Method find_ancestor_content

atomic-core/src/merge/engine.rs:336–377

Walk deleted forward edges from `parent` to find a dead vertex that was deleted by both `left_change` and `right_change`. Returns the content bytes of the ancestor, or `None` if no shared dead vertex could be found.

(
        &self,
        parent: &GraphNode<NodeId>,
        left_change: NodeId,
        right_change: NodeId,
    )

    /// Returns the content bytes of the ancestor, or `None` if no shared
    /// dead vertex could be found.
    fn find_ancestor_content(
        &self,
        parent: &GraphNode<NodeId>,
        left_change: NodeId,
        right_change: NodeId,
    ) -> Result<Option<Vec<u8>>, PristineError> {
        // Look at all forward edges from the parent, including deleted ones.
        let forward_edges = self.txn.iter_forward(*parent, true)?;

        for edge in &forward_edges {
            if !edge.kind.is_deleted() {
                continue;
            }

            let dead_vertex = self.txn.find_block(edge.dest)?;

            // Check whether this vertex was deleted by BOTH competing changes
            // by examining its parent edges.
            let parent_edges = self.txn.iter_parents(dead_vertex, true)?;

            let mut deleted_by_left = false;
            let mut deleted_by_right = false;

            for parent_edge in &parent_edges {
                if parent_edge.kind.is_deleted() {
                    if parent_edge.introduced_by == left_change {
                        deleted_by_left = true;
                    }
                    if parent_edge.introduced_by == right_change {
                        deleted_by_right = true;
                    }
                }
            }

            if deleted_by_left && deleted_by_right {
                let content = self.get_vertex_content(&dead_vertex)?;
                return Ok(Some(content));
            }
        }

        Ok(None)
    }
}

/// Check whether `sub`'s tokens are a subsequence of `sup`'s tokens.