From b110cb3dc6da68fc46b08d7b0ed40a48b3503306 Mon Sep 17 00:00:00 2001
From: Stepan Koltsov <stepan.koltsov@gmail.com>
Date: Fri, 29 Mar 2024 03:44:16 +0000
Subject: [PATCH] Require Debug for Pointee::Metadata

Useful for debugging
---
 library/core/src/ptr/metadata.rs |  2 +-
 library/core/tests/ptr.rs        | 10 +++++++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/library/core/src/ptr/metadata.rs b/library/core/src/ptr/metadata.rs
index fe19f66a31a..d3d1b3d053d 100644
--- a/library/core/src/ptr/metadata.rs
+++ b/library/core/src/ptr/metadata.rs
@@ -57,7 +57,7 @@ pub trait Pointee {
     // NOTE: Keep trait bounds in `static_assert_expected_bounds_for_metadata`
     // in `library/core/src/ptr/metadata.rs`
     // in sync with those here:
-    type Metadata: Copy + Send + Sync + Ord + Hash + Unpin;
+    type Metadata: fmt::Debug + Copy + Send + Sync + Ord + Hash + Unpin;
 }
 
 /// Pointers to types implementing this trait alias are “thin”.
diff --git a/library/core/tests/ptr.rs b/library/core/tests/ptr.rs
index 5c518e2d593..f0656f997fd 100644
--- a/library/core/tests/ptr.rs
+++ b/library/core/tests/ptr.rs
@@ -841,11 +841,19 @@ fn ptr_metadata_bounds() {
     fn static_assert_expected_bounds_for_metadata<Meta>()
     where
         // Keep this in sync with the associated type in `library/core/src/ptr/metadata.rs`
-        Meta: Copy + Send + Sync + Ord + std::hash::Hash + Unpin,
+        Meta: Debug + Copy + Send + Sync + Ord + std::hash::Hash + Unpin,
     {
     }
 }
 
+#[test]
+fn pointee_metadata_debug() {
+    assert_eq!("()", format!("{:?}", metadata::<u32>(&17)));
+    assert_eq!("2", format!("{:?}", metadata::<[u32]>(&[19, 23])));
+    let for_dyn = format!("{:?}", metadata::<dyn Debug>(&29));
+    assert!(for_dyn.starts_with("DynMetadata(0x"), "{:?}", for_dyn);
+}
+
 #[test]
 fn dyn_metadata() {
     #[derive(Debug)]