girt 0.17.0

An incremental, idiomatic Rust implementation of Git
Documentation 
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

//! The `ident` attribute: `$Id$` keywords.

use std::borrow::Cow;

use crate::ObjectId;

/// Each `$Id$`, or `$Id:` followed by text and `$` on the same line, as a byte range.
fn keywords(bytes: &[u8]) -> impl Iterator<Item = std::ops::Range<usize>> + '_ {
    let mut at = 0;
    std::iter::from_fn(move || {
        while let Some(found) = find(bytes.get(at..)?, b"$Id") {
            let start = at + found;
            let after = start + 3;
            match bytes.get(after) {
                Some(b'$') => {
                    at = after + 1;
                    return Some(start..at);
                }
                Some(b':') => {
                    let line = bytes.get(after + 1..).unwrap_or_default();
                    let close = line.iter().position(|&byte| byte == b'$' || byte == b'\n');
                    match close {
                        Some(close) if line.get(close) == Some(&b'$') => {
                            at = after + 1 + close + 1;
                            return Some(start..at);
                        }
                        _ => at = after,
                    }
                }
                _ => at = after,
            }
        }
        None
    })
}

fn find(haystack: &[u8], needle: &[u8]) -> Option<usize> {
    haystack
        .windows(needle.len())
        .position(|window| window == needle)
}

/// Whether an expanded keyword's text is someone else's: after one leading and one trailing
/// space, it still contains a space. Git writes those unchanged on checkout.
fn foreign(keyword: &[u8]) -> bool {
    let text = keyword
        .get(4..keyword.len().saturating_sub(1))
        .unwrap_or_default();
    let text = text.strip_prefix(b" ").unwrap_or(text);
    let text = text.strip_suffix(b" ").unwrap_or(text);
    text.contains(&b' ')
}

fn replace<'a>(bytes: Cow<'a, [u8]>, with: &[u8], collapsing: bool) -> Cow<'a, [u8]> {
    let ranges: Vec<_> = keywords(&bytes)
        .filter(|range| {
            let keyword = bytes.get(range.clone()).unwrap_or_default();
            if collapsing {
                range.len() != 4
            } else {
                !foreign(keyword)
            }
        })
        .collect();
    if ranges.is_empty() {
        return bytes;
    }
    let mut out = Vec::with_capacity(bytes.len() + ranges.len() * with.len());
    let mut start = 0;
    for range in ranges {
        out.extend_from_slice(bytes.get(start..range.start).unwrap_or_default());
        out.extend_from_slice(with);
        start = range.end;
    }
    out.extend_from_slice(bytes.get(start..).unwrap_or_default());
    Cow::Owned(out)
}

/// Collapses every keyword to `$Id$`, as Git stores it.
pub(super) fn collapse(bytes: Cow<'_, [u8]>) -> Cow<'_, [u8]> {
    replace(bytes, b"$Id$", true)
}

/// Expands every keyword to `$Id: <id> $`, except foreign ones.
pub(super) fn expand(bytes: Cow<'_, [u8]>, id: ObjectId) -> Cow<'_, [u8]> {
    let with = format!("$Id: {id} $");
    replace(bytes, with.as_bytes(), false)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn collapse_matches_git() {
        // Observed with `git add` under `ident`.
        let input = b"$Id$ x $Id: abc $ y $Id:$ z $Id: no\nclose $ w $Id:foo$ $ID$ $Id";
        let expected = b"$Id$ x $Id$ y $Id$ z $Id: no\nclose $ w $Id$ $ID$ $Id";
        assert_eq!(&*collapse(Cow::Borrowed(input)), expected);
    }

    #[test]
    fn expand_keeps_foreign_keywords() {
        // Observed with `git checkout` under `ident`.
        let id: ObjectId = "deb0e62babfba8c6f140ad6cdf6684e95f4b949e".parse().unwrap();
        for kept in [
            &b"$Id: foreign words $"[..],
            b"$Id: x y$",
            b"$Id:  x $",
            b"$Id: x  $",
        ] {
            assert_eq!(&*expand(Cow::Borrowed(kept), id), kept);
        }
        for replaced in [&b"$Id:  $"[..], b"$Id: a:b $", b"$Id:x $", b"$Id: x$"] {
            assert_ne!(&*expand(Cow::Borrowed(replaced), id), replaced);
        }
        // Collapsing ignores the rule.
        assert_eq!(&*collapse(Cow::Borrowed(b"$Id: foreign words $")), b"$Id$");
    }

    #[test]
    fn expand_replaces_closed_keywords() {
        let id: ObjectId = "deb0e62babfba8c6f140ad6cdf6684e95f4b949e".parse().unwrap();
        let out = expand(Cow::Borrowed(b"A $Id: old $ B $Id:x\nC $Id$\n"), id);
        assert_eq!(
            &*out,
            b"A $Id: deb0e62babfba8c6f140ad6cdf6684e95f4b949e $ B $Id:x\nC \
              $Id: deb0e62babfba8c6f140ad6cdf6684e95f4b949e $\n"
        );
    }
}