view rust/hg-core/src/testing.rs @ 47100:caa3031c9ed5

dirstate-tree: Add tree traversal/iteration

Like Python’s, Rust’s iterators are "external" in that they are driven
by a caller who calls a `next` method. This is as opposed to "internal"
iterators who drive themselves and call a callback for each item.

Writing an internal iterator traversing a tree is easy with recursion,
but internal iterators cannot rely on the call stack in that way,
they must save in an explicit object all state that they need to be
preserved across two `next` calls.

This algorithm uses a `Vec` as a stack that contains what would be
local variables on the call stack if we could use recursion.

Differential Revision: https://phab.mercurial-scm.org/D10370

// 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> {
        match rev {
            0 => Ok([NULL_REVISION, NULL_REVISION]),
            1 => Ok([0, NULL_REVISION]),
            2 => Ok([1, NULL_REVISION]),
            3 => Ok([1, NULL_REVISION]),
            4 => Ok([2, NULL_REVISION]),
            5 => Ok([4, NULL_REVISION]),
            6 => Ok([4, NULL_REVISION]),
            7 => Ok([4, NULL_REVISION]),
            8 => Ok([NULL_REVISION, NULL_REVISION]),
            9 => Ok([6, 7]),
            10 => Ok([5, NULL_REVISION]),
            11 => Ok([3, 7]),
            12 => Ok([9, NULL_REVISION]),
            13 => Ok([8, NULL_REVISION]),
            r => Err(GraphError::ParentOutOfRange(r)),
        }
    }
}

// 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 as usize])
    }
}