monochromatic-git-policy-cli 0.5.26

//! What:
//!  In-process answers for the reference and configuration command lines the wrapper issues:
//!  `config --list -z --show-scope`, `remote get-url <name>`, `rev-parse --verify --quiet <ref>^{commit}`,
//!  `for-each-ref --format=%(refname)%00%(objectname)%00%(symref)` and
//!  `rev-parse --abbrev-ref --symbolic-full-name @{upstream}`.
//! Why:
//!  Each reads only the configuration files, `HEAD`, the loose and packed refs and at most a few objects;
//!  every case where Git's output depends on more (a linked worktree, a conditional include, a rewritten URL, an
//!  ambiguous short name, a broken ref) is `None`, which starts Git.
//!
//! In TS you'd write (pseudocode):
//! ```ts
//! const answer = referenceAnswer(context, parsed); // undefined: start Git
//! ```

#![cfg(unix)]

use super::repo_read_config_list::{ListedEntry, list_config, listing_bytes};
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::{Lookup, RefValue, Refs, is_plain_ref_name};
use std::ffi::OsString;

/// The `--format` text of the one listing the wrapper asks for.
const LISTING_FORMAT: &str = "--format=%(refname)%00%(objectname)%00%(symref)";

/// How many tag levels are peeled.
const PEEL_LIMIT: usize = 8;

/// The refs of a context whose worktree owns the shared directory; `None` for a linked worktree.
fn shared_refs(context: &Context) -> Option<Refs> {
    if context.layout.git_dir != context.layout.common_dir {
        return None;
    }
    return Some(Refs::new(context.layout.common_dir.as_path(), context.layout.object_format.hex_length()));
}

/// The listing, or `None`.
fn listing(context: &Context) -> Option<Vec<ListedEntry>> {
    return list_config(context.layout.common_dir.as_path(), context.layout.git_dir.as_path(), &context.scope, context.variables.as_slice());
}

/// Every value of `key` among the listed entries, in order.
fn values_of<'a>(listed: &'a [ListedEntry], key: &str) -> Vec<&'a Option<Vec<u8>>> {
    return listed.iter().filter(|item| { return item.entry.key == key; }).map(|item| { return &item.entry.value; }).collect();
}

/// Whether the symbolic ref target `name` is a plain, non-symbolic ref or does not exist yet;
///  Git follows a chain of symbolic refs, so a target that is itself symbolic is left to it.
fn is_terminal(refs: &Refs, name: &str) -> bool {
    return matches!(refs.lookup(name), Lookup::Missing | Lookup::Found(RefValue::Direct(_)));
}

/// Whether Git's messages are in English under these variables, which the synthesized failures assume.
fn messages_are_english(variables: &[(OsString, OsString)]) -> bool {
    let find = |name: &str| -> Option<String> {
        return variables.iter().rev().find(|(candidate, _)| { return candidate == name; }).and_then(|(_, value)| { return value.to_str().map(str::to_string); }).filter(|value| { return !value.is_empty(); });
    };
    let english = |value: &str| -> bool { return value == "C" || value == "POSIX" || value.starts_with("en"); };
    let locale: Option<String> = find("LC_ALL").or_else(|| { return find("LC_MESSAGES"); }).or_else(|| { return find("LANG"); });
    return locale.as_deref().is_none_or(english) && find("LANGUAGE").as_deref().is_none_or(english);
}

/// `config --list -z --show-scope`.
pub(super) fn config_list(context: &Context, parsed: &Parsed<'_>) -> Option<Answer> {
    if !flags_are(&parsed.flags, &["--list", "-z", "--show-scope"], &[]) || !parsed.operands.is_empty() || !parsed.specs.is_empty() {
        return None;
    }
    let listed: Vec<ListedEntry> = listing(context)?;
    return Some(Answer { stdout: listing_bytes(listed.as_slice()), stderr: Vec::new(), code: 0 });
}

/// `remote get-url <name>` for a remote with one plain URL and no rewriting rule anywhere.
pub(super) fn remote_url(context: &Context, parsed: &Parsed<'_>) -> Option<Answer> {
    if !parsed.flags.is_empty() || !parsed.specs.is_empty() || parsed.operands.len() != 2 || parsed.operands[0] != b"get-url" {
        return None;
    }
    let name: &str = std::str::from_utf8(parsed.operands[1]).ok()?;
    if name.is_empty() || !name.bytes().all(|byte| { return byte.is_ascii_alphanumeric() || matches!(byte, b'-' | b'_' | b'.'); }) {
        return None;
    }
    let listed: Vec<ListedEntry> = listing(context)?;
    if listed.iter().any(|item| { return item.entry.key.starts_with("url.") && (item.entry.key.ends_with(".insteadof") || item.entry.key.ends_with(".pushinsteadof")); }) {
        return None;
    }
    let key: String = format!("remote.{name}.url");
    let urls: Vec<&ListedEntry> = listed.iter().filter(|item| { return item.entry.key == key; }).collect();
    if urls.is_empty() {
        // A remote that is configured nowhere, not even by a legacy `remotes/` or `branches/` file, is Git's own refusal.
        let prefix: String = format!("remote.{name}.");
        let legacy: bool = ["remotes", "branches"].iter().any(|directory| { return std::fs::symlink_metadata(context.layout.common_dir.join(directory).join(name)).is_ok(); });
        if legacy || listed.iter().any(|item| { return item.entry.key.starts_with(prefix.as_str()); }) {
            return None;
        }
        if !messages_are_english(context.variables.as_slice()) {
            return None;
        }
        let message: String = format!("error: No such remote '{name}'\n");
        return Some(Answer { stdout: Vec::new(), stderr: message.into_bytes(), code: 2 });
    }
    let [only] = urls.as_slice() else {
        return None;
    };
    let mut stdout: Vec<u8> = only.entry.value.clone().filter(|value| { return !value.is_empty(); })?;
    stdout.push(b'\n');
    return Some(Answer { stdout, stderr: Vec::new(), code: 0 });
}

/// The commit a ref name peels to, through at most a few tags.
fn peel_to_commit(database: &ObjectDatabase, context: &Context, start: &str) -> Option<String> {
    let mut current: Vec<u8> = from_hex(start.as_bytes(), context.layout.object_format)?;
    for _ in 0..PEEL_LIMIT {
        let object = database.read(current.as_slice())?;
        match object.kind {
            ObjectKind::Commit => return Some(super::repo_read_object::to_hex(current.as_slice())),
            ObjectKind::Tag => {
                let first: &[u8] = object.bytes.split(|byte| { return *byte == b'\n'; }).next()?;
                current = from_hex(first.strip_prefix(b"object ")?, context.layout.object_format)?;
            }
            ObjectKind::Tree | ObjectKind::Blob => return None,
        }
    }
    return None;
}

/// `for-each-ref` with the one format the wrapper uses.
pub(super) fn for_each_ref(context: &Context, parsed: &Parsed<'_>) -> Option<Answer> {
    if parsed.flags != [LISTING_FORMAT] || !parsed.operands.is_empty() || !parsed.specs.is_empty() {
        return None;
    }
    let refs: Refs = shared_refs(context)?;
    let database: ObjectDatabase = context.database()?;
    let mut stdout: Vec<u8> = Vec::new();
    for (name, value) in refs.list()? {
        let (object, symref): (String, &str) = match &value {
            RefValue::Direct(object) => (object.clone(), ""),
            RefValue::Symbolic(target) if is_terminal(&refs, target.as_str()) => (refs.resolve(name.as_str())?, target.as_str()),
            RefValue::Symbolic(_) => return None,
        };
        // Git skips, with a warning, a ref whose object is missing; that case is left to it.
        if !database.contains(from_hex(object.as_bytes(), context.layout.object_format)?.as_slice()) {
            return None;
        }
        stdout.extend_from_slice(format!("{name}\0{object}\0{symref}\n").as_bytes());
    }
    return Some(Answer { stdout, stderr: Vec::new(), code: 0 });
}

/// Whether some ref spelled `prefix` + `short` exists, which would make the short name ambiguous.
fn shadowed(refs: &Refs, prefix: &str, short: &str) -> Option<bool> {
    let name: String = format!("{prefix}{short}");
    if !is_plain_ref_name(name.as_str()) {
        return Some(false);
    }
    return match refs.lookup(name.as_str()) {
        Lookup::Missing => Some(false),
        Lookup::Found(_) => Some(true),
        Lookup::Unsure => None,
    };
}

/// The tracking ref a fetch refspec maps `merge` to.
pub(super) fn tracking_ref(listed: &[ListedEntry], remote: &str, merge: &str) -> Option<String> {
    let key: String = format!("remote.{remote}.fetch");
    for item in listed.iter().filter(|item| { return item.entry.key == key; }) {
        let spec: &str = std::str::from_utf8(item.entry.value.as_deref()?).ok()?;
        let (source, destination) = spec.strip_prefix('+').unwrap_or(spec).split_once(':')?;
        match (source.split_once('*'), destination.split_once('*')) {
            (Some((head, tail)), Some((to_head, to_tail))) => {
                if let Some(middle) = merge.strip_prefix(head).and_then(|rest| { return rest.strip_suffix(tail); }) {
                    return Some(format!("{to_head}{middle}{to_tail}"));
                }
            }
            (None, None) if source == merge => return Some(destination.to_string()),
            _ => {}
        }
    }
    return None;
}

/// `rev-parse --abbrev-ref --symbolic-full-name @{upstream}` for a branch with a plain upstream, or none at all.
fn upstream(context: &Context) -> Option<Answer> {
    let refs: Refs = shared_refs(context)?;
    let head = match refs.lookup_head(context.layout.git_dir.as_path()) {
        Some(RefValue::Symbolic(target)) => target,
        _ => return None,
    };
    let branch: &str = head.strip_prefix("refs/heads/")?;
    // A `HEAD` that names a branch which is itself symbolic follows the chain in Git.
    if !is_terminal(&refs, head.as_str()) {
        return None;
    }
    let listed: Vec<ListedEntry> = listing(context)?;
    let remotes = values_of(listed.as_slice(), &format!("branch.{branch}.remote"));
    let merges = values_of(listed.as_slice(), &format!("branch.{branch}.merge"));
    // More than one entry is a multi-valued setting whose choice Git makes; the reader declines it.
    let (remote_value, merge_value) = (remotes.as_slice(), merges.as_slice());
    let ([Some(remote)], [Some(merge)]) = (remote_value, merge_value) else {
        if remote_value.is_empty() && merge_value.is_empty() && messages_are_english(context.variables.as_slice()) {
            let message: String = format!("fatal: no upstream configured for branch '{branch}'\n");
            return Some(Answer { stdout: Vec::new(), stderr: message.into_bytes(), code: 128 });
        }
        return None;
    };
    let remote_name: &str = std::str::from_utf8(remote.as_slice()).ok()?;
    let merge_name: &str = std::str::from_utf8(merge.as_slice()).ok()?;
    if remote_name == "." || !is_plain_ref_name(merge_name) {
        return None;
    }
    let tracking: String = tracking_ref(listed.as_slice(), remote_name, merge_name)?;
    let short: &str = tracking.strip_prefix("refs/remotes/")?;
    // The tracking ref must exist and resolve, not be a symbolic ref that points nowhere.
    refs.resolve(tracking.as_str())?;
    // The first of Git's lookup rules is the bare name itself, a file in the Git directory.
    if std::fs::symlink_metadata(context.layout.common_dir.join(short)).is_ok() {
        return None;
    }
    for prefix in ["refs/", "refs/tags/", "refs/heads/"] {
        if shadowed(&refs, prefix, short)? {
            return None;
        }
    }
    if shadowed(&refs, "refs/remotes/", &format!("{short}/HEAD"))? {
        return None;
    }
    return Some(Answer { stdout: format!("{short}\n").into_bytes(), stderr: Vec::new(), code: 0 });
}

/// `symbolic-ref --quiet HEAD`: the branch `HEAD` names, or a silent failure for a detached `HEAD`.
pub(super) fn symbolic_ref(context: &Context, parsed: &Parsed<'_>) -> Option<Answer> {
    if !flags_are(&parsed.flags, &["--quiet"], &[]) || parsed.operands != [b"HEAD".as_slice()] || !parsed.specs.is_empty() {
        return None;
    }
    let refs: Refs = shared_refs(context)?;
    return match refs.lookup_head(context.layout.git_dir.as_path())? {
        // Git follows a chain of symbolic refs and prints the last; a target that is symbolic is left to it.
        RefValue::Symbolic(target) if !is_terminal(&refs, target.as_str()) => None,
        RefValue::Symbolic(target) => Some(Answer { stdout: format!("{target}\n").into_bytes(), stderr: Vec::new(), code: 0 }),
        RefValue::Direct(_) => Some(Answer { stdout: Vec::new(), stderr: Vec::new(), code: 1 }),
    };
}

/// `rev-parse --verify --quiet <ref>^{commit}` and the upstream query.
pub(super) fn rev_parse(context: &Context, parsed: &Parsed<'_>) -> Option<Answer> {
    if !parsed.specs.is_empty() || parsed.operands.len() != 1 {
        return None;
    }
    if parsed.operands[0] == b"@{upstream}" {
        if !flags_are(&parsed.flags, &["--abbrev-ref", "--symbolic-full-name"], &[]) {
            return None;
        }
        return upstream(context);
    }
    if !flags_are(&parsed.flags, &["--verify", "--quiet"], &[]) {
        return None;
    }
    let name: &str = std::str::from_utf8(parsed.operands[0]).ok()?.strip_suffix("^{commit}")?;
    let refs: Refs = shared_refs(context)?;
    let object: String = refs.resolve(name)?;
    let database: ObjectDatabase = context.database()?;
    let commit: String = peel_to_commit(&database, context, object.as_str())?;
    return Some(Answer { stdout: format!("{commit}\n").into_bytes(), stderr: Vec::new(), code: 0 });
}

#[cfg(test)]
#[path = "repo_read_query_refs_tests.rs"]
mod tests;