linera-views: make Sync a bound on View, except on the Web (#4060)

## Motivation

Currently we have a lot of implementations in `linera-views` that don't
work on the Web because they require `Sync` bounds. For example,
`MapView` and `QueueView` are not usable on the Web.

## Proposal

Conditionally use `trait-variant` to add bounds to the traits themselves
rather than the implementations. [Futures should ‘always’ be
`Sync`](https://internals.rust-lang.org/t/what-shall-sync-mean-across-an-await/12020/18)
anyway.

`linera_storage_service::client` contains an implementation of
`KeyValueStore` that is not `Sync` even though it isn't on the Web, due
to a trait object inside `tonic` that
[has](hyperium/tonic#81)
[caused](hyperium/tonic#82)
[some](hyperium/tonic#84)
[contention](hyperium/tonic#117). For that
implementation, follow the solution [given
there](hyperium/tonic#117 (comment))
and use
[`sync_wrapper::SyncFuture`](https://docs.rs/sync_wrapper/latest/sync_wrapper/struct.SyncFuture.html)
to make the futures `Sync` based on the fact that they can only be used
through `Pin<&mut Self>` anyway.

Ditto `aws-smithy-async`.

## Test Plan

CI.

## Release Plan

- Nothing to do / These changes follow the usual release cycle.

## Links

- [reviewer
checklist](https://github.com/linera-io/linera-protocol/blob/main/CONTRIBUTING.md#reviewer-checklist)

Author: Twey

Cargo.lock

@@ -220,6 +220,7 @@ similar-asserts = "1.5.0"
 static_assertions = "1.1.0"
 stdext = "0.3.3"
 syn = "2.0.52"
+sync_wrapper = { version = "1.0.1", features = ["futures"] }
 sysinfo = "0.33.1"
 tempfile = "3.20.0"
 test-case = "3.3.1"

Cargo.toml

@@ -23,6 +23,7 @@ use linera_views::{
         AdminKeyValueStore, CommonStoreInternalConfig, ReadableKeyValueStore, WithError,
         WritableKeyValueStore,
     },
+    FutureSyncExt,
 };
 use serde::de::DeserializeOwned;
 use tonic::transport::{Channel, Endpoint};
@@ -97,7 +98,7 @@ impl ReadableKeyValueStore for ServiceStoreClientInternal {
         let channel = self.channel.clone();
         let mut client = StoreProcessorClient::new(channel);
         let _guard = self.acquire().await;
-        let response = client.process_read_value(request).await?;
+        let response = client.process_read_value(request).make_sync().await?;
         let response = response.into_inner();
         let ReplyReadValue {
             value,
@@ -120,7 +121,7 @@ impl ReadableKeyValueStore for ServiceStoreClientInternal {
         let channel = self.channel.clone();
         let mut client = StoreProcessorClient::new(channel);
         let _guard = self.acquire().await;
-        let response = client.process_contains_key(request).await?;
+        let response = client.process_contains_key(request).make_sync().await?;
         let response = response.into_inner();
         let ReplyContainsKey { test } = response;
         Ok(test)
@@ -139,7 +140,7 @@ impl ReadableKeyValueStore for ServiceStoreClientInternal {
         let channel = self.channel.clone();
         let mut client = StoreProcessorClient::new(channel);
         let _guard = self.acquire().await;
-        let response = client.process_contains_keys(request).await?;
+        let response = client.process_contains_keys(request).make_sync().await?;
         let response = response.into_inner();
         let ReplyContainsKeys { tests } = response;
         Ok(tests)
@@ -161,7 +162,10 @@ impl ReadableKeyValueStore for ServiceStoreClientInternal {
         let channel = self.channel.clone();
         let mut client = StoreProcessorClient::new(channel);
         let _guard = self.acquire().await;
-        let response = client.process_read_multi_values(request).await?;
+        let response = client
+            .process_read_multi_values(request)
+            .make_sync()
+            .await?;
         let response = response.into_inner();
         let ReplyReadMultiValues {
             values,
@@ -193,7 +197,10 @@ impl ReadableKeyValueStore for ServiceStoreClientInternal {
         let channel = self.channel.clone();
         let mut client = StoreProcessorClient::new(channel);
         let _guard = self.acquire().await;
-        let response = client.process_find_keys_by_prefix(request).await?;
+        let response = client
+            .process_find_keys_by_prefix(request)
+            .make_sync()
+            .await?;
         let response = response.into_inner();
         let ReplyFindKeysByPrefix {
             keys,
@@ -224,7 +231,10 @@ impl ReadableKeyValueStore for ServiceStoreClientInternal {
         let channel = self.channel.clone();
         let mut client = StoreProcessorClient::new(channel);
         let _guard = self.acquire().await;
-        let response = client.process_find_key_values_by_prefix(request).await?;
+        let response = client
+            .process_find_key_values_by_prefix(request)
+            .make_sync()
+            .await?;
         let response = response.into_inner();
         let ReplyFindKeyValuesByPrefix {
             key_values,
@@ -340,7 +350,10 @@ impl ServiceStoreClientInternal {
             let channel = self.channel.clone();
             let mut client = StoreProcessorClient::new(channel);
             let _guard = self.acquire().await;
-            let _response = client.process_write_batch_extended(request).await?;
+            let _response = client
+                .process_write_batch_extended(request)
+                .make_sync()
+                .await?;
         }
         Ok(())
     }
@@ -383,7 +396,7 @@ impl ServiceStoreClientInternal {
         };
         let request = tonic::Request::new(query);
         let mut client = StoreProcessorClient::new(channel);
-        let response = client.process_specific_chunk(request).await?;
+        let response = client.process_specific_chunk(request).make_sync().await?;
         let response = response.into_inner();
         let ReplySpecificChunk { chunk } = response;
         Ok(chunk)
@@ -458,8 +471,8 @@ impl AdminKeyValueStore for ServiceStoreClientInternal {
     async fn list_all(config: &Self::Config) -> Result<Vec<String>, ServiceStoreError> {
         let endpoint = config.http_address();
         let endpoint = Endpoint::from_shared(endpoint)?;
-        let mut client = StoreProcessorClient::connect(endpoint).await?;
-        let response = client.process_list_all(()).await?;
+        let mut client = StoreProcessorClient::connect(endpoint).make_sync().await?;
+        let response = client.process_list_all(()).make_sync().await?;
         let response = response.into_inner();
         let ReplyListAll { namespaces } = response;
         let namespaces = namespaces
@@ -478,8 +491,8 @@ impl AdminKeyValueStore for ServiceStoreClientInternal {
         let request = tonic::Request::new(query);
         let endpoint = config.http_address();
         let endpoint = Endpoint::from_shared(endpoint)?;
-        let mut client = StoreProcessorClient::connect(endpoint).await?;
-        let response = client.process_list_root_keys(request).await?;
+        let mut client = StoreProcessorClient::connect(endpoint).make_sync().await?;
+        let response = client.process_list_root_keys(request).make_sync().await?;
         let response = response.into_inner();
         let ReplyListRootKeys { root_keys } = response;
         Ok(root_keys)
@@ -488,8 +501,8 @@ impl AdminKeyValueStore for ServiceStoreClientInternal {
     async fn delete_all(config: &Self::Config) -> Result<(), ServiceStoreError> {
         let endpoint = config.http_address();
         let endpoint = Endpoint::from_shared(endpoint)?;
-        let mut client = StoreProcessorClient::connect(endpoint).await?;
-        let _response = client.process_delete_all(()).await?;
+        let mut client = StoreProcessorClient::connect(endpoint).make_sync().await?;
+        let _response = client.process_delete_all(()).make_sync().await?;
         Ok(())
     }
 
@@ -499,8 +512,8 @@ impl AdminKeyValueStore for ServiceStoreClientInternal {
         let request = tonic::Request::new(query);
         let endpoint = config.http_address();
         let endpoint = Endpoint::from_shared(endpoint)?;
-        let mut client = StoreProcessorClient::connect(endpoint).await?;
-        let response = client.process_exists_namespace(request).await?;
+        let mut client = StoreProcessorClient::connect(endpoint).make_sync().await?;
+        let response = client.process_exists_namespace(request).make_sync().await?;
         let response = response.into_inner();
         let ReplyExistsNamespace { exists } = response;
         Ok(exists)
@@ -515,8 +528,8 @@ impl AdminKeyValueStore for ServiceStoreClientInternal {
         let request = tonic::Request::new(query);
         let endpoint = config.http_address();
         let endpoint = Endpoint::from_shared(endpoint)?;
-        let mut client = StoreProcessorClient::connect(endpoint).await?;
-        let _response = client.process_create_namespace(request).await?;
+        let mut client = StoreProcessorClient::connect(endpoint).make_sync().await?;
+        let _response = client.process_create_namespace(request).make_sync().await?;
         Ok(())
     }
 
@@ -526,8 +539,8 @@ impl AdminKeyValueStore for ServiceStoreClientInternal {
         let request = tonic::Request::new(query);
         let endpoint = config.http_address();
         let endpoint = Endpoint::from_shared(endpoint)?;
-        let mut client = StoreProcessorClient::connect(endpoint).await?;
-        let _response = client.process_delete_namespace(request).await?;
+        let mut client = StoreProcessorClient::connect(endpoint).make_sync().await?;
+        let _response = client.process_delete_namespace(request).make_sync().await?;
         Ok(())
     }
 }

examples/Cargo.lock

@@ -217,7 +217,7 @@ fn generate_root_view_code(input: ItemStruct) -> TokenStream2 {
         impl #impl_generics linera_views::views::RootView for #struct_name #type_generics
         where
             #(#input_constraints,)*
-            Self: linera_views::views::View + Sync,
+            Self: linera_views::views::View,
         {
             async fn save(&mut self) -> Result<(), linera_views::ViewError> {
                 use linera_views::{context::Context, batch::Batch, store::WritableKeyValueStore as _, views::View};
@@ -255,7 +255,7 @@ fn generate_hash_view_code(input: ItemStruct) -> TokenStream2 {
         where
             #(#field_types: linera_views::views::HashableView,)*
             #(#input_constraints,)*
-            Self: linera_views::views::View + Sync,
+            Self: linera_views::views::View,
         {
             type Hasher = linera_views::sha3::Sha3_256;
 
@@ -293,7 +293,7 @@ fn generate_crypto_hash_code(input: ItemStruct) -> TokenStream2 {
         where
             #(#field_types: linera_views::views::HashableView,)*
             #(#input_constraints,)*
-            Self: linera_views::views::View + Sync,
+            Self: linera_views::views::View,
         {
             async fn crypto_hash(&self) -> Result<linera_base::crypto::CryptoHash, linera_views::ViewError> {
                 use linera_base::crypto::{BcsHashable, CryptoHash};
@@ -353,7 +353,7 @@ fn generate_clonable_view_code(input: ItemStruct) -> TokenStream2 {
         where
             #(#input_constraints,)*
             #(#clone_constraints,)*
-            Self: linera_views::views::View + Sync,
+            Self: linera_views::views::View,
         {
             fn clone_unchecked(&mut self) -> Result<Self, linera_views::ViewError> {
                 Ok(Self {

linera-storage-service/src/client.rs

@@ -7,7 +7,7 @@ where
     MyParam: Send + Sync + 'static,
     RegisterView<C, usize>: ClonableView,
     CollectionView<C, usize, RegisterView<C, usize>>: ClonableView,
-    Self: linera_views::views::View + Sync,
+    Self: linera_views::views::View,
 {
     fn clone_unchecked(&mut self) -> Result<Self, linera_views::ViewError> {
         Ok(Self {

linera-views-derive/src/lib.rs

@@ -10,7 +10,7 @@ where
         usize,
         RegisterView<CustomContext, usize>,
     >: ClonableView,
-    Self: linera_views::views::View + Sync,
+    Self: linera_views::views::View,
 {
     fn clone_unchecked(&mut self) -> Result<Self, linera_views::ViewError> {
         Ok(Self {

linera-views-derive/src/snapshots/linera_views_derive__tests__generate_clonable_view_code-2.snap

@@ -11,7 +11,7 @@ where
         usize,
         RegisterView<CustomContext, usize>,
     >: ClonableView,
-    Self: linera_views::views::View + Sync,
+    Self: linera_views::views::View,
 {
     fn clone_unchecked(&mut self) -> Result<Self, linera_views::ViewError> {
         Ok(Self {

linera-views-derive/src/snapshots/linera_views_derive__tests__generate_clonable_view_code-3.snap

@@ -10,7 +10,7 @@ where
         usize,
         RegisterView<custom::path::to::ContextType, usize>,
     >: ClonableView,
-    Self: linera_views::views::View + Sync,
+    Self: linera_views::views::View,
 {
     fn clone_unchecked(&mut self) -> Result<Self, linera_views::ViewError> {
         Ok(Self {

linera-views-derive/src/snapshots/linera_views_derive__tests__generate_clonable_view_code-4.snap

@@ -11,7 +11,7 @@ where
         usize,
         RegisterView<custom::path::to::ContextType, usize>,
     >: ClonableView,
-    Self: linera_views::views::View + Sync,
+    Self: linera_views::views::View,
 {
     fn clone_unchecked(&mut self) -> Result<Self, linera_views::ViewError> {
         Ok(Self {