From 614951142627294161f093adcddaeee299edad69 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fran=C3=A7ois=20Garillot?= <francois@garillot.net>
Date: Wed, 27 Sep 2023 08:25:29 -0400
Subject: [PATCH] feat: Implement Debug trait for sync variants FrozenMap and
 FrozenVec

- partially contributes to #32,
- Implements `Debug` trait for those structures where checking for reentrancy is straightforward.
---
 src/sync.rs | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/src/sync.rs b/src/sync.rs
index a551b9a..c936846 100644
--- a/src/sync.rs
+++ b/src/sync.rs
@@ -11,6 +11,7 @@ use std::alloc::Layout;
 use std::borrow::Borrow;
 use std::collections::BTreeMap;
 use std::collections::HashMap;
+use std::fmt;
 use std::hash::Hash;
 use std::iter::{FromIterator, IntoIterator};
 use std::ops::Index;
@@ -27,6 +28,26 @@ pub struct FrozenMap<K, V> {
     map: RwLock<HashMap<K, V>>,
 }
 
+impl<K, V> fmt::Debug for FrozenMap<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut d = f.debug_struct("FrozenMap");
+        match self.map.try_read() {
+            Ok(guard) => {
+                d.field("map", &&*guard);
+            },
+            Err(TryLockError::WouldBlock) => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                        f.write_str("<locked>")
+                    }
+                }
+                d.field("map", &LockedPlaceholder);
+            },
+        }
+        d.finish_non_exhaustive()
+}
+
 impl<K, V> Default for FrozenMap<K, V> {
     fn default() -> Self {
         Self {
@@ -387,6 +408,26 @@ pub struct FrozenVec<T> {
     vec: RwLock<Vec<T>>,
 }
 
+impl<K, V> fmt::Debug for FrozenVec<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut d = f.debug_struct("FrozenVec");
+        match self.map.try_read() {
+            Ok(guard) => {
+                d.field("vec", &&*guard);
+            },
+            Err(TryLockError::WouldBlock) => {
+                struct LockedPlaceholder;
+                impl fmt::Debug for LockedPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                        f.write_str("<locked>")
+                    }
+                }
+                d.field("vec", &LockedPlaceholder);
+            },
+        }
+        d.finish_non_exhaustive()
+}
+
 impl<T> FrozenVec<T> {
     /// Returns the number of elements in the vector.
     pub fn len(&self) -> usize {