specfold-core 0.5.1

Library behind specfold: typed Markdown documents, owners, a derived graph and checks.
Documentation 
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//! Revisions: HEAD, the upstream branch, and whether a commit is in HEAD's history.

use super::repo::git;
use std::path::Path;
use std::process::{Command, Stdio};

/// The full hash of HEAD.
pub fn head(root: &Path) -> Option<String> {
    let out = git(root, &["rev-parse", "HEAD"])?;
    Some(String::from_utf8_lossy(&out).trim().to_string())
}

/// The full hash `rev` names, None when git does not know it (C4).
pub fn resolve(root: &Path, rev: &str) -> Option<String> {
    let out = git(root, &["rev-parse", "--verify", "--quiet", &format!("{rev}^{{commit}}")])?;
    let s = String::from_utf8_lossy(&out).trim().to_string();
    if s.is_empty() { None } else { Some(s) }
}

/// The tree git diffs a root commit against.
const EMPTY_TREE: &str = "4b825dc642cb6eb9a060e54bf8d69288fbee4904";

/// What `sha` is diffed against: its first parent, or the empty tree for a root commit (C260).
pub fn parent_or_empty(root: &Path, sha: &str) -> String {
    match resolve(root, &format!("{sha}^")) {
        Some(_) => format!("{sha}^"),
        None => EMPTY_TREE.to_string(),
    }
}

/// The diff range of one commit, `sha^..sha`, or from the empty tree for a root commit (C260).
pub fn commit_diff(root: &Path, sha: &str) -> String {
    format!("{}..{sha}", parent_or_empty(root, sha))
}

/// The log range of one commit: `sha^..sha`, or `sha` alone for a root commit (C260).
pub fn commit_log(root: &Path, sha: &str) -> String {
    match resolve(root, &format!("{sha}^")) {
        Some(_) => format!("{sha}^..{sha}"),
        None => sha.to_string(),
    }
}

/// The upstream of the current branch, used as the default push range base.
pub fn upstream(root: &Path) -> Option<String> {
    let out = git(root, &["rev-parse", "--abbrev-ref", "--symbolic-full-name", "@{upstream}"])?;
    let s = String::from_utf8(out).ok()?.trim().to_string();
    if s.is_empty() { None } else { Some(s) }
}

/// Whether `rev` is HEAD or one of its ancestors; None when git cannot tell (unknown revision).
pub fn is_ancestor_of_head(root: &Path, rev: &str) -> Option<bool> {
    let status = Command::new("git")
        .arg("-C")
        .arg(root)
        .args(["merge-base", "--is-ancestor", rev, "HEAD"])
        .stderr(Stdio::null())
        .status()
        .ok()?;
    match status.code() {
        Some(0) => Some(true),
        Some(1) => Some(false),
        _ => None,
    }
}