From dbe6930286a202c024cfab1236437d64689181d7 Mon Sep 17 00:00:00 2001
From: Jack Wrenn <jack@wrenn.fyi>
Date: Tue, 4 Jun 2024 13:56:40 +0000
Subject: [PATCH] privacy: normalize associated types before visiting

This permits associated types to reference private types and
traits, so long as the normalized type does not itself violate
type privacy.

Fixes #45713
---
 compiler/rustc_privacy/src/lib.rs    | 12 +++++++++++-
 tests/ui/privacy/projections2.rs     |  3 +--
 tests/ui/privacy/projections2.stderr | 19 +++++--------------
 3 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
index 2039e994aaae0..004de9f01725d 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -1298,7 +1298,17 @@ impl SearchInterfaceForPrivateItemsVisitor<'_> {
 
     fn ty(&mut self) -> &mut Self {
         self.in_primary_interface = true;
-        self.visit(self.tcx.type_of(self.item_def_id).instantiate_identity());
+        let ty = self.tcx.type_of(self.item_def_id).instantiate_identity();
+
+        // if `in_assoc_ty`, attempt to normalize `ty`
+        let maybe_normalized_ty = if self.in_assoc_ty {
+            let param_env = self.tcx.param_env(self.item_def_id);
+            self.tcx.try_normalize_erasing_regions(param_env, ty).ok()
+        } else {
+            None
+        };
+
+        self.visit(maybe_normalized_ty.unwrap_or(ty));
         self
     }
 
diff --git a/tests/ui/privacy/projections2.rs b/tests/ui/privacy/projections2.rs
index 1afbf6d196e58..b389526fcc0f7 100644
--- a/tests/ui/privacy/projections2.rs
+++ b/tests/ui/privacy/projections2.rs
@@ -17,8 +17,7 @@ mod m {
 
     impl Trait4 for u8 {
         type A<T: Trait> = <u8 as Trait3>::A<T>;
-        //~^ ERROR: private associated type `Trait3::A` in public interface
-        //~| ERROR: private trait `Trait3` in public interface
+        //~^ ERROR: private type `Priv` in public interface
     }
 }
 
diff --git a/tests/ui/privacy/projections2.stderr b/tests/ui/privacy/projections2.stderr
index 6eae9643c5a8e..9723feaa37981 100644
--- a/tests/ui/privacy/projections2.stderr
+++ b/tests/ui/privacy/projections2.stderr
@@ -11,24 +11,15 @@ LL |     struct Priv;
    |     ^^^^^^^^^^^
    = note: `#[warn(private_interfaces)]` on by default
 
-error[E0446]: private associated type `Trait3::A` in public interface
+error[E0446]: private type `Priv` in public interface
   --> $DIR/projections2.rs:19:9
    |
-LL |         type A<T: Trait>;
-   |         ---------------- `Trait3::A` declared as private
-...
-LL |         type A<T: Trait> = <u8 as Trait3>::A<T>;
-   |         ^^^^^^^^^^^^^^^^ can't leak private associated type
-
-error[E0446]: private trait `Trait3` in public interface
-  --> $DIR/projections2.rs:19:9
-   |
-LL |     trait Trait3 {
-   |     ------------ `Trait3` declared as private
+LL |     struct Priv;
+   |     ----------- `Priv` declared as private
 ...
 LL |         type A<T: Trait> = <u8 as Trait3>::A<T>;
-   |         ^^^^^^^^^^^^^^^^ can't leak private trait
+   |         ^^^^^^^^^^^^^^^^ can't leak private type
 
-error: aborting due to 2 previous errors; 1 warning emitted
+error: aborting due to 1 previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0446`.