annotate rust/hg-core/src/copy_tracing.rs @ 46623:aa19d60ac974

copies-rust: use simpler overwrite when value on both side are identical

If the value are the same, their "overwritten" set is the same and we don't need
to combine them.


It helps our slower cases

Repo            Case                                  Source-Rev   Dest-Rev      # of revisions  old time    new time      Difference    Factor    time per rev
---------------------------------------------------------------------------------------------------------------------------------------------------------------
mozilla-try     x00000_revs_x00000_added_x0000_copies 1b661134e2ca 1ae03d022d6d : 228985 revs,  86.722016 s,  80.828689 s,  -5.893327 s, × 0.9320,   352 µs/rev
mozilla-try     x00000_revs_x00000_added_x000_copies  9b2a99adc05e 8e29777b48e6 : 382065 revs,  35.113727 s,  34.094064 s,  -1.019663 s, × 0.9710,    89 µs/rev

Full comparison with the previous revision below:

Repo            Case                                  Source-Rev   Dest-Rev      # of revisions  old time    new time      Difference    Factor    time per rev
---------------------------------------------------------------------------------------------------------------------------------------------------------------
mercurial       x_revs_x_added_0_copies               ad6b123de1c7 39cfcef4f463 :      1 revs,   0.000043 s,   0.000043 s,  +0.000000 s, × 1.0000,    43 µs/rev
mercurial       x_revs_x_added_x_copies               2b1c78674230 0c1d10351869 :      6 revs,   0.000114 s,   0.000114 s,  +0.000000 s, × 1.0000,    19 µs/rev
mercurial       x000_revs_x000_added_x_copies         81f8ff2a9bf2 dd3267698d84 :   1032 revs,   0.004899 s,   0.004899 s,  +0.000000 s, × 1.0000,     4 µs/rev
pypy            x_revs_x_added_0_copies               aed021ee8ae8 099ed31b181b :      9 revs,   0.000196 s,   0.000196 s,  +0.000000 s, × 1.0000,    21 µs/rev
pypy            x_revs_x000_added_0_copies            4aa4e1f8e19a 359343b9ac0e :      1 revs,   0.000050 s,   0.000049 s,  -0.000001 s, × 0.9800,    49 µs/rev
pypy            x_revs_x_added_x_copies               ac52eb7bbbb0 72e022663155 :      7 revs,   0.000125 s,   0.000117 s,  -0.000008 s, × 0.9360,    16 µs/rev
pypy            x_revs_x00_added_x_copies             c3b14617fbd7 ace7255d9a26 :      1 revs,   0.000321 s,   0.6f1f4a s,  +0.000001 s, × 1.0031,   322 µs/rev
pypy            x_revs_x000_added_x000_copies         df6f7a526b60 a83dc6a2d56f :      6 revs,   0.011948 s,   0.011856 s,  -0.000092 s, × 0.9923,  1976 µs/rev
pypy            x000_revs_xx00_added_0_copies         89a76aede314 2f22446ff07e :   4785 revs,   0.051267 s,   0.050992 s,  -0.000275 s, × 0.9946,    10 µs/rev
pypy            x000_revs_x000_added_x_copies         8a3b5bfd266e 2c68e87c3efe :   6780 revs,   0.087755 s,   0.087444 s,  -0.000311 s, × 0.9965,    12 µs/rev
pypy            x000_revs_x000_added_x000_copies      89a76aede314 7b3dda341c84 :   5441 revs,   0.061818 s,   0.062487 s,  +0.000669 s, × 1.0108,    11 µs/rev
pypy            x0000_revs_x_added_0_copies           d1defd0dc478 c9cb1334cc78 :  43645 revs,   0.634253 s,   0.634909 s,  +0.000656 s, × 1.0010,    14 µs/rev
pypy            x0000_revs_xx000_added_0_copies       bf2c629d0071 4ffed77c095c :      2 revs,   0.013179 s,   0.013360 s,  +0.000181 s, × 1.0137,  6680 µs/rev
pypy            x0000_revs_xx000_added_x000_copies    08ea3258278e d9fa043f30c0 :  11316 revs,   0.119643 s,   0.120775 s,  +0.001132 s, × 1.0095,    10 µs/rev
netbeans        x_revs_x_added_0_copies               fb0955ffcbcd a01e9239f9e7 :      2 revs,   0.000085 s,   0.000085 s,  +0.000000 s, × 1.0000,    42 µs/rev
netbeans        x_revs_x000_added_0_copies            6f360122949f 20eb231cc7d0 :      2 revs,   0.000107 s,   0.000108 s,  +0.000001 s, × 1.0093,    54 µs/rev
netbeans        x_revs_x_added_x_copies               1ada3faf6fb6 5a39d12eecf4 :      3 revs,   0.000176 s,   0.000176 s,  +0.000000 s, × 1.0000,    58 µs/rev
netbeans        x_revs_x00_added_x_copies             35be93ba1e2c 9eec5e90c05f :      9 revs,   0.000743 s,   0.000747 s,  +0.000004 s, × 1.0054,    83 µs/rev
netbeans        x000_revs_xx00_added_0_copies         eac3045b4fdd 51d4ae7f1290 :   1421 revs,   0.010246 s,   0.010128 s,  -0.000118 s, × 0.9885,     7 µs/rev
netbeans        x000_revs_x000_added_x_copies         e2063d266acd 6081d72689dc :   1533 revs,   0.015853 s,   0.015899 s,  +0.000046 s, × 1.0029,    10 µs/rev
netbeans        x000_revs_x000_added_x000_copies      ff453e9fee32 411350406ec2 :   5750 revs,   0.062971 s,   0.062215 s,  -0.000756 s, × 0.9880,    10 µs/rev
netbeans        x0000_revs_xx000_added_x000_copies    588c2d1ced70 1aad62e59ddd :  66949 revs,   0.518337 s,   0.521004 s,  +0.002667 s, × 1.0051,     7 µs/rev
mozilla-central x_revs_x_added_0_copies               3697f962bb7b 7015fcdd43a2 :      2 revs,   0.000090 s,   0.000090 s,  +0.000000 s, × 1.0000,    45 µs/rev
mozilla-central x_revs_x000_added_0_copies            dd390860c6c9 40d0c5bed75d :      8 revs,   0.000268 s,   0.000264 s,  -0.000004 s, × 0.9851,    33 µs/rev
mozilla-central x_revs_x_added_x_copies               8d198483ae3b 14207ffc2b2f :      9 revs,   0.000187 s,   0.000186 s,  -0.000001 s, × 0.9947,    20 µs/rev
mozilla-central x_revs_x00_added_x_copies             98cbc58cc6bc 446a150332c3 :      7 revs,   0.000661 s,   0.000660 s,  -0.000001 s, × 0.9985,    94 µs/rev
mozilla-central x_revs_x000_added_x000_copies         3c684b4b8f68 0a5e72d1b479 :      3 revs,   0.003494 s,   0.003542 s,  +0.000048 s, × 1.0137,  1180 µs/rev
mozilla-central x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :      6 revs,   0.070509 s,   0.071574 s,  +0.001065 s, × 1.0151, 11929 µs/rev
mozilla-central x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :   1593 revs,   0.006489 s,   0.006498 s,  +0.000009 s, × 1.0014,     4 µs/rev
mozilla-central x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :     41 revs,   0.005070 s,   0.005206 s,  +0.000136 s, × 1.0268,   126 µs/rev
mozilla-central x000_revs_x000_added_x000_copies      7c97034feb78 4407bd0c6330 :   7839 revs,   0.065241 s,   0.065535 s,  +0.000294 s, × 1.0045,     8 µs/rev
mozilla-central x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :    615 revs,   0.027284 s,   0.027139 s,  -0.000145 s, × 0.9947,    44 µs/rev
mozilla-central x0000_revs_xx000_added_x000_copies    f78c615a656c 96a38b690156 :  30263 revs,   0.203671 s,   0.201924 s,  -0.001747 s, × 0.9914,     6 µs/rev
mozilla-central x00000_revs_x0000_added_x0000_copies  6832ae71433c 4c222a1d9a00 : 153721 revs,   1.239373 s,   1.257201 s,  +0.017828 s, × 1.0144,     8 µs/rev
mozilla-central x00000_revs_x00000_added_x000_copies  76caed42cf7c 1daa622bbe42 : 204976 revs,   1.649803 s,   1.663045 s,  +0.013242 s, × 1.0080,     8 µs/rev
mozilla-try     x_revs_x_added_0_copies               aaf6dde0deb8 9790f499805a :      2 revs,   0.000868 s,   0.000866 s,  -0.000002 s, × 0.9977,   433 µs/rev
mozilla-try     x_revs_x000_added_0_copies            d8d0222927b4 5bb8ce8c7450 :      2 revs,   0.000885 s,   0.000883 s,  -0.000002 s, × 0.9977,   441 µs/rev
mozilla-try     x_revs_x_added_x_copies               092fcca11bdb 936255a0384a :      4 revs,   0.000165 s,   0.000163 s,  -0.000002 s, × 0.9879,    40 µs/rev
mozilla-try     x_revs_x00_added_x_copies             b53d2fadbdb5 017afae788ec :      2 revs,   0.001147 s,   0.001139 s,  -0.000008 s, × 0.9930,   569 µs/rev
mozilla-try     x_revs_x000_added_x000_copies         20408ad61ce5 6f0ee96e21ad :      1 revs,   0.032885 s,   0.032753 s,  -0.000132 s, × 0.9960, 32752 µs/rev
mozilla-try     x_revs_x0000_added_x0000_copies       effb563bb7e5 c07a39dc4e80 :      6 revs,   0.071304 s,   0.073266 s,  +0.001962 s, × 1.0275, 12211 µs/rev
mozilla-try     x000_revs_xx00_added_0_copies         6100d773079a 04a55431795e :   1593 revs,   0.006506 s,   0.006567 s,  +0.000061 s, × 1.0094,     4 µs/rev
mozilla-try     x000_revs_x000_added_x_copies         9f17a6fc04f9 2d37b966abed :     41 revs,   0.005486 s,   0.005427 s,  -0.000059 s, × 0.9892,   132 µs/rev
mozilla-try     x000_revs_x000_added_x000_copies      1346fd0130e4 4c65cbdabc1f :   6657 revs,   0.064677 s,   0.064058 s,  -0.000619 s, × 0.9904,     9 µs/rev
mozilla-try     x0000_revs_x_added_0_copies           63519bfd42ee a36a2a865d92 :  40314 revs,   0.306000 s,   0.303320 s,  -0.002680 s, × 0.9912,     7 µs/rev
mozilla-try     x0000_revs_x_added_x_copies           9fe69ff0762d bcabf2a78927 :  38690 revs,   0.288217 s,   0.288456 s,  +0.000239 s, × 1.0008,     7 µs/rev
mozilla-try     x0000_revs_xx000_added_x_copies       156f6e2674f2 4d0f2c178e66 :   8598 revs,   0.086117 s,   0.085925 s,  -0.000192 s, × 0.9978,     9 µs/rev
mozilla-try     x0000_revs_xx000_added_0_copies       9eec5917337d 67118cc6dcad :    615 revs,   0.027512 s,   0.027302 s,  -0.000210 s, × 0.9924,    44 µs/rev
mozilla-try     x0000_revs_xx000_added_x000_copies    89294cd501d9 7ccb2fc7ccb5 :  97052 revs,   1.998239 s,   2.034596 s,  +0.036357 s, × 1.0182,    20 µs/rev
mozilla-try     x0000_revs_x0000_added_x0000_copies   e928c65095ed e951f4ad123a :  52031 revs,   0.688201 s,   0.694030 s,  +0.005829 s, × 1.0085,    13 µs/rev
mozilla-try     x00000_revs_x_added_0_copies          6a320851d377 1ebb79acd503 : 363753 revs,   4.389428 s,   4.407723 s,  +0.018295 s, × 1.0042,    12 µs/rev
mozilla-try     x00000_revs_x00000_added_0_copies     dc8a3ca7010e d16fde900c9c :  34414 revs,   0.578736 s,   0.574355 s,  -0.004381 s, × 0.9924,    16 µs/rev
mozilla-try     x00000_revs_x_added_x_copies          5173c4b6f97c 95d83ee7242d : 362229 revs,   4.363599 s,   4.457827 s,  +0.094228 s, × 1.0216,    12 µs/rev
mozilla-try     x00000_revs_x000_added_x_copies       9126823d0e9c ca82787bb23c : 359344 revs,   4.324129 s,   4.351696 s,  +0.027567 s, × 1.0064,    12 µs/rev
mozilla-try     x00000_revs_x0000_added_x0000_copies  8d3fafa80d4b eb884023b810 : 192665 revs,   1.565727 s,   1.570065 s,  +0.004338 s, × 1.0028,     8 µs/rev
mozilla-try     x00000_revs_x00000_added_x0000_copies 1b661134e2ca 1ae03d022d6d : 228985 revs,  86.722016 s,  80.828689 s,  -5.893327 s, × 0.9320,   352 µs/rev
mozilla-try     x00000_revs_x00000_added_x000_copies  9b2a99adc05e 8e29777b48e6 : 382065 revs,  35.113727 s,  34.094064 s,  -1.019663 s, × 0.9710,    89 µs/rev
private                                                                         : 459513 revs,  27.397070 s,  27.435529 s,  +0.038459 s, × 1.0014,    59 µs/rev

Differential Revision: https://phab.mercurial-scm.org/D9655

use crate::utils::hg_path::HgPath;
use crate::utils::hg_path::HgPathBuf;
use crate::Revision;
use crate::NULL_REVISION;

use im_rc::ordmap::DiffItem;
use im_rc::ordmap::Entry;
use im_rc::ordmap::OrdMap;

use std::cmp::Ordering;
use std::collections::HashMap;
use std::collections::HashSet;
use std::convert::TryInto;

pub type PathCopies = HashMap<HgPathBuf, HgPathBuf>;

type PathToken = usize;

#[derive(Clone, Debug)]
struct CopySource {
    /// revision at which the copy information was added
    rev: Revision,
    /// the copy source, (Set to None in case of deletion of the associated
    /// key)
    path: Option<PathToken>,
    /// a set of previous `CopySource.rev` value directly or indirectly
    /// overwritten by this one.
    overwritten: HashSet<Revision>,
}

impl CopySource {
    /// create a new CopySource
    ///
    /// Use this when no previous copy source existed.
    fn new(rev: Revision, path: Option<PathToken>) -> Self {
        Self {
            rev,
            path,
            overwritten: HashSet::new(),
        }
    }

    /// create a new CopySource from merging two others
    ///
    /// Use this when merging two InternalPathCopies requires active merging of
    /// some entries.
    fn new_from_merge(rev: Revision, winner: &Self, loser: &Self) -> Self {
        let mut overwritten = HashSet::new();
        overwritten.extend(winner.overwritten.iter().copied());
        overwritten.extend(loser.overwritten.iter().copied());
        overwritten.insert(winner.rev);
        overwritten.insert(loser.rev);
        Self {
            rev,
            path: winner.path,
            overwritten: overwritten,
        }
    }

    /// Update the value of a pre-existing CopySource
    ///
    /// Use this when recording copy information from  parent → child edges
    fn overwrite(&mut self, rev: Revision, path: Option<PathToken>) {
        self.overwritten.insert(self.rev);
        self.rev = rev;
        self.path = path;
    }

    /// Mark pre-existing copy information as "dropped" by a file deletion
    ///
    /// Use this when recording copy information from  parent → child edges
    fn mark_delete(&mut self, rev: Revision) {
        self.overwritten.insert(self.rev);
        self.rev = rev;
        self.path = None;
    }

    /// Mark pre-existing copy information as "dropped" by a file deletion
    ///
    /// Use this when recording copy information from  parent → child edges
    fn mark_delete_with_pair(&mut self, rev: Revision, other: &Self) {
        self.overwritten.insert(self.rev);
        if other.rev != rev {
            self.overwritten.insert(other.rev);
        }
        self.overwritten.extend(other.overwritten.iter().copied());
        self.rev = rev;
        self.path = None;
    }

    fn is_overwritten_by(&self, other: &Self) -> bool {
        other.overwritten.contains(&self.rev)
    }
}

// For the same "dest", content generated for a given revision will always be
// the same.
impl PartialEq for CopySource {
    fn eq(&self, other: &Self) -> bool {
        #[cfg(debug_assertions)]
        {
            if self.rev == other.rev {
                debug_assert!(self.path == other.path);
                debug_assert!(self.overwritten == other.overwritten);
            }
        }
        self.rev == other.rev
    }
}

/// maps CopyDestination to Copy Source (+ a "timestamp" for the operation)
type InternalPathCopies = OrdMap<PathToken, CopySource>;

/// hold parent 1, parent 2 and relevant files actions.
pub type RevInfo<'a> = (Revision, Revision, ChangedFiles<'a>);

/// represent the files affected by a changesets
///
/// This hold a subset of mercurial.metadata.ChangingFiles as we do not need
/// all the data categories tracked by it.
/// This hold a subset of mercurial.metadata.ChangingFiles as we do not need
/// all the data categories tracked by it.
pub struct ChangedFiles<'a> {
    nb_items: u32,
    index: &'a [u8],
    data: &'a [u8],
}

/// Represent active changes that affect the copy tracing.
enum Action<'a> {
    /// The parent ? children edge is removing a file
    ///
    /// (actually, this could be the edge from the other parent, but it does
    /// not matters)
    Removed(&'a HgPath),
    /// The parent ? children edge introduce copy information between (dest,
    /// source)
    CopiedFromP1(&'a HgPath, &'a HgPath),
    CopiedFromP2(&'a HgPath, &'a HgPath),
}

/// This express the possible "special" case we can get in a merge
///
/// See mercurial/metadata.py for details on these values.
#[derive(PartialEq)]
enum MergeCase {
    /// Merged: file had history on both side that needed to be merged
    Merged,
    /// Salvaged: file was candidate for deletion, but survived the merge
    Salvaged,
    /// Normal: Not one of the two cases above
    Normal,
}

type FileChange<'a> = (u8, &'a HgPath, &'a HgPath);

const EMPTY: &[u8] = b"";
const COPY_MASK: u8 = 3;
const P1_COPY: u8 = 2;
const P2_COPY: u8 = 3;
const ACTION_MASK: u8 = 28;
const REMOVED: u8 = 12;
const MERGED: u8 = 8;
const SALVAGED: u8 = 16;

impl<'a> ChangedFiles<'a> {
    const INDEX_START: usize = 4;
    const ENTRY_SIZE: u32 = 9;
    const FILENAME_START: u32 = 1;
    const COPY_SOURCE_START: u32 = 5;

    pub fn new(data: &'a [u8]) -> Self {
        assert!(
            data.len() >= 4,
            "data size ({}) is too small to contain the header (4)",
            data.len()
        );
        let nb_items_raw: [u8; 4] = (&data[0..=3])
            .try_into()
            .expect("failed to turn 4 bytes into 4 bytes");
        let nb_items = u32::from_be_bytes(nb_items_raw);

        let index_size = (nb_items * Self::ENTRY_SIZE) as usize;
        let index_end = Self::INDEX_START + index_size;

        assert!(
            data.len() >= index_end,
            "data size ({}) is too small to fit the index_data ({})",
            data.len(),
            index_end
        );

        let ret = ChangedFiles {
            nb_items,
            index: &data[Self::INDEX_START..index_end],
            data: &data[index_end..],
        };
        let max_data = ret.filename_end(nb_items - 1) as usize;
        assert!(
            ret.data.len() >= max_data,
            "data size ({}) is too small to fit all data ({})",
            data.len(),
            index_end + max_data
        );
        ret
    }

    pub fn new_empty() -> Self {
        ChangedFiles {
            nb_items: 0,
            index: EMPTY,
            data: EMPTY,
        }
    }

    /// internal function to return an individual entry at a given index
    fn entry(&'a self, idx: u32) -> FileChange<'a> {
        if idx >= self.nb_items {
            panic!(
                "index for entry is higher that the number of file {} >= {}",
                idx, self.nb_items
            )
        }
        let flags = self.flags(idx);
        let filename = self.filename(idx);
        let copy_idx = self.copy_idx(idx);
        let copy_source = self.filename(copy_idx);
        (flags, filename, copy_source)
    }

    /// internal function to return the filename of the entry at a given index
    fn filename(&self, idx: u32) -> &HgPath {
        let filename_start;
        if idx == 0 {
            filename_start = 0;
        } else {
            filename_start = self.filename_end(idx - 1)
        }
        let filename_end = self.filename_end(idx);
        let filename_start = filename_start as usize;
        let filename_end = filename_end as usize;
        HgPath::new(&self.data[filename_start..filename_end])
    }

    /// internal function to return the flag field of the entry at a given
    /// index
    fn flags(&self, idx: u32) -> u8 {
        let idx = idx as usize;
        self.index[idx * (Self::ENTRY_SIZE as usize)]
    }

    /// internal function to return the end of a filename part at a given index
    fn filename_end(&self, idx: u32) -> u32 {
        let start = (idx * Self::ENTRY_SIZE) + Self::FILENAME_START;
        let end = (idx * Self::ENTRY_SIZE) + Self::COPY_SOURCE_START;
        let start = start as usize;
        let end = end as usize;
        let raw = (&self.index[start..end])
            .try_into()
            .expect("failed to turn 4 bytes into 4 bytes");
        u32::from_be_bytes(raw)
    }

    /// internal function to return index of the copy source of the entry at a
    /// given index
    fn copy_idx(&self, idx: u32) -> u32 {
        let start = (idx * Self::ENTRY_SIZE) + Self::COPY_SOURCE_START;
        let end = (idx + 1) * Self::ENTRY_SIZE;
        let start = start as usize;
        let end = end as usize;
        let raw = (&self.index[start..end])
            .try_into()
            .expect("failed to turn 4 bytes into 4 bytes");
        u32::from_be_bytes(raw)
    }

    /// Return an iterator over all the `Action` in this instance.
    fn iter_actions(&self) -> ActionsIterator {
        ActionsIterator {
            changes: &self,
            current: 0,
        }
    }

    /// return the MergeCase value associated with a filename
    fn get_merge_case(&self, path: &HgPath) -> MergeCase {
        if self.nb_items == 0 {
            return MergeCase::Normal;
        }
        let mut low_part = 0;
        let mut high_part = self.nb_items;

        while low_part < high_part {
            let cursor = (low_part + high_part - 1) / 2;
            let (flags, filename, _source) = self.entry(cursor);
            match path.cmp(filename) {
                Ordering::Less => low_part = cursor + 1,
                Ordering::Greater => high_part = cursor,
                Ordering::Equal => {
                    return match flags & ACTION_MASK {
                        MERGED => MergeCase::Merged,
                        SALVAGED => MergeCase::Salvaged,
                        _ => MergeCase::Normal,
                    };
                }
            }
        }
        MergeCase::Normal
    }
}

struct ActionsIterator<'a> {
    changes: &'a ChangedFiles<'a>,
    current: u32,
}

impl<'a> Iterator for ActionsIterator<'a> {
    type Item = Action<'a>;

    fn next(&mut self) -> Option<Action<'a>> {
        while self.current < self.changes.nb_items {
            let (flags, file, source) = self.changes.entry(self.current);
            self.current += 1;
            if (flags & ACTION_MASK) == REMOVED {
                return Some(Action::Removed(file));
            }
            let copy = flags & COPY_MASK;
            if copy == P1_COPY {
                return Some(Action::CopiedFromP1(file, source));
            } else if copy == P2_COPY {
                return Some(Action::CopiedFromP2(file, source));
            }
        }
        return None;
    }
}

/// A small struct whose purpose is to ensure lifetime of bytes referenced in
/// ChangedFiles
///
/// It is passed to the RevInfoMaker callback who can assign any necessary
/// content to the `data` attribute. The copy tracing code is responsible for
/// keeping the DataHolder alive at least as long as the ChangedFiles object.
pub struct DataHolder<D> {
    /// RevInfoMaker callback should assign data referenced by the
    /// ChangedFiles struct it return to this attribute. The DataHolder
    /// lifetime will be at least as long as the ChangedFiles one.
    pub data: Option<D>,
}

pub type RevInfoMaker<'a, D> =
    Box<dyn for<'r> Fn(Revision, &'r mut DataHolder<D>) -> RevInfo<'r> + 'a>;

/// A small "tokenizer" responsible of turning full HgPath into lighter
/// PathToken
///
/// Dealing with small object, like integer is much faster, so HgPath input are
/// turned into integer "PathToken" and converted back in the end.
#[derive(Clone, Debug, Default)]
struct TwoWayPathMap {
    token: HashMap<HgPathBuf, PathToken>,
    path: Vec<HgPathBuf>,
}

impl TwoWayPathMap {
    fn tokenize(&mut self, path: &HgPath) -> PathToken {
        match self.token.get(path) {
            Some(a) => *a,
            None => {
                let a = self.token.len();
                let buf = path.to_owned();
                self.path.push(buf.clone());
                self.token.insert(buf, a);
                a
            }
        }
    }

    fn untokenize(&self, token: PathToken) -> &HgPathBuf {
        assert!(token < self.path.len(), format!("Unknown token: {}", token));
        &self.path[token]
    }
}

/// Same as mercurial.copies._combine_changeset_copies, but in Rust.
///
/// Arguments are:
///
/// revs: all revisions to be considered
/// children: a {parent ? [childrens]} mapping
/// target_rev: the final revision we are combining copies to
/// rev_info(rev): callback to get revision information:
///   * first parent
///   * second parent
///   * ChangedFiles
/// isancestors(low_rev, high_rev): callback to check if a revision is an
///                                 ancestor of another
pub fn combine_changeset_copies<D>(
    revs: Vec<Revision>,
    mut children_count: HashMap<Revision, usize>,
    target_rev: Revision,
    rev_info: RevInfoMaker<D>,
) -> PathCopies {
    let mut all_copies = HashMap::new();

    let mut path_map = TwoWayPathMap::default();

    for rev in revs {
        let mut d: DataHolder<D> = DataHolder { data: None };
        let (p1, p2, changes) = rev_info(rev, &mut d);

        // We will chain the copies information accumulated for the parent with
        // the individual copies information the curent revision.  Creating a
        // new TimeStampedPath for each `rev` → `children` vertex.
        // Retrieve data computed in a previous iteration
        let p1_copies = match p1 {
            NULL_REVISION => None,
            _ => get_and_clean_parent_copies(
                &mut all_copies,
                &mut children_count,
                p1,
            ), // will be None if the vertex is not to be traversed
        };
        let p2_copies = match p2 {
            NULL_REVISION => None,
            _ => get_and_clean_parent_copies(
                &mut all_copies,
                &mut children_count,
                p2,
            ), // will be None if the vertex is not to be traversed
        };
        // combine it with data for that revision
        let (p1_copies, p2_copies) =
            chain_changes(&mut path_map, p1_copies, p2_copies, &changes, rev);
        let copies = match (p1_copies, p2_copies) {
            (None, None) => None,
            (c, None) => c,
            (None, c) => c,
            (Some(p1_copies), Some(p2_copies)) => Some(merge_copies_dict(
                &path_map, rev, p2_copies, p1_copies, &changes,
            )),
        };
        if let Some(c) = copies {
            all_copies.insert(rev, c);
        }
    }

    // Drop internal information (like the timestamp) and return the final
    // mapping.
    let tt_result = all_copies
        .remove(&target_rev)
        .expect("target revision was not processed");
    let mut result = PathCopies::default();
    for (dest, tt_source) in tt_result {
        if let Some(path) = tt_source.path {
            let path_dest = path_map.untokenize(dest).to_owned();
            let path_path = path_map.untokenize(path).to_owned();
            result.insert(path_dest, path_path);
        }
    }
    result
}

/// fetch previous computed information
///
/// If no other children are expected to need this information, we drop it from
/// the cache.
///
/// If parent is not part of the set we are expected to walk, return None.
fn get_and_clean_parent_copies(
    all_copies: &mut HashMap<Revision, InternalPathCopies>,
    children_count: &mut HashMap<Revision, usize>,
    parent_rev: Revision,
) -> Option<InternalPathCopies> {
    let count = children_count.get_mut(&parent_rev)?;
    *count -= 1;
    if *count == 0 {
        match all_copies.remove(&parent_rev) {
            Some(c) => Some(c),
            None => Some(InternalPathCopies::default()),
        }
    } else {
        match all_copies.get(&parent_rev) {
            Some(c) => Some(c.clone()),
            None => Some(InternalPathCopies::default()),
        }
    }
}

/// Combine ChangedFiles with some existing PathCopies information and return
/// the result
fn chain_changes(
    path_map: &mut TwoWayPathMap,
    base_p1_copies: Option<InternalPathCopies>,
    base_p2_copies: Option<InternalPathCopies>,
    changes: &ChangedFiles,
    current_rev: Revision,
) -> (Option<InternalPathCopies>, Option<InternalPathCopies>) {
    // Fast path the "nothing to do" case.
    if let (None, None) = (&base_p1_copies, &base_p2_copies) {
        return (None, None);
    }

    let mut p1_copies = base_p1_copies.clone();
    let mut p2_copies = base_p2_copies.clone();
    for action in changes.iter_actions() {
        match action {
            Action::CopiedFromP1(path_dest, path_source) => {
                match &mut p1_copies {
                    None => (), // This is not a vertex we should proceed.
                    Some(copies) => add_one_copy(
                        current_rev,
                        path_map,
                        copies,
                        base_p1_copies.as_ref().unwrap(),
                        path_dest,
                        path_source,
                    ),
                }
            }
            Action::CopiedFromP2(path_dest, path_source) => {
                match &mut p2_copies {
                    None => (), // This is not a vertex we should proceed.
                    Some(copies) => add_one_copy(
                        current_rev,
                        path_map,
                        copies,
                        base_p2_copies.as_ref().unwrap(),
                        path_dest,
                        path_source,
                    ),
                }
            }
            Action::Removed(deleted_path) => {
                // We must drop copy information for removed file.
                //
                // We need to explicitly record them as dropped to
                // propagate this information when merging two
                // InternalPathCopies object.
                let deleted = path_map.tokenize(deleted_path);

                let p1_entry = match &mut p1_copies {
                    None => None,
                    Some(copies) => match copies.entry(deleted) {
                        Entry::Occupied(e) => Some(e),
                        Entry::Vacant(_) => None,
                    },
                };
                let p2_entry = match &mut p2_copies {
                    None => None,
                    Some(copies) => match copies.entry(deleted) {
                        Entry::Occupied(e) => Some(e),
                        Entry::Vacant(_) => None,
                    },
                };

                match (p1_entry, p2_entry) {
                    (None, None) => (),
                    (Some(mut e), None) => {
                        e.get_mut().mark_delete(current_rev)
                    }
                    (None, Some(mut e)) => {
                        e.get_mut().mark_delete(current_rev)
                    }
                    (Some(mut e1), Some(mut e2)) => {
                        let cs1 = e1.get_mut();
                        let cs2 = e2.get();
                        if cs1 == cs2 {
                            cs1.mark_delete(current_rev);
                        } else {
                            cs1.mark_delete_with_pair(current_rev, &cs2);
                        }
                        e2.insert(cs1.clone());
                    }
                }
            }
        }
    }
    (p1_copies, p2_copies)
}

// insert one new copy information in an InternalPathCopies
//
// This deal with chaining and overwrite.
fn add_one_copy(
    current_rev: Revision,
    path_map: &mut TwoWayPathMap,
    copies: &mut InternalPathCopies,
    base_copies: &InternalPathCopies,
    path_dest: &HgPath,
    path_source: &HgPath,
) {
    let dest = path_map.tokenize(path_dest);
    let source = path_map.tokenize(path_source);
    let entry;
    if let Some(v) = base_copies.get(&source) {
        entry = match &v.path {
            Some(path) => Some((*(path)).to_owned()),
            None => Some(source.to_owned()),
        }
    } else {
        entry = Some(source.to_owned());
    }
    // Each new entry is introduced by the children, we
    // record this information as we will need it to take
    // the right decision when merging conflicting copy
    // information. See merge_copies_dict for details.
    match copies.entry(dest) {
        Entry::Vacant(slot) => {
            let ttpc = CopySource::new(current_rev, entry);
            slot.insert(ttpc);
        }
        Entry::Occupied(mut slot) => {
            let ttpc = slot.get_mut();
            ttpc.overwrite(current_rev, entry);
        }
    }
}

/// merge two copies-mapping together, minor and major
///
/// In case of conflict, value from "major" will be picked, unless in some
/// cases. See inline documentation for details.
fn merge_copies_dict(
    path_map: &TwoWayPathMap,
    current_merge: Revision,
    mut minor: InternalPathCopies,
    mut major: InternalPathCopies,
    changes: &ChangedFiles,
) -> InternalPathCopies {
    // This closure exist as temporary help while multiple developper are
    // actively working on this code. Feel free to re-inline it once this
    // code is more settled.
    let cmp_value =
        |dest: &PathToken, src_minor: &CopySource, src_major: &CopySource| {
            compare_value(
                path_map,
                current_merge,
                changes,
                dest,
                src_minor,
                src_major,
            )
        };
    if minor.is_empty() {
        major
    } else if major.is_empty() {
        minor
    } else if minor.len() * 2 < major.len() {
        // Lets says we are merging two InternalPathCopies instance A and B.
        //
        // If A contains N items, the merge result will never contains more
        // than N values differents than the one in A
        //
        // If B contains M items, with M > N, the merge result will always
        // result in a minimum of M - N value differents than the on in
        // A
        //
        // As a result, if N < (M-N), we know that simply iterating over A will
        // yield less difference than iterating over the difference
        // between A and B.
        //
        // This help performance a lot in case were a tiny
        // InternalPathCopies is merged with a much larger one.
        for (dest, src_minor) in minor {
            let src_major = major.get(&dest);
            match src_major {
                None => {
                    major.insert(dest, src_minor);
                }
                Some(src_major) => {
                    let (pick, overwrite) =
                        cmp_value(&dest, &src_minor, src_major);
                    if overwrite {
                        let src = match pick {
                            MergePick::Major => CopySource::new_from_merge(
                                current_merge,
                                src_major,
                                &src_minor,
                            ),
                            MergePick::Minor => CopySource::new_from_merge(
                                current_merge,
                                &src_minor,
                                src_major,
                            ),
                            MergePick::Any => CopySource::new_from_merge(
                                current_merge,
                                src_major,
                                &src_minor,
                            ),
                        };
                        major.insert(dest, src);
                    } else {
                        match pick {
                            MergePick::Any | MergePick::Major => None,
                            MergePick::Minor => major.insert(dest, src_minor),
                        };
                    }
                }
            };
        }
        major
    } else if major.len() * 2 < minor.len() {
        // This use the same rational than the previous block.
        // (Check previous block documentation for details.)
        for (dest, src_major) in major {
            let src_minor = minor.get(&dest);
            match src_minor {
                None => {
                    minor.insert(dest, src_major);
                }
                Some(src_minor) => {
                    let (pick, overwrite) =
                        cmp_value(&dest, src_minor, &src_major);
                    if overwrite {
                        let src = match pick {
                            MergePick::Major => CopySource::new_from_merge(
                                current_merge,
                                &src_major,
                                src_minor,
                            ),
                            MergePick::Minor => CopySource::new_from_merge(
                                current_merge,
                                src_minor,
                                &src_major,
                            ),
                            MergePick::Any => CopySource::new_from_merge(
                                current_merge,
                                &src_major,
                                src_minor,
                            ),
                        };
                        minor.insert(dest, src);
                    } else {
                        match pick {
                            MergePick::Any | MergePick::Minor => None,
                            MergePick::Major => minor.insert(dest, src_major),
                        };
                    }
                }
            };
        }
        minor
    } else {
        let mut override_minor = Vec::new();
        let mut override_major = Vec::new();

        let mut to_major = |k: &PathToken, v: &CopySource| {
            override_major.push((k.clone(), v.clone()))
        };
        let mut to_minor = |k: &PathToken, v: &CopySource| {
            override_minor.push((k.clone(), v.clone()))
        };

        // The diff function leverage detection of the identical subpart if
        // minor and major has some common ancestors. This make it very
        // fast is most case.
        //
        // In case where the two map are vastly different in size, the current
        // approach is still slowish because the iteration will iterate over
        // all the "exclusive" content of the larger on. This situation can be
        // frequent when the subgraph of revision we are processing has a lot
        // of roots. Each roots adding they own fully new map to the mix (and
        // likely a small map, if the path from the root to the "main path" is
        // small.
        //
        // We could do better by detecting such situation and processing them
        // differently.
        for d in minor.diff(&major) {
            match d {
                DiffItem::Add(k, v) => to_minor(k, v),
                DiffItem::Remove(k, v) => to_major(k, v),
                DiffItem::Update { old, new } => {
                    let (dest, src_major) = new;
                    let (_, src_minor) = old;
                    let (pick, overwrite) =
                        cmp_value(dest, src_minor, src_major);
                    if overwrite {
                        let src = match pick {
                            MergePick::Major => CopySource::new_from_merge(
                                current_merge,
                                src_major,
                                src_minor,
                            ),
                            MergePick::Minor => CopySource::new_from_merge(
                                current_merge,
                                src_minor,
                                src_major,
                            ),
                            MergePick::Any => CopySource::new_from_merge(
                                current_merge,
                                src_major,
                                src_minor,
                            ),
                        };
                        to_minor(dest, &src);
                        to_major(dest, &src);
                    } else {
                        match pick {
                            MergePick::Major => to_minor(dest, src_major),
                            MergePick::Minor => to_major(dest, src_minor),
                            // If the two entry are identical, no need to do
                            // anything (but diff should not have yield them)
                            MergePick::Any => unreachable!(),
                        }
                    }
                }
            };
        }

        let updates;
        let mut result;
        if override_major.is_empty() {
            result = major
        } else if override_minor.is_empty() {
            result = minor
        } else {
            if override_minor.len() < override_major.len() {
                updates = override_minor;
                result = minor;
            } else {
                updates = override_major;
                result = major;
            }
            for (k, v) in updates {
                result.insert(k, v);
            }
        }
        result
    }
}

/// represent the side that should prevail when merging two
/// InternalPathCopies
enum MergePick {
    /// The "major" (p1) side prevails
    Major,
    /// The "minor" (p2) side prevails
    Minor,
    /// Any side could be used (because they are the same)
    Any,
}

/// decide which side prevails in case of conflicting values
#[allow(clippy::if_same_then_else)]
fn compare_value(
    path_map: &TwoWayPathMap,
    current_merge: Revision,
    changes: &ChangedFiles,
    dest: &PathToken,
    src_minor: &CopySource,
    src_major: &CopySource,
) -> (MergePick, bool) {
    if src_major == src_minor {
        (MergePick::Any, false)
    } else if src_major.rev == current_merge {
        // minor is different according to per minor == major check earlier
        debug_assert!(src_minor.rev != current_merge);

        // The last value comes the current merge, this value -will- win
        // eventually.
        (MergePick::Major, true)
    } else if src_minor.rev == current_merge {
        // The last value comes the current merge, this value -will- win
        // eventually.
        (MergePick::Minor, true)
    } else if src_major.path == src_minor.path {
        debug_assert!(src_major.rev != src_major.rev);
        // we have the same value, but from other source;
        if src_major.is_overwritten_by(src_minor) {
            (MergePick::Minor, false)
        } else if src_minor.is_overwritten_by(src_major) {
            (MergePick::Major, false)
        } else {
            (MergePick::Any, true)
        }
    } else {
        debug_assert!(src_major.rev != src_major.rev);
        let dest_path = path_map.untokenize(*dest);
        let action = changes.get_merge_case(dest_path);
        if src_minor.path.is_some()
            && src_major.path.is_none()
            && action == MergeCase::Salvaged
        {
            // If the file is "deleted" in the major side but was
            // salvaged by the merge, we keep the minor side alive
            (MergePick::Minor, true)
        } else if src_major.path.is_some()
            && src_minor.path.is_none()
            && action == MergeCase::Salvaged
        {
            // If the file is "deleted" in the minor side but was
            // salvaged by the merge, unconditionnaly preserve the
            // major side.
            (MergePick::Major, true)
        } else if src_minor.is_overwritten_by(src_major) {
            // The information from the minor version are strictly older than
            // the major version
            if action == MergeCase::Merged {
                // If the file was actively merged, its means some non-copy
                // activity happened on the other branch. It
                // mean the older copy information are still relevant.
                //
                // The major side wins such conflict.
                (MergePick::Major, true)
            } else {
                // No activity on the minor branch, pick the newer one.
                (MergePick::Major, false)
            }
        } else if src_major.is_overwritten_by(src_minor) {
            if action == MergeCase::Merged {
                // If the file was actively merged, its means some non-copy
                // activity happened on the other branch. It
                // mean the older copy information are still relevant.
                //
                // The major side wins such conflict.
                (MergePick::Major, true)
            } else {
                // No activity on the minor branch, pick the newer one.
                (MergePick::Minor, false)
            }
        } else if src_minor.path.is_none() {
            // the minor side has no relevant information, pick the alive one
            (MergePick::Major, true)
        } else if src_major.path.is_none() {
            // the major side has no relevant information, pick the alive one
            (MergePick::Minor, true)
        } else {
            // by default the major side wins
            (MergePick::Major, true)
        }
    }
}