fix: readable Debug for Layers (#3575)

#3536 added the custom Debug implementations but it using derived Debug
on Key lead to too verbose output. Instead of making `Key`'s `Debug`
unconditionally or conditionally do the `Display` variant (for table
space'd keys), opted to build a newtype to provide `Debug` for
`Range<Key>` via `Display` which seemed to work unconditionally.

Also orders Key to have: 1. comment, 2. derive, 3. `struct Key`.

pageserver/src/repository.rs

@@ -7,11 +7,11 @@ use std::fmt;
 use std::ops::{AddAssign, Range};
 use std::time::Duration;
 
-#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, Ord, PartialOrd, Serialize, Deserialize)]
 /// Key used in the Repository kv-store.
 ///
 /// The Repository treats this as an opaque struct, but see the code in pgdatadir_mapping.rs
 /// for what we actually store in these fields.
+#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, Ord, PartialOrd, Serialize, Deserialize)]
 pub struct Key {
     pub field1: u8,
     pub field2: u32,

pageserver/src/tenant/storage_layer.rs

@@ -448,3 +448,14 @@ enum PathOrConf {
     Path(PathBuf),
     Conf(&'static PageServerConf),
 }
+
+/// Range wrapping newtype, which uses display to render Debug.
+///
+/// Useful with `Key`, which has too verbose `{:?}` for printing multiple layers.
+struct RangeDisplayDebug<'a, T: std::fmt::Display>(&'a Range<T>);
+
+impl<'a, T: std::fmt::Display> std::fmt::Debug for RangeDisplayDebug<'a, T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}..{}", self.0.start, self.0.end)
+    }
+}

pageserver/src/tenant/storage_layer/delta_layer.rs

@@ -194,8 +194,10 @@ pub struct DeltaLayer {
 
 impl std::fmt::Debug for DeltaLayer {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        use super::RangeDisplayDebug;
+
         f.debug_struct("DeltaLayer")
-            .field("key_range", &self.key_range)
+            .field("key_range", &RangeDisplayDebug(&self.key_range))
             .field("lsn_range", &self.lsn_range)
             .field("file_size", &self.file_size)
             .field("inner", &self.inner)

pageserver/src/tenant/storage_layer/filename.rs

@@ -10,12 +10,23 @@ use std::str::FromStr;
 use utils::lsn::Lsn;
 
 // Note: Timeline::load_layer_map() relies on this sort order
-#[derive(Debug, PartialEq, Eq, Clone, Hash)]
+#[derive(PartialEq, Eq, Clone, Hash)]
 pub struct DeltaFileName {
     pub key_range: Range<Key>,
     pub lsn_range: Range<Lsn>,
 }
 
+impl std::fmt::Debug for DeltaFileName {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use super::RangeDisplayDebug;
+
+        f.debug_struct("DeltaFileName")
+            .field("key_range", &RangeDisplayDebug(&self.key_range))
+            .field("lsn_range", &self.lsn_range)
+            .finish()
+    }
+}
+
 impl PartialOrd for DeltaFileName {
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
         Some(self.cmp(other))
@@ -100,12 +111,23 @@ impl fmt::Display for DeltaFileName {
     }
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, Hash)]
+#[derive(PartialEq, Eq, Clone, Hash)]
 pub struct ImageFileName {
     pub key_range: Range<Key>,
     pub lsn: Lsn,
 }
 
+impl std::fmt::Debug for ImageFileName {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use super::RangeDisplayDebug;
+
+        f.debug_struct("ImageFileName")
+            .field("key_range", &RangeDisplayDebug(&self.key_range))
+            .field("lsn", &self.lsn)
+            .finish()
+    }
+}
+
 impl PartialOrd for ImageFileName {
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
         Some(self.cmp(other))

pageserver/src/tenant/storage_layer/image_layer.rs

@@ -119,8 +119,10 @@ pub struct ImageLayer {
 
 impl std::fmt::Debug for ImageLayer {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        use super::RangeDisplayDebug;
+
         f.debug_struct("ImageLayer")
-            .field("key_range", &self.key_range)
+            .field("key_range", &RangeDisplayDebug(&self.key_range))
             .field("file_size", &self.file_size)
             .field("lsn", &self.lsn)
             .field("inner", &self.inner)