icechunk 2.0.0-alpha.6

Transactional storage engine for Zarr designed for use on cloud object storage
Documentation 
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//! Configurable conflict resolution with policies for common conflict types.

use async_trait::async_trait;

use crate::{
    change_set::ChangeSet,
    format::transaction_log::TransactionLog,
    session::{Session, SessionResult},
};

use super::{Conflict, ConflictResolution, ConflictSolver, detector::ConflictDetector};

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum VersionSelection {
    Fail,
    UseOurs,
    UseTheirs,
}

#[derive(Debug, Clone)]
pub struct BasicConflictSolver {
    pub on_chunk_conflict: VersionSelection,
    pub fail_on_delete_of_updated_array: bool,
    pub fail_on_delete_of_updated_group: bool,
}

impl Default for BasicConflictSolver {
    fn default() -> Self {
        Self {
            on_chunk_conflict: VersionSelection::UseOurs,
            fail_on_delete_of_updated_array: false,
            fail_on_delete_of_updated_group: false,
        }
    }
}

#[async_trait]
impl ConflictSolver for BasicConflictSolver {
    async fn solve(
        &self,
        previous_change: &TransactionLog,
        previous_repo: &Session,
        current_changes: ChangeSet,
        current_repo: &Session,
    ) -> SessionResult<ConflictResolution> {
        match ConflictDetector
            .solve(previous_change, previous_repo, current_changes, current_repo)
            .await?
        {
            res @ ConflictResolution::Patched(_) => Ok(res),
            ConflictResolution::Unsolvable { reason, unmodified } => {
                self.solve_conflicts(
                    previous_change,
                    previous_repo,
                    unmodified,
                    current_repo,
                    reason,
                )
                .await
            }
        }
    }
}

impl BasicConflictSolver {
    async fn solve_conflicts(
        &self,
        _previous_change: &TransactionLog,
        _previous_repo: &Session,
        current_changes: ChangeSet,
        _current_repo: &Session,
        conflicts: Vec<Conflict>,
    ) -> SessionResult<ConflictResolution> {
        use Conflict::*;
        let unsolvable = conflicts.iter().any(|conflict| {
            matches!(
                conflict,
                NewNodeConflictsWithExistingNode(_)
                    | NewNodeInInvalidGroup(_)
                    | ZarrMetadataDoubleUpdate(_)
                    | ZarrMetadataUpdateOfDeletedArray(_)
                    | ZarrMetadataUpdateOfDeletedGroup(_)
                    | ChunksUpdatedInDeletedArray { .. }
                    | ChunksUpdatedInUpdatedArray { .. }
                    | MoveOperationCannotBeRebased
            ) || matches!(conflict,
                ChunkDoubleUpdate{..} if self.on_chunk_conflict == VersionSelection::Fail
            ) || matches!(conflict,
                DeleteOfUpdatedArray{..} if self.fail_on_delete_of_updated_array
            ) || matches!(conflict,
                DeleteOfUpdatedGroup{..} if self.fail_on_delete_of_updated_group
            )
        });

        if unsolvable {
            return Ok(ConflictResolution::Unsolvable {
                reason: conflicts,
                unmodified: current_changes,
            });
        }

        let mut current_changes = current_changes;
        for conflict in conflicts {
            match conflict {
                ChunkDoubleUpdate { node_id, chunk_coordinates, .. } => {
                    match self.on_chunk_conflict {
                        VersionSelection::UseOurs => {
                            // this is a no-op, our change will override the conflicting change
                        }
                        VersionSelection::UseTheirs => current_changes
                            .drop_chunk_changes(&node_id, |coord| {
                                chunk_coordinates.contains(coord)
                            })?,
                        // we can panic here because we have returned from the function if there
                        // were any unsolvable conflicts
                        #[expect(clippy::panic)]
                        VersionSelection::Fail => panic!(
                            "Bug in conflict resolution: ChunkDoubleUpdate flagged as unrecoverable"
                        ),
                    }
                }
                DeleteOfUpdatedArray { .. } => {
                    assert!(!self.fail_on_delete_of_updated_array);
                    // this is a no-op, the solution is to still delete the array
                }
                DeleteOfUpdatedGroup { .. } => {
                    assert!(!self.fail_on_delete_of_updated_group);
                    // this is a no-op, the solution is to still delete the group
                }
                // we can panic here because we have returned from the function if there
                // were any unsolvable conflicts
                #[expect(clippy::panic)]
                _ => panic!("bug in conflict resolution, conflict: {conflict:?}"),
            }
        }

        Ok(ConflictResolution::Patched(current_changes))
    }
}