view rust/rhg/src/main.rs @ 51725:bbe59cc5d2e1

rust-changelog: accessing the index

The `Index` object is currently the one providing all DAG related
algorithms, starting with simple ancestors iteration up to more
advanced ones (ranges, common ancestors…).

From pure Rust code, there was no way to access the changelog index for
a given `Repository`, probably because `rhg` does not use any such algorithm
yet.

extern crate log;
use crate::error::CommandError;
use crate::ui::{local_to_utf8, Ui};
use clap::{command, Arg, ArgMatches};
use format_bytes::{format_bytes, join};
use hg::config::{Config, ConfigSource, PlainInfo};
use hg::repo::{Repo, RepoError};
use hg::utils::files::{get_bytes_from_os_str, get_path_from_bytes};
use hg::utils::SliceExt;
use hg::{exit_codes, requirements};
use std::borrow::Cow;
use std::collections::HashSet;
use std::ffi::OsString;
use std::os::unix::prelude::CommandExt;
use std::path::PathBuf;
use std::process::Command;

mod blackbox;
mod color;
mod error;
mod ui;
pub mod utils {
    pub mod path_utils;
}

fn main_with_result(
    argv: Vec<OsString>,
    process_start_time: &blackbox::ProcessStartTime,
    ui: &ui::Ui,
    repo: Result<&Repo, &NoRepoInCwdError>,
    config: &Config,
) -> Result<(), CommandError> {
    check_unsupported(config, repo)?;

    let app = command!()
        .subcommand_required(true)
        .arg(
            Arg::new("repository")
                .help("repository root directory")
                .short('R')
                .value_name("REPO")
                // Both ok: `hg -R ./foo log` or `hg log -R ./foo`
                .global(true),
        )
        .arg(
            Arg::new("config")
                .help("set/override config option (use 'section.name=value')")
                .value_name("CONFIG")
                .global(true)
                .long("config")
                // Ok: `--config section.key1=val --config section.key2=val2`
                // Not ok: `--config section.key1=val section.key2=val2`
                .action(clap::ArgAction::Append),
        )
        .arg(
            Arg::new("cwd")
                .help("change working directory")
                .value_name("DIR")
                .long("cwd")
                .global(true),
        )
        .arg(
            Arg::new("color")
                .help("when to colorize (boolean, always, auto, never, or debug)")
                .value_name("TYPE")
                .long("color")
                .global(true),
        )
        .version("0.0.1");
    let app = add_subcommand_args(app);

    let matches = app.try_get_matches_from(argv.iter())?;

    let (subcommand_name, subcommand_args) =
        matches.subcommand().expect("subcommand required");

    // Mercurial allows users to define "defaults" for commands, fallback
    // if a default is detected for the current command
    let defaults = config.get_str(b"defaults", subcommand_name.as_bytes())?;
    match defaults {
        // Programmatic usage might set defaults to an empty string to unset
        // it; allow that
        None | Some("") => {}
        Some(_) => {
            let msg = "`defaults` config set";
            return Err(CommandError::unsupported(msg));
        }
    }

    for prefix in ["pre", "post", "fail"].iter() {
        // Mercurial allows users to define generic hooks for commands,
        // fallback if any are detected
        let item = format!("{}-{}", prefix, subcommand_name);
        let hook_for_command =
            config.get_str_no_default(b"hooks", item.as_bytes())?;
        if hook_for_command.is_some() {
            let msg = format!("{}-{} hook defined", prefix, subcommand_name);
            return Err(CommandError::unsupported(msg));
        }
    }
    let run = subcommand_run_fn(subcommand_name)
        .expect("unknown subcommand name from clap despite Command::subcommand_required");

    let invocation = CliInvocation {
        ui,
        subcommand_args,
        config,
        repo,
    };

    if let Ok(repo) = repo {
        // We don't support subrepos, fallback if the subrepos file is present
        if repo.working_directory_vfs().join(".hgsub").exists() {
            let msg = "subrepos (.hgsub is present)";
            return Err(CommandError::unsupported(msg));
        }
    }

    if config.is_extension_enabled(b"blackbox") {
        let blackbox =
            blackbox::Blackbox::new(&invocation, process_start_time)?;
        blackbox.log_command_start(argv.iter());
        let result = run(&invocation);
        blackbox.log_command_end(
            argv.iter(),
            exit_code(
                &result,
                // TODO: show a warning or combine with original error if
                // `get_bool` returns an error
                config
                    .get_bool(b"ui", b"detailed-exit-code")
                    .unwrap_or(false),
            ),
        );
        result
    } else {
        run(&invocation)
    }
}

fn rhg_main(argv: Vec<OsString>) -> ! {
    // Run this first, before we find out if the blackbox extension is even
    // enabled, in order to include everything in-between in the duration
    // measurements. Reading config files can be slow if they’re on NFS.
    let process_start_time = blackbox::ProcessStartTime::now();

    env_logger::init();

    // Make sure nothing in a future version of `rhg` sets the global
    // threadpool before we can cap default threads. (This is also called
    // in core because Python uses the same code path, we're adding a
    // redundant check.)
    hg::utils::cap_default_rayon_threads()
        .expect("Rayon threadpool already initialized");

    let early_args = EarlyArgs::parse(&argv);

    let initial_current_dir = early_args.cwd.map(|cwd| {
        let cwd = get_path_from_bytes(&cwd);
        std::env::current_dir()
            .and_then(|initial| {
                std::env::set_current_dir(cwd)?;
                Ok(initial)
            })
            .unwrap_or_else(|error| {
                exit(
                    &argv,
                    &None,
                    &Ui::new_infallible(&Config::empty()),
                    OnUnsupported::Abort,
                    Err(CommandError::abort(format!(
                        "abort: {}: '{}'",
                        error,
                        cwd.display()
                    ))),
                    false,
                )
            })
    });

    let mut non_repo_config =
        Config::load_non_repo().unwrap_or_else(|error| {
            // Normally this is decided based on config, but we don’t have that
            // available. As of this writing config loading never returns an
            // "unsupported" error but that is not enforced by the type system.
            let on_unsupported = OnUnsupported::Abort;

            exit(
                &argv,
                &initial_current_dir,
                &Ui::new_infallible(&Config::empty()),
                on_unsupported,
                Err(error.into()),
                false,
            )
        });

    non_repo_config
        .load_cli_args(early_args.config, early_args.color)
        .unwrap_or_else(|error| {
            exit(
                &argv,
                &initial_current_dir,
                &Ui::new_infallible(&non_repo_config),
                OnUnsupported::from_config(&non_repo_config),
                Err(error.into()),
                non_repo_config
                    .get_bool(b"ui", b"detailed-exit-code")
                    .unwrap_or(false),
            )
        });

    if let Some(repo_path_bytes) = &early_args.repo {
        lazy_static::lazy_static! {
            static ref SCHEME_RE: regex::bytes::Regex =
                // Same as `_matchscheme` in `mercurial/util.py`
                regex::bytes::Regex::new("^[a-zA-Z0-9+.\\-]+:").unwrap();
        }
        if SCHEME_RE.is_match(repo_path_bytes) {
            exit(
                &argv,
                &initial_current_dir,
                &Ui::new_infallible(&non_repo_config),
                OnUnsupported::from_config(&non_repo_config),
                Err(CommandError::UnsupportedFeature {
                    message: format_bytes!(
                        b"URL-like --repository {}",
                        repo_path_bytes
                    ),
                }),
                // TODO: show a warning or combine with original error if
                // `get_bool` returns an error
                non_repo_config
                    .get_bool(b"ui", b"detailed-exit-code")
                    .unwrap_or(false),
            )
        }
    }
    let repo_arg = early_args.repo.unwrap_or_default();
    let repo_path: Option<PathBuf> = {
        if repo_arg.is_empty() {
            None
        } else {
            let local_config = {
                if std::env::var_os("HGRCSKIPREPO").is_none() {
                    // TODO: handle errors from find_repo_root
                    if let Ok(current_dir_path) = Repo::find_repo_root() {
                        let config_files = vec![
                            ConfigSource::AbsPath(
                                current_dir_path.join(".hg/hgrc"),
                            ),
                            ConfigSource::AbsPath(
                                current_dir_path.join(".hg/hgrc-not-shared"),
                            ),
                        ];
                        // TODO: handle errors from
                        // `load_from_explicit_sources`
                        Config::load_from_explicit_sources(config_files).ok()
                    } else {
                        None
                    }
                } else {
                    None
                }
            };

            let non_repo_config_val = {
                let non_repo_val = non_repo_config.get(b"paths", &repo_arg);
                match &non_repo_val {
                    Some(val) if !val.is_empty() => home::home_dir()
                        .unwrap_or_else(|| PathBuf::from("~"))
                        .join(get_path_from_bytes(val))
                        .canonicalize()
                        // TODO: handle error and make it similar to python
                        // implementation maybe?
                        .ok(),
                    _ => None,
                }
            };

            let config_val = match &local_config {
                None => non_repo_config_val,
                Some(val) => {
                    let local_config_val = val.get(b"paths", &repo_arg);
                    match &local_config_val {
                        Some(val) if !val.is_empty() => {
                            // presence of a local_config assures that
                            // current_dir
                            // wont result in an Error
                            let canpath = hg::utils::current_dir()
                                .unwrap()
                                .join(get_path_from_bytes(val))
                                .canonicalize();
                            canpath.ok().or(non_repo_config_val)
                        }
                        _ => non_repo_config_val,
                    }
                }
            };
            config_val
                .or_else(|| Some(get_path_from_bytes(&repo_arg).to_path_buf()))
        }
    };

    let simple_exit =
        |ui: &Ui, config: &Config, result: Result<(), CommandError>| -> ! {
            exit(
                &argv,
                &initial_current_dir,
                ui,
                OnUnsupported::from_config(config),
                result,
                // TODO: show a warning or combine with original error if
                // `get_bool` returns an error
                non_repo_config
                    .get_bool(b"ui", b"detailed-exit-code")
                    .unwrap_or(false),
            )
        };
    let early_exit = |config: &Config, error: CommandError| -> ! {
        simple_exit(&Ui::new_infallible(config), config, Err(error))
    };
    let repo_result = match Repo::find(&non_repo_config, repo_path.to_owned())
    {
        Ok(repo) => Ok(repo),
        Err(RepoError::NotFound { at }) if repo_path.is_none() => {
            // Not finding a repo is not fatal yet, if `-R` was not given
            Err(NoRepoInCwdError { cwd: at })
        }
        Err(error) => early_exit(&non_repo_config, error.into()),
    };

    let config = if let Ok(repo) = &repo_result {
        repo.config()
    } else {
        &non_repo_config
    };

    let mut config_cow = Cow::Borrowed(config);
    config_cow.to_mut().apply_plain(PlainInfo::from_env());
    if !ui::plain(Some("tweakdefaults"))
        && config_cow
            .as_ref()
            .get_bool(b"ui", b"tweakdefaults")
            .unwrap_or_else(|error| early_exit(config, error.into()))
    {
        config_cow.to_mut().tweakdefaults()
    };
    let config = config_cow.as_ref();
    let ui = Ui::new(config)
        .unwrap_or_else(|error| early_exit(config, error.into()));

    if let Ok(true) = config.get_bool(b"rhg", b"fallback-immediately") {
        exit(
            &argv,
            &initial_current_dir,
            &ui,
            OnUnsupported::fallback(config),
            Err(CommandError::unsupported(
                "`rhg.fallback-immediately is true`",
            )),
            false,
        )
    }

    let result = main_with_result(
        argv.iter().map(|s| s.to_owned()).collect(),
        &process_start_time,
        &ui,
        repo_result.as_ref(),
        config,
    );
    simple_exit(&ui, config, result)
}

fn main() -> ! {
    rhg_main(std::env::args_os().collect())
}

fn exit_code(
    result: &Result<(), CommandError>,
    use_detailed_exit_code: bool,
) -> i32 {
    match result {
        Ok(()) => exit_codes::OK,
        Err(CommandError::Abort {
            detailed_exit_code, ..
        }) => {
            if use_detailed_exit_code {
                *detailed_exit_code
            } else {
                exit_codes::ABORT
            }
        }
        Err(CommandError::Unsuccessful) => exit_codes::UNSUCCESSFUL,
        // Exit with a specific code and no error message to let a potential
        // wrapper script fallback to Python-based Mercurial.
        Err(CommandError::UnsupportedFeature { .. }) => {
            exit_codes::UNIMPLEMENTED
        }
        Err(CommandError::InvalidFallback { .. }) => {
            exit_codes::INVALID_FALLBACK
        }
    }
}

fn exit(
    original_args: &[OsString],
    initial_current_dir: &Option<PathBuf>,
    ui: &Ui,
    mut on_unsupported: OnUnsupported,
    result: Result<(), CommandError>,
    use_detailed_exit_code: bool,
) -> ! {
    if let (
        OnUnsupported::Fallback { executable },
        Err(CommandError::UnsupportedFeature { message }),
    ) = (&on_unsupported, &result)
    {
        let mut args = original_args.iter();
        let executable = match executable {
            None => {
                exit_no_fallback(
                    ui,
                    OnUnsupported::Abort,
                    Err(CommandError::abort(
                        "abort: 'rhg.on-unsupported=fallback' without \
                                'rhg.fallback-executable' set.",
                    )),
                    false,
                );
            }
            Some(executable) => executable,
        };
        let executable_path = get_path_from_bytes(executable);
        let this_executable = args.next().expect("exepcted argv[0] to exist");
        if executable_path == *this_executable {
            // Avoid spawning infinitely many processes until resource
            // exhaustion.
            let _ = ui.write_stderr(&format_bytes!(
                b"Blocking recursive fallback. The 'rhg.fallback-executable = {}' config \
                points to `rhg` itself.\n",
                executable
            ));
            on_unsupported = OnUnsupported::Abort
        } else {
            log::debug!("falling back (see trace-level log)");
            log::trace!("{}", local_to_utf8(message));
            if let Err(err) = which::which(executable_path) {
                exit_no_fallback(
                    ui,
                    OnUnsupported::Abort,
                    Err(CommandError::InvalidFallback {
                        path: executable.to_owned(),
                        err: err.to_string(),
                    }),
                    use_detailed_exit_code,
                )
            }
            // `args` is now `argv[1..]` since we’ve already consumed
            // `argv[0]`
            let mut command = Command::new(executable_path);
            command.args(args);
            if let Some(initial) = initial_current_dir {
                command.current_dir(initial);
            }
            // We don't use subprocess because proper signal handling is harder
            // and we don't want to keep `rhg` around after a fallback anyway.
            // For example, if `rhg` is run in the background and falls back to
            // `hg` which, in turn, waits for a signal, we'll get stuck if
            // we're doing plain subprocess.
            //
            // If `exec` returns, we can only assume our process is very broken
            // (see its documentation), so only try to forward the error code
            // when exiting.
            let err = command.exec();
            std::process::exit(
                err.raw_os_error().unwrap_or(exit_codes::ABORT),
            );
        }
    }
    exit_no_fallback(ui, on_unsupported, result, use_detailed_exit_code)
}

fn exit_no_fallback(
    ui: &Ui,
    on_unsupported: OnUnsupported,
    result: Result<(), CommandError>,
    use_detailed_exit_code: bool,
) -> ! {
    match &result {
        Ok(_) => {}
        Err(CommandError::Unsuccessful) => {}
        Err(CommandError::Abort { message, hint, .. }) => {
            // Ignore errors when writing to stderr, we’re already exiting
            // with failure code so there’s not much more we can do.
            if !message.is_empty() {
                let _ = ui.write_stderr(&format_bytes!(b"{}\n", message));
            }
            if let Some(hint) = hint {
                let _ = ui.write_stderr(&format_bytes!(b"({})\n", hint));
            }
        }
        Err(CommandError::UnsupportedFeature { message }) => {
            match on_unsupported {
                OnUnsupported::Abort => {
                    let _ = ui.write_stderr(&format_bytes!(
                        b"unsupported feature: {}\n",
                        message
                    ));
                }
                OnUnsupported::AbortSilent => {}
                OnUnsupported::Fallback { .. } => unreachable!(),
            }
        }
        Err(CommandError::InvalidFallback { path, err }) => {
            let _ = ui.write_stderr(&format_bytes!(
                b"abort: invalid fallback '{}': {}\n",
                path,
                err.as_bytes(),
            ));
        }
    }
    std::process::exit(exit_code(&result, use_detailed_exit_code))
}

mod commands {
    pub mod cat;
    pub mod config;
    pub mod debugdata;
    pub mod debugignorerhg;
    pub mod debugrequirements;
    pub mod debugrhgsparse;
    pub mod files;
    pub mod root;
    pub mod status;
}

macro_rules! subcommands {
    ($( $command: ident )+) => {

        fn add_subcommand_args(app: clap::Command) -> clap::Command {
            app
            $(
                .subcommand(commands::$command::args())
            )+
        }

        pub type RunFn = fn(&CliInvocation) -> Result<(), CommandError>;

        fn subcommand_run_fn(name: &str) -> Option<RunFn> {
            match name {
                $(
                    stringify!($command) => Some(commands::$command::run),
                )+
                _ => None,
            }
        }
    };
}

subcommands! {
    cat
    debugdata
    debugrequirements
    debugignorerhg
    debugrhgsparse
    files
    root
    config
    status
}

pub struct CliInvocation<'a> {
    ui: &'a Ui,
    subcommand_args: &'a ArgMatches,
    config: &'a Config,
    /// References inside `Result` is a bit peculiar but allow
    /// `invocation.repo?` to work out with `&CliInvocation` since this
    /// `Result` type is `Copy`.
    repo: Result<&'a Repo, &'a NoRepoInCwdError>,
}

struct NoRepoInCwdError {
    cwd: PathBuf,
}

/// CLI arguments to be parsed "early" in order to be able to read
/// configuration before using Clap. Ideally we would also use Clap for this,
/// see <https://github.com/clap-rs/clap/discussions/2366>.
///
/// These arguments are still declared when we do use Clap later, so that Clap
/// does not return an error for their presence.
struct EarlyArgs {
    /// Values of all `--config` arguments. (Possibly none)
    config: Vec<Vec<u8>>,
    /// Value of all the `--color` argument, if any.
    color: Option<Vec<u8>>,
    /// Value of the `-R` or `--repository` argument, if any.
    repo: Option<Vec<u8>>,
    /// Value of the `--cwd` argument, if any.
    cwd: Option<Vec<u8>>,
}

impl EarlyArgs {
    fn parse<'a>(args: impl IntoIterator<Item = &'a OsString>) -> Self {
        let mut args = args.into_iter().map(get_bytes_from_os_str);
        let mut config = Vec::new();
        let mut color = None;
        let mut repo = None;
        let mut cwd = None;
        // Use `while let` instead of `for` so that we can also call
        // `args.next()` inside the loop.
        while let Some(arg) = args.next() {
            if arg == b"--config" {
                if let Some(value) = args.next() {
                    config.push(value)
                }
            } else if let Some(value) = arg.drop_prefix(b"--config=") {
                config.push(value.to_owned())
            }

            if arg == b"--color" {
                if let Some(value) = args.next() {
                    color = Some(value)
                }
            } else if let Some(value) = arg.drop_prefix(b"--color=") {
                color = Some(value.to_owned())
            }

            if arg == b"--cwd" {
                if let Some(value) = args.next() {
                    cwd = Some(value)
                }
            } else if let Some(value) = arg.drop_prefix(b"--cwd=") {
                cwd = Some(value.to_owned())
            }

            if arg == b"--repository" || arg == b"-R" {
                if let Some(value) = args.next() {
                    repo = Some(value)
                }
            } else if let Some(value) = arg.drop_prefix(b"--repository=") {
                repo = Some(value.to_owned())
            } else if let Some(value) = arg.drop_prefix(b"-R") {
                repo = Some(value.to_owned())
            }
        }
        Self {
            config,
            color,
            repo,
            cwd,
        }
    }
}

/// What to do when encountering some unsupported feature.
///
/// See `HgError::UnsupportedFeature` and `CommandError::UnsupportedFeature`.
enum OnUnsupported {
    /// Print an error message describing what feature is not supported,
    /// and exit with code 252.
    Abort,
    /// Silently exit with code 252.
    AbortSilent,
    /// Try running a Python implementation
    Fallback { executable: Option<Vec<u8>> },
}

impl OnUnsupported {
    const DEFAULT: Self = OnUnsupported::Abort;

    fn fallback_executable(config: &Config) -> Option<Vec<u8>> {
        config
            .get(b"rhg", b"fallback-executable")
            .map(|x| x.to_owned())
    }

    fn fallback(config: &Config) -> Self {
        OnUnsupported::Fallback {
            executable: Self::fallback_executable(config),
        }
    }

    fn from_config(config: &Config) -> Self {
        match config
            .get(b"rhg", b"on-unsupported")
            .map(|value| value.to_ascii_lowercase())
            .as_deref()
        {
            Some(b"abort") => OnUnsupported::Abort,
            Some(b"abort-silent") => OnUnsupported::AbortSilent,
            Some(b"fallback") => Self::fallback(config),
            None => Self::DEFAULT,
            Some(_) => {
                // TODO: warn about unknown config value
                Self::DEFAULT
            }
        }
    }
}

/// The `*` extension is an edge-case for config sub-options that apply to all
/// extensions. For now, only `:required` exists, but that may change in the
/// future.
const SUPPORTED_EXTENSIONS: &[&[u8]] = &[
    b"blackbox",
    b"share",
    b"sparse",
    b"narrow",
    b"*",
    b"strip",
    b"rebase",
];

fn check_extensions(config: &Config) -> Result<(), CommandError> {
    if let Some(b"*") = config.get(b"rhg", b"ignored-extensions") {
        // All extensions are to be ignored, nothing to do here
        return Ok(());
    }

    let enabled: HashSet<&[u8]> = config
        .iter_section(b"extensions")
        .filter_map(|(extension, value)| {
            if value == b"!" {
                // Filter out disabled extensions
                return None;
            }
            // Ignore extension suboptions. Only `required` exists for now.
            // `rhg` either supports an extension or doesn't, so it doesn't
            // make sense to consider the loading of an extension.
            let actual_extension =
                extension.split_2(b':').unwrap_or((extension, b"")).0;
            Some(actual_extension)
        })
        .collect();

    let mut unsupported = enabled;
    for supported in SUPPORTED_EXTENSIONS {
        unsupported.remove(supported);
    }

    if let Some(ignored_list) = config.get_list(b"rhg", b"ignored-extensions")
    {
        for ignored in ignored_list {
            unsupported.remove(ignored.as_slice());
        }
    }

    if unsupported.is_empty() {
        Ok(())
    } else {
        let mut unsupported: Vec<_> = unsupported.into_iter().collect();
        // Sort the extensions to get a stable output
        unsupported.sort();
        Err(CommandError::UnsupportedFeature {
            message: format_bytes!(
                b"extensions: {} (consider adding them to 'rhg.ignored-extensions' config)",
                join(unsupported, b", ")
            ),
        })
    }
}

/// Array of tuples of (auto upgrade conf, feature conf, local requirement)
#[allow(clippy::type_complexity)]
const AUTO_UPGRADES: &[((&str, &str), (&str, &str), &str)] = &[
    (
        ("format", "use-share-safe.automatic-upgrade-of-mismatching-repositories"),
        ("format", "use-share-safe"),
        requirements::SHARESAFE_REQUIREMENT,
    ),
    (
        ("format", "use-dirstate-tracked-hint.automatic-upgrade-of-mismatching-repositories"),
        ("format", "use-dirstate-tracked-hint"),
        requirements::DIRSTATE_TRACKED_HINT_V1,
    ),
    (
        ("format", "use-dirstate-v2.automatic-upgrade-of-mismatching-repositories"),
        ("format", "use-dirstate-v2"),
        requirements::DIRSTATE_V2_REQUIREMENT,
    ),
];

/// Mercurial allows users to automatically upgrade their repository.
/// `rhg` does not have the ability to upgrade yet, so fallback if an upgrade
/// is needed.
fn check_auto_upgrade(
    config: &Config,
    reqs: &HashSet<String>,
) -> Result<(), CommandError> {
    for (upgrade_conf, feature_conf, local_req) in AUTO_UPGRADES.iter() {
        let auto_upgrade = config
            .get_bool(upgrade_conf.0.as_bytes(), upgrade_conf.1.as_bytes())?;

        if auto_upgrade {
            let want_it = config.get_bool(
                feature_conf.0.as_bytes(),
                feature_conf.1.as_bytes(),
            )?;
            let have_it = reqs.contains(*local_req);

            let action = match (want_it, have_it) {
                (true, false) => Some("upgrade"),
                (false, true) => Some("downgrade"),
                _ => None,
            };
            if let Some(action) = action {
                let message = format!(
                    "automatic {} {}.{}",
                    action, upgrade_conf.0, upgrade_conf.1
                );
                return Err(CommandError::unsupported(message));
            }
        }
    }
    Ok(())
}

fn check_unsupported(
    config: &Config,
    repo: Result<&Repo, &NoRepoInCwdError>,
) -> Result<(), CommandError> {
    check_extensions(config)?;

    if std::env::var_os("HG_PENDING").is_some() {
        // TODO: only if the value is `== repo.working_directory`?
        // What about relative v.s. absolute paths?
        Err(CommandError::unsupported("$HG_PENDING"))?
    }

    if let Ok(repo) = repo {
        if repo.has_subrepos()? {
            Err(CommandError::unsupported("sub-repositories"))?
        }
        check_auto_upgrade(config, repo.requirements())?;
    }

    if config.has_non_empty_section(b"encode") {
        Err(CommandError::unsupported("[encode] config"))?
    }

    if config.has_non_empty_section(b"decode") {
        Err(CommandError::unsupported("[decode] config"))?
    }

    Ok(())
}