store: use block_on from pollster when reading conflicts

This avoids rust-lang/futures-rs#2090. I
don't think we need to worry about reading legacy conflicts
asynchronously - async is really only useful for Google's backend
right now, and we don't use the legacy format at Google. It's
unfortunate that we need another dependency just for this, but it's a
tiny crate at least.

Cargo.toml

@@ -53,6 +53,7 @@ num_cpus = "1.16.0"
 once_cell = "1.18.0"
 pest = "2.7.5"
 pest_derive = "2.7.5"
+pollster = "0.3.0"
 pretty_assertions = "1.4.0"
 prost = "0.11.9"
 prost-build = "0.11.9"

lib/Cargo.toml

@@ -19,7 +19,7 @@ harness = false
 version_check = { workspace = true }
 
 [dependencies]
-async-trait = { workspace = true}
+async-trait = { workspace = true }
 backoff = { workspace = true }
 blake2 = { workspace = true }
 byteorder = { workspace = true }
@@ -37,6 +37,7 @@ maplit = { workspace = true }
 once_cell = { workspace = true }
 pest = { workspace = true }
 pest_derive = { workspace = true }
+pollster = { workspace = true }
 prost = { workspace = true }
 rand = { workspace = true }
 rand_chacha = { workspace = true }

lib/src/store.rs

@@ -21,6 +21,7 @@ use std::io::Read;
 use std::sync::{Arc, RwLock};
 
 use futures::executor::block_on;
+use pollster::FutureExt as _;
 
 use crate::backend;
 use crate::backend::{
@@ -229,7 +230,7 @@ impl Store {
         path: &RepoPath,
         id: &ConflictId,
     ) -> BackendResult<MergedTreeValue> {
-        let backend_conflict = block_on(self.backend.read_conflict(path, id))?;
+        let backend_conflict = self.backend.read_conflict(path, id).block_on()?;
         Ok(Merge::from_backend_conflict(backend_conflict))
     }