Async backends are here

Cargo.toml

@@ -20,6 +20,7 @@ keywords = ["VCS", "DVCS", "SCM", "Git", "Mercurial"]
 anyhow = "1.0.75"
 assert_cmd = "2.0.8"
 assert_matches = "1.5.0"
+async-trait = "0.1.73"
 backoff = "0.4.0"
 blake2 = "0.10.6"
 byteorder = "1.5.0"
@@ -39,6 +40,7 @@ digest = "0.10.7"
 dirs = "5.0.1"
 either = "1.9.0"
 esl01-renderdag = "0.3.0"
+futures = "0.3.28"
 glob = "0.3.1"
 git2 = "0.17.2"
 hex = "0.4.3"

cli/Cargo.toml

@@ -69,6 +69,7 @@ libc = { workspace = true }
 
 [dev-dependencies]
 anyhow = { workspace = true }
+async-trait = { workspace = true }
 assert_cmd = { workspace = true }
 assert_matches = { workspace = true }
 insta = { workspace = true }

cli/examples/custom-backend/main.rs

@@ -16,6 +16,7 @@ use std::any::Any;
 use std::io::Read;
 use std::path::Path;
 
+use async_trait::async_trait;
 use jj_cli::cli_util::{CliRunner, CommandError, CommandHelper};
 use jj_cli::ui::Ui;
 use jj_lib::backend::{
@@ -86,6 +87,7 @@ impl JitBackend {
     }
 }
 
+#[async_trait]
 impl Backend for JitBackend {
     fn as_any(&self) -> &dyn Any {
         self
@@ -115,40 +117,40 @@ impl Backend for JitBackend {
         self.inner.empty_tree_id()
     }
 
-    fn read_file(&self, path: &RepoPath, id: &FileId) -> BackendResult<Box<dyn Read>> {
-        self.inner.read_file(path, id)
+    async fn read_file(&self, path: &RepoPath, id: &FileId) -> BackendResult<Box<dyn Read>> {
+        self.inner.read_file(path, id).await
     }
 
     fn write_file(&self, path: &RepoPath, contents: &mut dyn Read) -> BackendResult<FileId> {
         self.inner.write_file(path, contents)
     }
 
-    fn read_symlink(&self, path: &RepoPath, id: &SymlinkId) -> BackendResult<String> {
-        self.inner.read_symlink(path, id)
+    async fn read_symlink(&self, path: &RepoPath, id: &SymlinkId) -> BackendResult<String> {
+        self.inner.read_symlink(path, id).await
     }
 
     fn write_symlink(&self, path: &RepoPath, target: &str) -> BackendResult<SymlinkId> {
         self.inner.write_symlink(path, target)
     }
 
-    fn read_tree(&self, path: &RepoPath, id: &TreeId) -> BackendResult<Tree> {
-        self.inner.read_tree(path, id)
+    async fn read_tree(&self, path: &RepoPath, id: &TreeId) -> BackendResult<Tree> {
+        self.inner.read_tree(path, id).await
     }
 
     fn write_tree(&self, path: &RepoPath, contents: &Tree) -> BackendResult<TreeId> {
         self.inner.write_tree(path, contents)
     }
 
-    fn read_conflict(&self, path: &RepoPath, id: &ConflictId) -> BackendResult<Conflict> {
-        self.inner.read_conflict(path, id)
+    async fn read_conflict(&self, path: &RepoPath, id: &ConflictId) -> BackendResult<Conflict> {
+        self.inner.read_conflict(path, id).await
     }
 
     fn write_conflict(&self, path: &RepoPath, contents: &Conflict) -> BackendResult<ConflictId> {
         self.inner.write_conflict(path, contents)
     }
 
-    fn read_commit(&self, id: &CommitId) -> BackendResult<Commit> {
-        self.inner.read_commit(id)
+    async fn read_commit(&self, id: &CommitId) -> BackendResult<Commit> {
+        self.inner.read_commit(id).await
     }
 
     fn write_commit(&self, contents: Commit) -> BackendResult<(CommitId, Commit)> {

lib/Cargo.toml

@@ -19,13 +19,15 @@ harness = false
 version_check = { workspace = true }
 
 [dependencies]
+async-trait = { workspace = true}
 backoff = { workspace = true }
 blake2 = { workspace = true }
 byteorder = { workspace = true }
 bytes = { workspace = true }
 chrono = { workspace = true }
 config = { workspace = true }
 digest = { workspace = true }
+futures = { workspace = true }
 either = { workspace = true }
 git2 = { workspace = true }
 hex = { workspace = true }
@@ -63,6 +65,7 @@ num_cpus = { workspace = true }
 pretty_assertions = { workspace = true }
 test-case = { workspace = true }
 testutils = { workspace = true }
+tokio = { workspace = true, features = ["full"] }
 
 [features]
 default = []

lib/src/backend.rs

@@ -21,6 +21,7 @@ use std::io::Read;
 use std::result::Result;
 use std::vec::Vec;
 
+use async_trait::async_trait;
 use thiserror::Error;
 
 use crate::content_hash::ContentHash;
@@ -465,6 +466,7 @@ pub fn make_root_commit(root_change_id: ChangeId, empty_tree_id: TreeId) -> Comm
     }
 }
 
+#[async_trait]
 pub trait Backend: Send + Sync + Debug {
     fn as_any(&self) -> &dyn Any;
 
@@ -484,23 +486,23 @@ pub trait Backend: Send + Sync + Debug {
 
     fn empty_tree_id(&self) -> &TreeId;
 
-    fn read_file(&self, path: &RepoPath, id: &FileId) -> BackendResult<Box<dyn Read>>;
+    async fn read_file(&self, path: &RepoPath, id: &FileId) -> BackendResult<Box<dyn Read>>;
 
     fn write_file(&self, path: &RepoPath, contents: &mut dyn Read) -> BackendResult<FileId>;
 
-    fn read_symlink(&self, path: &RepoPath, id: &SymlinkId) -> BackendResult<String>;
+    async fn read_symlink(&self, path: &RepoPath, id: &SymlinkId) -> BackendResult<String>;
 
     fn write_symlink(&self, path: &RepoPath, target: &str) -> BackendResult<SymlinkId>;
 
-    fn read_tree(&self, path: &RepoPath, id: &TreeId) -> BackendResult<Tree>;
+    async fn read_tree(&self, path: &RepoPath, id: &TreeId) -> BackendResult<Tree>;
 
     fn write_tree(&self, path: &RepoPath, contents: &Tree) -> BackendResult<TreeId>;
 
-    fn read_conflict(&self, path: &RepoPath, id: &ConflictId) -> BackendResult<Conflict>;
+    async fn read_conflict(&self, path: &RepoPath, id: &ConflictId) -> BackendResult<Conflict>;
 
     fn write_conflict(&self, path: &RepoPath, contents: &Conflict) -> BackendResult<ConflictId>;
 
-    fn read_commit(&self, id: &CommitId) -> BackendResult<Commit>;
+    async fn read_commit(&self, id: &CommitId) -> BackendResult<Commit>;
 
     /// Writes a commit and returns its ID and the commit itself. The commit
     /// should contain the data that was actually written, which may differ