Improve vortex-buffer Debug repr (#1901)

Author: gatesn

vortex-buffer/src/buffer.rs

@@ -1,10 +1,12 @@
+use std::any::type_name;
 use std::collections::Bound;
 use std::fmt::{Debug, Formatter};
 use std::ops::{Deref, RangeBounds};
 
 use bytes::{Buf, Bytes};
 use vortex_error::{vortex_panic, VortexExpect};
 
+use crate::debug::TruncatedDebug;
 use crate::{Alignment, BufferMut, ByteBuffer};
 
 /// An immutable buffer of items of `T`.
@@ -281,21 +283,13 @@ impl<T> Buffer<T> {
     }
 }
 
-impl<T> Debug for Buffer<T> {
+impl<T: Debug> Debug for Buffer<T> {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
-        const TRUNC_SIZE: usize = 512;
-        let mut binding = f.debug_struct("Buffer");
-        let mut fields = binding
+        f.debug_struct(&format!("Buffer<{}>", type_name::<T>()))
             .field("length", &self.length)
-            .field("alignment", &self.alignment);
-
-        let mut bytes = self.bytes.clone();
-        if bytes.len() > TRUNC_SIZE {
-            fields = fields.field("truncated", &true);
-        }
-
-        bytes.truncate(TRUNC_SIZE);
-        fields.field("bytes", &bytes).finish()
+            .field("alignment", &self.alignment)
+            .field("as_slice", &TruncatedDebug(self.as_slice()))
+            .finish()
     }
 }
 

vortex-buffer/src/buffer_mut.rs

@@ -1,11 +1,13 @@
 use core::mem::MaybeUninit;
+use std::any::type_name;
 use std::fmt::{Debug, Formatter};
 use std::ops::{Deref, DerefMut};
 
 use bytes::buf::UninitSlice;
 use bytes::{Buf, BufMut, BytesMut};
 use vortex_error::{vortex_panic, VortexExpect};
 
+use crate::debug::TruncatedDebug;
 use crate::{Alignment, Buffer, ByteBufferMut};
 
 /// A mutable buffer that maintains a runtime-defined alignment through resizing operations.
@@ -338,21 +340,13 @@ impl<T> Clone for BufferMut<T> {
     }
 }
 
-impl<T> Debug for BufferMut<T> {
+impl<T: Debug> Debug for BufferMut<T> {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
-        const TRUNC_SIZE: usize = 512;
-        let mut binding = f.debug_struct("Buffer");
-        let mut fields = binding
+        f.debug_struct(&format!("BufferMut<{}>", type_name::<T>()))
             .field("length", &self.length)
-            .field("alignment", &self.alignment);
-
-        let mut bytes = self.bytes.clone();
-        if bytes.len() > TRUNC_SIZE {
-            fields = fields.field("truncated", &true);
-        }
-
-        bytes.truncate(TRUNC_SIZE);
-        fields.field("bytes", &bytes).finish()
+            .field("alignment", &self.alignment)
+            .field("as_slice", &TruncatedDebug(self.as_slice()))
+            .finish()
     }
 }
 

vortex-buffer/src/debug.rs

@@ -0,0 +1,20 @@
+use std::fmt::{Debug, Formatter};
+
+/// A wrapper around a slice that truncates the debug output if it is too long.
+pub(crate) struct TruncatedDebug<'a, T>(pub(crate) &'a [T]);
+
+impl<T: Debug> Debug for TruncatedDebug<'_, T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        const TRUNC_SIZE: usize = 16;
+        if self.0.len() <= TRUNC_SIZE {
+            write!(f, "{:?}", self.0)
+        } else {
+            write!(f, "[")?;
+            for elem in self.0.iter().take(TRUNC_SIZE) {
+                write!(f, "{:?}, ", *elem)?;
+            }
+            write!(f, "...")?;
+            write!(f, "]")
+        }
+    }
+}

vortex-buffer/src/lib.rs

@@ -57,6 +57,7 @@ mod buffer;
 mod buffer_mut;
 mod bytes;
 mod r#const;
+mod debug;
 mod macros;
 mod string;