rust/hg-core/src/checkexec.rs

rust-dirstate: merge `dirstate_tree` module into `dirstate`

The historical reasonning for `dirstate_tree` existing in the first place is
that a new approach was needed for the tree-like dirstate and it was easier
to start somewhat fresh. Now that the former dirstate is (long) gone, we
can merge those two modules to avoid the confusion that even the module
creators sometimes get.

use std::fs;
use std::io;
use std::os::unix::fs::{MetadataExt, PermissionsExt};
use std::path::Path;

const EXECFLAGS: u32 = 0o111;

fn is_executable(path: impl AsRef<Path>) -> Result<bool, io::Error> {
    let metadata = fs::metadata(path)?;
    let mode = metadata.mode();
    Ok(mode & EXECFLAGS != 0)
}

fn make_executable(path: impl AsRef<Path>) -> Result<(), io::Error> {
    let mode = fs::metadata(path.as_ref())?.mode();
    fs::set_permissions(
        path,
        fs::Permissions::from_mode((mode & 0o777) | EXECFLAGS),
    )?;
    Ok(())
}

fn copy_mode(
    src: impl AsRef<Path>,
    dst: impl AsRef<Path>,
) -> Result<(), io::Error> {
    let mode = match fs::symlink_metadata(src) {
        Ok(metadata) => metadata.mode(),
        Err(e) if e.kind() == io::ErrorKind::NotFound =>
        // copymode in python has a more complicated handling of FileNotFound
        // error, which we don't need because all it does is applying
        // umask, which the OS already does when we mkdir.
        {
            return Ok(())
        }
        Err(e) => return Err(e),
    };
    fs::set_permissions(dst, fs::Permissions::from_mode(mode))?;
    Ok(())
}

fn check_exec_impl(path: impl AsRef<Path>) -> Result<bool, io::Error> {
    let basedir = path.as_ref().join(".hg");
    let cachedir = basedir.join("wcache");
    let storedir = basedir.join("store");

    if !cachedir.exists() {
        // we want to create the 'cache' directory, not the '.hg' one.
        // Automatically creating '.hg' directory could silently spawn
        // invalid Mercurial repositories. That seems like a bad idea.
        fs::create_dir(&cachedir)
            .and_then(|()| {
                if storedir.exists() {
                    copy_mode(&storedir, &cachedir)
                } else {
                    copy_mode(&basedir, &cachedir)
                }
            })
            .ok();
    }

    let leave_file: bool;
    let checkdir: &Path;
    let checkisexec = cachedir.join("checkisexec");
    let checknoexec = cachedir.join("checknoexec");
    if cachedir.is_dir() {
        // Check if both files already exist in cache and have correct
        // permissions. if so, we assume that permissions work.
        // If not, we delete the files and try again.
        match is_executable(&checkisexec) {
            Err(e) if e.kind() == io::ErrorKind::NotFound => (),
            Err(e) => return Err(e),
            Ok(is_exec) => {
                if is_exec {
                    let noexec_is_exec = match is_executable(&checknoexec) {
                        Err(e) if e.kind() == io::ErrorKind::NotFound => {
                            fs::write(&checknoexec, "")?;
                            is_executable(&checknoexec)?
                        }
                        Err(e) => return Err(e),
                        Ok(exec) => exec,
                    };
                    if !noexec_is_exec {
                        // check-exec is exec and check-no-exec is not exec
                        return Ok(true);
                    }
                    fs::remove_file(&checknoexec)?;
                }
                fs::remove_file(&checkisexec)?;
            }
        }
        checkdir = &cachedir;
        leave_file = true;
    } else {
        // no cache directory (probably because .hg doesn't exist):
        // check directly in `path` and don't leave the temp file behind
        checkdir = path.as_ref();
        leave_file = false;
    };

    let tmp_file = tempfile::NamedTempFile::new_in(checkdir)?;
    if !is_executable(tmp_file.path())? {
        make_executable(tmp_file.path())?;
        if is_executable(tmp_file.path())? {
            if leave_file {
                tmp_file.persist(checkisexec).ok();
            }
            return Ok(true);
        }
    }

    Ok(false)
}

/// This function is a Rust rewrite of the `checkexec` function from
/// `posix.py`.
///
/// Returns `true` if the filesystem supports execute permissions.
pub fn check_exec(path: impl AsRef<Path>) -> bool {
    check_exec_impl(path).unwrap_or(false)
}