view rust/hg-core/src/testing.rs @ 50979:4c5f6e95df84

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 tests¹), 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

// testing.rs
//
// Copyright 2018 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.

use crate::{Graph, GraphError, Revision, NULL_REVISION};

/// A stub `Graph`, same as the one from `test-ancestor.py`
///
/// o  13
/// |
/// | o  12
/// | |
/// | | o    11
/// | | |\
/// | | | | o  10
/// | | | | |
/// | o---+ |  9
/// | | | | |
/// o | | | |  8
///  / / / /
/// | | o |  7
/// | | | |
/// o---+ |  6
///  / / /
/// | | o  5
/// | |/
/// | o  4
/// | |
/// o |  3
/// | |
/// | o  2
/// |/
/// o  1
/// |
/// o  0
#[derive(Clone, Debug)]
pub struct SampleGraph;

impl Graph for SampleGraph {
    fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
        let null_rev = NULL_REVISION.0;
        let res = match rev.0 {
            0 => Ok([null_rev, null_rev]),
            1 => Ok([0, null_rev]),
            2 => Ok([1, null_rev]),
            3 => Ok([1, null_rev]),
            4 => Ok([2, null_rev]),
            5 => Ok([4, null_rev]),
            6 => Ok([4, null_rev]),
            7 => Ok([4, null_rev]),
            8 => Ok([null_rev, null_rev]),
            9 => Ok([6, 7]),
            10 => Ok([5, null_rev]),
            11 => Ok([3, 7]),
            12 => Ok([9, null_rev]),
            13 => Ok([8, null_rev]),
            r => Err(GraphError::ParentOutOfRange(Revision(r))),
        };
        match res {
            Ok([a, b]) => Ok([Revision(a), Revision(b)]),
            Err(e) => Err(e),
        }
    }
}

// A Graph represented by a vector whose indices are revisions
// and values are parents of the revisions
pub type VecGraph = Vec<[Revision; 2]>;

impl Graph for VecGraph {
    fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
        Ok(self[rev.0 as usize])
    }
}