zagens_runtime_adapters/snapshot/
paths.rs

1//! Path resolution for the per-workspace snapshot side-repos.
2//!
3//! Snapshots live in `~/.zagens/snapshots/<project_hash>/<worktree_hash>/`.
4//! The two-level hash split lets us snapshot multiple worktrees of the same
5//! project independently — `git worktree list` users won't get cross-talk
6//! between feature branches.
7
8use std::io;
9use std::path::{Path, PathBuf};
10
11/// Compute the snapshot directory for a given workspace path.
12///
13/// Returns `~/.zagens/snapshots/<project_hash>/<worktree_hash>/`. The
14/// caller is responsible for creating it on disk; we purposefully don't
15/// touch the filesystem here so this is cheap to call repeatedly.
16///
17/// The `project_hash` is derived from the canonicalized workspace path
18/// after stripping any `.worktrees/<name>` suffix — multiple worktrees
19/// of the same repo share the same `project_hash` so users can browse
20/// snapshots cross-worktree if they want, but the `worktree_hash` keeps
21/// commits isolated by default.
22pub fn snapshot_dir_for(workspace: &Path) -> PathBuf {
23    snapshot_dir_with_home(workspace, dirs::home_dir())
24}
25
26/// Same as [`snapshot_dir_for`] but with an injectable home directory.
27/// Used by tests so we never touch the user's real `~/.zagens/`.
28pub fn snapshot_dir_with_home(workspace: &Path, home: Option<PathBuf>) -> PathBuf {
29    let home = home.unwrap_or_else(|| PathBuf::from("."));
30    let canonical = workspace
31        .canonicalize()
32        .unwrap_or_else(|_| workspace.to_path_buf());
33    let project_root = strip_worktree_suffix(&canonical);
34    let project_hash = stable_hex(&project_root);
35    let worktree_hash = stable_hex(&canonical);
36    home.join(zagens_config::USER_DATA_DIR_NAME)
37        .join("snapshots")
38        .join(project_hash)
39        .join(worktree_hash)
40}
41
42/// Resolve the `.git` directory inside the snapshot dir.
43pub fn snapshot_git_dir(workspace: &Path) -> PathBuf {
44    snapshot_dir_for(workspace).join(".git")
45}
46
47/// Ensure the snapshot dir exists on disk and return its path.
48pub fn ensure_snapshot_dir(workspace: &Path) -> io::Result<PathBuf> {
49    let dir = snapshot_dir_for(workspace);
50    std::fs::create_dir_all(&dir)?;
51    Ok(dir)
52}
53
54/// Strip a trailing `.worktrees/<name>` segment so all worktrees of the
55/// same checkout share a `project_hash`. If the path doesn't look like a
56/// worktree it's returned unchanged.
57fn strip_worktree_suffix(path: &Path) -> PathBuf {
58    let mut components: Vec<_> = path.components().collect();
59    if components.len() >= 2
60        && let Some(parent) = components.get(components.len() - 2)
61        && parent.as_os_str() == ".worktrees"
62    {
63        components.truncate(components.len() - 2);
64        let mut p = PathBuf::new();
65        for c in components {
66            p.push(c.as_os_str());
67        }
68        return p;
69    }
70    path.to_path_buf()
71}
72
73/// Hex-encoded deterministic FNV-1a digest. This is only a directory tag, not
74/// a security boundary, but it must remain stable across process launches.
75fn stable_hex(path: &Path) -> String {
76    let mut hash = 0xcbf2_9ce4_8422_2325u64;
77    for byte in path.to_string_lossy().as_bytes() {
78        hash ^= u64::from(*byte);
79        hash = hash.wrapping_mul(0x0000_0100_0000_01b3);
80    }
81    format!("{hash:016x}")
82}
83
84#[cfg(test)]
85mod tests {
86    use super::*;
87    use tempfile::tempdir;
88
89    #[test]
90    fn snapshot_dir_layout_two_levels_under_zagens() {
91        let tmp = tempdir().expect("tempdir");
92        let dir = snapshot_dir_with_home(tmp.path(), Some(tmp.path().to_path_buf()));
93        let mut iter = dir.strip_prefix(tmp.path()).unwrap().components();
94        assert_eq!(iter.next().unwrap().as_os_str(), ".zagens");
95        assert_eq!(iter.next().unwrap().as_os_str(), "snapshots");
96        assert!(iter.next().is_some()); // project_hash
97        assert!(iter.next().is_some()); // worktree_hash
98        assert!(iter.next().is_none());
99    }
100
101    #[test]
102    fn worktree_suffix_stripped_for_project_hash() {
103        let tmp = tempdir().expect("tempdir");
104        let main_path = tmp.path().join("repo");
105        let wt_path = tmp.path().join("repo").join(".worktrees").join("featX");
106        std::fs::create_dir_all(&main_path).unwrap();
107        std::fs::create_dir_all(&wt_path).unwrap();
108
109        let main_dir = snapshot_dir_with_home(&main_path, Some(tmp.path().to_path_buf()));
110        let wt_dir = snapshot_dir_with_home(&wt_path, Some(tmp.path().to_path_buf()));
111
112        // Same project_hash (parent component before the worktree-specific tail).
113        let main_components: Vec<_> = main_dir.components().collect();
114        let wt_components: Vec<_> = wt_dir.components().collect();
115        assert_eq!(
116            main_components[main_components.len() - 2],
117            wt_components[wt_components.len() - 2],
118            "worktrees should share project_hash",
119        );
120        // But different worktree_hash (the tail).
121        assert_ne!(main_components.last(), wt_components.last());
122    }
123
124    #[test]
125    fn ensure_snapshot_dir_creates_path() {
126        let tmp = tempdir().expect("tempdir");
127        // Use scoped HOME so we don't pollute the real one.
128        let dir = snapshot_dir_with_home(tmp.path(), Some(tmp.path().to_path_buf()));
129        std::fs::create_dir_all(&dir).unwrap();
130        assert!(dir.exists());
131    }
132
133    #[test]
134    fn snapshot_git_dir_appends_dot_git() {
135        let tmp = tempdir().expect("tempdir");
136        let git_dir = snapshot_git_dir(tmp.path());
137        assert_eq!(git_dir.file_name().unwrap(), ".git");
138    }
139}
zagens_runtime_adapters/snapshot/paths.rs

zagens_runtime_adapters/snapshot/
paths.rs
