#
cargo_test_support/
diff.rs

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    46
    47
    48
    49
    50
    51
    52
    53
    54
    55
    56
    57
    58
    59
    60
    61
    62
    63
    64
    65
    66
    67
    68
    69
    70
    71
    72
    73
    74
    75
    76
    77
    78
    79
    80
    81
    82
    83
    84
    85
    86
    87
    88
    89
    90
    91
    92
    93
    94
    95
    96
    97
    98
    99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166

    //! A simple Myers diff implementation.
    //!
    //! This focuses on being short and simple, and the expense of being
    //! inefficient. A key characteristic here is that this supports cargotest's
    //! `[..]` wildcard matching. That means things like hashing can't be used.
    //! Since Cargo's output tends to be small, this should be sufficient.

    use std::fmt;
    use std::io::Write;

    /// A single line change to be applied to the original.
    #[derive(Debug, Eq, PartialEq)]
    pub enum Change<T> {
        Add(usize, T),
        Remove(usize, T),
        Keep(usize, usize, T),
    }

    pub fn diff<'a, T>(a: &'a [T], b: &'a [T]) -> Vec<Change<&'a T>>
    where
        T: PartialEq,
    {
        if a.is_empty() && b.is_empty() {
            return vec![];
        }
        let mut diff = vec![];
        for (prev_x, prev_y, x, y) in backtrack(&a, &b) {
            if x == prev_x {
                diff.push(Change::Add(prev_y + 1, &b[prev_y]));
            } else if y == prev_y {
                diff.push(Change::Remove(prev_x + 1, &a[prev_x]));
            } else {
                diff.push(Change::Keep(prev_x + 1, prev_y + 1, &a[prev_x]));
            }
        }
        diff.reverse();
        diff
    }

    fn shortest_edit<T>(a: &[T], b: &[T]) -> Vec<Vec<usize>>
    where
        T: PartialEq,
    {
        let max = a.len() + b.len();
        let mut v = vec![0; 2 * max + 1];
        let mut trace = vec![];
        for d in 0..=max {
            trace.push(v.clone());
            for k in (0..=(2 * d)).step_by(2) {
                let mut x = if k == 0 || (k != 2 * d && v[max - d + k - 1] < v[max - d + k + 1]) {
                    // Move down
                    v[max - d + k + 1]
                } else {
                    // Move right
                    v[max - d + k - 1] + 1
                };
                let mut y = x + d - k;
                // Step diagonally as far as possible.
                while x < a.len() && y < b.len() && a[x] == b[y] {
                    x += 1;
                    y += 1;
                }
                v[max - d + k] = x;
                // Return if reached the bottom-right position.
                if x >= a.len() && y >= b.len() {
                    return trace;
                }
            }
        }
        panic!("finished without hitting end?");
    }

    fn backtrack<T>(a: &[T], b: &[T]) -> Vec<(usize, usize, usize, usize)>
    where
        T: PartialEq,
    {
        let mut result = vec![];
        let mut x = a.len();
        let mut y = b.len();
        let max = x + y;
        for (d, v) in shortest_edit(a, b).iter().enumerate().rev() {
            let k = x + d - y;
            let prev_k = if k == 0 || (k != 2 * d && v[max - d + k - 1] < v[max - d + k + 1]) {
                k + 1
            } else {
                k - 1
            };
            let prev_x = v[max - d + prev_k];
            let prev_y = (prev_x + d).saturating_sub(prev_k);
            while x > prev_x && y > prev_y {
                result.push((x - 1, y - 1, x, y));
                x -= 1;
                y -= 1;
            }
            if d > 0 {
                result.push((prev_x, prev_y, x, y));
            }
            x = prev_x;
            y = prev_y;
        }
        return result;
    }

    pub fn colored_diff<'a, T>(a: &'a [T], b: &'a [T]) -> String
    where
        T: PartialEq + fmt::Display,
    {
        let changes = diff(a, b);
        render_colored_changes(&changes)
    }

    pub fn render_colored_changes<T: fmt::Display>(changes: &[Change<T>]) -> String {
        // anstyle is not very ergonomic, but I don't want to bring in another dependency.
        let red = anstyle::AnsiColor::Red.on_default().render();
        let green = anstyle::AnsiColor::Green.on_default().render();
        let dim = (anstyle::Style::new() | anstyle::Effects::DIMMED).render();
        let bold = (anstyle::Style::new() | anstyle::Effects::BOLD).render();
        let reset = anstyle::Reset.render();

        let choice = if crate::is_ci() {
            // Don't use color on CI. Even though GitHub can display colors, it
            // makes reading the raw logs more difficult.
            anstream::ColorChoice::Never
        } else {
            anstream::AutoStream::choice(&std::io::stdout())
        };
        let mut buffer = anstream::AutoStream::new(Vec::new(), choice);

        for change in changes {
            let (nums, sign, color, text) = match change {
                Change::Add(i, s) => (format!("    {:<4} ", i), '+', green, s),
                Change::Remove(i, s) => (format!("{:<4}     ", i), '-', red, s),
                Change::Keep(x, y, s) => (format!("{:<4}{:<4} ", x, y), ' ', dim, s),
            };
            writeln!(
                buffer,
                "{dim}{nums}{reset}{bold}{sign}{reset}{color}{text}{reset}"
            )
            .unwrap();
        }
        String::from_utf8(buffer.into_inner()).unwrap()
    }

    #[cfg(test)]
    pub fn compare(a: &str, b: &str) {
        let a: Vec<_> = a.chars().collect();
        let b: Vec<_> = b.chars().collect();
        let changes = diff(&a, &b);
        let mut result = vec![];
        for change in changes {
            match change {
                Change::Add(_, s) => result.push(*s),
                Change::Remove(_, _s) => {}
                Change::Keep(_, _, s) => result.push(*s),
            }
        }
        assert_eq!(b, result);
    }

    #[test]
    fn basic_tests() {
        compare("", "");
        compare("A", "");
        compare("", "B");
        compare("ABCABBA", "CBABAC");
    }