conflicts: make materialization async

We need to let async-ness propagate up from the backend because
`block_on()` doesn't like to be called recursively. The conflict
materialization code is a good place to make async because it doesn't
depends on anything that isn't already async-ready.

Cargo.lock

@@ -1001,6 +1001,7 @@ dependencies = [
  "crossterm 0.26.1",
  "dirs",
  "esl01-renderdag",
+ "futures 0.3.28",
  "git2",
  "glob",
  "hex",

cli/Cargo.toml

@@ -39,6 +39,7 @@ criterion = { workspace = true, optional = true }
 crossterm = { workspace = true }
 dirs = { workspace = true }
 esl01-renderdag = { workspace = true }
+futures = { workspace = true }
 git2 = { workspace = true }
 glob = { workspace = true }
 hex = { workspace = true }
@@ -89,4 +90,4 @@ watchman = ["jj-lib/watchman"]
 [package.metadata.binstall]
 # The archive name is jj, not jj-cli. Also, `cargo binstall` gets
 # confused by the `v` before versions in archive name.
-pkg-url="{ repo }/releases/download/v{ version }/jj-v{ version }-{ target }.{ archive-format }"
+pkg-url = "{ repo }/releases/download/v{ version }/jj-v{ version }-{ target }.{ archive-format }"

cli/src/commands/mod.rs

@@ -29,6 +29,7 @@ use std::{fmt, fs, io};
 use clap::builder::NonEmptyStringValueParser;
 use clap::parser::ValueSource;
 use clap::{ArgGroup, Command, CommandFactory, FromArgMatches, Subcommand};
+use futures::executor::block_on;
 use indexmap::{IndexMap, IndexSet};
 use itertools::Itertools;
 use jj_lib::backend::{CommitId, ObjectId, TreeValue};
@@ -1521,7 +1522,13 @@ fn cmd_cat(ui: &mut Ui, command: &CommandHelper, args: &CatArgs) -> Result<(), C
         }
         Err(conflict) => {
             let mut contents = vec![];
-            conflicts::materialize(&conflict, repo.store(), &path, &mut contents).unwrap();
+            block_on(conflicts::materialize(
+                &conflict,
+                repo.store(),
+                &path,
+                &mut contents,
+            ))
+            .unwrap();
             ui.request_pager();
             ui.stdout_formatter().write_all(&contents)?;
         }

cli/src/diff_util.rs

@@ -18,6 +18,7 @@ use std::io;
 use std::ops::Range;
 use std::sync::Arc;
 
+use futures::executor::block_on;
 use itertools::Itertools;
 use jj_lib::backend::{ObjectId, TreeValue};
 use jj_lib::commit::Commit;
@@ -363,7 +364,13 @@ fn diff_content(
         }
         None => {
             let mut content = vec![];
-            conflicts::materialize(value, repo.store(), path, &mut content).unwrap();
+            block_on(conflicts::materialize(
+                value,
+                repo.store(),
+                path,
+                &mut content,
+            ))
+            .unwrap();
             Ok(content)
         }
         Some(Some(TreeValue::Tree(_))) | Some(Some(TreeValue::Conflict(_))) => {
@@ -516,7 +523,13 @@ fn git_diff_part(
         None => {
             mode = "100644".to_string();
             hash = "0000000000".to_string();
-            conflicts::materialize(value, repo.store(), path, &mut content).unwrap();
+            block_on(conflicts::materialize(
+                value,
+                repo.store(),
+                path,
+                &mut content,
+            ))
+            .unwrap();
         }
         Some(Some(TreeValue::Tree(_))) | Some(Some(TreeValue::Conflict(_))) | Some(None) => {
             panic!("Unexpected {value:?} in diff at path {path:?}");

cli/src/merge_tools/builtin.rs

@@ -542,6 +542,7 @@ pub fn edit_merge_builtin(
 
 #[cfg(test)]
 mod tests {
+    use futures::executor::block_on;
     use jj_lib::conflicts::extract_as_single_hunk;
     use jj_lib::repo::Repo;
     use testutils::TestRepo;
@@ -724,7 +725,7 @@ mod tests {
                 to_file_id(right_tree.path_value(&path)),
             ],
         );
-        let content = extract_as_single_hunk(&merge, store, &path);
+        let content = block_on(extract_as_single_hunk(&merge, store, &path));
         let slices = content.map(|ContentHunk(buf)| buf.as_slice());
         let merge_result = files::merge(slices);
         let sections = make_merge_sections(merge_result).unwrap();

cli/src/merge_tools/external.rs

@@ -6,6 +6,7 @@ use std::process::{Command, ExitStatus, Stdio};
 use std::sync::Arc;
 
 use config::ConfigError;
+use futures::executor::block_on;
 use itertools::Itertools;
 use jj_lib::backend::{FileId, MergedTreeId, TreeValue};
 use jj_lib::conflicts::{self, materialize_merge_result};
@@ -357,12 +358,12 @@ pub fn run_mergetool_external(
     }
 
     let new_file_ids = if editor.merge_tool_edits_conflict_markers {
-        conflicts::update_from_content(
+        block_on(conflicts::update_from_content(
             &file_merge,
             tree.store(),
             repo_path,
             output_file_contents.as_slice(),
-        )?
+        ))?
     } else {
         let new_file_id = tree
             .store()

cli/src/merge_tools/mod.rs

@@ -18,6 +18,7 @@ mod external;
 use std::sync::Arc;
 
 use config::ConfigError;
+use futures::executor::block_on;
 use jj_lib::backend::MergedTreeId;
 use jj_lib::conflicts::extract_as_single_hunk;
 use jj_lib::gitignore::GitIgnoreFile;
@@ -112,7 +113,7 @@ pub fn run_mergetool(
             sides: file_merge.num_sides(),
         });
     };
-    let content = extract_as_single_hunk(&file_merge, tree.store(), repo_path);
+    let content = block_on(extract_as_single_hunk(&file_merge, tree.store(), repo_path));
 
     let editor = get_merge_tool_from_settings(ui, settings)?;
     match editor {

lib/src/conflicts.rs

@@ -17,6 +17,7 @@
 use std::io::Write;
 use std::iter::zip;
 
+use futures::StreamExt;
 use itertools::Itertools;
 
 use crate::backend::{BackendResult, FileId, TreeValue};
@@ -57,12 +58,13 @@ fn write_diff_hunks(hunks: &[DiffHunk], file: &mut dyn Write) -> std::io::Result
     Ok(())
 }
 
-fn get_file_contents(store: &Store, path: &RepoPath, term: &Option<FileId>) -> ContentHunk {
+async fn get_file_contents(store: &Store, path: &RepoPath, term: &Option<FileId>) -> ContentHunk {
     match term {
         Some(id) => {
             let mut content = vec![];
             store
-                .read_file(path, id)
+                .read_file_async(path, id)
+                .await
                 .unwrap()
                 .read_to_end(&mut content)
                 .unwrap();
@@ -74,22 +76,26 @@ fn get_file_contents(store: &Store, path: &RepoPath, term: &Option<FileId>) -> C
     }
 }
 
-pub fn extract_as_single_hunk(
+pub async fn extract_as_single_hunk(
     merge: &Merge<Option<FileId>>,
     store: &Store,
     path: &RepoPath,
 ) -> Merge<ContentHunk> {
-    merge.map(|term| get_file_contents(store, path, term))
+    let builder: MergeBuilder<ContentHunk> = futures::stream::iter(merge.iter())
+        .then(|term| get_file_contents(store, path, term))
+        .collect()
+        .await;
+    builder.build()
 }
 
-pub fn materialize(
+pub async fn materialize(
     conflict: &Merge<Option<TreeValue>>,
     store: &Store,
     path: &RepoPath,
     output: &mut dyn Write,
 ) -> std::io::Result<()> {
     if let Some(file_merge) = conflict.to_file_merge() {
-        let content = extract_as_single_hunk(&file_merge, store, path);
+        let content = extract_as_single_hunk(&file_merge, store, path).await;
         materialize_merge_result(&content, output)
     } else {
         // Unless all terms are regular files, we can't do much better than to try to
@@ -285,7 +291,7 @@ fn parse_conflict_hunk(input: &[u8]) -> Merge<ContentHunk> {
 /// Parses conflict markers in `content` and returns an updated version of
 /// `file_ids` with the new contents. If no (valid) conflict markers remain, a
 /// single resolves `FileId` will be returned.
-pub fn update_from_content(
+pub async fn update_from_content(
     file_ids: &Merge<Option<FileId>>,
     store: &Store,
     path: &RepoPath,
@@ -297,7 +303,7 @@ pub fn update_from_content(
     // conflicts (for example) are not converted to regular files in the working
     // copy.
     let mut old_content = Vec::with_capacity(content.len());
-    let merge_hunk = extract_as_single_hunk(file_ids, store, path);
+    let merge_hunk = extract_as_single_hunk(file_ids, store, path).await;
     materialize_merge_result(&merge_hunk, &mut old_content).unwrap();
     if content == old_content {
         return Ok(file_ids.clone());

lib/src/local_working_copy.rs

@@ -30,6 +30,7 @@ use std::sync::mpsc::{channel, Sender};
 use std::sync::Arc;
 use std::time::UNIX_EPOCH;
 
+use futures::executor::block_on;
 use itertools::Itertools;
 use once_cell::unsync::OnceCell;
 use prost::Message;
@@ -955,12 +956,12 @@ impl TreeState {
                 message: format!("Failed to open file {}", disk_path.display()),
                 err: err.into(),
             })?;
-            let new_file_ids = conflicts::update_from_content(
+            let new_file_ids = block_on(conflicts::update_from_content(
                 &old_file_ids,
                 self.store.as_ref(),
                 repo_path,
                 &content,
-            )?;
+            ))?;
             match new_file_ids.into_resolved() {
                 Ok(file_id) => {
                     #[cfg(windows)]
@@ -1062,8 +1063,13 @@ impl TreeState {
                 err: err.into(),
             })?;
         let mut conflict_data = vec![];
-        conflicts::materialize(conflict, self.store.as_ref(), path, &mut conflict_data)
+        block_on(conflicts::materialize(
-            .expect("Failed to materialize conflict to in-memory buffer");
+            conflict,
+            self.store.as_ref(),
+            path,
+            &mut conflict_data,
+        ))
+        .expect("Failed to materialize conflict to in-memory buffer");
         file.write_all(&conflict_data)
             .map_err(|err| CheckoutError::Other {
                 message: format!("Failed to write conflict to file {}", disk_path.display()),

lib/tests/test_conflicts.rs

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use futures::executor::block_on;
 use jj_lib::backend::FileId;
 use jj_lib::conflicts::{
     extract_as_single_hunk, materialize_merge_result, parse_conflict, update_from_content,
@@ -629,7 +630,7 @@ fn test_update_conflict_from_content() {
     // If the content is unchanged compared to the materialized value, we get the
     // old conflict id back.
     let materialized = materialize_conflict_string(store, &path, &conflict);
-    let parse = |content| update_from_content(&conflict, store, &path, content).unwrap();
+    let parse = |content| block_on(update_from_content(&conflict, store, &path, content)).unwrap();
     assert_eq!(parse(materialized.as_bytes()), conflict);
 
     // If the conflict is resolved, we get None back to indicate that.
@@ -673,7 +674,7 @@ fn test_update_conflict_from_content_modify_delete() {
     // If the content is unchanged compared to the materialized value, we get the
     // old conflict id back.
     let materialized = materialize_conflict_string(store, &path, &conflict);
-    let parse = |content| update_from_content(&conflict, store, &path, content).unwrap();
+    let parse = |content| block_on(update_from_content(&conflict, store, &path, content)).unwrap();
     assert_eq!(parse(materialized.as_bytes()), conflict);
 
     // If the conflict is resolved, we get None back to indicate that.
@@ -704,7 +705,7 @@ fn materialize_conflict_string(
     conflict: &Merge<Option<FileId>>,
 ) -> String {
     let mut result: Vec<u8> = vec![];
-    let contents = extract_as_single_hunk(conflict, store, path);
+    let contents = block_on(extract_as_single_hunk(conflict, store, path));
     materialize_merge_result(&contents, &mut result).unwrap();
     String::from_utf8(result).unwrap()
 }