no-op: type aliases for Layer::iter and Layer::key_iter return types

Not needed by anything right now, but the next commit adds a `Result<>`
around iter() and key_iter()'s return types, and that makes clippy
complain.

pageserver/src/tenant/delta_layer.rs

@@ -55,7 +55,7 @@ use utils::{
 };
 
 use super::filename::LayerFileName;
-use super::storage_layer::Layer;
+use super::storage_layer::{Layer, LayerIter, LayerKeyIter};
 
 ///
 /// Header stored in the beginning of the file
@@ -391,7 +391,7 @@ impl PersistentLayer for DeltaLayer {
         self.path()
     }
 
-    fn iter<'a>(&'a self) -> Box<dyn Iterator<Item = anyhow::Result<(Key, Lsn, Value)>> + 'a> {
+    fn iter(&self) -> LayerIter<'_> {
         let inner = match self.load() {
             Ok(inner) => inner,
             Err(e) => panic!("Failed to load a delta layer: {e:?}"),
@@ -403,7 +403,7 @@ impl PersistentLayer for DeltaLayer {
         }
     }
 
-    fn key_iter<'a>(&'a self) -> Box<dyn Iterator<Item = (Key, Lsn, u64)> + 'a> {
+    fn key_iter(&self) -> LayerKeyIter<'_> {
         let inner = match self.load() {
             Ok(inner) => inner,
             Err(e) => panic!("Failed to load a delta layer: {e:?}"),

pageserver/src/tenant/image_layer.rs

@@ -21,7 +21,7 @@
 //! actual page images are stored in the "values" part.
 use crate::config::PageServerConf;
 use crate::page_cache::PAGE_SZ;
-use crate::repository::{Key, Value, KEY_SIZE};
+use crate::repository::{Key, KEY_SIZE};
 use crate::tenant::blob_io::{BlobCursor, BlobWriter, WriteBlobWriter};
 use crate::tenant::block_io::{BlockBuf, BlockReader, FileBlockReader};
 use crate::tenant::disk_btree::{DiskBtreeBuilder, DiskBtreeReader, VisitDirection};
@@ -51,7 +51,7 @@ use utils::{
 };
 
 use super::filename::LayerFileName;
-use super::storage_layer::Layer;
+use super::storage_layer::{Layer, LayerIter};
 
 ///
 /// Header stored in the beginning of the file
@@ -219,7 +219,7 @@ impl PersistentLayer for ImageLayer {
     fn get_timeline_id(&self) -> TimelineId {
         self.timeline_id
     }
-    fn iter(&self) -> Box<dyn Iterator<Item = Result<(Key, Lsn, Value)>>> {
+    fn iter(&self) -> LayerIter<'_> {
         unimplemented!();
     }
 

pageserver/src/tenant/storage_layer.rs

@@ -116,6 +116,12 @@ pub trait Layer: Send + Sync {
     fn dump(&self, verbose: bool) -> Result<()>;
 }
 
+/// Returned by [`Layer::iter`]
+pub type LayerIter<'i> = Box<dyn Iterator<Item = Result<(Key, Lsn, Value)>> + 'i>;
+
+/// Returned by [`Layer::key_iter`]
+pub type LayerKeyIter<'i> = Box<dyn Iterator<Item = (Key, Lsn, u64)> + 'i>;
+
 /// A Layer contains all data in a "rectangle" consisting of a range of keys and
 /// range of LSNs.
 ///
@@ -144,11 +150,11 @@ pub trait PersistentLayer: Layer {
     fn local_path(&self) -> PathBuf;
 
     /// Iterate through all keys and values stored in the layer
-    fn iter(&self) -> Box<dyn Iterator<Item = Result<(Key, Lsn, Value)>> + '_>;
+    fn iter(&self) -> LayerIter<'_>;
 
     /// Iterate through all keys stored in the layer. Returns key, lsn and value size
     /// It is used only for compaction and so is currently implemented only for DeltaLayer
-    fn key_iter(&self) -> Box<dyn Iterator<Item = (Key, Lsn, u64)> + '_> {
+    fn key_iter(&self) -> LayerKeyIter<'_> {
         panic!("Not implemented")
     }