typeck: Use LocalDefIds for the unused trait import set

src/librustc_middle/arena.rs

@@ -114,6 +114,7 @@ macro_rules! arena_types {
 
             // This is used to decode the &'tcx [Span] for InlineAsm's line_spans.
             [decode] span: rustc_span::Span, rustc_span::Span;
+            [decode] used_trait_imports: rustc_data_structures::fx::FxHashSet<rustc_hir::def_id::LocalDefId>, rustc_data_structures::fx::FxHashSet<rustc_hir::def_id::LocalDefId>;
         ], $tcx);
     )
 }

src/librustc_middle/query/mod.rs

@@ -526,7 +526,7 @@ rustc_queries! {
     }
 
     Other {
-        query used_trait_imports(key: LocalDefId) -> &'tcx DefIdSet {
+        query used_trait_imports(key: LocalDefId) -> &'tcx FxHashSet<LocalDefId> {
             desc { |tcx| "used_trait_imports `{}`", tcx.def_path_str(key.to_def_id()) }
             cache_on_disk_if { true }
         }

src/librustc_middle/ty/context.rs

@@ -35,7 +35,7 @@ use rustc_data_structures::sync::{self, Lock, Lrc, WorkerLocal};
 use rustc_errors::ErrorReported;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, DefIdSet, LocalDefId, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
 use rustc_hir::definitions::{DefPathHash, Definitions};
 use rustc_hir::lang_items::{self, PanicLocationLangItem};
 use rustc_hir::{HirId, ItemKind, ItemLocalId, ItemLocalMap, ItemLocalSet, Node, TraitCandidate};
@@ -392,7 +392,7 @@ pub struct TypeckTables<'tcx> {
     /// This is used for warning unused imports. During type
     /// checking, this `Lrc` should not be cloned: it must have a ref-count
     /// of 1 so that we can insert things into the set mutably.
-    pub used_trait_imports: Lrc<DefIdSet>,
+    pub used_trait_imports: Lrc<FxHashSet<LocalDefId>>,
 
     /// If any errors occurred while type-checking this body,
     /// this field will be set to `Some(ErrorReported)`.

src/librustc_typeck/check/method/mod.rs

@@ -197,7 +197,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             debug!("used_trait_import: {:?}", import_id);
             Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
                 .unwrap()
-                .insert(import_id.to_def_id());
+                .insert(*import_id);
         }
 
         self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span);
@@ -461,7 +461,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let used_trait_imports = Lrc::get_mut(&mut tables.used_trait_imports).unwrap();
             for import_id in pick.import_ids {
                 debug!("resolve_ufcs: used_trait_import: {:?}", import_id);
-                used_trait_imports.insert(import_id.to_def_id());
+                used_trait_imports.insert(import_id);
             }
         }
 

src/librustc_typeck/check/mod.rs

@@ -96,7 +96,7 @@ use rustc_errors::ErrorReported;
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, DiagnosticId};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, DefIdSet, LocalDefId, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::lang_items::{
@@ -839,7 +839,7 @@ fn has_typeck_tables(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
     }
 }
 
-fn used_trait_imports(tcx: TyCtxt<'_>, def_id: LocalDefId) -> &DefIdSet {
+fn used_trait_imports(tcx: TyCtxt<'_>, def_id: LocalDefId) -> &FxHashSet<LocalDefId> {
     &*tcx.typeck_tables_of(def_id).used_trait_imports
 }
 

src/librustc_typeck/check/writeback.rs

@@ -4,10 +4,8 @@
 
 use crate::check::FnCtxt;
 
-use rustc_data_structures::sync::Lrc;
 use rustc_errors::ErrorReported;
 use rustc_hir as hir;
-use rustc_hir::def_id::DefIdSet;
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc_infer::infer::error_reporting::TypeAnnotationNeeded::E0282;
 use rustc_infer::infer::InferCtxt;
@@ -67,10 +65,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         wbcx.visit_user_provided_sigs();
         wbcx.visit_generator_interior_types();
 
-        let used_trait_imports = mem::replace(
+        let used_trait_imports = mem::take(&mut self.tables.borrow_mut().used_trait_imports);
-            &mut self.tables.borrow_mut().used_trait_imports,
-            Lrc::new(DefIdSet::default()),
-        );
         debug!("used_trait_imports({:?}) = {:?}", item_def_id, used_trait_imports);
         wbcx.tables.used_trait_imports = used_trait_imports;
 

src/librustc_typeck/check_unused.rs

@@ -1,14 +1,14 @@
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::Applicability;
 use rustc_hir as hir;
-use rustc_hir::def_id::{DefId, DefIdSet, LocalDefId, LOCAL_CRATE};
+use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::lint;
 use rustc_span::{Span, Symbol};
 
 pub fn check_crate(tcx: TyCtxt<'_>) {
-    let mut used_trait_imports = DefIdSet::default();
+    let mut used_trait_imports = FxHashSet::default();
     for &body_id in tcx.hir().krate().bodies.keys() {
         let item_def_id = tcx.hir().body_owner_def_id(body_id);
         let imports = tcx.used_trait_imports(item_def_id);
@@ -39,7 +39,7 @@ impl ItemLikeVisitor<'v> for CheckVisitor<'tcx> {
 
 struct CheckVisitor<'tcx> {
     tcx: TyCtxt<'tcx>,
-    used_trait_imports: DefIdSet,
+    used_trait_imports: FxHashSet<LocalDefId>,
 }
 
 impl CheckVisitor<'tcx> {
@@ -49,7 +49,7 @@ impl CheckVisitor<'tcx> {
             return;
         }
 
-        if self.used_trait_imports.contains(&def_id.to_def_id()) {
+        if self.used_trait_imports.contains(&def_id) {
             return;
         }