OXYGENHUB
# f0406c3b40ed oxygen / crates / oxy-core / src / graph.rs
63.0 KiB · Rust · last changed A kept order takes no line that arrives deleted 1 month ago source blame history raw
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//! The per-file atom graph (spec §7.3), its materialization, and text conflict
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//! detection (spec §9.1, §9.5).
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//!
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//! The graph is a pure function of the set of changes applied to it: inserts
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//! add vertices and edges, deletes set a flag, and nothing is ever removed.
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use crate::fasthash::{FastMap as HashMap, FastSet as HashSet};
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use crate::hash::ChangeHash;
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use crate::lines::{LineRef, Lines};
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use crate::objects::AtomRange;
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use std::collections::{BTreeMap, BTreeSet};
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/// `(introducing change, index within that change for this node)`.
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pub type AtomKey = (ChangeHash, u32);
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#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Debug)]
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pub enum Vertex {
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    Start,
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    Atom(AtomKey),
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    End,
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}
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/// Transitive dependency test between changes; `depends_on(a, a)` is true.
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pub trait DepOracle {
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    fn depends_on(&self, a: &ChangeHash, b: &ChangeHash) -> bool;
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}
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/// No change depends on any other: every pair commutes.
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pub struct NoDeps;
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impl DepOracle for NoDeps {
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    fn depends_on(&self, a: &ChangeHash, b: &ChangeHash) -> bool {
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        a == b
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    }
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}
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#[derive(Default, Clone, Debug)]
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struct AtomInfo {
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    /// `None` until the introducing change has been applied; a line of the
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    /// insert's shared buffer.
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    content: Option<LineRef>,
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    deleted_by: BTreeSet<ChangeHash>,
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}
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#[derive(Clone, Debug)]
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pub struct FileGraph {
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    atoms: HashMap<AtomKey, AtomInfo>,
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    /// Every vertex, with its direct successors.
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    succ: HashMap<Vertex, Edges>,
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    /// The live atoms' order, once known to be the graph's only one.
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    order: OrderSlot,
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}
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/// A file graph's live atoms in order, when the graph orders them one way
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/// only: found by [`FileGraph::materialize`] and brought up to date by
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/// [`Order::splice`] as a change's edits apply, so a long-lived file
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/// renders in time that follows its live lines rather than every line it
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/// ever had. Any other change to the graph drops it.
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#[derive(Debug)]
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pub struct Order {
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    atoms: Vec<AtomKey>,
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    /// Atoms deleted since the order was last confirmed: it holds while
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    /// none of them is a ghost (spec §9.1), which only a render can ask,
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    /// since it needs to know how the changes depend on each other.
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    unchecked: Vec<AtomKey>,
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    confirmed: std::sync::atomic::AtomicBool,
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}
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/// Holds a graph's [`Order`]; filled in by a render, which only reads the
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/// graph.
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#[derive(Debug, Default)]
71 
struct OrderSlot(std::sync::Mutex<Option<std::sync::Arc<Order>>>);
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impl OrderSlot {
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    fn get(&self) -> Option<std::sync::Arc<Order>> {
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        self.0.lock().unwrap_or_else(|e| e.into_inner()).clone()
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    }
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    fn set(&self, o: Option<std::sync::Arc<Order>>) {
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        *self.0.lock().unwrap_or_else(|e| e.into_inner()) = o;
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    }
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    fn take(&mut self) -> Option<std::sync::Arc<Order>> {
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        self.0.get_mut().unwrap_or_else(|e| e.into_inner()).take()
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    }
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}
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impl Clone for OrderSlot {
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    fn clone(&self) -> Self {
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        OrderSlot(std::sync::Mutex::new(self.get()))
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    }
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}
90
91 
impl Order {
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    fn known(atoms: Vec<AtomKey>) -> Order {
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        Order {
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            atoms,
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            unchecked: Vec::new(),
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            confirmed: std::sync::atomic::AtomicBool::new(true),
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        }
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    }
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    /// The order after change `h` inserts the runs `inserts` (after,
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    /// before, first index, count) and deletes `deleted`, as its edits
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    /// apply; `None` where that is not certain to be the graph's only
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    /// order: an anchor not in the order, live lines between an insert's
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    /// anchors, or two inserts with nothing kept between them.
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    fn splice(
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        &self,
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        h: ChangeHash,
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        inserts: &[(Vertex, Vertex, u32, u32)],
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        deleted: &[AtomKey],
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    ) -> Option<std::sync::Arc<Order>> {
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        let mut want: HashSet<AtomKey> = deleted.iter().copied().collect();
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        for (a, b, _, _) in inserts {
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            for v in [a, b] {
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                if let Vertex::Atom(k) = v {
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                    want.insert(*k);
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                }
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            }
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        }
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        let mut pos: HashMap<AtomKey, usize> = HashMap::default();
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        for (i, k) in self.atoms.iter().enumerate() {
121 
            if want.contains(k) {
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                pos.insert(*k, i);
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            }
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        }
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        let len = self.atoms.len();
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        let mut gone = vec![false; len];
127 
        let mut unchecked = if self.confirmed.load(std::sync::atomic::Ordering::Relaxed) {
128 
            Vec::new()
129 
        } else {
130 
            self.unchecked.clone()
131 
        };
132 
        for k in deleted {
133 
            if k.0 == h {
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                return None;
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            }
136 
            if let Some(&i) = pos.get(k) {
137 
                if !gone[i] {
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                    gone[i] = true;
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                    unchecked.push(*k);
140 
                }
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            }
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        }
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        // Each run goes in the gap its anchors leave (slot `i`: before
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        // `atoms[i]`), which must hold nothing that stays.
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        let mut slots: Vec<(usize, usize, u32, u32)> = Vec::with_capacity(inserts.len());
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        for &(a, b, first, count) in inserts {
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            let from = match a {
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                Vertex::Start => 0,
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                Vertex::Atom(k) => pos.get(&k)? + 1,
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                Vertex::End => return None,
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            };
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            let to = match b {
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                Vertex::End => len,
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                Vertex::Atom(k) => *pos.get(&k)?,
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                Vertex::Start => return None,
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            };
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            if from > to || gone[from..to].iter().any(|g| !g) {
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                return None;
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            }
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            slots.push((from, to, first, count));
161 
        }
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        // Runs one after another need a kept line between them, or the
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        // graph would not say which comes first.
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        slots.sort_unstable();
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        for w in slots.windows(2) {
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            let (end, next) = (w[0].1, w[1].0);
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            if end >= next || !gone[end..next].iter().any(|g| !g) {
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                return None;
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            }
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        }
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        let added: usize = slots.iter().map(|s| s.3 as usize).sum();
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        let mut atoms = Vec::with_capacity(len + added);
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        let mut slots = slots.into_iter().peekable();
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        let mut runs_at = |i: usize, atoms: &mut Vec<AtomKey>| {
175 
            while let Some(&(from, _, first, count)) = slots.peek() {
176 
                if from != i {
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                    break;
178 
                }
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                atoms.extend((first..first + count).map(|j| (h, j)));
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                slots.next();
181 
            }
182 
        };
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        for (i, (k, g)) in self.atoms.iter().zip(&gone).enumerate() {
184 
            runs_at(i, &mut atoms);
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            if !g {
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                atoms.push(*k);
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            }
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        }
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        runs_at(len, &mut atoms);
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        let confirmed = unchecked.is_empty();
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        Some(std::sync::Arc::new(Order {
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            atoms,
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            unchecked,
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            confirmed: std::sync::atomic::AtomicBool::new(confirmed),
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        }))
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    }
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}
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/// A vertex's direct successors, sorted and without repeats. Nearly every
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/// vertex has one, which is kept inline without an allocation.
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#[derive(Clone, Debug, Default, PartialEq, Eq)]
202 
enum Edges {
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    #[default]
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    None,
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    One(Vertex),
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    Many(Vec<Vertex>),
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}
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impl Edges {
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    fn insert(&mut self, v: Vertex) {
211 
        match self {
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            Edges::None => *self = Edges::One(v),
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            Edges::One(a) if *a == v => {}
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            Edges::One(a) => {
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                let a = *a;
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                *self = Edges::Many(if a < v { vec![a, v] } else { vec![v, a] });
217 
            }
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            Edges::Many(list) => {
219 
                if let Err(i) = list.binary_search(&v) {
220 
                    list.insert(i, v);
221 
                }
222 
            }
223 
        }
224 
    }
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    fn as_slice(&self) -> &[Vertex] {
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        match self {
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            Edges::None => &[],
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            Edges::One(v) => std::slice::from_ref(v),
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            Edges::Many(list) => list,
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        }
232 
    }
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    fn iter(&self) -> std::slice::Iter<'_, Vertex> {
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        self.as_slice().iter()
236 
    }
237 
}
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239 
impl Default for FileGraph {
240 
    fn default() -> Self {
241 
        Self::new()
242 
    }
243 
}
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245 
/// One piece of a materialized file.
246 
#[derive(Clone, Debug, PartialEq, Eq)]
247 
pub enum Segment {
248 
    Lines(Vec<AtomKey>),
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    /// Order conflict: alternatives that cannot be ordered against each other.
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    Conflict(Vec<Vec<AtomKey>>),
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    /// Delete/insert conflict: `inserted` was anchored to `deleted` by a change
252 
    /// that commutes with the deletion.
253 
    Zombie {
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        deleted: Vec<AtomKey>,
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        inserted: Vec<AtomKey>,
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    },
257 
}
258
259 
#[derive(Clone, Debug, PartialEq, Eq, Default)]
260 
pub struct Materialized {
261 
    pub segments: Vec<Segment>,
262 
}
263
264 
impl Materialized {
265 
    pub fn is_conflicted(&self) -> bool {
266 
        self.segments
267 
            .iter()
268 
            .any(|s| !matches!(s, Segment::Lines(_)))
269 
    }
270 
    pub fn conflict_count(&self) -> usize {
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        self.segments
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            .iter()
273 
            .filter(|s| !matches!(s, Segment::Lines(_)))
274 
            .count()
275 
    }
276 
    /// Every live atom in materialized order, conflict sides concatenated.
277 
    pub fn live_atoms(&self) -> Vec<AtomKey> {
278 
        let mut out = Vec::new();
279 
        for s in &self.segments {
280 
            match s {
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                Segment::Lines(a) => out.extend(a),
282 
                Segment::Conflict(sides) => sides.iter().for_each(|x| out.extend(x)),
283 
                Segment::Zombie { inserted, .. } => out.extend(inserted),
284 
            }
285 
        }
286 
        out
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    }
288 
}
289
290 
impl FileGraph {
291 
    pub fn new() -> Self {
292 
        let mut g = FileGraph {
293 
            atoms: HashMap::default(),
294 
            succ: HashMap::default(),
295 
            order: OrderSlot::default(),
296 
        };
297 
        g.edge(Vertex::Start, Vertex::End);
298 
        g
299 
    }
300
301 
    fn edge(&mut self, a: Vertex, b: Vertex) {
302 
        self.succ.entry(a).or_default().insert(b);
303 
        self.succ.entry(b).or_default();
304 
    }
305
306 
    /// Apply an `Insert` by `change` whose first new atom has index `first_index`.
307 
    pub fn insert(
308 
        &mut self,
309 
        change: ChangeHash,
310 
        first_index: u32,
311 
        after: Vertex,
312 
        before: Vertex,
313 
        lines: &Lines,
314 
    ) {
315 
        self.insert_owned(change, first_index, after, before, lines.clone());
316 
    }
317
318 
    /// [`FileGraph::insert`] taking the lines, so loading a state moves
319 
    /// them in rather than copying. Each new atom's entry is made once, as
320 
    /// the source of the next edge, and the chain's ends are ensured last.
321 
    pub fn insert_owned(
322 
        &mut self,
323 
        change: ChangeHash,
324 
        first_index: u32,
325 
        after: Vertex,
326 
        before: Vertex,
327 
        lines: Lines,
328 
    ) {
329 
        self.order.take();
330 
        self.atoms.reserve(lines.len());
331 
        self.succ.reserve(lines.len() + 1);
332 
        let mut prev = after;
333 
        for i in 0..lines.len() {
334 
            let key = (change, first_index + i as u32);
335 
            self.atoms.entry(key).or_default().content =
336 
                Some(LineRef::new(lines.clone(), i as u32));
337 
            let v = Vertex::Atom(key);
338 
            self.succ.entry(prev).or_default().insert(v);
339 
            prev = v;
340 
        }
341 
        self.succ.entry(prev).or_default().insert(before);
342 
        self.succ.entry(before).or_default();
343 
    }
344
345 
    /// Apply a `Delete` of `range` by change `by`.
346 
    pub fn delete(&mut self, by: ChangeHash, range: &AtomRange) {
347 
        self.order.take();
348 
        for i in range.from..range.to {
349 
            self.atoms
350 
                .entry((range.change, i))
351 
                .or_default()
352 
                .deleted_by
353 
                .insert(by);
354 
        }
355 
    }
356
357 
    pub fn is_live(&self, k: &AtomKey) -> bool {
358 
        self.atoms
359 
            .get(k)
360 
            .is_some_and(|a| a.content.is_some() && a.deleted_by.is_empty())
361 
    }
362
363 
    pub fn content(&self, k: &AtomKey) -> Option<&[u8]> {
364 
        self.atoms
365 
            .get(k)
366 
            .and_then(|a| a.content.as_ref().map(LineRef::bytes))
367 
    }
368
369 
    pub fn deleters(&self, k: &AtomKey) -> impl Iterator<Item = &ChangeHash> {
370 
        self.atoms
371 
            .get(k)
372 
            .into_iter()
373 
            .flat_map(|a| a.deleted_by.iter())
374 
    }
375
376 
    /// Number of atoms introduced by `change` in this graph (for index bookkeeping).
377 
    pub fn atom_count(&self) -> usize {
378 
        self.atoms.len()
379 
    }
380
381 
    /// The changes that inserted a live atom directly after `k`. A change
382 
    /// that deletes `k` must depend on them (spec §8.1), or `is_ghost`
383 
    /// reads the deletion as concurrent with those insertions.
384 
    /// Every atom on some path from `first` to `last`, both included, live
385 
    /// or deleted (spec §8): the atoms a range of lines is made of, and
386 
    /// those that were deleted from between them. Empty when `last` does
387 
    /// not follow `first`.
388 
    pub fn between(&self, first: &AtomKey, last: &AtomKey) -> Vec<AtomKey> {
389 
        let (from, to) = (Vertex::Atom(*first), Vertex::Atom(*last));
390 
        let mut ahead: HashSet<Vertex> = HashSet::default();
391 
        let mut stack = vec![from];
392 
        while let Some(v) = stack.pop() {
393 
            if ahead.insert(v) {
394 
                stack.extend(
395 
                    self.succ
396 
                        .get(&v)
397 
                        .map(|e| e.as_slice())
398 
                        .unwrap_or(&[])
399 
                        .iter()
400 
                        .copied(),
401 
                );
402 
            }
403 
        }
404 
        if !ahead.contains(&to) {
405 
            return vec![];
406 
        }
407 
        let mut pred: HashMap<Vertex, Vec<Vertex>> = HashMap::default();
408 
        for (u, es) in &self.succ {
409 
            if ahead.contains(u) {
410 
                for w in es.iter() {
411 
                    pred.entry(*w).or_default().push(*u);
412 
                }
413 
            }
414 
        }
415 
        let mut behind: HashSet<Vertex> = HashSet::default();
416 
        let mut stack = vec![to];
417 
        while let Some(v) = stack.pop() {
418 
            if behind.insert(v) {
419 
                stack.extend(pred.get(&v).into_iter().flatten().copied());
420 
            }
421 
        }
422 
        let mut out: Vec<AtomKey> = ahead
423 
            .intersection(&behind)
424 
            .filter_map(|v| match v {
425 
                Vertex::Atom(k) if self.atoms.contains_key(k) => Some(*k),
426 
                _ => None,
427 
            })
428 
            .collect();
429 
        out.sort();
430 
        out
431 
    }
432
433 
    /// The changes that inserted or deleted any of `atoms`.
434 
    pub fn touching(&self, atoms: &[AtomKey]) -> BTreeSet<ChangeHash> {
435 
        let mut out = BTreeSet::new();
436 
        for k in atoms {
437 
            out.insert(k.0);
438 
            if let Some(info) = self.atoms.get(k) {
439 
                out.extend(info.deleted_by.iter().copied());
440 
            }
441 
        }
442 
        out
443 
    }
444
445 
    pub fn live_successor_changes(&self, k: &AtomKey) -> Vec<ChangeHash> {
446 
        self.succ
447 
            .get(&Vertex::Atom(*k))
448 
            .map(|ss| {
449 
                ss.iter()
450 
                    .filter_map(|s| match s {
451 
                        Vertex::Atom(y) if self.is_live(y) => Some(y.0),
452 
                        _ => None,
453 
                    })
454 
                    .collect()
455 
            })
456 
            .unwrap_or_default()
457 
    }
458
459 
    fn is_ghost(&self, k: &AtomKey, info: &AtomInfo, deps: &dyn DepOracle) -> bool {
460 
        // A deleted atom is a ghost when a live direct successor was inserted
461 
        // by a change that commutes with every deleter: neither depends on
462 
        // the other (spec §9.1, delete/insert). If the inserter came after the
463 
        // deletion, or the deleter saw the insertion, there is no conflict.
464 
        self.succ.get(&Vertex::Atom(*k)).is_some_and(|ss| {
465 
            ss.iter().any(|s| match s {
466 
                Vertex::Atom(y) if self.is_live(y) => !info
467 
                    .deleted_by
468 
                    .iter()
469 
                    .any(|d| deps.depends_on(d, &y.0) || deps.depends_on(&y.0, d)),
470 
                _ => false,
471 
            })
472 
        })
473 
    }
474
475 
    /// Successors of `v` in the graph with non-kept vertices contracted away.
476 
    fn reduced_succ(
477 
        &self,
478 
        v: Vertex,
479 
        kept: &HashSet<Vertex>,
480 
        memo: &mut HashMap<Vertex, BTreeSet<Vertex>>,
481 
    ) -> BTreeSet<Vertex> {
482 
        let direct = self.succ.get(&v).map(Edges::as_slice).unwrap_or_default();
483 
        // The common case, a successor that is itself kept: nothing to
484 
        // contract.
485 
        if direct.iter().all(|s| kept.contains(s)) {
486 
            return direct.iter().copied().collect();
487 
        }
488 
        let mut out = BTreeSet::new();
489 
        let mut stack: Vec<Vertex> = direct.to_vec();
490 
        let mut seen = HashSet::default();
491 
        while let Some(s) = stack.pop() {
492 
            if kept.contains(&s) {
493 
                out.insert(s);
494 
            } else if seen.insert(s) {
495 
                if let Some(m) = memo.get(&s) {
496 
                    out.extend(m.iter().copied());
497 
                } else if let Some(next) = self.succ.get(&s) {
498 
                    stack.extend(next.iter().copied());
499 
                }
500 
            }
501 
        }
502 
        out
503 
    }
504
505 
    /// The atoms in order when the graph is one chain from Start to End with
506 
    /// nothing deleted: a file only ever inserted into in sequence, as every
507 
    /// file of a fresh commit or a clone is. Such a graph has no conflict.
508 
    /// An edge to End besides the chain's next atom (Start's own, or an
509 
    /// append's anchor) orders nothing, since End is last anyway.
510 
    fn as_chain(&self) -> Option<Vec<AtomKey>> {
511 
        if self
512 
            .atoms
513 
            .values()
514 
            .any(|a| a.content.is_none() || !a.deleted_by.is_empty())
515 
        {
516 
            return None;
517 
        }
518 
        let mut order = Vec::with_capacity(self.atoms.len());
519 
        let mut v = Vertex::Start;
520 
        loop {
521 
            let succ = self.succ.get(&v)?.as_slice();
522 
            let mut atoms = succ.iter().filter(|s| **s != Vertex::End);
523 
            match (atoms.next(), atoms.next()) {
524 
                (None, _) if succ.contains(&Vertex::End) => break,
525 
                (Some(Vertex::Atom(k)), None) if order.len() < self.atoms.len() => {
526 
                    order.push(*k);
527 
                    v = Vertex::Atom(*k);
528 
                }
529 
                _ => return None,
530 
            }
531 
        }
532 
        (order.len() == self.atoms.len()).then_some(order)
533 
    }
534
535 
    /// Order the live atoms and locate conflicts.
536 
    pub fn materialize(&self, deps: &dyn DepOracle) -> Materialized {
537 
        let lines = |order: Vec<AtomKey>| Materialized {
538 
            segments: if order.is_empty() {
539 
                vec![]
540 
            } else {
541 
                vec![Segment::Lines(order)]
542 
            },
543 
        };
544 
        use std::sync::atomic::Ordering::Relaxed;
545 
        if let Some(o) = self.order.get() {
546 
            let holds = o.confirmed.load(Relaxed)
547 
                || o.unchecked.iter().all(|k| {
548 
                    self.atoms
549 
                        .get(k)
550 
                        .is_none_or(|info| !self.is_ghost(k, info, deps))
551 
                });
552 
            if holds {
553 
                o.confirmed.store(true, Relaxed);
554 
                return lines(o.atoms.clone());
555 
            }
556 
            self.order.set(None);
557 
        }
558 
        // A chain (nothing ever deleted) is quick to walk, and a fresh tree
559 
        // is all chains: no order is kept for one.
560 
        if let Some(order) = self.as_chain() {
561 
            return lines(order);
562 
        }
563 
        if let Some(order) = self.as_order(deps) {
564 
            self.order
565 
                .set(Some(std::sync::Arc::new(Order::known(order.clone()))));
566 
            return lines(order);
567 
        }
568 
        self.materialize_general(deps)
569 
    }
570
571 
    /// Take the kept order, to [`Order::splice`] it once a change's edits
572 
    /// have applied (they drop it).
573 
    pub fn take_order(&mut self) -> Option<std::sync::Arc<Order>> {
574 
        self.order.take()
575 
    }
576
577 
    /// Keep `order` (taken before change `h`'s edits applied) spliced by
578 
    /// them: `inserts` (after, before, first index, count) and `deleted`.
579 
    /// Changes may apply in any order, so a line may arrive already
580 
    /// deleted by a change applied before it: then the order is dropped.
581 
    pub fn keep_spliced(
582 
        &mut self,
583 
        order: std::sync::Arc<Order>,
584 
        h: ChangeHash,
585 
        inserts: &[(Vertex, Vertex, u32, u32)],
586 
        deleted: &[AtomKey],
587 
    ) {
588 
        let live = inserts
589 
            .iter()
590 
            .all(|&(_, _, first, count)| (first..first + count).all(|i| self.is_live(&(h, i))));
591 
        let spliced = if live {
592 
            order.splice(h, inserts, deleted)
593 
        } else {
594 
            None
595 
        };
596 
        *self.order.0.get_mut().unwrap_or_else(|e| e.into_inner()) = spliced;
597 
    }
598
599 
    /// The live atoms in order when, with the dead ones contracted away,
600 
    /// the graph orders them one way only: no deleted atom is a ghost, and
601 
    /// at every step of the topological sort one vertex is next. A file
602 
    /// edited without concurrent edits is such a graph, however long its
603 
    /// history. `None` otherwise, for [`FileGraph::materialize_general`]
604 
    /// to find the conflicts; where this answers, it gives the same order.
605 
    fn as_order(&self, deps: &dyn DepOracle) -> Option<Vec<AtomKey>> {
606 
        // Kept vertices by dense index: Start, End, then the live atoms.
607 
        let mut index: HashMap<Vertex, u32> =
608 
            HashMap::with_capacity_and_hasher(self.atoms.len() + 2, Default::default());
609 
        let mut verts: Vec<Vertex> = Vec::with_capacity(self.atoms.len() + 2);
610 
        verts.extend([Vertex::Start, Vertex::End]);
611 
        index.insert(Vertex::Start, 0);
612 
        index.insert(Vertex::End, 1);
613 
        for (k, info) in &self.atoms {
614 
            if info.content.is_none() {
615 
                continue;
616 
            }
617 
            if info.deleted_by.is_empty() {
618 
                index.insert(Vertex::Atom(*k), verts.len() as u32);
619 
                verts.push(Vertex::Atom(*k));
620 
            } else if self.is_ghost(k, info, deps) {
621 
                return None;
622 
            }
623 
        }
624 
        // Each kept vertex's successors, contracting the others: what a
625 
        // contracted vertex reaches is worked out once (post-order).
626 
        let mut reach: HashMap<Vertex, Vec<u32>> = HashMap::default();
627 
        let contracted = |v: Vertex, reach: &mut HashMap<Vertex, Vec<u32>>| {
628 
            let mut stack: Vec<(Vertex, bool)> = vec![(v, false)];
629 
            while let Some((x, done)) = stack.pop() {
630 
                if reach.contains_key(&x) {
631 
                    continue;
632 
                }
633 
                let next = self.succ.get(&x).map(Edges::as_slice).unwrap_or_default();
634 
                if !done {
635 
                    stack.push((x, true));
636 
                    for s in next {
637 
                        if !index.contains_key(s) && !reach.contains_key(s) {
638 
                            stack.push((*s, false));
639 
                        }
640 
                    }
641 
                    continue;
642 
                }
643 
                let mut out: Vec<u32> = Vec::new();
644 
                for s in next {
645 
                    match index.get(s) {
646 
                        Some(i) => out.push(*i),
647 
                        None => out.extend(reach.get(s).into_iter().flatten()),
648 
                    }
649 
                }
650 
                out.sort_unstable();
651 
                out.dedup();
652 
                reach.insert(x, out);
653 
            }
654 
        };
655 
        // Successors of vertex `i`: `succ[starts[i]..starts[i + 1]]`.
656 
        let mut succ: Vec<u32> = Vec::with_capacity(verts.len() * 2);
657 
        let mut starts: Vec<usize> = Vec::with_capacity(verts.len() + 1);
658 
        let mut indeg: Vec<u32> = vec![0; verts.len()];
659 
        for v in &verts {
660 
            let from = succ.len();
661 
            starts.push(from);
662 
            for s in self.succ.get(v).map(Edges::as_slice).unwrap_or_default() {
663 
                match index.get(s) {
664 
                    Some(i) => succ.push(*i),
665 
                    None => {
666 
                        contracted(*s, &mut reach);
667 
                        succ.extend(reach.get(s).into_iter().flatten());
668 
                    }
669 
                }
670 
            }
671 
            if succ.len() - from > 1 {
672 
                succ[from..].sort_unstable();
673 
                let mut kept = from;
674 
                for i in from..succ.len() {
675 
                    if i == from || succ[i] != succ[kept - 1] {
676 
                        succ[kept] = succ[i];
677 
                        kept += 1;
678 
                    }
679 
                }
680 
                succ.truncate(kept);
681 
            }
682 
            for &w in &succ[from..] {
683 
                indeg[w as usize] += 1;
684 
            }
685 
        }
686 
        starts.push(succ.len());
687 
        // Kahn's algorithm, giving up where two vertices are ready at once.
688 
        let mut ready: Vec<u32> = (0..verts.len() as u32)
689 
            .filter(|&i| indeg[i as usize] == 0)
690 
            .collect();
691 
        let mut order: Vec<AtomKey> = Vec::with_capacity(verts.len());
692 
        let mut seen = 0;
693 
        while let Some(v) = ready.pop() {
694 
            if !ready.is_empty() {
695 
                return None;
696 
            }
697 
            seen += 1;
698 
            if let Vertex::Atom(k) = verts[v as usize] {
699 
                order.push(k);
700 
            }
701 
            for &w in &succ[starts[v as usize]..starts[v as usize + 1]] {
702 
                indeg[w as usize] -= 1;
703 
                if indeg[w as usize] == 0 {
704 
                    ready.push(w);
705 
                }
706 
            }
707 
            if ready.len() > 1 {
708 
                return None;
709 
            }
710 
        }
711 
        (seen == verts.len()).then_some(order)
712 
    }
713
714 
    /// [`FileGraph::materialize`] for any graph: contraction, then a
715 
    /// topological order with conflict regions.
716 
    fn materialize_general(&self, deps: &dyn DepOracle) -> Materialized {
717 
        // 1. Vertices that survive contraction: live atoms, ghosts, Start, End.
718 
        let mut kept: HashSet<Vertex> = HashSet::default();
719 
        let mut ghosts: HashSet<AtomKey> = HashSet::default();
720 
        kept.insert(Vertex::Start);
721 
        kept.insert(Vertex::End);
722 
        for (k, info) in &self.atoms {
723 
            if info.content.is_none() {
724 
                continue;
725 
            }
726 
            if info.deleted_by.is_empty() {
727 
                kept.insert(Vertex::Atom(*k));
728 
            } else if self.is_ghost(k, info, deps) {
729 
                kept.insert(Vertex::Atom(*k));
730 
                ghosts.insert(*k);
731 
            }
732 
        }
733
734 
        // 2. Reduced graph over kept vertices.
735 
        let mut memo = HashMap::default();
736 
        let mut rsucc: HashMap<Vertex, BTreeSet<Vertex>> = HashMap::default();
737 
        let mut indeg: HashMap<Vertex, usize> = HashMap::default();
738 
        for &u in &kept {
739 
            indeg.entry(u).or_insert(0);
740 
            let rs = self.reduced_succ(u, &kept, &mut memo);
741 
            for &w in &rs {
742 
                *indeg.entry(w).or_insert(0) += 1;
743 
            }
744 
            rsucc.insert(u, rs);
745 
        }
746
747 
        // 3. Kahn's algorithm with side labelling for conflict regions.
748 
        let mut ready: BTreeSet<Vertex> = indeg
749 
            .iter()
750 
            .filter(|(_, &d)| d == 0)
751 
            .map(|(v, _)| *v)
752 
            .collect();
753 
        let mut side: HashMap<Vertex, u32> = HashMap::default();
754 
        let mut joins: HashSet<Vertex> = HashSet::default();
755 
        let mut next_side = 0u32;
756 
        let mut plain: Vec<Vertex> = Vec::new();
757 
        let mut conflict: Option<BTreeMap<u32, Vec<Vertex>>> = None;
758 
        let mut segments: Vec<Segment> = Vec::new();
759
760 
        let flush_plain = |plain: &mut Vec<Vertex>, segments: &mut Vec<Segment>| {
761 
            let atoms: Vec<AtomKey> = plain
762 
                .iter()
763 
                .filter_map(|v| {
764 
                    if let Vertex::Atom(k) = v {
765 
                        Some(*k)
766 
                    } else {
767 
                        None
768 
                    }
769 
                })
770 
                .collect();
771 
            plain.clear();
772 
            if !atoms.is_empty() {
773 
                segments.extend(split_zombies(atoms, &ghosts));
774 
            }
775 
        };
776 
        let finish_conflict = |c: BTreeMap<u32, Vec<Vertex>>, segments: &mut Vec<Segment>| {
777 
            let sides: Vec<Vec<AtomKey>> = c
778 
                .into_values()
779 
                .map(|vs| {
780 
                    vs.into_iter()
781 
                        .filter_map(|v| match v {
782 
                            Vertex::Atom(k) if !ghosts.contains(&k) => Some(k),
783 
                            _ => None,
784 
                        })
785 
                        .collect::<Vec<_>>()
786 
                })
787 
                .filter(|s| !s.is_empty())
788 
                .collect();
789 
            match sides.len() {
790 
                0 => {}
791 
                1 => segments.push(Segment::Lines(sides.into_iter().next().unwrap())),
792 
                _ => segments.push(Segment::Conflict(sides)),
793 
            }
794 
        };
795
796 
        while !ready.is_empty() {
797 
            if ready.len() >= 2 {
798 
                if conflict.is_none() {
799 
                    flush_plain(&mut plain, &mut segments);
800 
                    conflict = Some(BTreeMap::new());
801 
                }
802 
                for r in &ready {
803 
                    if !side.contains_key(r) {
804 
                        side.insert(*r, next_side);
805 
                        next_side += 1;
806 
                    }
807 
                }
808 
            }
809 
            let v = ready.pop_first().unwrap();
810 
            let my_side = side.get(&v).copied();
811 
            match (&mut conflict, my_side) {
812 
                (Some(c), Some(s)) => c.entry(s).or_default().push(v),
813 
                (Some(_), None) => {
814 
                    let c = conflict.take().unwrap();
815 
                    finish_conflict(c, &mut segments);
816 
                    plain.push(v);
817 
                }
818 
                (None, _) => plain.push(v),
819 
            }
820 
            for &w in &rsucc[&v] {
821 
                let d = indeg.get_mut(&w).unwrap();
822 
                *d -= 1;
823 
                if conflict.is_some() && !joins.contains(&w) {
824 
                    match (my_side, side.get(&w).copied()) {
825 
                        (Some(s), None) => {
826 
                            side.insert(w, s);
827 
                        }
828 
                        (Some(s), Some(t)) if s != t => {
829 
                            side.remove(&w);
830 
                            joins.insert(w);
831 
                        }
832 
                        (None, Some(_)) => {
833 
                            side.remove(&w);
834 
                            joins.insert(w);
835 
                        }
836 
                        _ => {}
837 
                    }
838 
                }
839 
                if *d == 0 {
840 
                    ready.insert(w);
841 
                }
842 
            }
843 
        }
844 
        if let Some(c) = conflict.take() {
845 
            finish_conflict(c, &mut segments);
846 
        }
847 
        flush_plain(&mut plain, &mut segments);
848 
        Materialized { segments }
849 
    }
850
851 
    /// Render a materialization to bytes with conflict markers (spec §9.5).
852 
    /// `label` gives the short description of a change for marker headers.
853 
    pub fn render(&self, m: &Materialized, label: &dyn Fn(&ChangeHash) -> String) -> Vec<u8> {
854 
        let total = m.conflict_count();
855 
        let mut n = 0;
856 
        let mut out: Vec<u8> = Vec::new();
857 
        let push_atoms = |out: &mut Vec<u8>, atoms: &[AtomKey]| {
858 
            for a in atoms {
859 
                if let Some(c) = self.content(a) {
860 
                    out.extend_from_slice(c);
861 
                }
862 
            }
863 
        };
864 
        let newline_if_needed = |out: &mut Vec<u8>| {
865 
            if !out.is_empty() && *out.last().unwrap() != b'\n' {
866 
                out.push(b'\n');
867 
            }
868 
        };
869 
        for seg in &m.segments {
870 
            match seg {
871 
                Segment::Lines(a) => push_atoms(&mut out, a),
872 
                Segment::Conflict(sides) => {
873 
                    n += 1;
874 
                    let k = sides.len();
875 
                    for (i, s) in sides.iter().enumerate() {
876 
                        newline_if_needed(&mut out);
877 
                        let who = s.first().map(|a| label(&a.0)).unwrap_or_default();
878 
                        let marker = if i == 0 { "<<<<<<<" } else { "=======" };
879 
                        out.extend_from_slice(
880 
                            format!("{marker} oxy conflict {n} of {total}, side {} of {k}: change {who}\n", i + 1).as_bytes(),
881 
                        );
882 
                        push_atoms(&mut out, s);
883 
                    }
884 
                    newline_if_needed(&mut out);
885 
                    out.extend_from_slice(
886 
                        format!(">>>>>>> oxy conflict {n} of {total} end\n").as_bytes(),
887 
                    );
888 
                }
889 
                Segment::Zombie { deleted, inserted } => {
890 
                    n += 1;
891 
                    newline_if_needed(&mut out);
892 
                    let deleter = deleted
893 
                        .first()
894 
                        .and_then(|a| self.deleters(a).next().copied())
895 
                        .map(|d| label(&d))
896 
                        .unwrap_or_default();
897 
                    let inserter = inserted.first().map(|a| label(&a.0)).unwrap_or_default();
898 
                    out.extend_from_slice(
899 
                        format!("<<<<<<< oxy conflict {n} of {total}, side 1 of 2: deleted by change {deleter}\n-------\n").as_bytes(),
900 
                    );
901 
                    push_atoms(&mut out, deleted);
902 
                    newline_if_needed(&mut out);
903 
                    out.extend_from_slice(
904 
                        format!(
905 
                            "======= oxy conflict {n} of {total}, side 2 of 2: change {inserter}\n"
906 
                        )
907 
                        .as_bytes(),
908 
                    );
909 
                    push_atoms(&mut out, inserted);
910 
                    newline_if_needed(&mut out);
911 
                    out.extend_from_slice(
912 
                        format!(">>>>>>> oxy conflict {n} of {total} end\n").as_bytes(),
913 
                    );
914 
                }
915 
            }
916 
        }
917 
        out
918 
    }
919 
}
920
921 
fn vertex_value(v: &Vertex) -> crate::cbor::Value {
922 
    use crate::cbor::Value;
923 
    match v {
924 
        Vertex::Start => Value::Uint(0),
925 
        Vertex::End => Value::Uint(1),
926 
        Vertex::Atom((c, i)) => {
927 
            Value::Array(vec![Value::Bytes(c.0.to_vec()), Value::Uint(*i as u64)])
928 
        }
929 
    }
930 
}
931
932 
fn vertex_from(v: &crate::cbor::Value) -> Result<Vertex, crate::objects::ObjectError> {
933 
    use crate::cbor::Value;
934 
    use crate::objects::ObjectError;
935 
    match v {
936 
        Value::Uint(0) => Ok(Vertex::Start),
937 
        Value::Uint(1) => Ok(Vertex::End),
938 
        Value::Array(a) if a.len() == 2 => Ok(Vertex::Atom((
939 
            crate::objects::oref(&a[0], "vertex")?,
940 
            crate::objects::u32_(&a[1], "vertex")?,
941 
        ))),
942 
        _ => Err(ObjectError::Schema(
943 
            "vertex: expected 0, 1, or [hash, index]".into(),
944 
        )),
945 
    }
946 
}
947
948 
impl FileGraph {
949 
    /// Serialize for a checkpoint: `{0: atoms [[hash, index, content|null, [deleters]]], 1: edges [[from, to]]}`.
950 
    pub fn to_value(&self) -> crate::cbor::Value {
951 
        use crate::cbor::Value;
952 
        let mut atoms: Vec<(&AtomKey, &AtomInfo)> = self.atoms.iter().collect();
953 
        atoms.sort_by_key(|(k, _)| **k);
954 
        let mut edges: Vec<(Vertex, Vertex)> = self
955 
            .succ
956 
            .iter()
957 
            .flat_map(|(a, bs)| bs.iter().map(move |b| (*a, *b)))
958 
            .collect();
959 
        edges.sort();
960 
        Value::map([
961 
            (
962 
                0,
963 
                Value::Array(
964 
                    atoms
965 
                        .into_iter()
966 
                        .map(|((c, i), info)| {
967 
                            Value::Array(vec![
968 
                                Value::Bytes(c.0.to_vec()),
969 
                                Value::Uint(*i as u64),
970 
                                info.content
971 
                                    .as_ref()
972 
                                    .map(|b| Value::Bytes(b.bytes().to_vec()))
973 
                                    .unwrap_or(Value::Null),
974 
                                Value::Array(
975 
                                    info.deleted_by
976 
                                        .iter()
977 
                                        .map(|d| Value::Bytes(d.0.to_vec()))
978 
                                        .collect(),
979 
                                ),
980 
                            ])
981 
                        })
982 
                        .collect(),
983 
                ),
984 
            ),
985 
            (
986 
                1,
987 
                Value::Array(
988 
                    edges
989 
                        .iter()
990 
                        .map(|(a, b)| Value::Array(vec![vertex_value(a), vertex_value(b)]))
991 
                        .collect(),
992 
                ),
993 
            ),
994 
        ])
995 
    }
996
997 
    pub fn from_value(v: &crate::cbor::Value) -> Result<FileGraph, crate::objects::ObjectError> {
998 
        use crate::objects::{array, bytes, field, map, oref, u32_, ObjectError};
999 
        let m = map(v, "file graph")?;
1000 
        let mut g = FileGraph {
1001 
            atoms: HashMap::default(),
1002 
            succ: HashMap::default(),
1003 
            order: OrderSlot::default(),
1004 
        };
1005 
        let atoms = array(field(m, 0, "atoms")?, "atoms")?;
1006 
        // Every atom's line in one buffer.
1007 
        let mut texts: Vec<&[u8]> = Vec::new();
1008 
        for a in atoms {
1009 
            let e = array(a, "atom")?;
1010 
            if e.len() == 4 && !e[2].is_null() {
1011 
                texts.push(bytes(&e[2], "atom content")?);
1012 
            }
1013 
        }
1014 
        let all: Lines = texts.into_iter().collect();
1015 
        let mut next = 0u32;
1016 
        for a in atoms {
1017 
            let e = array(a, "atom")?;
1018 
            if e.len() != 4 {
1019 
                return Err(ObjectError::Schema("atom: expected 4 fields".into()));
1020 
            }
1021 
            let key = (oref(&e[0], "atom change")?, u32_(&e[1], "atom index")?);
1022 
            let content = if e[2].is_null() {
1023 
                None
1024 
            } else {
1025 
                next += 1;
1026 
                Some(LineRef::new(all.clone(), next - 1))
1027 
            };
1028 
            let deleted_by = array(&e[3], "deleters")?
1029 
                .iter()
1030 
                .map(|d| oref(d, "deleter"))
1031 
                .collect::<Result<BTreeSet<_>, _>>()?;
1032 
            g.atoms.insert(
1033 
                key,
1034 
                AtomInfo {
1035 
                    content,
1036 
                    deleted_by,
1037 
                },
1038 
            );
1039 
        }
1040 
        for e in array(field(m, 1, "edges")?, "edges")? {
1041 
            let pair = array(e, "edge")?;
1042 
            if pair.len() != 2 {
1043 
                return Err(ObjectError::Schema("edge: expected [from, to]".into()));
1044 
            }
1045 
            g.edge(vertex_from(&pair[0])?, vertex_from(&pair[1])?);
1046 
        }
1047 
        Ok(g)
1048 
    }
1049 
}
1050
1051 
/// Split a plain run into `Lines` and `Zombie` segments around ghost atoms.
1052 
fn split_zombies(atoms: Vec<AtomKey>, ghosts: &HashSet<AtomKey>) -> Vec<Segment> {
1053 
    let mut out = Vec::new();
1054 
    let mut lines: Vec<AtomKey> = Vec::new();
1055 
    let mut i = 0;
1056 
    while i < atoms.len() {
1057 
        if !ghosts.contains(&atoms[i]) {
1058 
            lines.push(atoms[i]);
1059 
            i += 1;
1060 
            continue;
1061 
        }
1062 
        if !lines.is_empty() {
1063 
            out.push(Segment::Lines(std::mem::take(&mut lines)));
1064 
        }
1065 
        let mut deleted = Vec::new();
1066 
        while i < atoms.len() && ghosts.contains(&atoms[i]) {
1067 
            deleted.push(atoms[i]);
1068 
            i += 1;
1069 
        }
1070 
        let mut inserted = Vec::new();
1071 
        if i < atoms.len() {
1072 
            let ch = atoms[i].0;
1073 
            while i < atoms.len() && atoms[i].0 == ch && !ghosts.contains(&atoms[i]) {
1074 
                inserted.push(atoms[i]);
1075 
                i += 1;
1076 
            }
1077 
        }
1078 
        out.push(Segment::Zombie { deleted, inserted });
1079 
    }
1080 
    if !lines.is_empty() {
1081 
        out.push(Segment::Lines(lines));
1082 
    }
1083 
    out
1084 
}
1085
1086 
#[cfg(test)]
1087 
mod tests {
1088 
    use super::*;
1089 
    use crate::hash::ObjectRef;
1090
1091 
    fn h(n: u8) -> ChangeHash {
1092 
        ObjectRef([n; 32])
1093 
    }
1094 
    fn lines(v: &[&str]) -> Lines {
1095 
        v.iter().map(|s| s.as_bytes()).collect()
1096 
    }
1097 
    fn text(g: &FileGraph, m: &Materialized) -> String {
1098 
        String::from_utf8(g.render(m, &|c| c.short(4))).unwrap()
1099 
    }
1100
1101 
    struct Deps(HashMap<ChangeHash, Vec<ChangeHash>>);
1102 
    impl DepOracle for Deps {
1103 
        fn depends_on(&self, a: &ChangeHash, b: &ChangeHash) -> bool {
1104 
            if a == b {
1105 
                return true;
1106 
            }
1107 
            let mut stack = vec![*a];
1108 
            let mut seen = HashSet::default();
1109 
            while let Some(x) = stack.pop() {
1110 
                if let Some(ds) = self.0.get(&x) {
1111 
                    for d in ds {
1112 
                        if d == b {
1113 
                            return true;
1114 
                        }
1115 
                        if seen.insert(*d) {
1116 
                            stack.push(*d);
1117 
                        }
1118 
                    }
1119 
                }
1120 
            }
1121 
            false
1122 
        }
1123 
    }
1124
1125 
    /// Linear history: each change depends on every earlier one.
1126 
    struct Linear;
1127 
    impl DepOracle for Linear {
1128 
        fn depends_on(&self, a: &ChangeHash, b: &ChangeHash) -> bool {
1129 
            a.0[..2] >= b.0[..2]
1130 
        }
1131 
    }
1132
1133 
    /// A file of `n` lines edited `revs` times, `per` lines replaced each
1134 
    /// time, as a long-lived file is: most atoms dead, one live chain.
1135 
    fn edited_file(n: usize, revs: usize, per: usize) -> FileGraph {
1136 
        let hn = |i: usize| {
1137 
            let mut b = [0u8; 32];
1138 
            b[..2].copy_from_slice(&(i as u16).to_be_bytes());
1139 
            ObjectRef(b)
1140 
        };
1141 
        let mut g = FileGraph::new();
1142 
        let first: Vec<String> = (0..n).map(|i| format!("line {i}\n")).collect();
1143 
        let first: Vec<&str> = first.iter().map(String::as_str).collect();
1144 
        g.insert(hn(1), 0, Vertex::Start, Vertex::End, &lines(&first));
1145 
        for r in 2..revs + 2 {
1146 
            let order = g.materialize(&Linear).live_atoms();
1147 
            let step = order.len() / per;
1148 
            for j in 0..per {
1149 
                let at = j * step + (r % step.max(1));
1150 
                let k = order[at];
1151 
                g.delete(
1152 
                    hn(r),
1153 
                    &AtomRange {
1154 
                        change: k.0,
1155 
                        from: k.1,
1156 
                        to: k.1 + 1,
1157 
                    },
1158 
                );
1159 
                let after = if at == 0 {
1160 
                    Vertex::Start
1161 
                } else {
1162 
                    Vertex::Atom(order[at - 1])
1163 
                };
1164 
                let before = order
1165 
                    .get(at + 1)
1166 
                    .map(|k| Vertex::Atom(*k))
1167 
                    .unwrap_or(Vertex::End);
1168 
                g.insert(hn(r), j as u32, after, before, &lines(&["new\n"]));
1169 
            }
1170 
        }
1171 
        g
1172 
    }
1173
1174 
    /// The single-order shortcut gives what the general algorithm gives.
1175 
    #[test]
1176 
    fn the_order_shortcut_agrees_with_the_general_order() {
1177 
        let g = edited_file(500, 10, 20);
1178 
        assert!(g.as_chain().is_none());
1179 
        let fast = g.as_order(&Linear).expect("a single order");
1180 
        assert_eq!(
1181 
            Materialized {
1182 
                segments: vec![Segment::Lines(fast)]
1183 
            },
1184 
            g.materialize_general(&Linear)
1185 
        );
1186 
        // Two changes inserting at one place concurrently: a conflict,
1187 
        // which the shortcut leaves to the general algorithm.
1188 
        let mut g = FileGraph::new();
1189 
        g.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["a\n"]));
1190 
        let a = Vertex::Atom((h(1), 0));
1191 
        g.insert(h(2), 0, a, Vertex::End, &lines(&["b\n"]));
1192 
        g.insert(h(3), 0, a, Vertex::End, &lines(&["c\n"]));
1193 
        assert!(g.as_order(&NoDeps).is_none());
1194 
        assert!(g.materialize(&NoDeps).is_conflicted());
1195 
    }
1196
1197 
    /// Applied as the state applies a change's edits: the kept order is
1198 
    /// spliced by them.
1199 
    fn apply_spliced(
1200 
        g: &mut FileGraph,
1201 
        h: ChangeHash,
1202 
        inserts: &[(Vertex, Vertex, usize)],
1203 
        deleted: &[AtomKey],
1204 
    ) {
1205 
        let order = g.take_order();
1206 
        let mut runs = Vec::new();
1207 
        let mut next = 0u32;
1208 
        for (i, &(a, b, n)) in inserts.iter().enumerate() {
1209 
            let text: Vec<String> = (0..n).map(|j| format!("{i}.{j}\n")).collect();
1210 
            let text: Vec<&str> = text.iter().map(String::as_str).collect();
1211 
            g.insert(h, next, a, b, &lines(&text));
1212 
            runs.push((a, b, next, n as u32));
1213 
            next += n as u32;
1214 
        }
1215 
        for k in deleted {
1216 
            g.delete(
1217 
                h,
1218 
                &AtomRange {
1219 
                    change: k.0,
1220 
                    from: k.1,
1221 
                    to: k.1 + 1,
1222 
                },
1223 
            );
1224 
        }
1225 
        if let Some(o) = order {
1226 
            g.keep_spliced(o, h, &runs, deleted);
1227 
        }
1228 
    }
1229
1230 
    /// Edits as a diff makes them from the order `l`: hunks with a kept
1231 
    /// line between them, each deleting some lines and inserting some.
1232 
    fn random_edits(
1233 
        l: &[AtomKey],
1234 
        rnd: &mut impl FnMut(usize) -> usize,
1235 
    ) -> (Vec<(Vertex, Vertex, usize)>, Vec<AtomKey>) {
1236 
        let (mut inserts, mut deleted) = (Vec::new(), Vec::new());
1237 
        let mut i = rnd(3);
1238 
        while i <= l.len() {
1239 
            let del = rnd(3).min(l.len() - i);
1240 
            let add = rnd(3);
1241 
            let after = if i == 0 {
1242 
                Vertex::Start
1243 
            } else {
1244 
                Vertex::Atom(l[i - 1])
1245 
            };
1246 
            let before = l.get(i).map(|k| Vertex::Atom(*k)).unwrap_or(Vertex::End);
1247 
            deleted.extend(&l[i..i + del]);
1248 
            if add > 0 {
1249 
                inserts.push((after, before, add));
1250 
            }
1251 
            i += del + 1 + rnd(6);
1252 
        }
1253 
        (inserts, deleted)
1254 
    }
1255
1256 
    /// The kept order, spliced change by change, is what the general
1257 
    /// algorithm finds, through sequential edits and through concurrent
1258 
    /// ones that leave conflicts and ghosts (where it must stand aside).
1259 
    #[test]
1260 
    fn the_kept_order_follows_edits() {
1261 
        let hn = |i: usize| {
1262 
            let mut b = [0u8; 32];
1263 
            b[..2].copy_from_slice(&(i as u16).to_be_bytes());
1264 
            ObjectRef(b)
1265 
        };
1266 
        let mut seed = 7u64;
1267 
        let mut rnd = move |n: usize| {
1268 
            seed = seed
1269 
                .wrapping_mul(6364136223846793005)
1270 
                .wrapping_add(1442695040888963407);
1271 
            ((seed >> 33) as usize) % n.max(1)
1272 
        };
1273 
        let mut deps = Deps(HashMap::default());
1274 
        let mut g = FileGraph::new();
1275 
        let first: Vec<String> = (0..40).map(|i| format!("{i}\n")).collect();
1276 
        let first: Vec<&str> = first.iter().map(String::as_str).collect();
1277 
        g.insert(hn(1), 0, Vertex::Start, Vertex::End, &lines(&first));
1278 
        let mut known: Vec<ChangeHash> = vec![hn(1)];
1279 
        let mut c = 2;
1280 
        let (mut spliced, mut conflicted) = (0, 0);
1281 
        for step in 0..400 {
1282 
            let l = g.materialize(&deps).live_atoms();
1283 
            // Now and then two changes from the same base, neither knowing
1284 
            // the other.
1285 
            let pair = step % 7 == 3;
1286 
            let base = known.clone();
1287 
            for _ in 0..if pair { 2 } else { 1 } {
1288 
                let h = hn(c);
1289 
                c += 1;
1290 
                let (inserts, deleted) = random_edits(&l, &mut rnd);
1291 
                deps.0.insert(h, base.clone());
1292 
                apply_spliced(&mut g, h, &inserts, &deleted);
1293 
                known.push(h);
1294 
                if g.order.get().is_some() {
1295 
                    spliced += 1;
1296 
                }
1297 
                let m = g.materialize(&deps);
1298 
                assert_eq!(m, g.materialize_general(&deps), "step {step}");
1299 
                if m.is_conflicted() {
1300 
                    conflicted += 1;
1301 
                }
1302 
            }
1303 
            // A change that knows everything settles any conflict by
1304 
            // rewriting the file.
1305 
            if g.materialize(&deps).is_conflicted() {
1306 
                let h = hn(c);
1307 
                c += 1;
1308 
                let all = g.materialize(&deps).live_atoms();
1309 
                deps.0.insert(h, known.clone());
1310 
                apply_spliced(&mut g, h, &[(Vertex::Start, Vertex::End, 5)], &all);
1311 
                known.push(h);
1312 
                assert_eq!(g.materialize(&deps), g.materialize_general(&deps));
1313 
            }
1314 
        }
1315 
        assert!(
1316 
            spliced > 100 && conflicted > 0,
1317 
            "{spliced} spliced, {conflicted} conflicted"
1318 
        );
1319 
    }
1320
1321 
    /// A change applied before the one whose line it deletes (as a merge
1322 
    /// adds the other side, newest first): the line arrives dead, and the
1323 
    /// kept order must not take it in.
1324 
    #[test]
1325 
    fn the_kept_order_takes_no_line_that_arrives_deleted() {
1326 
        let mut deps = Deps(HashMap::default());
1327 
        let mut g = FileGraph::new();
1328 
        g.insert(
1329 
            h(1),
1330 
            0,
1331 
            Vertex::Start,
1332 
            Vertex::End,
1333 
            &lines(&["a\n", "b\n", "c\n"]),
1334 
        );
1335 
        // A deletion, so the order is kept rather than walked as a chain.
1336 
        apply_spliced(&mut g, h(2), &[], &[(h(1), 2)]);
1337 
        deps.0.insert(h(2), vec![h(1)]);
1338 
        let _ = g.materialize(&deps);
1339 
        assert!(g.order.get().is_some());
1340 
        let (a, b) = (Vertex::Atom((h(1), 0)), Vertex::Atom((h(1), 1)));
1341 
        // h(3) inserts x between a and b; h(4) deletes it. h(4) first.
1342 
        deps.0.insert(h(3), vec![h(2)]);
1343 
        deps.0.insert(h(4), vec![h(3)]);
1344 
        apply_spliced(&mut g, h(4), &[], &[(h(3), 0)]);
1345 
        apply_spliced(&mut g, h(3), &[(a, b, 1)], &[]);
1346 
        let m = g.materialize(&deps);
1347 
        assert_eq!(m, g.materialize_general(&deps));
1348 
        assert_eq!(text(&g, &m), "a\nb\n");
1349 
    }
1350
1351 
    /// How long rendering a long-lived file takes (run by hand, in release).
1352 
    #[test]
1353 
    #[ignore]
1354 
    fn bench_materialize_edited_file() {
1355 
        let g = edited_file(20_000, 50, 100);
1356 
        let t = std::time::Instant::now();
1357 
        let mut n = 0;
1358 
        for _ in 0..20 {
1359 
            n += g.materialize(&Linear).live_atoms().len();
1360 
        }
1361 
        eprintln!(
1362 
            "materialize: {:.2} ms each ({n} atoms)",
1363 
            t.elapsed().as_secs_f64() * 1000.0 / 20.0
1364 
        );
1365 
    }
1366
1367 
    /// The chain shortcut agrees with the general algorithm wherever it
1368 
    /// applies, and stands aside wherever it does not.
1369 
    #[test]
1370 
    fn the_chain_shortcut_agrees_with_the_general_order() {
1371 
        let mut g = FileGraph::new();
1372 
        g.insert(
1373 
            h(1),
1374 
            0,
1375 
            Vertex::Start,
1376 
            Vertex::End,
1377 
            &lines(&["a\n", "b\n", "c\n"]),
1378 
        );
1379 
        assert!(g.as_chain().is_some());
1380 
        assert_eq!(g.materialize(&NoDeps), g.materialize_general(&NoDeps));
1381 
        // Appended after the last line: still a chain.
1382 
        g.insert(
1383 
            h(2),
1384 
            0,
1385 
            Vertex::Atom((h(1), 2)),
1386 
            Vertex::End,
1387 
            &lines(&["d\n"]),
1388 
        );
1389 
        assert!(g.as_chain().is_some());
1390 
        assert_eq!(g.materialize(&NoDeps), g.materialize_general(&NoDeps));
1391 
        // Inserted between two lines: not a chain (a has two successors).
1392 
        g.insert(
1393 
            h(4),
1394 
            0,
1395 
            Vertex::Atom((h(1), 0)),
1396 
            Vertex::Atom((h(1), 1)),
1397 
            &lines(&["x\n"]),
1398 
        );
1399 
        assert!(g.as_chain().is_none());
1400 
        assert_eq!(text(&g, &g.materialize(&NoDeps)), "a\nx\nb\nc\nd\n");
1401 
        // Two inserts at one anchor: a conflict, never a chain.
1402 
        let mut c = FileGraph::new();
1403 
        c.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["a\n"]));
1404 
        c.insert(h(2), 0, Vertex::Start, Vertex::End, &lines(&["b\n"]));
1405 
        assert!(c.as_chain().is_none());
1406 
        assert!(c.materialize(&NoDeps).is_conflicted());
1407 
        // A deletion: not a chain.
1408 
        let mut d = FileGraph::new();
1409 
        d.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["a\n", "b\n"]));
1410 
        d.delete(
1411 
            h(3),
1412 
            &AtomRange {
1413 
                change: h(1),
1414 
                from: 0,
1415 
                to: 1,
1416 
            },
1417 
        );
1418 
        assert!(d.as_chain().is_none());
1419 
        assert_eq!(d.materialize(&NoDeps), d.materialize_general(&NoDeps));
1420 
        // Empty.
1421 
        let e = FileGraph::new();
1422 
        assert_eq!(e.materialize(&NoDeps), e.materialize_general(&NoDeps));
1423 
    }
1424
1425 
    #[test]
1426 
    fn sequential_inserts_and_deletes() {
1427 
        let mut g = FileGraph::new();
1428 
        g.insert(
1429 
            h(1),
1430 
            0,
1431 
            Vertex::Start,
1432 
            Vertex::End,
1433 
            &lines(&["a\n", "b\n", "c\n"]),
1434 
        );
1435 
        let m = g.materialize(&NoDeps);
1436 
        assert!(!m.is_conflicted());
1437 
        assert_eq!(text(&g, &m), "a\nb\nc\n");
1438
1439 
        // Change 2 depends on 1, inserts between b and c and deletes a.
1440 
        g.insert(
1441 
            h(2),
1442 
            0,
1443 
            Vertex::Atom((h(1), 1)),
1444 
            Vertex::Atom((h(1), 2)),
1445 
            &lines(&["x\n"]),
1446 
        );
1447 
        g.delete(
1448 
            h(2),
1449 
            &AtomRange {
1450 
                change: h(1),
1451 
                from: 0,
1452 
                to: 1,
1453 
            },
1454 
        );
1455 
        let deps = Deps([(h(2), vec![h(1)])].into_iter().collect());
1456 
        let m = g.materialize(&deps);
1457 
        assert!(!m.is_conflicted());
1458 
        assert_eq!(text(&g, &m), "b\nx\nc\n");
1459 
        assert_eq!(m.live_atoms(), vec![(h(1), 1), (h(2), 0), (h(1), 2)]);
1460 
    }
1461
1462 
    #[test]
1463 
    fn concurrent_inserts_at_same_anchor_conflict() {
1464 
        let mut g = FileGraph::new();
1465 
        g.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["a\n", "b\n"]));
1466 
        g.insert(
1467 
            h(2),
1468 
            0,
1469 
            Vertex::Atom((h(1), 0)),
1470 
            Vertex::Atom((h(1), 1)),
1471 
            &lines(&["from-2\n"]),
1472 
        );
1473 
        g.insert(
1474 
            h(3),
1475 
            0,
1476 
            Vertex::Atom((h(1), 0)),
1477 
            Vertex::Atom((h(1), 1)),
1478 
            &lines(&["from-3\n", "more-3\n"]),
1479 
        );
1480 
        let deps = Deps(
1481 
            [(h(2), vec![h(1)]), (h(3), vec![h(1)])]
1482 
                .into_iter()
1483 
                .collect(),
1484 
        );
1485 
        let m = g.materialize(&deps);
1486 
        assert!(m.is_conflicted());
1487 
        assert_eq!(m.conflict_count(), 1);
1488 
        assert_eq!(
1489 
            m.segments,
1490 
            vec![
1491 
                Segment::Lines(vec![(h(1), 0)]),
1492 
                Segment::Conflict(vec![vec![(h(2), 0)], vec![(h(3), 0), (h(3), 1)]]),
1493 
                Segment::Lines(vec![(h(1), 1)]),
1494 
            ]
1495 
        );
1496 
        let t = text(&g, &m);
1497 
        assert!(t.starts_with("a\n<<<<<<< oxy conflict 1 of 1, side 1 of 2: change 0202\nfrom-2\n======= oxy conflict 1 of 1, side 2 of 2: change 0303\nfrom-3\nmore-3\n>>>>>>> oxy conflict 1 of 1 end\nb\n"), "{t}");
1498 
    }
1499
1500 
    #[test]
1501 
    fn concurrent_inserts_at_different_anchors_do_not_conflict() {
1502 
        let mut g = FileGraph::new();
1503 
        g.insert(
1504 
            h(1),
1505 
            0,
1506 
            Vertex::Start,
1507 
            Vertex::End,
1508 
            &lines(&["a\n", "b\n", "c\n"]),
1509 
        );
1510 
        g.insert(
1511 
            h(2),
1512 
            0,
1513 
            Vertex::Start,
1514 
            Vertex::Atom((h(1), 0)),
1515 
            &lines(&["top\n"]),
1516 
        );
1517 
        g.insert(
1518 
            h(3),
1519 
            0,
1520 
            Vertex::Atom((h(1), 2)),
1521 
            Vertex::End,
1522 
            &lines(&["bottom\n"]),
1523 
        );
1524 
        let deps = Deps(
1525 
            [(h(2), vec![h(1)]), (h(3), vec![h(1)])]
1526 
                .into_iter()
1527 
                .collect(),
1528 
        );
1529 
        let m = g.materialize(&deps);
1530 
        assert!(!m.is_conflicted());
1531 
        assert_eq!(text(&g, &m), "top\na\nb\nc\nbottom\n");
1532 
    }
1533
1534 
    #[test]
1535 
    fn concurrent_deletes_of_the_same_line_agree() {
1536 
        let mut g = FileGraph::new();
1537 
        g.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["a\n", "b\n"]));
1538 
        g.delete(
1539 
            h(2),
1540 
            &AtomRange {
1541 
                change: h(1),
1542 
                from: 0,
1543 
                to: 1,
1544 
            },
1545 
        );
1546 
        g.delete(
1547 
            h(3),
1548 
            &AtomRange {
1549 
                change: h(1),
1550 
                from: 0,
1551 
                to: 1,
1552 
            },
1553 
        );
1554 
        let deps = Deps(
1555 
            [(h(2), vec![h(1)]), (h(3), vec![h(1)])]
1556 
                .into_iter()
1557 
                .collect(),
1558 
        );
1559 
        let m = g.materialize(&deps);
1560 
        assert!(!m.is_conflicted());
1561 
        assert_eq!(text(&g, &m), "b\n");
1562 
    }
1563
1564 
    #[test]
1565 
    fn delete_insert_conflict_is_a_zombie() {
1566 
        let mut g = FileGraph::new();
1567 
        g.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["a\n", "b\n"]));
1568 
        // 2 deletes a; 3 (concurrent) inserts after a.
1569 
        g.delete(
1570 
            h(2),
1571 
            &AtomRange {
1572 
                change: h(1),
1573 
                from: 0,
1574 
                to: 1,
1575 
            },
1576 
        );
1577 
        g.insert(
1578 
            h(3),
1579 
            0,
1580 
            Vertex::Atom((h(1), 0)),
1581 
            Vertex::Atom((h(1), 1)),
1582 
            &lines(&["after-a\n"]),
1583 
        );
1584 
        let deps = Deps(
1585 
            [(h(2), vec![h(1)]), (h(3), vec![h(1)])]
1586 
                .into_iter()
1587 
                .collect(),
1588 
        );
1589 
        let m = g.materialize(&deps);
1590 
        assert!(m.is_conflicted());
1591 
        assert_eq!(
1592 
            m.segments,
1593 
            vec![
1594 
                Segment::Zombie {
1595 
                    deleted: vec![(h(1), 0)],
1596 
                    inserted: vec![(h(3), 0)]
1597 
                },
1598 
                Segment::Lines(vec![(h(1), 1)]),
1599 
            ]
1600 
        );
1601 
        let t = text(&g, &m);
1602 
        assert!(t.contains("-------\na\n======="), "{t}");
1603 
        assert!(t.contains("after-a\n>>>>>>>"), "{t}");
1604
1605 
        // If the deleter saw the insert (depends on 3), there is no conflict.
1606 
        let deps = Deps(
1607 
            [(h(2), vec![h(1), h(3)]), (h(3), vec![h(1)])]
1608 
                .into_iter()
1609 
                .collect(),
1610 
        );
1611 
        let m = g.materialize(&deps);
1612 
        assert!(!m.is_conflicted());
1613 
        assert_eq!(text(&g, &m), "after-a\nb\n");
1614 
    }
1615
1616 
    #[test]
1617 
    fn insert_after_a_line_deleted_by_a_dependency_is_not_a_conflict() {
1618 
        // 1 inserts a,b; 2 deletes b (depends on 1); 3 depends on 2 yet anchors
1619 
        // after the dead b (a rewritten change may do this): no conflict.
1620 
        let mut g = FileGraph::new();
1621 
        g.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["a\n", "b\n"]));
1622 
        g.delete(
1623 
            h(2),
1624 
            &AtomRange {
1625 
                change: h(1),
1626 
                from: 1,
1627 
                to: 2,
1628 
            },
1629 
        );
1630 
        g.insert(
1631 
            h(3),
1632 
            0,
1633 
            Vertex::Atom((h(1), 1)),
1634 
            Vertex::End,
1635 
            &lines(&["c\n"]),
1636 
        );
1637 
        let deps = Deps(
1638 
            [(h(2), vec![h(1)]), (h(3), vec![h(2)])]
1639 
                .into_iter()
1640 
                .collect(),
1641 
        );
1642 
        let m = g.materialize(&deps);
1643 
        assert!(!m.is_conflicted(), "{:?}", m.segments);
1644 
        assert_eq!(text(&g, &m), "a\nc\n");
1645 
        // A change that deletes a line it introduced itself, with a dependent
1646 
        // anchoring after it, is likewise fine.
1647 
        let mut g = FileGraph::new();
1648 
        g.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["x\n"]));
1649 
        g.delete(
1650 
            h(1),
1651 
            &AtomRange {
1652 
                change: h(1),
1653 
                from: 0,
1654 
                to: 1,
1655 
            },
1656 
        );
1657 
        g.insert(
1658 
            h(2),
1659 
            0,
1660 
            Vertex::Atom((h(1), 0)),
1661 
            Vertex::End,
1662 
            &lines(&["y\n"]),
1663 
        );
1664 
        let deps = Deps([(h(2), vec![h(1)])].into_iter().collect());
1665 
        let m = g.materialize(&deps);
1666 
        assert!(!m.is_conflicted());
1667 
        assert_eq!(text(&g, &m), "y\n");
1668 
    }
1669
1670 
    #[test]
1671 
    fn resolution_collapses_a_conflict() {
1672 
        let mut g = FileGraph::new();
1673 
        g.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["a\n"]));
1674 
        g.insert(
1675 
            h(2),
1676 
            0,
1677 
            Vertex::Start,
1678 
            Vertex::Atom((h(1), 0)),
1679 
            &lines(&["x\n"]),
1680 
        );
1681 
        g.insert(
1682 
            h(3),
1683 
            0,
1684 
            Vertex::Start,
1685 
            Vertex::Atom((h(1), 0)),
1686 
            &lines(&["y\n"]),
1687 
        );
1688 
        let mut deps: HashMap<_, _> = [(h(2), vec![h(1)]), (h(3), vec![h(1)])]
1689 
            .into_iter()
1690 
            .collect();
1691 
        assert!(g.materialize(&Deps(deps.clone())).is_conflicted());
1692 
        // Resolution keeps y, drops x.
1693 
        g.delete(
1694 
            h(4),
1695 
            &AtomRange {
1696 
                change: h(2),
1697 
                from: 0,
1698 
                to: 1,
1699 
            },
1700 
        );
1701 
        deps.insert(h(4), vec![h(2), h(3)]);
1702 
        let m = g.materialize(&Deps(deps));
1703 
        assert!(!m.is_conflicted());
1704 
        assert_eq!(text(&g, &m), "y\na\n");
1705 
    }
1706
1707 
    #[test]
1708 
    fn empty_and_unterminated_files() {
1709 
        let g = FileGraph::new();
1710 
        let m = g.materialize(&NoDeps);
1711 
        assert_eq!(m.segments, vec![]);
1712 
        assert_eq!(text(&g, &m), "");
1713 
        let mut g = FileGraph::new();
1714 
        g.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["no newline"]));
1715 
        assert_eq!(text(&g, &g.materialize(&NoDeps)), "no newline");
1716 
    }
1717
1718 
    #[test]
1719 
    fn serialization_round_trip() {
1720 
        let mut g = FileGraph::new();
1721 
        g.insert(h(1), 0, Vertex::Start, Vertex::End, &lines(&["a\n", "b\n"]));
1722 
        g.insert(
1723 
            h(2),
1724 
            0,
1725 
            Vertex::Atom((h(1), 0)),
1726 
            Vertex::Atom((h(1), 1)),
1727 
            &lines(&["x\n"]),
1728 
        );
1729 
        g.delete(
1730 
            h(3),
1731 
            &AtomRange {
1732 
                change: h(1),
1733 
                from: 1,
1734 
                to: 2,
1735 
            },
1736 
        );
1737 
        let v = g.to_value();
1738 
        let bytes = crate::cbor::encode(&v);
1739 
        let back = FileGraph::from_value(&crate::cbor::decode(&bytes).unwrap()).unwrap();
1740 
        let deps = Deps(
1741 
            [(h(2), vec![h(1)]), (h(3), vec![h(1)])]
1742 
                .into_iter()
1743 
                .collect(),
1744 
        );
1745 
        assert_eq!(back.materialize(&deps), g.materialize(&deps));
1746 
        assert_eq!(text(&back, &back.materialize(&deps)), "a\nx\n");
1747 
        assert_eq!(
1748 
            crate::cbor::encode(&back.to_value()),
1749 
            bytes,
1750 
            "deterministic"
1751 
        );
1752 
    }
1753
1754 
    /// Spec §7.3: the graph is a function of the set of changes, not their order.
1755 
    #[test]
1756 
    fn application_order_is_irrelevant() {
1757 
        use rand::seq::SliceRandom;
1758 
        type Op = (
1759 
            ChangeHash,
1760 
            Vec<(u32, Vertex, Vertex, Lines)>,
1761 
            Vec<AtomRange>,
1762 
        );
1763 
        let ops: Vec<Op> = vec![
1764 
            (
1765 
                h(1),
1766 
                vec![(0, Vertex::Start, Vertex::End, lines(&["a\n", "b\n", "c\n"]))],
1767 
                vec![],
1768 
            ),
1769 
            (
1770 
                h(2),
1771 
                vec![(
1772 
                    0,
1773 
                    Vertex::Atom((h(1), 0)),
1774 
                    Vertex::Atom((h(1), 1)),
1775 
                    lines(&["p\n"]),
1776 
                )],
1777 
                vec![],
1778 
            ),
1779 
            (
1780 
                h(3),
1781 
                vec![(
1782 
                    0,
1783 
                    Vertex::Atom((h(1), 0)),
1784 
                    Vertex::Atom((h(1), 1)),
1785 
                    lines(&["q\n", "r\n"]),
1786 
                )],
1787 
                vec![AtomRange {
1788 
                    change: h(1),
1789 
                    from: 2,
1790 
                    to: 3,
1791 
                }],
1792 
            ),
1793 
            (
1794 
                h(4),
1795 
                vec![(
1796 
                    0,
1797 
                    Vertex::Atom((h(3), 1)),
1798 
                    Vertex::Atom((h(1), 1)),
1799 
                    lines(&["s\n"]),
1800 
                )],
1801 
                vec![AtomRange {
1802 
                    change: h(1),
1803 
                    from: 1,
1804 
                    to: 2,
1805 
                }],
1806 
            ),
1807 
            (
1808 
                h(5),
1809 
                vec![(0, Vertex::Atom((h(1), 2)), Vertex::End, lines(&["z\n"]))],
1810 
                vec![],
1811 
            ),
1812 
        ];
1813 
        let deps = Deps(
1814 
            [
1815 
                (h(2), vec![h(1)]),
1816 
                (h(3), vec![h(1)]),
1817 
                (h(4), vec![h(3), h(1)]),
1818 
                (h(5), vec![h(1)]),
1819 
            ]
1820 
            .into_iter()
1821 
            .collect(),
1822 
        );
1823 
        let build = |order: &[usize]| {
1824 
            let mut g = FileGraph::new();
1825 
            for &i in order {
1826 
                let (c, ins, dels) = &ops[i];
1827 
                for (idx, a, b, l) in ins {
1828 
                    g.insert(*c, *idx, *a, *b, l);
1829 
                }
1830 
                for d in dels {
1831 
                    g.delete(*c, d);
1832 
                }
1833 
            }
1834 
            let m = g.materialize(&deps);
1835 
            (m.clone(), text(&g, &m))
1836 
        };
1837 
        let reference = build(&[0, 1, 2, 3, 4]);
1838 
        assert!(reference.0.is_conflicted());
1839 
        let mut rng = rand::thread_rng();
1840 
        let mut order: Vec<usize> = (0..ops.len()).collect();
1841 
        for _ in 0..50 {
1842 
            order.shuffle(&mut rng);
1843 
            assert_eq!(build(&order), reference, "order {order:?}");
1844 
        }
1845 
    }
1846 
}