From b01976aa267620719afdd0effcc0501648bbefd4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
Date: Sat, 30 Jan 2021 00:00:00 +0000
Subject: [PATCH] Precompute ancestors when checking privacy

Precompute ancestors of the old error node set so that check for private
types and traits in public interfaces can in constant time determine if
the current item has any descendants in the old error set.

No functional changes intended.
---
 compiler/rustc_privacy/src/lib.rs | 54 ++++++++++++-------------------
 1 file changed, 21 insertions(+), 33 deletions(-)

diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
index 66206ca46c3a7..3317ac2af18e5 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -1822,41 +1822,18 @@ impl DefIdVisitor<'tcx> for SearchInterfaceForPrivateItemsVisitor<'tcx> {
     }
 }
 
-struct PrivateItemsInPublicInterfacesVisitor<'a, 'tcx> {
+struct PrivateItemsInPublicInterfacesVisitor<'tcx> {
     tcx: TyCtxt<'tcx>,
     has_pub_restricted: bool,
-    old_error_set: &'a HirIdSet,
+    old_error_set_ancestry: HirIdSet,
 }
 
-impl<'a, 'tcx> PrivateItemsInPublicInterfacesVisitor<'a, 'tcx> {
+impl<'tcx> PrivateItemsInPublicInterfacesVisitor<'tcx> {
     fn check(
         &self,
         item_id: hir::HirId,
         required_visibility: ty::Visibility,
     ) -> SearchInterfaceForPrivateItemsVisitor<'tcx> {
-        let mut has_old_errors = false;
-
-        // Slow path taken only if there any errors in the crate.
-        for &id in self.old_error_set {
-            // Walk up the nodes until we find `item_id` (or we hit a root).
-            let mut id = id;
-            loop {
-                if id == item_id {
-                    has_old_errors = true;
-                    break;
-                }
-                let parent = self.tcx.hir().get_parent_node(id);
-                if parent == id {
-                    break;
-                }
-                id = parent;
-            }
-
-            if has_old_errors {
-                break;
-            }
-        }
-
         SearchInterfaceForPrivateItemsVisitor {
             tcx: self.tcx,
             item_id,
@@ -1864,7 +1841,7 @@ impl<'a, 'tcx> PrivateItemsInPublicInterfacesVisitor<'a, 'tcx> {
             span: self.tcx.hir().span(item_id),
             required_visibility,
             has_pub_restricted: self.has_pub_restricted,
-            has_old_errors,
+            has_old_errors: self.old_error_set_ancestry.contains(&item_id),
             in_assoc_ty: false,
         }
     }
@@ -1890,7 +1867,7 @@ impl<'a, 'tcx> PrivateItemsInPublicInterfacesVisitor<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for PrivateItemsInPublicInterfacesVisitor<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for PrivateItemsInPublicInterfacesVisitor<'tcx> {
     type Map = Map<'tcx>;
 
     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
@@ -2114,11 +2091,22 @@ fn check_private_in_public(tcx: TyCtxt<'_>, krate: CrateNum) {
         pub_restricted_visitor.has_pub_restricted
     };
 
+    let mut old_error_set_ancestry = HirIdSet::default();
+    for mut id in visitor.old_error_set.iter().copied() {
+        loop {
+            if !old_error_set_ancestry.insert(id) {
+                break;
+            }
+            let parent = tcx.hir().get_parent_node(id);
+            if parent == id {
+                break;
+            }
+            id = parent;
+        }
+    }
+
     // Check for private types and traits in public interfaces.
-    let mut visitor = PrivateItemsInPublicInterfacesVisitor {
-        tcx,
-        has_pub_restricted,
-        old_error_set: &visitor.old_error_set,
-    };
+    let mut visitor =
+        PrivateItemsInPublicInterfacesVisitor { tcx, has_pub_restricted, old_error_set_ancestry };
     krate.visit_all_item_likes(&mut DeepVisitor::new(&mut visitor));
 }