view rust/hg-core/examples/nodemap/index.rs @ 47418:22e21deed474

transaction: explain why some recovery failed

Right now we issue a message about failing to recover some file, but not why.
It seems useful to add some information about that.

(This is an opportunity improvement while looking at something next to that.)

Differential Revision: https://phab.mercurial-scm.org/D10842

// Copyright 2019-2020 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.

//! Minimal `RevlogIndex`, readable from standard Mercurial file format
use hg::*;
use memmap::*;
use std::fs::File;
use std::ops::Deref;
use std::path::Path;
use std::slice;

pub struct Index {
    data: Box<dyn Deref<Target = [IndexEntry]> + Send>,
}

/// A fixed sized index entry. All numbers are big endian
#[repr(C)]
pub struct IndexEntry {
    not_used_yet: [u8; 24],
    p1: Revision,
    p2: Revision,
    node: Node,
    unused_node: [u8; 12],
}

pub const INDEX_ENTRY_SIZE: usize = 64;

impl IndexEntry {
    fn parents(&self) -> [Revision; 2] {
        [Revision::from_be(self.p1), Revision::from_be(self.p1)]
    }
}

impl RevlogIndex for Index {
    fn len(&self) -> usize {
        self.data.len()
    }

    fn node(&self, rev: Revision) -> Option<&Node> {
        if rev == NULL_REVISION {
            return None;
        }
        let i = rev as usize;
        if i >= self.len() {
            None
        } else {
            Some(&self.data[i].node)
        }
    }
}

impl Graph for &Index {
    fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
        let [p1, p2] = (*self).data[rev as usize].parents();
        let len = (*self).len();
        if p1 < NULL_REVISION
            || p2 < NULL_REVISION
            || p1 as usize >= len
            || p2 as usize >= len
        {
            return Err(GraphError::ParentOutOfRange(rev));
        }
        Ok([p1, p2])
    }
}

struct IndexMmap(Mmap);

impl Deref for IndexMmap {
    type Target = [IndexEntry];

    fn deref(&self) -> &[IndexEntry] {
        let ptr = self.0.as_ptr() as *const IndexEntry;
        // Any misaligned data will be ignored.
        debug_assert_eq!(
            self.0.len() % std::mem::align_of::<IndexEntry>(),
            0,
            "Misaligned data in mmap"
        );
        unsafe { slice::from_raw_parts(ptr, self.0.len() / INDEX_ENTRY_SIZE) }
    }
}

impl Index {
    pub fn load_mmap(path: impl AsRef<Path>) -> Self {
        let file = File::open(path).unwrap();
        let msg = "Index file is missing, or missing permission";
        let mmap = unsafe { MmapOptions::new().map(&file) }.expect(msg);
        Self {
            data: Box::new(IndexMmap(mmap)),
        }
    }
}