annotate rust/hg-core/src/ancestors.rs @ 40300:72b94f946e90

rust: rustlazyancestors.__contains__

This changeset provides a Rust implementation of
the iteration performed by lazyancestor.__contains__

It has the advantage over the Python iteration to use
the 'seen' set encapsuled into the dedicated iterator (self._containsiter),
rather than storing emitted items in another set (self._containsseen),
and hence should reduce the memory footprint.

Also, there's no need to convert intermediate emitted revisions back into
Python integers.

At this point, it would be tempting to implement the whole lazyancestor object
in Rust, but that would lead to more C wrapping code (two objects) for
little expected benefits.

// ancestors.rs
//
// Copyright 2018 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.

//! Rust versions of generic DAG ancestors algorithms for Mercurial

use super::{Graph, GraphError, Revision, NULL_REVISION};
use std::collections::{BinaryHeap, HashSet};

/// Iterator over the ancestors of a given list of revisions
/// This is a generic type, defined and implemented for any Graph, so that
/// it's easy to
///
/// - unit test in pure Rust
/// - bind to main Mercurial code, potentially in several ways and have these
///   bindings evolve over time
pub struct AncestorsIterator<G: Graph> {
    graph: G,
    visit: BinaryHeap<Revision>,
    seen: HashSet<Revision>,
    stoprev: Revision,
}

impl<G: Graph> AncestorsIterator<G> {
    /// Constructor.
    ///
    /// if `inclusive` is true, then the init revisions are emitted in
    /// particular, otherwise iteration starts from their parents.
    pub fn new<I>(
        graph: G,
        initrevs: I,
        stoprev: Revision,
        inclusive: bool,
    ) -> Result<Self, GraphError>
    where
        I: IntoIterator<Item = Revision>,
    {
        let filtered_initrevs = initrevs.into_iter().filter(|&r| r >= stoprev);
        if inclusive {
            let visit: BinaryHeap<Revision> = filtered_initrevs.collect();
            let seen = visit.iter().map(|&x| x).collect();
            return Ok(AncestorsIterator {
                visit: visit,
                seen: seen,
                stoprev: stoprev,
                graph: graph,
            });
        }
        let mut this = AncestorsIterator {
            visit: BinaryHeap::new(),
            seen: HashSet::new(),
            stoprev: stoprev,
            graph: graph,
        };
        this.seen.insert(NULL_REVISION);
        for rev in filtered_initrevs {
            this.conditionally_push_parents(rev)?;
        }
        Ok(this)
    }

    #[inline]
    fn conditionally_push_rev(&mut self, rev: Revision) {
        if self.stoprev <= rev && !self.seen.contains(&rev) {
            self.seen.insert(rev);
            self.visit.push(rev);
        }
    }

    #[inline]
    fn conditionally_push_parents(
        &mut self,
        rev: Revision,
    ) -> Result<(), GraphError> {
        let parents = self.graph.parents(rev)?;
        self.conditionally_push_rev(parents.0);
        self.conditionally_push_rev(parents.1);
        Ok(())
    }

    /// Consumes partially the iterator to tell if the given target
    /// revision
    /// is in the ancestors it emits.
    /// This is meant for iterators actually dedicated to that kind of
    /// purpose
    pub fn contains(&mut self, target: Revision) -> bool {
        if self.seen.contains(&target) && target != NULL_REVISION {
            return true;
        }
        for rev in self {
            if rev == target {
                return true;
            }
            if rev < target {
                return false;
            }
        }
        false
    }
}

/// Main implementation.
///
/// The algorithm is the same as in `_lazyancestorsiter()` from `ancestors.py`
/// with a few non crucial differences:
///
/// - there's no filtering of invalid parent revisions. Actually, it should be
///   consistent and more efficient to filter them from the end caller.
/// - we don't use the equivalent of `heapq.heapreplace()`, but we should, for
///   the same reasons (using `peek_mut`)
/// - we don't have the optimization for adjacent revs (case where p1 == rev-1)
/// - we save a few pushes by comparing with `stoprev` before pushing
///
/// Error treatment:
/// We swallow the possible GraphError of conditionally_push_parents() to
/// respect the Iterator trait in a simple manner: never emitting parents
/// for the returned revision. We finds this good enough for now, because:
///
/// - there's a good chance that invalid revisionss are fed from the start,
///   and `new()` doesn't swallow the error result.
/// - this is probably what the Python implementation produces anyway, due
///   to filtering at each step, and Python code is currently the only
///   concrete caller we target, so we shouldn't need a finer error treatment
///   for the time being.
impl<G: Graph> Iterator for AncestorsIterator<G> {
    type Item = Revision;

    fn next(&mut self) -> Option<Revision> {
        let current = match self.visit.pop() {
            None => {
                return None;
            }
            Some(i) => i,
        };
        self.conditionally_push_parents(current).unwrap_or(());
        Some(current)
    }
}

#[cfg(test)]
mod tests {

    use super::*;

    #[derive(Clone, Debug)]
    struct Stub;

    /// This is the same as the dict from test-ancestors.py
    impl Graph for Stub {
        fn parents(
            &self,
            rev: Revision,
        ) -> Result<(Revision, Revision), GraphError> {
            match rev {
                0 => Ok((-1, -1)),
                1 => Ok((0, -1)),
                2 => Ok((1, -1)),
                3 => Ok((1, -1)),
                4 => Ok((2, -1)),
                5 => Ok((4, -1)),
                6 => Ok((4, -1)),
                7 => Ok((4, -1)),
                8 => Ok((-1, -1)),
                9 => Ok((6, 7)),
                10 => Ok((5, -1)),
                11 => Ok((3, 7)),
                12 => Ok((9, -1)),
                13 => Ok((8, -1)),
                r => Err(GraphError::ParentOutOfRange(r)),
            }
        }
    }

    fn list_ancestors<G: Graph>(
        graph: G,
        initrevs: Vec<Revision>,
        stoprev: Revision,
        inclusive: bool,
    ) -> Vec<Revision> {
        AncestorsIterator::new(graph, initrevs, stoprev, inclusive)
            .unwrap()
            .collect()
    }

    #[test]
    /// Same tests as test-ancestor.py, without membership
    /// (see also test-ancestor.py.out)
    fn test_list_ancestor() {
        assert_eq!(list_ancestors(Stub, vec![], 0, false), vec![]);
        assert_eq!(
            list_ancestors(Stub, vec![11, 13], 0, false),
            vec![8, 7, 4, 3, 2, 1, 0]
        );
        assert_eq!(list_ancestors(Stub, vec![1, 3], 0, false), vec![1, 0]);
        assert_eq!(
            list_ancestors(Stub, vec![11, 13], 0, true),
            vec![13, 11, 8, 7, 4, 3, 2, 1, 0]
        );
        assert_eq!(list_ancestors(Stub, vec![11, 13], 6, false), vec![8, 7]);
        assert_eq!(
            list_ancestors(Stub, vec![11, 13], 6, true),
            vec![13, 11, 8, 7]
        );
        assert_eq!(list_ancestors(Stub, vec![11, 13], 11, true), vec![13, 11]);
        assert_eq!(list_ancestors(Stub, vec![11, 13], 12, true), vec![13]);
        assert_eq!(
            list_ancestors(Stub, vec![10, 1], 0, true),
            vec![10, 5, 4, 2, 1, 0]
        );
    }

    #[test]
    /// Corner case that's not directly in test-ancestors.py, but
    /// that happens quite often, as demonstrated by running the whole
    /// suite.
    /// For instance, run tests/test-obsolete-checkheads.t
    fn test_nullrev_input() {
        let mut iter =
            AncestorsIterator::new(Stub, vec![-1], 0, false).unwrap();
        assert_eq!(iter.next(), None)
    }

    #[test]
    fn test_contains() {
        let mut lazy =
            AncestorsIterator::new(Stub, vec![10, 1], 0, true).unwrap();
        assert!(lazy.contains(1));
        assert!(!lazy.contains(3));

        let mut lazy =
            AncestorsIterator::new(Stub, vec![0], 0, false).unwrap();
        assert!(!lazy.contains(NULL_REVISION));
    }

    /// A corrupted Graph, supporting error handling tests
    struct Corrupted;

    impl Graph for Corrupted {
        fn parents(
            &self,
            rev: Revision,
        ) -> Result<(Revision, Revision), GraphError> {
            match rev {
                1 => Ok((0, -1)),
                r => Err(GraphError::ParentOutOfRange(r)),
            }
        }
    }

    #[test]
    fn test_initrev_out_of_range() {
        // inclusive=false looks up initrev's parents right away
        match AncestorsIterator::new(Stub, vec![25], 0, false) {
            Ok(_) => panic!("Should have been ParentOutOfRange"),
            Err(e) => assert_eq!(e, GraphError::ParentOutOfRange(25)),
        }
    }

    #[test]
    fn test_next_out_of_range() {
        // inclusive=false looks up initrev's parents right away
        let mut iter =
            AncestorsIterator::new(Corrupted, vec![1], 0, false).unwrap();
        assert_eq!(iter.next(), Some(0));
        assert_eq!(iter.next(), None);
    }
}