conflicts: extract materialize_merge_result_to_bytes() helper

We have many callers of materialize_merge_result() who just want in-memory
buffer.

cli/src/diff_util.rs

···
 use jj_lib::backend::CopyRecord;
 use jj_lib::backend::TreeValue;
 use jj_lib::commit::Commit;
-use jj_lib::conflicts::materialize_merge_result;
+use jj_lib::conflicts::materialize_merge_result_to_bytes;
 use jj_lib::conflicts::materialized_diff_stream;
 use jj_lib::conflicts::MaterializedTreeDiffEntry;
 use jj_lib::conflicts::MaterializedTreeValue;
···
             id: _,
             contents,
             executable: _,
-        } => {
-            let mut data = vec![];
-            materialize_merge_result(&contents, &mut data)
-                .expect("Failed to materialize conflict to in-memory buffer");
-            Ok(FileContent {
-                is_binary: false,
-                contents: data,
-            })
-        }
+        } => Ok(FileContent {
+            is_binary: false,
+            contents: materialize_merge_result_to_bytes(&contents).into(),
+        }),
         MaterializedTreeValue::OtherConflict { id } => Ok(FileContent {
             is_binary: false,
             contents: id.describe().into_bytes(),
···
         } => {
             mode = if executable { "100755" } else { "100644" };
             hash = DUMMY_HASH.to_owned();
-            let mut data = vec![];
-            materialize_merge_result(&contents, &mut data)
-                .expect("Failed to materialize conflict to in-memory buffer");
             content = FileContent {
                 is_binary: false, // TODO: are we sure this is never binary?
-                contents: data,
+                contents: materialize_merge_result_to_bytes(&contents).into(),
             };
         }
         MaterializedTreeValue::OtherConflict { id } => {

cli/src/merge_tools/builtin.rs

···
 use jj_lib::backend::FileId;
 use jj_lib::backend::MergedTreeId;
 use jj_lib::backend::TreeValue;
-use jj_lib::conflicts::materialize_merge_result;
+use jj_lib::conflicts::materialize_merge_result_to_bytes;
 use jj_lib::conflicts::materialize_tree_value;
 use jj_lib::conflicts::MaterializedTreeValue;
 use jj_lib::diff::Diff;
···
             contents,
             executable: _,
         } => {
-            let mut buf = Vec::new();
-            materialize_merge_result(&contents, &mut buf)
-                .expect("Failed to materialize conflict to in-memory buffer");
+            let buf = materialize_merge_result_to_bytes(&contents).into();
             // TODO: Render the ID somehow?
             let contents = buf_to_file_contents(None, buf);
             Ok(FileInfo {

cli/src/merge_tools/external.rs

···
 use jj_lib::backend::MergedTreeId;
 use jj_lib::backend::TreeValue;
 use jj_lib::conflicts;
-use jj_lib::conflicts::materialize_merge_result;
+use jj_lib::conflicts::materialize_merge_result_to_bytes;
 use jj_lib::gitignore::GitIgnoreFile;
 use jj_lib::matchers::Matcher;
 use jj_lib::merge::Merge;
···
     conflict: MergedTreeValue,
     tree: &MergedTree,
 ) -> Result<MergedTreeId, ConflictResolveError> {
-    let initial_output_content: Vec<u8> = if editor.merge_tool_edits_conflict_markers {
-        let mut materialized_conflict = vec![];
-        materialize_merge_result(&content, &mut materialized_conflict)
-            .expect("Writing to an in-memory buffer should never fail");
-        materialized_conflict
+    let initial_output_content = if editor.merge_tool_edits_conflict_markers {
+        materialize_merge_result_to_bytes(&content)
     } else {
-        vec![]
+        BString::default()
     };
     assert_eq!(content.num_sides(), 2);
     let files: HashMap<&str, &[u8]> = maplit::hashmap! {

lib/src/annotate.rs

···
 use crate::backend::BackendError;
 use crate::backend::CommitId;
 use crate::commit::Commit;
-use crate::conflicts::materialize_merge_result;
+use crate::conflicts::materialize_merge_result_to_bytes;
 use crate::conflicts::materialize_tree_value;
 use crate::conflicts::MaterializedTreeValue;
 use crate::diff::Diff;
···
                 })?;
             Ok(file_contents)
         }
-        MaterializedTreeValue::FileConflict { id, contents, .. } => {
-            let mut materialized_conflict_buffer = Vec::new();
-            materialize_merge_result(&contents, &mut materialized_conflict_buffer).map_err(
-                |io_err| BackendError::ReadFile {
-                    path: path.to_owned(),
-                    source: Box::new(io_err),
-                    id: id.first().clone().unwrap(),
-                },
-            )?;
-            Ok(materialized_conflict_buffer)
+        MaterializedTreeValue::FileConflict { contents, .. } => {
+            Ok(materialize_merge_result_to_bytes(&contents).into())
         }
         _ => Ok(Vec::new()),
     }

lib/src/conflicts.rs

···
     }
 }
 
+pub fn materialize_merge_result_to_bytes<T: AsRef<[u8]>>(single_hunk: &Merge<T>) -> BString {
+    let merge_result = files::merge(single_hunk);
+    match merge_result {
+        MergeResult::Resolved(content) => content,
+        MergeResult::Conflict(hunks) => {
+            let mut output = Vec::new();
+            materialize_conflict_hunks(&hunks, &mut output)
+                .expect("writing to an in-memory buffer should never fail");
+            output.into()
+        }
+    }
+}
+
 fn materialize_conflict_hunks(hunks: &[Merge<BString>], output: &mut dyn Write) -> io::Result<()> {
     let num_conflicts = hunks
         .iter()

lib/src/default_index/revset_engine.rs

···
 use crate::backend::CommitId;
 use crate::backend::MillisSinceEpoch;
 use crate::commit::Commit;
-use crate::conflicts::materialize_merge_result;
+use crate::conflicts::materialize_merge_result_to_bytes;
 use crate::conflicts::materialize_tree_value;
 use crate::conflicts::MaterializedTreeValue;
 use crate::default_index::AsCompositeIndex;
···
         MaterializedTreeValue::Symlink { id: _, target } => Ok(target.into_bytes()),
         MaterializedTreeValue::GitSubmodule(_) => Ok(vec![]),
         MaterializedTreeValue::FileConflict { contents, .. } => {
-            let mut content = vec![];
-            materialize_merge_result(&contents, &mut content)
-                .expect("Failed to materialize conflict to in-memory buffer");
-            Ok(content)
+            Ok(materialize_merge_result_to_bytes(&contents).into())
         }
         MaterializedTreeValue::OtherConflict { .. } => Ok(vec![]),
         MaterializedTreeValue::Tree(id) => {

lib/src/local_working_copy.rs

···
 use crate::backend::TreeValue;
 use crate::commit::Commit;
 use crate::conflicts;
-use crate::conflicts::materialize_merge_result;
+use crate::conflicts::materialize_merge_result_to_bytes;
 use crate::conflicts::materialize_tree_value;
 use crate::conflicts::MaterializedTreeValue;
 use crate::file_util::check_symlink_support;
···
                     contents,
                     executable,
                 } => {
-                    let mut data = vec![];
-                    materialize_merge_result(&contents, &mut data)
-                        .expect("Failed to materialize conflict to in-memory buffer");
+                    let data = materialize_merge_result_to_bytes(&contents).into();
                     self.write_conflict(&disk_path, data, executable)?
                 }
                 MaterializedTreeValue::OtherConflict { id } => {

lib/tests/test_conflicts.rs

···
 use indoc::indoc;
 use jj_lib::backend::FileId;
 use jj_lib::conflicts::extract_as_single_hunk;
-use jj_lib::conflicts::materialize_merge_result;
+use jj_lib::conflicts::materialize_merge_result_to_bytes;
 use jj_lib::conflicts::parse_conflict;
 use jj_lib::conflicts::update_from_content;
 use jj_lib::merge::Merge;
···
     path: &RepoPath,
     conflict: &Merge<Option<FileId>>,
 ) -> String {
-    let mut result: Vec<u8> = vec![];
     let contents = extract_as_single_hunk(conflict, store, path)
         .block_on()
         .unwrap();
-    materialize_merge_result(&contents, &mut result).unwrap();
-    String::from_utf8(result).unwrap()
+    String::from_utf8(materialize_merge_result_to_bytes(&contents).into()).unwrap()
 }