monochromatic-git-policy-cli 0.5.28

//! What:
//!  The exit status of `git diff-index --cached --quiet <commit-or-HEAD> [-- <paths>]` without starting Git: 0 when the index
//!  holds exactly the commit's tree for those paths, 1 when it differs.
//! Why:
//!  The wrapper asks this before every merge, before every commit's index check and when it proves a restored worktree; each
//!  start cost a process (and, under load, more than forty seconds) for a question two files answer. The rules are
//!  `diff-lib.c` (`diff_cache`, `oneway_diff`, `do_oneway_diff`) and `diff.c` (`diff_addremove`, `diff_change`,
//!  `is_submodule_ignored`) of Git 2.56.0: an unmerged entry is always a difference (`diff_unmerge`), an intent-to-add entry
//!  is an ordinary entry with the empty blob (`diff-index` never sets `ita_invisible_in_index`), and a submodule difference
//!  can be hidden by `.gitmodules`, so that one case is left to Git when a `.gitmodules` exists anywhere.
//!
//! In TS you'd write (pseudocode):
//! ```ts
//! const code: 0 | 1 | undefined = diffIndexQuiet({ commit, paths }); // undefined: start Git
//! ```

use super::repo_read_diff::PathFilter;
use super::repo_read_index::IndexEntry;
use super::repo_read_object::{ObjectKind, from_hex};
use super::repo_read_odb::ObjectDatabase;
use super::repo_read_query::{Answer, Context, Parsed, flags_are};
use super::repo_read_refs::{RefValue, Refs};
use super::repo_read_tree::{FlatEntry, MODE_GITLINK, flatten_tree_shared, parse_commit};

/// The commit `HEAD` names, for a branch under `refs/heads/` or a detached head.
fn head_commit(context: &Context) -> Option<String> {
    let refs: Refs = Refs::new(context.layout.common_dir.as_path(), context.layout.object_format.hex_length());
    return match refs.lookup_head(context.layout.git_dir.as_path())? {
        RefValue::Direct(object) => Some(object),
        RefValue::Symbolic(target) if target.starts_with("refs/heads/") => refs.resolve(target.as_str()),
        RefValue::Symbolic(_) => None,
    };
}

/// The root tree of the commit or tree `operand` names (a hexadecimal name or `HEAD`).
fn tree_of_operand(context: &Context, database: &ObjectDatabase, operand: &[u8]) -> Option<Vec<u8>> {
    let hex: Vec<u8> = if operand == b"HEAD" { head_commit(context)?.into_bytes() } else { operand.to_vec() };
    let name: Vec<u8> = from_hex(hex.as_slice(), context.layout.object_format)?;
    let object = database.read(name.as_slice())?;
    return match object.kind {
        ObjectKind::Tree => Some(name),
        ObjectKind::Commit => Some(parse_commit(object.bytes.as_slice(), context.layout.object_format)?.tree),
        ObjectKind::Blob | ObjectKind::Tag => None,
    };
}

/// Whether a `.gitmodules` file is in the worktree or in either list, so a submodule difference might be configured away.
fn has_gitmodules(context: &Context, tree: &[FlatEntry], index: &[IndexEntry]) -> bool {
    return context.layout.worktree_root.join(".gitmodules").symlink_metadata().is_ok()
        || tree.iter().any(|entry| { return entry.path == b".gitmodules"; })
        || index.iter().any(|entry| { return entry.path == b".gitmodules"; });
}

/// How the two sorted lists differ: whether a difference Git always reports exists, and whether one that only a submodule
/// setting could hide exists.
fn compare(tree: &[&FlatEntry], index: &[&IndexEntry]) -> (bool, bool) {
    let is_link = |mode: u32| -> bool { return mode & 0o170_000 == MODE_GITLINK; };
    let (mut left, mut right): (usize, usize) = (0, 0);
    let mut hideable: bool = false;
    while left < tree.len() || right < index.len() {
        let order = match (tree.get(left), index.get(right)) {
            (Some(old), Some(new)) => old.path.cmp(&new.path),
            (Some(_), None) => std::cmp::Ordering::Less,
            (None, _) => std::cmp::Ordering::Greater,
        };
        let mode: u32 = match order {
            std::cmp::Ordering::Less => {
                left += 1;
                tree[left - 1].mode
            }
            std::cmp::Ordering::Greater => {
                right += 1;
                index[right - 1].mode
            }
            std::cmp::Ordering::Equal => {
                let (old, new): (&FlatEntry, &IndexEntry) = (tree[left], index[right]);
                left += 1;
                right += 1;
                // A pair whose two sides are both submodules is the one `diff_change` can skip; any other pair is reported.
                if old.mode == new.mode && old.id == new.id {
                    continue;
                }
                if is_link(old.mode) && is_link(new.mode) {
                    hideable = true;
                    continue;
                }
                return (true, hideable);
            }
        };
        if is_link(mode) {
            hideable = true;
        } else {
            return (true, hideable);
        }
    }
    return (false, hideable);
}

/// `diff-index --cached --quiet <commit> [-- <paths>]`.
pub(super) fn diff_index_quiet(context: &Context, parsed: &Parsed<'_>) -> Option<Answer> {
    if !flags_are(&parsed.flags, &["--cached", "--quiet"], &[]) || parsed.operands.len() != 1 {
        return None;
    }
    let filter: PathFilter = PathFilter::parse(parsed.specs.as_slice(), context.layout.prefix.is_empty())?;
    let database: ObjectDatabase = context.database()?;
    let tree: std::rc::Rc<Vec<FlatEntry>> = flatten_tree_shared(&database, tree_of_operand(context, &database, parsed.operands[0])?.as_slice(), context.layout.object_format)?;
    let index: Vec<IndexEntry> = context.index()?;
    let answer = |differs: bool| -> Option<Answer> {
        return Some(Answer { stdout: Vec::new(), stderr: Vec::new(), code: i32::from(differs) });
    };
    let wanted_index: Vec<&IndexEntry> = index.iter().filter(|entry| { return filter.matches(entry.path.as_slice()); }).collect();
    // An unmerged path is a pair of its own (`diff_unmerge`), whatever the tree holds.
    if wanted_index.iter().any(|entry| { return entry.stage != 0; }) {
        return answer(true);
    }
    let wanted_tree: Vec<&FlatEntry> = tree.iter().filter(|entry| { return filter.matches(entry.path.as_slice()); }).collect();
    let (reported, hideable) = compare(wanted_tree.as_slice(), wanted_index.as_slice());
    if reported {
        return answer(true);
    }
    if hideable && has_gitmodules(context, tree.as_slice(), index.as_slice()) {
        return None;
    }
    return answer(hideable);
}

/// Controls for the quiet comparison against real Git stay out of the release executable.
#[cfg(test)]
#[path = "repo_read_query_quiet_tests.rs"]
mod tests;