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
//! What:
//! The object name of the empty tree under each object format Git supports,
//! known without asking Git.
//! Why:
//! The invocation capture needs the empty tree as the baseline of an unborn branch.
//! Git hashes the framed bytes `tree 0` followed by a NUL byte,
//! so the name depends on the object format alone and never on the repository's contents.
//! Spawning `git hash-object -t tree --stdin` for a constant cost a process on every commit.
//!
//! In TS you'd write (pseudocode):
//! ```ts
//! const EMPTY_TREE = { sha1: '4b825d...', sha256: '6ef19b...' } as const;
//! ```
/// The empty tree under SHA-1,
/// the object format of nearly every repository.
pub const SHA1_EMPTY_TREE: &str = "4b825dc642cb6eb9a060e54bf8d69288fbee4904";
/// The empty tree under SHA-256.
pub const SHA256_EMPTY_TREE: &str = "6ef19b41225c5369f1c104d45d8d85efa9b057b53b14b4b9b939dd74decc5321";
/// What:
/// The empty tree's object name for an object format as `git rev-parse --show-object-format` spells it,
/// or `None` for a format this table does not know.
/// Why:
/// `None` sends the caller to ask Git,
/// so a future object format is answered by Git and never guessed here.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// function emptyTreeName(objectFormat: string): string | undefined;
/// ```
pub fn empty_tree_name(object_format: &str) -> Option<&'static str> {
return match object_format {
"sha1" => Some(SHA1_EMPTY_TREE),
"sha256" => Some(SHA256_EMPTY_TREE),
_ => None,
};
}
/// Empty-tree controls stay out of the release executable.
#[cfg(test)]
#[path = "empty_tree_tests.rs"]
mod tests;