-                let res = smallvec![self.lower_res(res)];
+                let res =
+                    self.expect_full_res_from_use(id).map(|res| self.lower_res(res)).collect();
                 let path = self.lower_use_path(res, &prefix, ParamMode::Explicit);
                 hir::ItemKind::Use(path, hir::UseKind::ListStem)
             }

compiler/rustc_ast_pretty/src/pprust/state/item.rs

@@ -663,7 +663,7 @@ impl<'a> State<'a> {
 
     fn print_use_tree(&mut self, tree: &ast::UseTree) {
         match &tree.kind {
-            ast::UseTreeKind::Simple(rename, ..) => {
+            ast::UseTreeKind::Simple(rename) => {
                 self.print_path(&tree.prefix, false, 0);
                 if let &Some(rename) = rename {
                     self.nbsp();

compiler/rustc_builtin_macros/src/assert/context.rs

@@ -106,7 +106,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
             (
                 UseTree {
                     prefix: this.cx.path(this.span, vec![Ident::with_dummy_span(sym)]),
-                    kind: UseTreeKind::Simple(None, DUMMY_NODE_ID, DUMMY_NODE_ID),
+                    kind: UseTreeKind::Simple(None),
                     span: this.span,
                 },
                 DUMMY_NODE_ID,

compiler/rustc_lint/src/unused.rs

@@ -1264,7 +1264,7 @@ impl UnusedImportBraces {
 
             // Trigger the lint if the nested item is a non-self single item
             let node_name = match items[0].0.kind {
-                ast::UseTreeKind::Simple(rename, ..) => {
+                ast::UseTreeKind::Simple(rename) => {
                     let orig_ident = items[0].0.prefix.segments.last().unwrap().ident;
                     if orig_ident.name == kw::SelfLower {
                         return;

compiler/rustc_parse/src/parser/item.rs

@@ -1012,7 +1012,7 @@ impl<'a> Parser<'a> {
                     prefix.span = lo.to(self.prev_token.span);
                 }
 
-                UseTreeKind::Simple(self.parse_rename()?, DUMMY_NODE_ID, DUMMY_NODE_ID)
+                UseTreeKind::Simple(self.parse_rename()?)
             }
         };
 

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -445,19 +445,13 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
             prefix.is_empty() || prefix.len() == 1 && prefix[0].ident.name == kw::PathRoot
         };
         match use_tree.kind {
-            ast::UseTreeKind::Simple(rename, id1, id2) => {
+            ast::UseTreeKind::Simple(rename) => {
                 let mut ident = use_tree.ident();
                 let mut module_path = prefix;
                 let mut source = module_path.pop().unwrap();
                 let mut type_ns_only = false;
 
                 self.r.visibilities.insert(self.r.local_def_id(id), vis);
-                if id1 != ast::DUMMY_NODE_ID {
-                    self.r.visibilities.insert(self.r.local_def_id(id1), vis);
-                }
-                if id2 != ast::DUMMY_NODE_ID {
-                    self.r.visibilities.insert(self.r.local_def_id(id2), vis);
-                }
 
                 if nested {
                     // Correctly handle `self`
@@ -565,7 +559,6 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                     type_ns_only,
                     nested,
                     id,
-                    additional_ids: (id1, id2),
                 };
 
                 self.add_import(module_path, kind, use_tree.span, item, root_span, item.id, vis);
@@ -621,11 +614,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                     let new_span = prefix[prefix.len() - 1].ident.span;
                     let tree = ast::UseTree {
                         prefix: ast::Path::from_ident(Ident::new(kw::SelfLower, new_span)),
-                        kind: ast::UseTreeKind::Simple(
-                            Some(Ident::new(kw::Underscore, new_span)),
-                            ast::DUMMY_NODE_ID,
-                            ast::DUMMY_NODE_ID,
-                        ),
+                        kind: ast::UseTreeKind::Simple(Some(Ident::new(kw::Underscore, new_span))),
                         span: use_tree.span,
                     };
                     self.build_reduced_graph_for_use_tree(

compiler/rustc_resolve/src/def_collector.rs

@@ -158,14 +158,6 @@ impl<'a, 'b> visit::Visitor<'a> for DefCollector<'a, 'b> {
 
     fn visit_use_tree(&mut self, use_tree: &'a UseTree, id: NodeId, _nested: bool) {
         self.create_def(id, DefPathData::Use, use_tree.span);
-        match use_tree.kind {
-            UseTreeKind::Simple(_, id1, id2) => {
-                self.create_def(id1, DefPathData::Use, use_tree.prefix.span);
-                self.create_def(id2, DefPathData::Use, use_tree.prefix.span);
-            }
-            UseTreeKind::Glob => (),
-            UseTreeKind::Nested(..) => {}
-        }
         visit::walk_use_tree(self, use_tree, id);
     }
 

compiler/rustc_resolve/src/effective_visibilities.rs

@@ -1,4 +1,4 @@
-use crate::{ImportKind, NameBinding, NameBindingKind, Resolver, ResolverTree};
+use crate::{NameBinding, NameBindingKind, Resolver, ResolverTree};
 use rustc_ast::ast;
 use rustc_ast::visit;
 use rustc_ast::visit::Visitor;
@@ -104,28 +104,11 @@ impl<'r, 'a> EffectiveVisibilitiesVisitor<'r, 'a> {
         for (binding, eff_vis) in visitor.import_effective_visibilities.iter() {
             let NameBindingKind::Import { import, .. } = binding.kind else { unreachable!() };
             if let Some(node_id) = import.id() {
-                let mut update = |node_id| {
-                    r.effective_visibilities.update_eff_vis(
-                        r.local_def_id(node_id),
-                        eff_vis,
-                        ResolverTree(&r.definitions, &r.crate_loader),
-                    )
-                };
-                update(node_id);
-                if let ImportKind::Single { additional_ids: (id1, id2), .. } = import.kind {
-                    // In theory all the single import IDs have individual visibilities and
-                    // effective visibilities, but in practice these IDs go straight to HIR
-                    // where all their few uses assume that their (effective) visibility
-                    // applies to the whole syntactic `use` item. So they all get the same
-                    // value which is the maximum of all bindings. Maybe HIR for imports
-                    // shouldn't use three IDs at all.
-                    if id1 != ast::DUMMY_NODE_ID {
-                        update(id1);
-                    }
-                    if id2 != ast::DUMMY_NODE_ID {
-                        update(id2);
-                    }
-                }
+                r.effective_visibilities.update_eff_vis(
+                    r.local_def_id(node_id),
+                    eff_vis,
+                    ResolverTree(&r.definitions, &r.crate_loader),
+                )
             }
         }
 

compiler/rustc_resolve/src/imports.rs

@@ -56,9 +56,6 @@ pub enum ImportKind<'a> {
         /// If this is the import for `foo::bar::a`, we would have the ID of the `UseTree`
         /// for `a` in this field.
         id: NodeId,
-        /// Additional `NodeId`s allocated to a `ast::UseTree` for automatically generated `use` statement
-        /// (eg. implicit struct constructors)
-        additional_ids: (NodeId, NodeId),
     },
     Glob {
         is_prelude: bool,
@@ -88,7 +85,6 @@ impl<'a> std::fmt::Debug for ImportKind<'a> {
                 ref type_ns_only,
                 ref nested,
                 ref id,
-                ref additional_ids,
                 // Ignore the following to avoid an infinite loop while printing.
                 source_bindings: _,
                 target_bindings: _,
@@ -99,7 +95,6 @@ impl<'a> std::fmt::Debug for ImportKind<'a> {
                 .field("type_ns_only", type_ns_only)
                 .field("nested", nested)
                 .field("id", id)
-                .field("additional_ids", additional_ids)
                 .finish_non_exhaustive(),
             Glob { ref is_prelude, ref max_vis, ref id } => f
                 .debug_struct("Glob")

src/librustdoc/json/mod.rs

@@ -225,10 +225,10 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
 
                 types::ItemEnum::Function(_)
                 | types::ItemEnum::Module(_)
+                | types::ItemEnum::Import(_)
                 | types::ItemEnum::AssocConst { .. }
                 | types::ItemEnum::AssocType { .. } => true,
                 types::ItemEnum::ExternCrate { .. }
-                | types::ItemEnum::Import(_)
                 | types::ItemEnum::StructField(_)
                 | types::ItemEnum::Variant(_)
                 | types::ItemEnum::TraitAlias(_)

src/test/ui/consts/miri_unleashed/tls.stderr

@@ -2,13 +2,13 @@ error[E0080]: could not evaluate static initializer
   --> $DIR/tls.rs:11:25
    |
 LL |     unsafe { let _val = A; }
-   |                         ^ cannot access thread local static (DefId(0:6 ~ tls[78b0]::A))
+   |                         ^ cannot access thread local static (DefId(0:4 ~ tls[78b0]::A))
 
 error[E0080]: could not evaluate static initializer
   --> $DIR/tls.rs:18:26
    |
 LL |     unsafe { let _val = &A; }
-   |                          ^ cannot access thread local static (DefId(0:6 ~ tls[78b0]::A))
+   |                          ^ cannot access thread local static (DefId(0:4 ~ tls[78b0]::A))
 
 warning: skipping const checks
    |

src/test/ui/generator/print/generator-print-verbose-1.stderr

@@ -9,7 +9,7 @@ note: generator is not `Send` as this value is used across a yield
   --> $DIR/generator-print-verbose-1.rs:35:9
    |
 LL |         let _non_send_gen = make_non_send_generator();
-   |             ------------- has type `Opaque(DefId(0:44 ~ generator_print_verbose_1[749a]::make_non_send_generator::{opaque#0}), [])` which is not `Send`
+   |             ------------- has type `Opaque(DefId(0:34 ~ generator_print_verbose_1[749a]::make_non_send_generator::{opaque#0}), [])` which is not `Send`
 LL |         yield;
    |         ^^^^^ yield occurs here, with `_non_send_gen` maybe used later
 LL |     };
@@ -35,17 +35,17 @@ note: required because it's used within this generator
    |
 LL |     || {
    |     ^^
-note: required because it appears within the type `Opaque(DefId(0:45 ~ generator_print_verbose_1[749a]::make_gen2::{opaque#0}), [std::sync::Arc<std::cell::RefCell<i32>>])`
+note: required because it appears within the type `Opaque(DefId(0:35 ~ generator_print_verbose_1[749a]::make_gen2::{opaque#0}), [std::sync::Arc<std::cell::RefCell<i32>>])`
   --> $DIR/generator-print-verbose-1.rs:41:30
    |
 LL | pub fn make_gen2<T>(t: T) -> impl Generator<Return = T> {
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: required because it appears within the type `Opaque(DefId(0:46 ~ generator_print_verbose_1[749a]::make_non_send_generator2::{opaque#0}), [])`
+note: required because it appears within the type `Opaque(DefId(0:36 ~ generator_print_verbose_1[749a]::make_non_send_generator2::{opaque#0}), [])`
   --> $DIR/generator-print-verbose-1.rs:47:34
    |
 LL | fn make_non_send_generator2() -> impl Generator<Return = Arc<RefCell<i32>>> {
    |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: required because it captures the following types: `Opaque(DefId(0:46 ~ generator_print_verbose_1[749a]::make_non_send_generator2::{opaque#0}), [])`, `()`
+   = note: required because it captures the following types: `Opaque(DefId(0:36 ~ generator_print_verbose_1[749a]::make_non_send_generator2::{opaque#0}), [])`, `()`
 note: required because it's used within this generator
   --> $DIR/generator-print-verbose-1.rs:52:20
    |