Do not preallocate UseTree HirIds.

Author: cjgillot

Diff for: compiler/rustc_ast_lowering/src/item.rs

@@ -475,7 +475,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     }
                 }
 
-                let mut resolutions = self.expect_full_res_from_use(id);
+                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 = self.lower_res(resolutions.next().unwrap_or(Res::Err));
@@ -485,7 +485,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 // 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 (res, &new_node_id) in iter::zip(resolutions, &[id1, id2]) {
+                for new_node_id in [id1, id2] {
+                    // Associate an HirId to both ids even if there is no resolution.
+                    let new_id = self.allocate_hir_id_counter(new_node_id);
+
+                    let res = if let Some(res) = resolutions.next() { res } else { continue };
                     let ident = *ident;
                     let mut path = path.clone();
                     for seg in &mut path.segments {
@@ -494,17 +498,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     let span = path.span;
 
                     self.with_hir_id_owner(new_node_id, |this| {
-                        let new_id = this.lower_node_id(new_node_id);
                         let res = this.lower_res(res);
                         let path = this.lower_path_extra(res, &path, ParamMode::Explicit, None);
                         let kind = hir::ItemKind::Use(path, hir::UseKind::Single);
                         let vis = this.rebuild_vis(&vis);
                         if let Some(attrs) = attrs {
-                            this.attrs.insert(new_id, attrs);
+                            this.attrs.insert(hir::HirId::make_owner(new_id), attrs);
                         }
 
                         this.insert_item(hir::Item {
-                            def_id: new_id.expect_owner(),
+                            def_id: new_id,
                             ident: this.lower_ident(ident),
                             kind,
                             vis,
@@ -553,7 +556,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
                 // Add all the nested `PathListItem`s to the HIR.
                 for &(ref use_tree, id) in trees {
-                    let new_hir_id = self.lower_node_id(id);
+                    let new_hir_id = self.allocate_hir_id_counter(id);
 
                     let mut prefix = prefix.clone();
 
@@ -574,11 +577,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         let kind =
                             this.lower_use_tree(use_tree, &prefix, id, &mut vis, &mut ident, attrs);
                         if let Some(attrs) = attrs {
-                            this.attrs.insert(new_hir_id, attrs);
+                            this.attrs.insert(hir::HirId::make_owner(new_hir_id), attrs);
                         }
 
                         this.insert_item(hir::Item {
-                            def_id: new_hir_id.expect_owner(),
+                            def_id: new_hir_id,
                             ident: this.lower_ident(ident),
                             kind,
                             vis,

Diff for: compiler/rustc_ast_lowering/src/lib.rs

@@ -38,7 +38,7 @@
 use rustc_ast::node_id::NodeMap;
 use rustc_ast::token::{self, Token};
 use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, TokenStream, TokenTree};
-use rustc_ast::visit::{self, Visitor};
+use rustc_ast::visit;
 use rustc_ast::{self as ast, *};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::captures::Captures;
@@ -418,48 +418,9 @@ enum AnonymousLifetimeMode {
 
 impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_crate(mut self, c: &Crate) -> &'hir hir::Crate<'hir> {
-        /// Full-crate AST visitor that inserts into a fresh
-        /// `LoweringContext` any information that may be
-        /// needed from arbitrary locations in the crate,
-        /// e.g., the number of lifetime generic parameters
-        /// declared for every type and trait definition.
-        struct MiscCollector<'tcx, 'lowering, 'hir> {
-            lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
-        }
-
-        impl MiscCollector<'_, '_, '_> {
-            fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree) {
-                match tree.kind {
-                    UseTreeKind::Simple(_, id1, id2) => {
-                        for id in [id1, id2] {
-                            self.lctx.allocate_hir_id_counter(id);
-                        }
-                    }
-                    UseTreeKind::Glob => (),
-                    UseTreeKind::Nested(ref trees) => {
-                        for &(ref use_tree, id) in trees {
-                            self.lctx.allocate_hir_id_counter(id);
-                            self.allocate_use_tree_hir_id_counters(use_tree);
-                        }
-                    }
-                }
-            }
-        }
-
-        impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
-            fn visit_item(&mut self, item: &'tcx Item) {
-                if let ItemKind::Use(ref use_tree) = item.kind {
-                    self.allocate_use_tree_hir_id_counters(use_tree);
-                }
-
-                visit::walk_item(self, item);
-            }
-        }
-
         self.lower_node_id(CRATE_NODE_ID);
         debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == Some(hir::CRATE_HIR_ID));
 
-        visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c);
         visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
 
         let module = self.arena.alloc(self.lower_mod(&c.items, c.span));

Diff for: compiler/rustc_middle/src/hir/map/mod.rs

@@ -7,7 +7,7 @@ use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::svh::Svh;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_ID, CRATE_DEF_INDEX, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash};
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
@@ -206,11 +206,6 @@ impl<'hir> Map<'hir> {
     }
 
     pub fn opt_def_kind(&self, local_def_id: LocalDefId) -> Option<DefKind> {
-        // FIXME(eddyb) support `find` on the crate root.
-        if local_def_id.to_def_id().index == CRATE_DEF_INDEX {
-            return Some(DefKind::Mod);
-        }
-
         let hir_id = self.local_def_id_to_hir_id(local_def_id);
         let def_kind = match self.find(hir_id)? {
             Node::Item(item) => match item.kind {