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///pub mod ancestors {    use std::{        borrow::BorrowMut,        collections::{BTreeSet, VecDeque},    };     use git_hash::{oid, ObjectId};    use git_object::CommitRefIter;    use quick_error::quick_error;     quick_error! {        /// The error is part of the item returned by the [Ancestors] iterator.        #[derive(Debug)]        #[allow(missing_docs)]        pub enum Error {            NotFound{oid: ObjectId} {                display("The commit {} could not be found", oid)            }            ObjectDecode(err: git_object::decode::Error) {                display("An object could not be decoded")                source(err)                from()            }        }    }     /// The state used and potentially shared by multiple graph traversals.    #[derive(Default, Clone)]    pub struct State {        next: VecDeque<ObjectId>,        buf: Vec<u8>,        seen: BTreeSet<ObjectId>,    }     impl State {        fn clear(&mut self) {            self.next.clear();            self.buf.clear();            self.seen.clear();        }    }     /// An iterator over the ancestors one or more starting commits    pub struct Ancestors<Find, Predicate, StateMut> {        find: Find,        predicate: Predicate,        state: StateMut,    }     impl<Find, StateMut> Ancestors<Find, fn(&oid) -> bool, StateMut>    where        Find: for<'a> FnMut(&oid, &'a mut Vec<u8>) -> Option<CommitRefIter<'a>>,        StateMut: BorrowMut<State>,    {        /// Create a new instance.        ///        /// * `find` - a way to lookup new object data during traversal by their ObjectId, writing their data into buffer and returning        ///    an iterator over commit tokens if the object is present and is a commit. Caching should be implemented within this function        ///    as needed. The return value is `Option<CommitIter>` which degenerates all error information. Not finding a commit should also        ///    be considered an errors as all objects in the commit graph should be present in the database. Hence [`Error::NotFound`] should        ///    be escalated into a more specific error if its encountered by the caller.        /// * `state` - all state used for the traversal. If multiple traversals are performed, allocations can be minimized by reusing        ///   this state.        /// * `tips`        ///   * the starting points of the iteration, usually commits        ///   * each commit they lead to will only be returned once, including the tip that started it        pub fn new(tips: impl IntoIterator<Item = impl Into<ObjectId>>, state: StateMut, find: Find) -> Self {            Self::filtered(tips, state, find, |_| true)        }    }     impl<Find, Predicate, StateMut> Ancestors<Find, Predicate, StateMut>    where        Find: for<'a> FnMut(&oid, &'a mut Vec<u8>) -> Option<CommitRefIter<'a>>,        Predicate: FnMut(&oid) -> bool,        StateMut: BorrowMut<State>,    {        /// Create a new instance with commit filtering enabled.        ///        /// * `find` - a way to lookup new object data during traversal by their ObjectId, writing their data into buffer and returning        ///    an iterator over commit tokens if the object is present and is a commit. Caching should be implemented within this function        ///    as needed. The return value is `Option<CommitIter>` which degenerates all error information. Not finding a commit should also        ///    be considered an errors as all objects in the commit graph should be present in the database. Hence [`Error::NotFound`] should        ///    be escalated into a more specific error if its encountered by the caller.        /// * `state` - all state used for the traversal. If multiple traversals are performed, allocations can be minimized by reusing        ///   this state.        /// * `tips`        ///   * the starting points of the iteration, usually commits        ///   * each commit they lead to will only be returned once, including the tip that started it        /// * `predicate` - indicate whether a given commit should be included in the result as well        ///   as whether its parent commits should be traversed.        pub fn filtered(            tips: impl IntoIterator<Item = impl Into<ObjectId>>,            mut state: StateMut,            find: Find,            mut predicate: Predicate,        ) -> Self {            let tips = tips.into_iter();            {                let state = state.borrow_mut();                state.clear();                state.next.reserve(tips.size_hint().0);                for tip in tips.map(Into::into) {                    let was_inserted = state.seen.insert(tip);                    if was_inserted && predicate(&tip) {                        state.next.push_back(tip);                    }                }            }            Self { find, predicate, state }        }    }     impl<Find, Predicate, StateMut> Iterator for Ancestors<Find, Predicate, StateMut>    where        Find: for<'a> FnMut(&oid, &'a mut Vec<u8>) -> Option<CommitRefIter<'a>>,        Predicate: FnMut(&oid) -> bool,        StateMut: BorrowMut<State>,    {        type Item = Result<ObjectId, Error>;         fn next(&mut self) -> Option<Self::Item> {            let state = self.state.borrow_mut();            let res = state.next.pop_front();            if let Some(oid) = res {                match (self.find)(&oid, &mut state.buf) {                    Some(mut commit_iter) => {                        if let Some(Err(decode_tree_err)) = commit_iter.next() {                            return Some(Err(decode_tree_err.into()));                        }                        for token in commit_iter {                            match token {                                Ok(git_object::commit::ref_iter::Token::Parent { id }) => {                                    let was_inserted = state.seen.insert(id);                                    if was_inserted && (self.predicate)(&id) {                                        state.next.push_back(id);                                    }                                }                                Ok(_a_token_past_the_parents) => break,                                Err(err) => return Some(Err(err.into())),                            }                        }                    }                    None => return Some(Err(Error::NotFound { oid })),                }            }            res.map(Ok)        }    }}#[doc(inline)]pub use ancestors::Ancestors;