--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hg-core/src/dagops.rs Mon Jan 14 10:07:48 2019 +0100
@@ -0,0 +1,136 @@
+// dagops.rs
+//
+// Copyright 2019 Georges Racinet <georges.racinet@octobus.net>
+//
+// 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 std::collections::HashSet;
+
+fn remove_parents(
+ graph: &impl Graph,
+ rev: Revision,
+ set: &mut HashSet<Revision>,
+) -> 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 {
+ 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(
+ graph: &impl Graph,
+ revs: &mut HashSet<Revision>,
+) -> 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 {
+ remove_parents(graph, rev, revs)?;
+ }
+ Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+
+ use super::*;
+ use crate::testing::SampleGraph;
+
+ /// Apply `retain_heads()` to the given slice and return as a sorted `Vec`
+ fn retain_heads_sorted(
+ graph: &impl Graph,
+ revs: &[Revision],
+ ) -> Result<Vec<Revision>, GraphError> {
+ let mut revs: HashSet<Revision> = revs.iter().cloned().collect();
+ retain_heads(graph, &mut revs)?;
+ let mut as_vec: Vec<Revision> = revs.iter().cloned().collect();
+ as_vec.sort();
+ 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: &[Revision],
+ ) -> Result<Vec<Revision>, GraphError> {
+ let heads = heads(graph, revs.iter())?;
+ let mut as_vec: Vec<Revision> = heads.iter().cloned().collect();
+ as_vec.sort();
+ 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(())
+ }
+
+}