git-harvest 0.2.0

Harvest a CHANGELOG from your Git history.
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

/*********************** GNU General Public License 3.0 ***********************\
|                                                                              |
|  Copyright (C) 2026 Kevin Matthes                                            |
|                                                                              |
|  This program is free software: you can redistribute it and/or modify        |
|  it under the terms of the GNU General Public License as published by        |
|  the Free Software Foundation, either version 3 of the License, or           |
|  (at your option) any later version.                                         |
|                                                                              |
|  This program is distributed in the hope that it will be useful,             |
|  but WITHOUT ANY WARRANTY; without even the implied warranty of              |
|  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the               |
|  GNU General Public License for more details.                                |
|                                                                              |
|  You should have received a copy of the GNU General Public License           |
|  along with this program.  If not, see <https://www.gnu.org/licenses/>.      |
|                                                                              |
\******************************************************************************/

//! The one place `git-harvest` touches Git.
//!
//! Everything here is read-only and goes through `gix`'s high-level API, so
//! a later change of library stays contained to this file (`git-harvest.md`
//! D27).

/// One commit on the branch, reduced to what the harvest needs.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Commit {
    /// The commit's abbreviated hash, for an entry's provenance.
    pub short_hash: String,

    /// The commit's subject line, trimmed.
    pub subject: String,
}

/// The leaf of the current branch's name, or `HEAD` when detached.
#[must_use]
pub fn branch_leaf(repository: &gix::Repository) -> String {
    repository.head_name().ok().flatten().map_or_else(
        || "HEAD".to_owned(),
        |name| {
            let short = name.shorten().to_string();
            short.rsplit('/').next().unwrap_or(&short).to_owned()
        },
    )
}

/// The non-merge commits reachable from `HEAD` but not from `base`.
///
/// The walk stops at the merge base of `HEAD` and `base`, so only the work
/// added on this branch is returned, newest first.
///
/// # Errors
///
/// [`sysexits::ExitCode::Usage`] when `HEAD` or `base` cannot be resolved,
/// [`sysexits::ExitCode::Unavailable`] when the two share no history, and
/// [`sysexits::ExitCode::Software`] when the object database cannot be read.
pub fn commits_since(
    repository: &gix::Repository,
    base: &str,
) -> sysexits::Result<Vec<Commit>> {
    let head = repository.head_commit().map_err(|reason| {
        eprintln!("git-harvest:  cannot read HEAD:  {reason}");
        sysexits::ExitCode::Usage
    })?;

    let base = repository.rev_parse_single(base).map_err(|reason| {
        eprintln!("git-harvest:  cannot resolve {base:?}:  {reason}");
        sysexits::ExitCode::Usage
    })?;

    let boundary =
        repository
            .merge_base(head.id(), base.detach())
            .map_err(|reason| {
                eprintln!(
                    "git-harvest:  no shared history with the base:  {reason}"
                );
                sysexits::ExitCode::Unavailable
            })?;

    let walk = repository
        .rev_walk([head.id().detach()])
        .with_boundary([boundary.detach()])
        .all()
        .map_err(|reason| {
            eprintln!("git-harvest:  cannot walk the history:  {reason}");
            sysexits::ExitCode::Software
        })?;

    let mut commits = Vec::new();

    for step in walk {
        let info = step.map_err(|reason| {
            eprintln!("git-harvest:  the history walk failed:  {reason}");
            sysexits::ExitCode::Software
        })?;

        if info.parent_ids.len() > 1 {
            continue;
        }

        let commit = repository.find_commit(info.id).map_err(|reason| {
            eprintln!("git-harvest:  cannot read a commit:  {reason}");
            sysexits::ExitCode::Software
        })?;

        let message = commit.message().map_err(|reason| {
            eprintln!("git-harvest:  cannot read a commit message:  {reason}");
            sysexits::ExitCode::Software
        })?;

        commits.push(Commit {
            short_hash: info.id.to_hex_with_len(7).to_string(),
            subject: message.title.to_string().trim().to_owned(),
        });
    }

    Ok(commits)
}

/// Open the repository containing the working directory.
///
/// # Errors
///
/// [`sysexits::ExitCode::Usage`] when the working directory is not inside a
/// Git repository.
pub fn open() -> sysexits::Result<gix::Repository> {
    gix::discover(".").map_err(|reason| {
        eprintln!("git-harvest:  not inside a Git repository:  {reason}");
        sysexits::ExitCode::Usage
    })
}

/******************************************************************************/