Implement safe metadata Debug output

src/guard.rs

@@ -1,4 +1,5 @@
 use crate::TypeErasedVec;
+use std::fmt;
 use std::marker::PhantomData;
 use std::mem::ManuallyDrop;
 
@@ -11,6 +12,17 @@ pub struct ContentGuard<'vec, T> {
     _phantom: PhantomData<T>,
 }
 
+impl<T> fmt::Debug for ContentGuard<'_, T> {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter
+            .debug_struct("ContentGuard")
+            .field("layout", &self.erased.layout())
+            .field("length", &self.erased.length())
+            .field("capacity", &self.erased.capacity())
+            .finish()
+    }
+}
+
 impl<'vec, T> ContentGuard<'vec, T> {
     pub(crate) fn new_scoped(erased: &'vec mut TypeErasedVec) -> Self {
         debug_assert!(!std::mem::needs_drop::<T>());

src/lib.rs

@@ -12,6 +12,7 @@ pub use guard::ContentGuard;
 pub use send::{SendSyncTypeErasedVec, SendTypeErasedVec, SendableTypeErasedVec};
 
 use std::alloc::Layout;
+use std::fmt;
 use vtable::TypeErasedVecVtable;
 
 use crate::parts::VecParts;
@@ -50,6 +51,17 @@ pub struct TypeErasedVec {
     pub(crate) vtable: TypeErasedVecVtable,
 }
 
+impl fmt::Debug for TypeErasedVec {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter
+            .debug_struct("TypeErasedVec")
+            .field("layout", &self.layout)
+            .field("length", &self.parts.len)
+            .field("capacity", &self.parts.cap)
+            .finish()
+    }
+}
+
 impl TypeErasedVec {
     /// Type erase the underlying Capacity of a `Vec` remembering the `Layout` it was allocated with.
     /// Elements inside the `Vec` are retained.

src/send.rs

@@ -1,5 +1,6 @@
 use crate::{ContentGuard, TypeErasedVec};
 use std::alloc::Layout;
+use std::fmt;
 
 macro_rules! define_thread_safe_erased_vec {
     (
@@ -10,6 +11,17 @@ macro_rules! define_thread_safe_erased_vec {
         $(#[$meta])*
         pub struct $name(TypeErasedVec);
 
+        impl fmt::Debug for $name {
+            fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+                formatter
+                    .debug_struct(stringify!($name))
+                    .field("layout", &self.0.layout())
+                    .field("length", &self.0.length())
+                    .field("capacity", &self.0.capacity())
+                    .finish()
+            }
+        }
+
         impl $name {
             /// Type erase a vector while retaining its elements and allocation.
             #[must_use]