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annotate rust/hg-core/examples/nodemap/index.rs @ 50976:4c5f6e95df84

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rust: make `Revision` a newtype This change is the one we've been building towards during this series. The aim is to make `Revision` mean more than a simple integer, holding the information that it is valid for a given revlog index. While this still allows for programmer error, since creating a revision directly and querying a different index with a "checked" revision are still possible, the friction created by the newtype will hopefully make us think twice about which type to use. Enough of the Rust ecosystem relies on the newtype pattern to be efficiently optimized away (even compiler in codegen tests?), so I'm not worried about this being a fundamental problem. [1] https://github.com/rust-lang/rust/blob/7a70647f195f6b0a0f1ebd72b1542ba91a32f43a/tests/codegen/vec-in-place.rs#L47
author Rapha?l Gom?s <rgomes@octobus.net>
date Fri, 18 Aug 2023 14:34:29 +0200
parents e834b79def74
children bd8081e9fd62
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1 // Copyright 2019-2020 Georges Racinet <georges.racinet@octobus.net>
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2 //
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3 // This software may be used and distributed according to the terms of the
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4 // GNU General Public License version 2 or any later version.
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5
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6 //! Minimal `RevlogIndex`, readable from standard Mercurial file format
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7 use hg::*;
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8 use memmap2::*;
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9 use std::fs::File;
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10 use std::ops::Deref;
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11 use std::path::Path;
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12 use std::slice;
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13
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14 pub struct Index {
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15 data: Box<dyn Deref<Target = [IndexEntry]> + Send>,
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16 }
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17
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18 /// A fixed sized index entry. All numbers are big endian
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19 #[repr(C)]
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20 pub struct IndexEntry {
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21 not_used_yet: [u8; 24],
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22 p1: Revision,
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23 p2: Revision,
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24 node: Node,
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25 unused_node: [u8; 12],
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26 }
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27
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28 pub const INDEX_ENTRY_SIZE: usize = 64;
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29
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30 impl IndexEntry {
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31 fn parents(&self) -> [Revision; 2] {
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32 [self.p1, self.p2]
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33 }
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34 }
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35
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36 impl RevlogIndex for Index {
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37 fn len(&self) -> usize {
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38 self.data.len()
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39 }
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40
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41 fn node(&self, rev: Revision) -> Option<&Node> {
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42 if rev == NULL_REVISION {
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43 return None;
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44 }
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45 Some(&self.data[rev.0 as usize].node)
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46 }
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47 }
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48
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49 impl Graph for &Index {
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50 fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
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51 let [p1, p2] = self.data[rev.0 as usize].parents();
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52 let len = (*self).len();
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53 if p1 < NULL_REVISION
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54 || p2 < NULL_REVISION
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55 || p1.0 as usize >= len
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56 || p2.0 as usize >= len
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57 {
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58 return Err(GraphError::ParentOutOfRange(rev));
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59 }
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60 Ok([p1, p2])
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61 }
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62 }
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63
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64 struct IndexMmap(Mmap);
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65
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66 impl Deref for IndexMmap {
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67 type Target = [IndexEntry];
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68
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69 fn deref(&self) -> &[IndexEntry] {
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70 let ptr = self.0.as_ptr() as *const IndexEntry;
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71 // Any misaligned data will be ignored.
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72 debug_assert_eq!(
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73 self.0.len() % std::mem::align_of::<IndexEntry>(),
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74 0,
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75 "Misaligned data in mmap"
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76 );
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77 unsafe { slice::from_raw_parts(ptr, self.0.len() / INDEX_ENTRY_SIZE) }
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78 }
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79 }
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80
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81 impl Index {
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82 pub fn load_mmap(path: impl AsRef<Path>) -> Self {
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83 let file = File::open(path).unwrap();
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84 let msg = "Index file is missing, or missing permission";
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85 let mmap = unsafe { MmapOptions::new().map(&file) }.expect(msg);
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86 Self {
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87 data: Box::new(IndexMmap(mmap)),
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88 }
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89 }
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90 }