view rust/hg-core/src/dagops.rs @ 51181:dcaa2df1f688

changelog: never inline changelog

The test suite mostly use small repositories, that implies that most changelog in the
tests are inlined. As a result, non-inlined changelog are quite poorly tested.
Since non-inline changelog are most common case for serious repositories, this
lack of testing is a significant problem that results in high profile issue like
the one recently fixed by 66417f55ea33 and 849745d7da89.

Inlining the changelog does not bring much to the table, the number of total
file saved is negligible, and the changelog will be read by most operation
anyway.

So this changeset is make it so we never inline the changelog, and de-inline the
one that are still inlined whenever we touch them.

By doing that, we remove the "dual code path" situation for writing new entry to
the changelog and move to a "single code path" situation. Having a single
code path simplify the code and make sure it is covered by test (if test cover
that situation obviously)


This impact all tests that care about the number of file and the exchange size,
but there is nothing too complicated in them just a lot of churn.

The churn is made "worse" by the fact rust will use the persistent nodemap on
any changelog now. Which is overall a win as it means testing the persistent
nodemap more and having less special cases.

In short, having inline changelog is mostly useless and an endless source of
pain. We get rid of it.

// dagops.rs
//
// Copyright 2019 Georges Racinet <[e-mail]>
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2 or any later version.

//! Miscellaneous DAG operations
//!
//! # Terminology
//! - By *relative heads* of a collection of revision numbers (`Revision`), we
//!   mean those revisions that have no children among the collection.
//! - Similarly *relative roots* of a collection of `Revision`, we mean those
//!   whose parents, if any, don't belong to the collection.
use super::{Graph, GraphError, Revision, NULL_REVISION};
use crate::ancestors::AncestorsIterator;
use std::collections::{BTreeSet, HashSet};

fn remove_parents<S: std::hash::BuildHasher>(
    graph: &impl Graph,
    rev: Revision,
    set: &mut HashSet<Revision, S>,
) -> Result<(), GraphError> {
    for parent in graph.parents(rev)?.iter() {
        if *parent != NULL_REVISION {
            set.remove(parent);
        }
    }
    Ok(())
}

/// Relative heads out of some revisions, passed as an iterator.
///
/// These heads are defined as those revisions that have no children
/// among those emitted by the iterator.
///
/// # Performance notes
/// Internally, this clones the iterator, and builds a `HashSet` out of it.
///
/// This function takes an `Iterator` instead of `impl IntoIterator` to
/// guarantee that cloning the iterator doesn't result in cloning the full
/// construct it comes from.
pub fn heads<'a>(
    graph: &impl Graph,
    iter_revs: impl Clone + Iterator<Item = &'a Revision>,
) -> Result<HashSet<Revision>, GraphError> {
    let mut heads: HashSet<Revision> = iter_revs.clone().cloned().collect();
    heads.remove(&NULL_REVISION);
    for rev in iter_revs {
        if *rev != NULL_REVISION {
            remove_parents(graph, *rev, &mut heads)?;
        }
    }
    Ok(heads)
}

/// Retain in `revs` only its relative heads.
///
/// This is an in-place operation, so that control of the incoming
/// set is left to the caller.
/// - a direct Python binding would probably need to build its own `HashSet`
///   from an incoming iterable, even if its sole purpose is to extract the
///   heads.
/// - a Rust caller can decide whether cloning beforehand is appropriate
///
/// # Performance notes
/// Internally, this function will store a full copy of `revs` in a `Vec`.
pub fn retain_heads<S: std::hash::BuildHasher>(
    graph: &impl Graph,
    revs: &mut HashSet<Revision, S>,
) -> Result<(), GraphError> {
    revs.remove(&NULL_REVISION);
    // we need to construct an iterable copy of revs to avoid itering while
    // mutating
    let as_vec: Vec<Revision> = revs.iter().cloned().collect();
    for rev in as_vec {
        if rev != NULL_REVISION {
            remove_parents(graph, rev, revs)?;
        }
    }
    Ok(())
}

/// Roots of `revs`, passed as a `HashSet`
///
/// They are returned in arbitrary order
pub fn roots<G: Graph, S: std::hash::BuildHasher>(
    graph: &G,
    revs: &HashSet<Revision, S>,
) -> Result<Vec<Revision>, GraphError> {
    let mut roots: Vec<Revision> = Vec::new();
    for rev in revs {
        if graph
            .parents(*rev)?
            .iter()
            .filter(|p| **p != NULL_REVISION)
            .all(|p| !revs.contains(p))
        {
            roots.push(*rev);
        }
    }
    Ok(roots)
}

/// Compute the topological range between two collections of revisions
///
/// This is equivalent to the revset `<roots>::<heads>`.
///
/// Currently, the given `Graph` has to implement `Clone`, which means
/// actually cloning just a reference-counted Python pointer if
/// it's passed over through `rust-cpython`. This is due to the internal
/// use of `AncestorsIterator`
///
/// # Algorithmic details
///
/// This is a two-pass swipe inspired from what `reachableroots2` from
/// `mercurial.cext.parsers` does to obtain the same results.
///
/// - first, we climb up the DAG from `heads` in topological order, keeping
///   them in the vector `heads_ancestors` vector, and adding any element of
///   `roots` we find among them to the resulting range.
/// - Then, we iterate on that recorded vector so that a revision is always
///   emitted after its parents and add all revisions whose parents are already
///   in the range to the results.
///
/// # Performance notes
///
/// The main difference with the C implementation is that
/// the latter uses a flat array with bit flags, instead of complex structures
/// like `HashSet`, making it faster in most scenarios. In theory, it's
/// possible that the present implementation could be more memory efficient
/// for very large repositories with many branches.
pub fn range(
    graph: &(impl Graph + Clone),
    roots: impl IntoIterator<Item = Revision>,
    heads: impl IntoIterator<Item = Revision>,
) -> Result<BTreeSet<Revision>, GraphError> {
    let mut range = BTreeSet::new();
    let roots: HashSet<Revision> = roots.into_iter().collect();
    let min_root: Revision = match roots.iter().cloned().min() {
        None => {
            return Ok(range);
        }
        Some(r) => r,
    };

    // Internally, AncestorsIterator currently maintains a `HashSet`
    // of all seen revision, which is also what we record, albeit in an ordered
    // way. There's room for improvement on this duplication.
    let ait = AncestorsIterator::new(graph.clone(), heads, min_root, true)?;
    let mut heads_ancestors: Vec<Revision> = Vec::new();
    for revres in ait {
        let rev = revres?;
        if roots.contains(&rev) {
            range.insert(rev);
        }
        heads_ancestors.push(rev);
    }

    for rev in heads_ancestors.into_iter().rev() {
        for parent in graph.parents(rev)?.iter() {
            if *parent != NULL_REVISION && range.contains(parent) {
                range.insert(rev);
            }
        }
    }
    Ok(range)
}

#[cfg(test)]
mod tests {

    use super::*;
    use crate::{testing::SampleGraph, BaseRevision};

    /// Apply `retain_heads()` to the given slice and return as a sorted `Vec`
    fn retain_heads_sorted(
        graph: &impl Graph,
        revs: &[BaseRevision],
    ) -> Result<Vec<Revision>, GraphError> {
        let mut revs: HashSet<Revision> =
            revs.iter().cloned().map(Revision).collect();
        retain_heads(graph, &mut revs)?;
        let mut as_vec: Vec<Revision> = revs.iter().cloned().collect();
        as_vec.sort_unstable();
        Ok(as_vec)
    }

    #[test]
    fn test_retain_heads() -> Result<(), GraphError> {
        assert_eq!(retain_heads_sorted(&SampleGraph, &[4, 5, 6])?, vec![5, 6]);
        assert_eq!(
            retain_heads_sorted(&SampleGraph, &[4, 1, 6, 12, 0])?,
            vec![1, 6, 12]
        );
        assert_eq!(
            retain_heads_sorted(&SampleGraph, &[1, 2, 3, 4, 5, 6, 7, 8, 9])?,
            vec![3, 5, 8, 9]
        );
        Ok(())
    }

    /// Apply `heads()` to the given slice and return as a sorted `Vec`
    fn heads_sorted(
        graph: &impl Graph,
        revs: &[BaseRevision],
    ) -> Result<Vec<Revision>, GraphError> {
        let iter_revs: Vec<_> = revs.iter().cloned().map(Revision).collect();
        let heads = heads(graph, iter_revs.iter())?;
        let mut as_vec: Vec<Revision> = heads.iter().cloned().collect();
        as_vec.sort_unstable();
        Ok(as_vec)
    }

    #[test]
    fn test_heads() -> Result<(), GraphError> {
        assert_eq!(heads_sorted(&SampleGraph, &[4, 5, 6])?, vec![5, 6]);
        assert_eq!(
            heads_sorted(&SampleGraph, &[4, 1, 6, 12, 0])?,
            vec![1, 6, 12]
        );
        assert_eq!(
            heads_sorted(&SampleGraph, &[1, 2, 3, 4, 5, 6, 7, 8, 9])?,
            vec![3, 5, 8, 9]
        );
        Ok(())
    }

    /// Apply `roots()` and sort the result for easier comparison
    fn roots_sorted(
        graph: &impl Graph,
        revs: &[BaseRevision],
    ) -> Result<Vec<Revision>, GraphError> {
        let set: HashSet<_> = revs.iter().cloned().map(Revision).collect();
        let mut as_vec = roots(graph, &set)?;
        as_vec.sort_unstable();
        Ok(as_vec)
    }

    #[test]
    fn test_roots() -> Result<(), GraphError> {
        assert_eq!(roots_sorted(&SampleGraph, &[4, 5, 6])?, vec![4]);
        assert_eq!(
            roots_sorted(&SampleGraph, &[4, 1, 6, 12, 0])?,
            vec![0, 4, 12]
        );
        assert_eq!(
            roots_sorted(&SampleGraph, &[1, 2, 3, 4, 5, 6, 7, 8, 9])?,
            vec![1, 8]
        );
        Ok(())
    }

    /// Apply `range()` and convert the result into a Vec for easier comparison
    fn range_vec(
        graph: impl Graph + Clone,
        roots: &[BaseRevision],
        heads: &[BaseRevision],
    ) -> Result<Vec<Revision>, GraphError> {
        range(
            &graph,
            roots.iter().cloned().map(Revision),
            heads.iter().cloned().map(Revision),
        )
        .map(|bs| bs.into_iter().collect())
    }

    #[test]
    fn test_range() -> Result<(), GraphError> {
        assert_eq!(range_vec(SampleGraph, &[0], &[4])?, vec![0, 1, 2, 4]);
        assert_eq!(
            range_vec(SampleGraph, &[0], &[8])?,
            Vec::<Revision>::new()
        );
        assert_eq!(
            range_vec(SampleGraph, &[5, 6], &[10, 11, 13])?,
            vec![5, 10]
        );
        assert_eq!(
            range_vec(SampleGraph, &[5, 6], &[10, 12])?,
            vec![5, 6, 9, 10, 12]
        );
        Ok(())
    }
}