OXYGENHUB
# 6caacfff1d4f oxygen / crates / oxy-core / src / lanes.rs
4.2 KiB · Rust · last changed Roadmap: phase A done 1 month ago source blame history raw
119bbf50 Andy McCall ↶ 1 
//! Lane layout for drawing history as a graph: each change takes a lane,
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//! its first dependency continues that lane, other dependencies take free
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//! lanes, so edges flow from a change down to what it depends on. Shared
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//! by `oxy log` and hosts, so every view draws the same picture.
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use crate::hash::ChangeHash;
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use std::collections::{HashMap, HashSet};
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/// A row of the graph: the change's lane and the edges drawn from it.
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#[derive(Clone, Debug, PartialEq, Eq)]
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pub struct Row {
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    pub lane: usize,
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    /// `(from_lane, to_lane)` for each dependency drawn from this row to
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    /// the rows below.
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    pub edges: Vec<(usize, usize)>,
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    /// Lanes that pass through this row without touching it.
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    pub through: Vec<usize>,
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}
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/// `changes` newest first as `(hash, deps)`. A dependency outside the
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/// list ends its lane at the bottom.
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pub fn layout(changes: &[(ChangeHash, Vec<ChangeHash>)]) -> Vec<Row> {
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    let mut active: Vec<Option<ChangeHash>> = Vec::new();
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    let mut rows = Vec::with_capacity(changes.len());
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    let known: HashSet<&ChangeHash> = changes.iter().map(|(h, _)| h).collect();
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    let mut lanes: HashMap<ChangeHash, usize> = HashMap::new();
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    for (hash, deps) in changes {
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        let lane = match active.iter().position(|a| a.as_ref() == Some(hash)) {
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            Some(l) => l,
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            None => match active.iter().position(|a| a.is_none()) {
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                Some(l) => {
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                    active[l] = Some(*hash);
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                    l
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                }
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                None => {
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                    active.push(Some(*hash));
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                    active.len() - 1
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                }
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            },
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        };
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        lanes.insert(*hash, lane);
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        let mut edges = Vec::new();
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        let deps: Vec<&ChangeHash> = deps.iter().filter(|d| known.contains(d)).collect();
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        active[lane] = None;
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        for (i, d) in deps.iter().enumerate() {
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            let target = match active.iter().position(|a| a.as_ref() == Some(*d)) {
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                Some(l) => l,
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                None => {
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                    let l = if i == 0 && active[lane].is_none() {
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                        lane
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                    } else {
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                        match active.iter().position(|a| a.is_none()) {
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                            Some(l) => l,
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                            None => {
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                                active.push(None);
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                                active.len() - 1
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                            }
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                        }
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                    };
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                    active[l] = Some(**d);
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                    l
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                }
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            };
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            edges.push((lane, target));
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        }
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        let through: Vec<usize> = active
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            .iter()
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            .enumerate()
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            .filter(|(l, a)| a.is_some() && *l != lane && !edges.iter().any(|e| e.1 == *l))
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            .map(|(l, _)| l)
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            .collect();
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        rows.push(Row {
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            lane,
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            edges,
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            through,
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        });
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        while active.last().is_some_and(|a| a.is_none()) {
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            active.pop();
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        }
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    }
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    rows
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}
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/// The number of lanes the rows use.
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pub fn width(rows: &[Row]) -> usize {
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    rows.iter()
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        .map(|r| {
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            r.lane
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                .max(r.edges.iter().map(|e| e.1).max().unwrap_or(0))
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                .max(r.through.iter().copied().max().unwrap_or(0))
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        })
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        .max()
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        .map(|m| m + 1)
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        .unwrap_or(1)
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}
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#[cfg(test)]
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mod tests {
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    use super::*;
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    use crate::hash::ObjectRef;
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    fn h(n: u8) -> ChangeHash {
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        ObjectRef([n; 32])
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    }
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    #[test]
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    fn linear_history_is_one_lane() {
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        let rows = layout(&[(h(3), vec![h(2)]), (h(2), vec![h(1)]), (h(1), vec![])]);
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        assert!(rows.iter().all(|r| r.lane == 0), "{rows:?}");
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        assert_eq!(rows[0].edges, vec![(0, 0)]);
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        assert_eq!(width(&rows), 1);
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    }
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    #[test]
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    fn a_diamond_takes_two_lanes_and_rejoins() {
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        let rows = layout(&[
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            (h(4), vec![h(2), h(3)]),
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            (h(2), vec![h(1)]),
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            (h(3), vec![h(1)]),
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            (h(1), vec![]),
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        ]);
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        assert_eq!(rows[0].edges, vec![(0, 0), (0, 1)]);
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        assert_eq!(rows[2].lane, 1);
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        assert_eq!(
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            rows[2].edges,
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            vec![(1, 0)],
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            "the second branch joins the first lane"
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        );
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        assert_eq!(width(&rows), 2);
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    }
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}