local_working_copy: store materialized conflict marker length

Storing the conflict marker length in the working copy makes conflict
parsing more consistent, and it allows us to parse valid conflict hunks
even if the user left some invalid conflict markers in the file while
resolving the conflicts.

cli/src/commands/debug/local_working_copy.rs

···
     for (file, state) in wc.file_states()? {
         writeln!(
             ui.stdout(),
-            "{:?} {:13?} {:10?} {:?}",
+            "{:?} {:13?} {:10?} {:?} {:?}",
             state.file_type,
             state.size,
             state.mtime.0,
+            state.materialized_conflict_data,
             file
         )?;
     }

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_to_bytes;
+use jj_lib::conflicts::choose_materialized_conflict_marker_len;
+use jj_lib::conflicts::materialize_merge_result_to_bytes_with_marker_len;
 use jj_lib::conflicts::ConflictMarkerStyle;
+use jj_lib::conflicts::MIN_CONFLICT_MARKER_LEN;
 use jj_lib::gitignore::GitIgnoreFile;
 use jj_lib::matchers::Matcher;
 use jj_lib::merge::Merge;
···
         .conflict_marker_style
         .unwrap_or(default_conflict_marker_style);
 
+    // If the merge tool doesn't get conflict markers pre-populated in the output
+    // file, we should default to accepting MIN_CONFLICT_MARKER_LEN since the
+    // merge tool is unlikely to know about our rules for conflict marker length.
+    // In the future, we may want to add a "$markerLength" variable.
+    let conflict_marker_len = if editor.merge_tool_edits_conflict_markers {
+        choose_materialized_conflict_marker_len(&content)
+    } else {
+        MIN_CONFLICT_MARKER_LEN
+    };
     let initial_output_content = if editor.merge_tool_edits_conflict_markers {
-        materialize_merge_result_to_bytes(&content, conflict_marker_style)
+        materialize_merge_result_to_bytes_with_marker_len(
+            &content,
+            conflict_marker_style,
+            conflict_marker_len,
+        )
     } else {
         BString::default()
     };
···
             repo_path,
             output_file_contents.as_slice(),
             conflict_marker_style,
+            conflict_marker_len,
         )
         .block_on()?
     } else {

cli/tests/test_working_copy.rs

···
 // limitations under the License.
 
 use indoc::indoc;
+use regex::Regex;
 
 use crate::common::TestEnvironment;
 
···
     2: invalid utf-8 sequence of 1 bytes from index 0
     "##);
 }
+
+#[test]
+fn test_conflict_marker_length_stored_in_working_copy() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    // Create a conflict in the working copy with long markers on one side
+    let conflict_file = repo_path.join("file");
+    std::fs::write(
+        &conflict_file,
+        indoc! {"
+            line 1
+            line 2
+            line 3
+        "},
+    )
+    .unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["commit", "-m", "base"]);
+    std::fs::write(
+        &conflict_file,
+        indoc! {"
+            line 1
+            line 2 - left
+            line 3 - left
+        "},
+    )
+    .unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["commit", "-m", "side-a"]);
+    test_env.jj_cmd_ok(&repo_path, &["new", "description(base)", "-m", "side-b"]);
+    std::fs::write(
+        &conflict_file,
+        indoc! {"
+            line 1
+            ======= fake marker
+            line 2 - right
+            ======= fake marker
+            line 3
+        "},
+    )
+    .unwrap();
+    test_env.jj_cmd_ok(
+        &repo_path,
+        &["new", "description(side-a)", "description(side-b)"],
+    );
+
+    // File should be materialized with long conflict markers
+    insta::assert_snapshot!(std::fs::read_to_string(&conflict_file).unwrap(), @r##"
+    line 1
+    <<<<<<<<<<< Conflict 1 of 1
+    %%%%%%%%%%% Changes from base to side #1
+    -line 2
+    -line 3
+    +line 2 - left
+    +line 3 - left
+    +++++++++++ Contents of side #2
+    ======= fake marker
+    line 2 - right
+    ======= fake marker
+    line 3
+    >>>>>>>>>>> Conflict 1 of 1 ends
+    "##);
+
+    // The timestamps in the `jj debug local-working-copy` output change, so we want
+    // to remove them before asserting the snapshot
+    let timestamp_regex = Regex::new(r"\b\d{10,}\b").unwrap();
+    // On Windows, executable is always `()`, but on Unix-like systems, it's `true`
+    // or `false`, so we want to remove it from the output as well
+    let executable_regex = Regex::new("executable: [^ ]+").unwrap();
+
+    let redact_output = |output: &str| {
+        let output = timestamp_regex.replace_all(output, "<timestamp>");
+        let output = executable_regex.replace_all(&output, "<executable>");
+        output.into_owned()
+    };
+
+    // Working copy should contain conflict marker length
+    let stdout = test_env.jj_cmd_success(&repo_path, &["debug", "local-working-copy"]);
+    insta::assert_snapshot!(redact_output(&stdout), @r#"
+    Current operation: OperationId("6feb53603f9f7324085d2d89dca19a6dac93fef6795cfd5d57090ff803d404ab1196b45d5b97faa641f6a78302ac0fbd149f5e5a880d1fd64d6520c31beab213")
+    Current tree: Merge(Conflicted([TreeId("381273b50cf73f8c81b3f1502ee89e9bbd6c1518"), TreeId("771f3d31c4588ea40a8864b2a981749888e596c2"), TreeId("f56b8223da0dab22b03b8323ced4946329aeb4e0")]))
+    Normal { <executable> }           249 <timestamp> Some(MaterializedConflictData { conflict_marker_len: 11 }) "file"
+    "#);
+
+    // Update the conflict with more fake markers, and it should still parse
+    // correctly (the markers should be ignored)
+    std::fs::write(
+        &conflict_file,
+        indoc! {"
+            line 1
+            <<<<<<<<<<< Conflict 1 of 1
+            %%%%%%%%%%% Changes from base to side #1
+            -line 2
+            -line 3
+            +line 2 - left
+            +line 3 - left
+            +++++++++++ Contents of side #2
+            <<<<<<< fake marker
+            ||||||| fake marker
+            line 2 - right
+            ======= fake marker
+            line 3
+            >>>>>>> fake marker
+            >>>>>>>>>>> Conflict 1 of 1 ends
+        "},
+    )
+    .unwrap();
+
+    // The file should still be conflicted, and the new content should be saved
+    let stdout = test_env.jj_cmd_success(&repo_path, &["st"]);
+    insta::assert_snapshot!(stdout, @r#"
+    Working copy changes:
+    M file
+    There are unresolved conflicts at these paths:
+    file    2-sided conflict
+    Working copy : mzvwutvl 3a981880 (conflict) (no description set)
+    Parent commit: rlvkpnrz ce613b49 side-a
+    Parent commit: zsuskuln 7b2b03ab side-b
+    "#);
+    insta::assert_snapshot!(test_env.jj_cmd_success(&repo_path, &["diff", "--git"]), @r##"
+    diff --git a/file b/file
+    --- a/file
+    +++ b/file
+    @@ -6,8 +6,10 @@
+     +line 2 - left
+     +line 3 - left
+     +++++++++++ Contents of side #2
+    -======= fake marker
+    +<<<<<<< fake marker
+    +||||||| fake marker
+     line 2 - right
+     ======= fake marker
+     line 3
+    +>>>>>>> fake marker
+     >>>>>>>>>>> Conflict 1 of 1 ends
+    "##);
+
+    // Working copy should still contain conflict marker length
+    let stdout = test_env.jj_cmd_success(&repo_path, &["debug", "local-working-copy"]);
+    insta::assert_snapshot!(redact_output(&stdout), @r#"
+    Current operation: OperationId("205bc702428a522e0b175938a51c51b59741c854a609ba63c89de76ffda6e5eff6fcc00725328b1a91f448401769773cefcff01fac3448190d2cea4e137d2166")
+    Current tree: Merge(Conflicted([TreeId("381273b50cf73f8c81b3f1502ee89e9bbd6c1518"), TreeId("771f3d31c4588ea40a8864b2a981749888e596c2"), TreeId("3329c18c95f7b7a55c278c2259e9c4ce711fae59")]))
+    Normal { <executable> }           289 <timestamp> Some(MaterializedConflictData { conflict_marker_len: 11 }) "file"
+    "#);
+
+    // Resolve the conflict
+    std::fs::write(
+        &conflict_file,
+        indoc! {"
+            line 1
+            <<<<<<< fake marker
+            ||||||| fake marker
+            line 2 - left
+            line 2 - right
+            ======= fake marker
+            line 3 - left
+            >>>>>>> fake marker
+        "},
+    )
+    .unwrap();
+
+    let stdout = test_env.jj_cmd_success(&repo_path, &["st"]);
+    insta::assert_snapshot!(stdout, @r#"
+    Working copy changes:
+    M file
+    Working copy : mzvwutvl 1aefd866 (no description set)
+    Parent commit: rlvkpnrz ce613b49 side-a
+    Parent commit: zsuskuln 7b2b03ab side-b
+    "#);
+
+    // When the file is resolved, the conflict marker length is removed from the
+    // working copy
+    let stdout = test_env.jj_cmd_success(&repo_path, &["debug", "local-working-copy"]);
+    insta::assert_snapshot!(redact_output(&stdout), @r#"
+    Current operation: OperationId("2206ce3c108b1573df0841138c226bba1ab3cff900a5899ed31ac69162c7d6f30d37fb5ab43da60dba88047b8ab22d453887fff688f26dfcf04f2c99420a5563")
+    Current tree: Merge(Resolved(TreeId("6120567b3cb2472d549753ed3e4b84183d52a650")))
+    Normal { <executable> }           130 <timestamp> None "file"
+    "#);
+}

lib/src/conflicts.rs

···
     }
 }
 
-fn materialize_merge_result_with_marker_len<T: AsRef<[u8]>>(
+pub fn materialize_merge_result_with_marker_len<T: AsRef<[u8]>>(
     single_hunk: &Merge<T>,
     conflict_marker_style: ConflictMarkerStyle,
     conflict_marker_len: usize,
···
         MergeResult::Resolved(content) => content,
         MergeResult::Conflict(hunks) => {
             let conflict_marker_len = choose_materialized_conflict_marker_len(single_hunk);
+            let mut output = Vec::new();
+            materialize_conflict_hunks(
+                &hunks,
+                conflict_marker_style,
+                conflict_marker_len,
+                &mut output,
+            )
+            .expect("writing to an in-memory buffer should never fail");
+            output.into()
+        }
+    }
+}
+
+pub fn materialize_merge_result_to_bytes_with_marker_len<T: AsRef<[u8]>>(
+    single_hunk: &Merge<T>,
+    conflict_marker_style: ConflictMarkerStyle,
+    conflict_marker_len: usize,
+) -> 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,
···
     path: &RepoPath,
     content: &[u8],
     conflict_marker_style: ConflictMarkerStyle,
+    conflict_marker_len: usize,
 ) -> BackendResult<Merge<Option<FileId>>> {
     let simplified_file_ids = file_ids.clone().simplify();
     let simplified_file_ids = &simplified_file_ids;
···
     // copy.
     let mut old_content = Vec::with_capacity(content.len());
     let merge_hunk = extract_as_single_hunk(simplified_file_ids, store, path).await?;
-    let conflict_marker_len = choose_materialized_conflict_marker_len(&merge_hunk);
     materialize_merge_result_with_marker_len(
         &merge_hunk,
         conflict_marker_style,

lib/src/local_working_copy.rs

···
 use crate::backend::TreeValue;
 use crate::commit::Commit;
 use crate::conflicts;
-use crate::conflicts::materialize_merge_result_to_bytes;
+use crate::conflicts::choose_materialized_conflict_marker_len;
+use crate::conflicts::materialize_merge_result_to_bytes_with_marker_len;
 use crate::conflicts::materialize_tree_value;
 use crate::conflicts::ConflictMarkerStyle;
 use crate::conflicts::MaterializedTreeValue;
+use crate::conflicts::MIN_CONFLICT_MARKER_LEN;
 use crate::file_util::check_symlink_support;
 use crate::file_util::try_symlink;
 #[cfg(feature = "watchman")]
···
     GitSubmodule,
 }
 
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub struct MaterializedConflictData {
+    pub conflict_marker_len: u32,
+}
+
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub struct FileState {
     pub file_type: FileType,
     pub mtime: MillisSinceEpoch,
     pub size: u64,
+    pub materialized_conflict_data: Option<MaterializedConflictData>,
     /* TODO: What else do we need here? Git stores a lot of fields.
      * TODO: Could possibly handle case-insensitive file systems keeping an
      *       Option<PathBuf> with the actual path here. */
 }
 
 impl FileState {
+    /// Check whether a file state appears clean compared to a previous file
+    /// state, ignoring materialized conflict data.
+    pub fn is_clean(&self, old_file_state: &Self) -> bool {
+        self.file_type == old_file_state.file_type
+            && self.mtime == old_file_state.mtime
+            && self.size == old_file_state.size
+    }
+
     /// Indicates that a file exists in the tree but that it needs to be
     /// re-stat'ed on the next snapshot.
     fn placeholder() -> Self {
···
             file_type: FileType::Normal { executable },
             mtime: MillisSinceEpoch(0),
             size: 0,
+            materialized_conflict_data: None,
         }
     }
 
-    fn for_file(executable: bool, size: u64, metadata: &Metadata) -> Self {
+    fn for_file(
+        executable: bool,
+        size: u64,
+        metadata: &Metadata,
+        materialized_conflict_data: Option<MaterializedConflictData>,
+    ) -> Self {
         #[cfg(windows)]
         let executable = {
             // Windows doesn't support executable bit.
···
             file_type: FileType::Normal { executable },
             mtime: mtime_from_metadata(metadata),
             size,
+            materialized_conflict_data,
         }
     }
 
···
             file_type: FileType::Symlink,
             mtime: mtime_from_metadata(metadata),
             size: metadata.len(),
+            materialized_conflict_data: None,
         }
     }
 
···
             file_type: FileType::GitSubmodule,
             mtime: MillisSinceEpoch(0),
             size: 0,
+            materialized_conflict_data: None,
         }
     }
 }
···
         file_type,
         mtime: MillisSinceEpoch(proto.mtime_millis_since_epoch),
         size: proto.size,
+        materialized_conflict_data: proto.materialized_conflict_data.as_ref().map(|data| {
+            MaterializedConflictData {
+                conflict_marker_len: data.conflict_marker_len,
+            }
+        }),
     }
 }
 
···
     proto.file_type = file_type as i32;
     proto.mtime_millis_since_epoch = file_state.mtime.0;
     proto.size = file_state.size;
+    proto.materialized_conflict_data = file_state.materialized_conflict_data.map(|data| {
+        crate::protos::working_copy::MaterializedConflictData {
+            conflict_marker_len: data.conflict_marker_len,
+        }
+    });
     proto
 }
 
···
             file_type,
             mtime,
             size,
+            materialized_conflict_data: None,
         }
     })
 }
···
         path: RepoPathBuf,
         disk_path: &Path,
         maybe_current_file_state: Option<&FileState>,
-        new_file_state: FileState,
+        mut new_file_state: FileState,
     ) -> Result<(), SnapshotError> {
         let update = self.get_updated_tree_value(
             &path,
···
             maybe_current_file_state,
             &new_file_state,
         )?;
+        // Preserve materialized conflict data for normal, non-resolved files
+        if matches!(new_file_state.file_type, FileType::Normal { .. })
+            && !update.as_ref().is_some_and(|update| update.is_resolved())
+        {
+            new_file_state.materialized_conflict_data =
+                maybe_current_file_state.and_then(|state| state.materialized_conflict_data);
+        }
         if let Some(tree_value) = update {
             self.tree_entries_tx.send((path.clone(), tree_value)).ok();
         }
···
             Some(current_file_state) => {
                 // If the file's mtime was set at the same time as this state file's own mtime,
                 // then we don't know if the file was modified before or after this state file.
-                current_file_state == new_file_state
+                new_file_state.is_clean(current_file_state)
                     && current_file_state.mtime < self.tree_state.own_mtime
             }
         };
···
             };
             let new_tree_values = match new_file_type {
                 FileType::Normal { executable } => self
-                    .write_path_to_store(repo_path, disk_path, &current_tree_values, executable)
+                    .write_path_to_store(
+                        repo_path,
+                        disk_path,
+                        &current_tree_values,
+                        executable,
+                        maybe_current_file_state.and_then(|state| state.materialized_conflict_data),
+                    )
                     .block_on()?,
                 FileType::Symlink => {
                     let id = self
···
         disk_path: &Path,
         current_tree_values: &MergedTreeValue,
         executable: FileExecutableFlag,
+        materialized_conflict_data: Option<MaterializedConflictData>,
     ) -> Result<MergedTreeValue, SnapshotError> {
         if let Some(current_tree_value) = current_tree_values.as_resolved() {
             #[cfg(unix)]
···
                 repo_path,
                 &content,
                 self.conflict_marker_style,
+                materialized_conflict_data.map_or(MIN_CONFLICT_MARKER_LEN, |data| {
+                    data.conflict_marker_len as usize
+                }),
             )
             .block_on()?;
             match new_file_ids.into_resolved() {
···
         let metadata = file
             .metadata()
             .map_err(|err| checkout_error_for_stat_error(err, disk_path))?;
-        Ok(FileState::for_file(executable, size, &metadata))
+        Ok(FileState::for_file(executable, size, &metadata, None))
     }
 
     fn write_symlink(&self, disk_path: &Path, target: String) -> Result<FileState, CheckoutError> {
···
         disk_path: &Path,
         conflict_data: Vec<u8>,
         executable: bool,
+        materialized_conflict_data: Option<MaterializedConflictData>,
     ) -> Result<FileState, CheckoutError> {
         let mut file = OpenOptions::new()
             .write(true)
···
         let metadata = file
             .metadata()
             .map_err(|err| checkout_error_for_stat_error(err, disk_path))?;
-        Ok(FileState::for_file(executable, size, &metadata))
+        Ok(FileState::for_file(
+            executable,
+            size,
+            &metadata,
+            materialized_conflict_data,
+        ))
     }
 
     #[cfg_attr(windows, allow(unused_variables))]
···
                     contents,
                     executable,
                 } => {
-                    let data =
-                        materialize_merge_result_to_bytes(&contents, conflict_marker_style).into();
-                    self.write_conflict(&disk_path, data, executable)?
+                    let conflict_marker_len = choose_materialized_conflict_marker_len(&contents);
+                    let data = materialize_merge_result_to_bytes_with_marker_len(
+                        &contents,
+                        conflict_marker_style,
+                        conflict_marker_len,
+                    )
+                    .into();
+                    let materialized_conflict_data = MaterializedConflictData {
+                        conflict_marker_len: conflict_marker_len.try_into().unwrap_or(u32::MAX),
+                    };
+                    self.write_conflict(
+                        &disk_path,
+                        data,
+                        executable,
+                        Some(materialized_conflict_data),
+                    )?
                 }
                 MaterializedTreeValue::OtherConflict { id } => {
                     // Unless all terms are regular files, we can't do much
                     // better than trying to describe the merge.
                     let data = id.describe().into_bytes();
                     let executable = false;
-                    self.write_conflict(&disk_path, data, executable)?
+                    self.write_conflict(&disk_path, data, executable, None)?
                 }
             };
             changed_file_states.push((path, file_state));
···
                     file_type,
                     mtime: MillisSinceEpoch(0),
                     size: 0,
+                    materialized_conflict_data: None,
                 };
                 changed_file_states.push((path, file_state));
             }
···
             },
             mtime: MillisSinceEpoch(0),
             size,
+            materialized_conflict_data: None,
         };
         let new_static_entry = |path: &'static str, size| (repo_path(path), new_state(size));
         let new_owned_entry = |path: &str, size| (repo_path(path).to_owned(), new_state(size));
···
             },
             mtime: MillisSinceEpoch(0),
             size,
+            materialized_conflict_data: None,
         };
         let new_proto_entry = |path: &str, size| {
             file_state_entry_to_proto(repo_path(path).to_owned(), &new_state(size))
···
             },
             mtime: MillisSinceEpoch(0),
             size,
+            materialized_conflict_data: None,
         };
         let new_proto_entry = |path: &str, size| {
             file_state_entry_to_proto(repo_path(path).to_owned(), &new_state(size))

lib/src/protos/working_copy.proto

···
   GitSubmodule = 4;
 }
 
+message MaterializedConflictData {
+  // TODO: maybe we should store num_sides here as well
+  uint32 conflict_marker_len = 1;
+}
+
 message FileState {
   int64 mtime_millis_since_epoch = 1;
   uint64 size = 2;
   FileType file_type = 3;
   // Set only if file_type is Conflict
   bytes conflict_id = 4 [deprecated = true];
+  MaterializedConflictData materialized_conflict_data = 5;
 }
 
 message FileStateEntry {

lib/src/protos/working_copy.rs

···
 // This file is @generated by prost-build.
 #[allow(clippy::derive_partial_eq_without_eq)]
 #[derive(Clone, PartialEq, ::prost::Message)]
+pub struct MaterializedConflictData {
+    /// TODO: maybe we should store num_sides here as well
+    #[prost(uint32, tag = "1")]
+    pub conflict_marker_len: u32,
+}
+#[allow(clippy::derive_partial_eq_without_eq)]
+#[derive(Clone, PartialEq, ::prost::Message)]
 pub struct FileState {
     #[prost(int64, tag = "1")]
     pub mtime_millis_since_epoch: i64,
···
     #[deprecated]
     #[prost(bytes = "vec", tag = "4")]
     pub conflict_id: ::prost::alloc::vec::Vec<u8>,
+    #[prost(message, optional, tag = "5")]
+    pub materialized_conflict_data: ::core::option::Option<MaterializedConflictData>,
 }
 #[allow(clippy::derive_partial_eq_without_eq)]
 #[derive(Clone, PartialEq, ::prost::Message)]

lib/tests/test_conflicts.rs

···
 use indoc::indoc;
 use itertools::Itertools;
 use jj_lib::backend::FileId;
+use jj_lib::conflicts::choose_materialized_conflict_marker_len;
 use jj_lib::conflicts::extract_as_single_hunk;
 use jj_lib::conflicts::materialize_merge_result_to_bytes;
 use jj_lib::conflicts::parse_conflict;
···
     for materialize_style in all_styles {
         let materialized = materialize_conflict_string(store, path, &conflict, materialize_style);
         for parse_style in all_styles {
-            let parsed =
-                update_from_content(&conflict, store, path, materialized.as_bytes(), parse_style)
-                    .block_on()
-                    .unwrap();
+            let parsed = update_from_content(
+                &conflict,
+                store,
+                path,
+                materialized.as_bytes(),
+                parse_style,
+                MIN_CONFLICT_MARKER_LEN,
+            )
+            .block_on()
+            .unwrap();
 
             assert_eq!(
                 parsed, conflict,
···
     let materialized =
         materialize_conflict_string(store, path, &conflict, ConflictMarkerStyle::Diff);
     let parse = |content| {
-        update_from_content(&conflict, store, path, content, ConflictMarkerStyle::Diff)
-            .block_on()
-            .unwrap()
+        update_from_content(
+            &conflict,
+            store,
+            path,
+            content,
+            ConflictMarkerStyle::Diff,
+            MIN_CONFLICT_MARKER_LEN,
+        )
+        .block_on()
+        .unwrap()
     };
     assert_eq!(parse(materialized.as_bytes()), conflict);
 
···
     let materialized =
         materialize_conflict_string(store, path, &conflict, ConflictMarkerStyle::Diff);
     let parse = |content| {
-        update_from_content(&conflict, store, path, content, ConflictMarkerStyle::Diff)
-            .block_on()
-            .unwrap()
+        update_from_content(
+            &conflict,
+            store,
+            path,
+            content,
+            ConflictMarkerStyle::Diff,
+            MIN_CONFLICT_MARKER_LEN,
+        )
+        .block_on()
+        .unwrap()
     };
     assert_eq!(parse(materialized.as_bytes()), conflict);
 
···
     let materialized_simplified =
         materialize_conflict_string(store, path, &simplified_conflict, ConflictMarkerStyle::Diff);
     let parse = |content| {
-        update_from_content(&conflict, store, path, content, ConflictMarkerStyle::Diff)
-            .block_on()
-            .unwrap()
+        update_from_content(
+            &conflict,
+            store,
+            path,
+            content,
+            ConflictMarkerStyle::Diff,
+            MIN_CONFLICT_MARKER_LEN,
+        )
+        .block_on()
+        .unwrap()
     };
     insta::assert_snapshot!(
         materialized,
···
     );
 
     // The conflict should be materialized using long conflict markers
+    let materialized_marker_len = choose_materialized_conflict_marker_len(
+        &extract_as_single_hunk(&conflict, store, path)
+            .block_on()
+            .unwrap(),
+    );
+    assert!(materialized_marker_len > MIN_CONFLICT_MARKER_LEN);
     let materialized =
         materialize_conflict_string(store, path, &conflict, ConflictMarkerStyle::Snapshot);
     insta::assert_snapshot!(materialized, @r##"
···
     // to avoid the two versions of the file being obviously identical, so that we
     // can test the actual parsing logic.
     let parse = |conflict, content| {
-        update_from_content(conflict, store, path, content, ConflictMarkerStyle::Diff)
-            .block_on()
-            .unwrap()
+        update_from_content(
+            conflict,
+            store,
+            path,
+            content,
+            ConflictMarkerStyle::Diff,
+            materialized_marker_len,
+        )
+        .block_on()
+        .unwrap()
     };
     assert_eq!(parse(&conflict, materialized.as_bytes()), conflict);
 
···
         new_conflict
     );
 
+    // If we add back the second conflict, it should still be parsed correctly
+    // (the fake conflict markers shouldn't be interpreted as conflict markers
+    // still, since they aren't the longest ones in the file).
+    assert_eq!(parse(&new_conflict, materialized.as_bytes()), conflict);
+
     // If the new conflict is materialized again, it should have shorter
     // conflict markers now
     insta::assert_snapshot!(
···
         vec![Some(left_file_id.clone()), Some(right_file_id.clone())],
     );
 
+    // The conflict should be materialized with normal markers
+    let materialized_marker_len = choose_materialized_conflict_marker_len(
+        &extract_as_single_hunk(&conflict, store, path)
+            .block_on()
+            .unwrap(),
+    );
+    assert!(materialized_marker_len == MIN_CONFLICT_MARKER_LEN);
+
     let materialized =
         materialize_conflict_string(store, path, &conflict, ConflictMarkerStyle::Diff);
     insta::assert_snapshot!(materialized, @r##"
···
     );
 
     let parse = |conflict, content| {
-        update_from_content(conflict, store, path, content, ConflictMarkerStyle::Diff)
-            .block_on()
-            .unwrap()
+        update_from_content(
+            conflict,
+            store,
+            path,
+            content,
+            ConflictMarkerStyle::Diff,
+            materialized_marker_len,
+        )
+        .block_on()
+        .unwrap()
     };
     assert_eq!(parse(&conflict, materialized.as_bytes()), conflict);
 
···
     line 5
     "##);
 
-    // Snapshotting again will cause the conflict to appear resolved
+    // Even though the file now contains markers of length 7, the materialized
+    // markers of length 7 are still parsed
     let second_snapshot = parse(&new_conflict, new_conflict_contents.as_bytes());
-    assert_ne!(second_snapshot, new_conflict);
-    assert!(second_snapshot.is_resolved());
+    assert_eq!(second_snapshot, new_conflict);
 }
 
 fn materialize_conflict_string(