Eliminate completely the "fn load" implementation from the native views (#4844)

## Motivation

The function "`fn load`" was of two different forms. Either pre-load,
read the values, and post-load. Or just post-load.

## Proposal

Implement the code directly in the trait.
The same work is not done for the derived code because the derive code
contains the metrics.

## Test Plan

The CI.

## Release Plan

Normal release cycle. Could be merged in TestNet Conway, but that is not
needed.

## Links

None.

Author: MathieuDutSik

linera-views/src/views/bucket_queue_view.rs

@@ -189,12 +189,6 @@ where
         })
     }
 
-    async fn load(context: C) -> Result<Self, ViewError> {
-        let keys = Self::pre_load(&context)?;
-        let values = context.store().read_multi_values_bytes(keys).await?;
-        Self::post_load(context, &values)
-    }
-
     fn rollback(&mut self) {
         self.delete_storage_first = false;
         self.cursor = Cursor::new(self.stored_data.len(), self.stored_position);

linera-views/src/views/collection_view.rs

@@ -121,10 +121,6 @@ impl<W: View> View for ByteCollectionView<W::Context, W> {
         })
     }
 
-    async fn load(context: Self::Context) -> Result<Self, ViewError> {
-        Self::post_load(context, &[])
-    }
-
     fn rollback(&mut self) {
         self.delete_storage_first = false;
         self.updates.get_mut().clear();
@@ -922,10 +918,6 @@ where
         })
     }
 
-    async fn load(context: Self::Context) -> Result<Self, ViewError> {
-        Self::post_load(context, &[])
-    }
-
     fn rollback(&mut self) {
         self.collection.rollback()
     }
@@ -1374,10 +1366,6 @@ impl<I: Send + Sync, W: View> View for CustomCollectionView<W::Context, I, W> {
         })
     }
 
-    async fn load(context: Self::Context) -> Result<Self, ViewError> {
-        Self::post_load(context, &[])
-    }
-
     fn rollback(&mut self) {
         self.collection.rollback()
     }

linera-views/src/views/hashable_wrapper.rs

@@ -13,7 +13,6 @@ use crate::{
     batch::Batch,
     common::from_bytes_option,
     context::Context,
-    store::ReadableKeyValueStore as _,
     views::{ClonableView, HashableView, Hasher, ReplaceContext, View, ViewError, MIN_VIEW_TAG},
 };
 
@@ -96,12 +95,6 @@ where
         })
     }
 
-    async fn load(context: Self::Context) -> Result<Self, ViewError> {
-        let keys = Self::pre_load(&context)?;
-        let values = context.store().read_multi_values_bytes(keys).await?;
-        Self::post_load(context, &values)
-    }
-
     fn rollback(&mut self) {
         self.inner.rollback();
         *self.hash.get_mut().unwrap() = self.stored_hash;

linera-views/src/views/key_value_store_view.rs

@@ -272,12 +272,6 @@ impl<C: Context> View for KeyValueStoreView<C> {
         })
     }
 
-    async fn load(context: C) -> Result<Self, ViewError> {
-        let keys = Self::pre_load(&context)?;
-        let values = context.store().read_multi_values_bytes(keys).await?;
-        Self::post_load(context, &values)
-    }
-
     fn rollback(&mut self) {
         self.deletion_set.rollback();
         self.updates.clear();

linera-views/src/views/log_view.rs

@@ -83,12 +83,6 @@ where
         })
     }
 
-    async fn load(context: C) -> Result<Self, ViewError> {
-        let keys = Self::pre_load(&context)?;
-        let values = context.store().read_multi_values_bytes(keys).await?;
-        Self::post_load(context, &values)
-    }
-
     fn rollback(&mut self) {
         self.delete_storage_first = false;
         self.new_values.clear();

linera-views/src/views/map_view.rs

@@ -143,10 +143,6 @@ where
         })
     }
 
-    async fn load(context: C) -> Result<Self, ViewError> {
-        Self::post_load(context, &[])
-    }
-
     fn rollback(&mut self) {
         self.updates.clear();
         self.deletion_set.rollback();
@@ -1040,10 +1036,6 @@ where
         })
     }
 
-    async fn load(context: C) -> Result<Self, ViewError> {
-        Self::post_load(context, &[])
-    }
-
     fn rollback(&mut self) {
         self.map.rollback()
     }
@@ -1598,10 +1590,6 @@ where
         })
     }
 
-    async fn load(context: C) -> Result<Self, ViewError> {
-        Self::post_load(context, &[])
-    }
-
     fn rollback(&mut self) {
         self.map.rollback()
     }

linera-views/src/views/mod.rs

@@ -1,7 +1,7 @@
 // Copyright (c) Zefchain Labs, Inc.
 // SPDX-License-Identifier: Apache-2.0
 
-use std::{fmt::Debug, io::Write};
+use std::{fmt::Debug, future::Future, io::Write};
 
 use linera_base::crypto::CryptoHash;
 pub use linera_views_derive::{
@@ -68,7 +68,18 @@ pub trait View: Sized {
     fn post_load(context: Self::Context, values: &[Option<Vec<u8>>]) -> Result<Self, ViewError>;
 
     /// Loads a view
-    async fn load(context: Self::Context) -> Result<Self, ViewError>;
+    fn load(context: Self::Context) -> impl Future<Output = Result<Self, ViewError>> {
+        async {
+            if Self::NUM_INIT_KEYS == 0 {
+                Self::post_load(context, &[])
+            } else {
+                use crate::{context::Context, store::ReadableKeyValueStore};
+                let keys = Self::pre_load(&context)?;
+                let values = context.store().read_multi_values_bytes(keys).await?;
+                Self::post_load(context, &values)
+            }
+        }
+    }
 
     /// Discards all pending changes. After that `flush` should have no effect to storage.
     fn rollback(&mut self);

linera-views/src/views/queue_view.rs

@@ -85,12 +85,6 @@ where
         })
     }
 
-    async fn load(context: C) -> Result<Self, ViewError> {
-        let keys = Self::pre_load(&context)?;
-        let values = context.store().read_multi_values_bytes(keys).await?;
-        Self::post_load(context, &values)
-    }
-
     fn rollback(&mut self) {
         self.delete_storage_first = false;
         self.front_delete_count = 0;

linera-views/src/views/reentrant_collection_view.rs

@@ -148,10 +148,6 @@ impl<W: View> View for ReentrantByteCollectionView<W::Context, W> {
         })
     }
 
-    async fn load(context: Self::Context) -> Result<Self, ViewError> {
-        Self::post_load(context, &[])
-    }
-
     fn rollback(&mut self) {
         self.delete_storage_first = false;
         self.updates.clear();
@@ -1135,10 +1131,6 @@ where
         })
     }
 
-    async fn load(context: Self::Context) -> Result<Self, ViewError> {
-        Self::post_load(context, &[])
-    }
-
     fn rollback(&mut self) {
         self.collection.rollback()
     }
@@ -1698,10 +1690,6 @@ where
         })
     }
 
-    async fn load(context: Self::Context) -> Result<Self, ViewError> {
-        Self::post_load(context, &[])
-    }
-
     fn rollback(&mut self) {
         self.collection.rollback()
     }

linera-views/src/views/register_view.rs

@@ -10,7 +10,6 @@ use crate::{
     common::{from_bytes_option_or_default, HasherOutput},
     context::Context,
     hashable_wrapper::WrappedHashableContainerView,
-    store::ReadableKeyValueStore as _,
     views::{ClonableView, HashableView, Hasher, ReplaceContext, View},
     ViewError,
 };
@@ -92,12 +91,6 @@ where
         })
     }
 
-    async fn load(context: C) -> Result<Self, ViewError> {
-        let keys = Self::pre_load(&context)?;
-        let values = context.store().read_multi_values_bytes(keys).await?;
-        Self::post_load(context, &values)
-    }
-
     fn rollback(&mut self) {
         self.delete_storage_first = false;
         self.update = None;