yash_env/

semantics.rs

// This file is part of yash, an extended POSIX shell.
// Copyright (C) 2021 WATANABE Yuki
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

//! Type definitions for command execution.

use crate::Env;
use crate::signal;
use crate::source::Location;
use crate::system::resource::{LimitPair, Resource, SetRlimit};
use crate::system::r#virtual::SignalEffect;
use crate::system::{Disposition, Exit, SendSignal, Sigaction, Sigmask, SigmaskOp, Signals};
use std::borrow::Cow;
use std::cell::RefCell;
use std::ffi::c_int;
use std::num::NonZero;
use std::ops::ControlFlow;
use std::pin::Pin;
use std::process::ExitCode;
use std::process::Termination;

/// Resultant string of word expansion.
///
/// A field is a string accompanied with the original word location.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Field {
    /// String value of the field.
    pub value: String,
    /// Location of the word this field resulted from.
    pub origin: Location,
}

impl Field {
    /// Creates a new field with a dummy origin location.
    ///
    /// The value of the resulting field will be `value.into()`.
    /// The origin of the field will be created by [`Location::dummy`] with a
    /// clone of the value.
    #[inline]
    pub fn dummy<S: Into<String>>(value: S) -> Field {
        fn with_value(value: String) -> Field {
            let origin = Location::dummy(value.clone());
            Field { value, origin }
        }
        with_value(value.into())
    }

    /// Creates an array of fields with dummy origin locations.
    ///
    /// This function calls [`dummy`](Self::dummy) to create the results.
    pub fn dummies<I, S>(values: I) -> Vec<Field>
    where
        I: IntoIterator<Item = S>,
        S: Into<String>,
    {
        values.into_iter().map(Self::dummy).collect()
    }
}

impl std::fmt::Display for Field {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.value.fmt(f)
    }
}

/// Number that summarizes the result of command execution.
///
/// An exit status is an integer returned from a utility (or command) when
/// executed. It usually is a summarized result of the execution.  Many
/// utilities return an exit status of zero when successful and non-zero
/// otherwise.
///
/// In the shell language, the special parameter `$?` expands to the exit status
/// of the last executed command. Exit statuses also affect the behavior of some
/// compound commands.
#[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct ExitStatus(pub c_int);

impl std::fmt::Display for ExitStatus {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.0.fmt(f)
    }
}

impl From<c_int> for ExitStatus {
    fn from(value: c_int) -> ExitStatus {
        ExitStatus(value)
    }
}

impl From<ExitStatus> for c_int {
    fn from(exit_status: ExitStatus) -> c_int {
        exit_status.0
    }
}

/// Converts a signal number to the corresponding exit status.
///
/// POSIX requires the exit status to be greater than 128. The current
/// implementation returns `signal_number + 384`.
///
/// See [`ExitStatus::to_signal`] for the reverse conversion.
impl From<signal::Number> for ExitStatus {
    fn from(number: signal::Number) -> Self {
        Self::from(number.as_raw() + 0x180)
    }
}

impl ExitStatus {
    /// Returns the signal name and number corresponding to the exit status.
    ///
    /// This function is the inverse of the `From<signal::Number>` implementation
    /// for `ExitStatus`. It tries to find a signal name and number by offsetting
    /// the exit status by 384. If the offsetting does not result in a valid signal
    /// name and number, it additionally tries with 128 and 0 unless `exact` is
    /// `true`.
    ///
    /// If `self` is not a valid signal exit status, this function returns `None`.
    #[must_use]
    pub fn to_signal<S: Signals + ?Sized>(
        self,
        system: &S,
        exact: bool,
    ) -> Option<(Cow<'static, str>, signal::Number)> {
        fn convert<S: Signals + ?Sized>(
            exit_status: ExitStatus,
            offset: c_int,
            system: &S,
        ) -> Option<(Cow<'static, str>, signal::Number)> {
            let number = exit_status.0.checked_sub(offset)?;
            let number = signal::Number::from_raw_unchecked(NonZero::new(number)?);
            let name = system.sig2str(number)?;
            Some((name, number))
        }

        if let Some(signal) = convert(self, 0x180, system) {
            return Some(signal);
        }
        if exact {
            return None;
        }
        if let Some(signal) = convert(self, 0x80, system) {
            return Some(signal);
        }
        if let Some(signal) = convert(self, 0, system) {
            return Some(signal);
        }
        None
    }
}

/// Converts the exit status to `ExitCode`.
///
/// Note that `ExitCode` only supports exit statuses in the range of 0 to 255.
/// Only the lowest 8 bits of the exit status are used in the conversion.
impl Termination for ExitStatus {
    fn report(self) -> ExitCode {
        (self.0 as u8).into()
    }
}

impl ExitStatus {
    /// Exit status of 0: success
    pub const SUCCESS: ExitStatus = ExitStatus(0);

    /// Exit status of 1: failure
    pub const FAILURE: ExitStatus = ExitStatus(1);

    /// Exit status of 2: error severer than failure
    pub const ERROR: ExitStatus = ExitStatus(2);

    /// Exit Status of 126: command not executable
    pub const NOEXEC: ExitStatus = ExitStatus(126);

    /// Exit status of 127: command not found
    pub const NOT_FOUND: ExitStatus = ExitStatus(127);

    /// Exit status of 128: unrecoverable read error
    pub const READ_ERROR: ExitStatus = ExitStatus(128);

    /// Returns true if and only if `self` is zero.
    pub const fn is_successful(&self) -> bool {
        self.0 == 0
    }
}

/// Result of interrupted command execution.
///
/// `Divert` implements `Ord`. Values are ordered by severity.
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub enum Divert {
    /// Continue the current loop.
    Continue {
        /// Number of loops to break before continuing.
        ///
        /// `0` for continuing the innermost loop, `1` for one-level outer, and so on.
        count: usize,
    },

    /// Break the current loop.
    Break {
        /// Number of loops to break.
        ///
        /// `0` for breaking the innermost loop, `1` for one-level outer, and so on.
        count: usize,
    },

    /// Return from the current function or script.
    Return(Option<ExitStatus>),

    /// Interrupt the current shell execution environment.
    ///
    /// This is the same as `Exit` in a non-interactive shell: it makes the
    /// shell exit after executing the EXIT trap, if any. If this is used inside
    /// the EXIT trap, the shell will exit immediately.
    ///
    /// In an interactive shell, this will abort the currently executed command
    /// and resume prompting for a next command line.
    Interrupt(Option<ExitStatus>),

    /// Exit from the current shell execution environment.
    ///
    /// This makes the shell exit after executing the EXIT trap, if any.
    /// If this is used inside the EXIT trap, the shell will exit immediately.
    Exit(Option<ExitStatus>),

    /// Exit from the current shell execution environment immediately.
    ///
    /// This makes the shell exit without executing the EXIT trap.
    Abort(Option<ExitStatus>),
}

impl Divert {
    /// Returns the exit status associated with the `Divert`.
    ///
    /// Returns the variant's value if `self` is `Exit` or `Interrupt`;
    /// otherwise, `None`.
    pub fn exit_status(&self) -> Option<ExitStatus> {
        use Divert::*;
        match self {
            Continue { .. } | Break { .. } => None,
            Return(exit_status)
            | Interrupt(exit_status)
            | Exit(exit_status)
            | Abort(exit_status) => *exit_status,
        }
    }
}

/// Result of command execution.
///
/// If the command was interrupted in the middle of execution, the result value
/// will be a `Break` having a [`Divert`] value which specifies what to execute
/// next.
pub type Result<T = ()> = ControlFlow<Divert, T>;

type PinFuture<'a, T> = Pin<Box<dyn Future<Output = T> + 'a>>;

/// Wrapper for running a read-eval-loop
///
/// This struct declares a function type for running a read-eval-loop. An
/// implementation of this function type should be provided and stored in the
/// environment's [`any`](Env::any) storage so that it can be used by modules
/// depending on read-eval-loop execution.
///
/// The function takes two arguments. The first argument is a mutable reference
/// to an environment wrapped in a [`RefCell`]. The second argument is a
/// [configuration](crate::parser::Config) for the parser, which contains the
/// [input function](crate::input::Input) and source information. The
/// configuration will be used by the function to create a lexer for reading
/// commands.
///
/// Note that the `RefCell` is passed as a shared reference. It can be shared
/// with the input function, allowing the input function to access and modify
/// the environment while reading commands. The input function must release
/// the borrow on the `RefCell` before returning control to the caller so that
/// the caller can borrow the `RefCell` mutably to execute commands read from
/// the parser.
///
/// The function returns a future which resolves to a [`Result`] when awaited.
/// The function should execute commands read from the lexer until the end of
/// input or a [`Divert`] is encountered.
///
/// The function should set [`Env::exit_status`] appropriately after the loop
/// ends. If the input contains no commands, the exit status should be set to
/// `ExitStatus(0)`.
///
/// The function should also
/// [update subshell statuses](Env::update_all_subshell_statuses) and handle
/// traps during the loop execution as specified in the shell semantics.
///
/// The most standard implementation of this function type is provided in the
/// [`yash-semantics` crate](https://crates.io/crates/yash-semantics):
///
/// ```
/// # use yash_env::Env;
/// # use yash_env::semantics::RunReadEvalLoop;
/// fn register_read_eval_loop<S: yash_semantics::Runtime + 'static>(env: &mut Env<S>) {
///     env.any.insert(Box::new(RunReadEvalLoop::<S>(|env, config| {
///         Box::pin(async move {
///             yash_semantics::read_eval_loop(env, &mut config.into()).await
///         })
///     })));
/// }
/// # register_read_eval_loop(&mut Env::new_virtual());
/// ```
pub struct RunReadEvalLoop<S>(
    pub for<'a> fn(&'a RefCell<&mut Env<S>>, crate::parser::Config<'a>) -> PinFuture<'a, Result>,
);

// Not derived automatically because S may not implement Clone, Copy, or Debug
impl<S> Clone for RunReadEvalLoop<S> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<S> Copy for RunReadEvalLoop<S> {}

impl<S> std::fmt::Debug for RunReadEvalLoop<S> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_tuple("RunReadEvalLoop").field(&self.0).finish()
    }
}

pub mod command;
pub mod expansion;

/// Terminates the current process with the given exit status, possibly sending
/// a signal to kill the process.
///
/// If the exit status represents a signal that killed the last executed
/// command, this function sends the signal to the current process to propagate
/// the termination status to the parent process. Otherwise, this function
/// terminates the process with the given exit status.
pub async fn exit_or_raise<S>(system: &S, exit_status: ExitStatus) -> !
where
    S: Signals + Sigmask + Sigaction + SendSignal + SetRlimit + Exit + ?Sized,
{
    async fn maybe_raise<S>(system: &S, exit_status: ExitStatus) -> crate::system::Result<()>
    where
        S: Signals + Sigmask + Sigaction + SendSignal + SetRlimit + ?Sized,
    {
        let Some(signal) = exit_status.to_signal(system, /* exact */ true) else {
            return Ok(());
        };

        let Ok(name) = signal.0.parse() else {
            return Ok(());
        };
        if !matches!(SignalEffect::of(name), SignalEffect::Terminate { .. }) {
            return Ok(());
        }

        // Disable core dump
        system.setrlimit(Resource::CORE, LimitPair { soft: 0, hard: 0 })?;

        if signal.1 != S::SIGKILL {
            // Reset signal disposition
            system.sigaction(signal.1, Disposition::Default)?;
        }

        // Unblock the signal
        system.sigmask(Some((SigmaskOp::Remove, &[signal.1])), None)?;

        // Send the signal to the current process
        system.raise(signal.1).await?;

        Ok(())
    }

    maybe_raise(system, exit_status).await.ok();
    match system.exit(exit_status).await {}
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::system::r#virtual::VirtualSystem;
    use crate::system::r#virtual::{SIGINT, SIGTERM};

    #[test]
    fn exit_status_to_signal() {
        let system = VirtualSystem::new();

        assert_eq!(ExitStatus(0).to_signal(&system, false), None);
        assert_eq!(ExitStatus(0).to_signal(&system, true), None);

        assert_eq!(
            ExitStatus(SIGINT.as_raw()).to_signal(&system, false),
            Some(("INT".into(), SIGINT))
        );
        assert_eq!(ExitStatus(SIGINT.as_raw()).to_signal(&system, true), None);

        assert_eq!(
            ExitStatus(SIGINT.as_raw() + 0x80).to_signal(&system, false),
            Some(("INT".into(), SIGINT))
        );
        assert_eq!(
            ExitStatus(SIGINT.as_raw() + 0x80).to_signal(&system, true),
            None
        );

        assert_eq!(
            ExitStatus(SIGINT.as_raw() + 0x180).to_signal(&system, false),
            Some(("INT".into(), SIGINT))
        );
        assert_eq!(
            ExitStatus(SIGINT.as_raw() + 0x180).to_signal(&system, true),
            Some(("INT".into(), SIGINT))
        );

        assert_eq!(
            ExitStatus(SIGTERM.as_raw() + 0x180).to_signal(&system, false),
            Some(("TERM".into(), SIGTERM))
        );
        assert_eq!(
            ExitStatus(SIGTERM.as_raw() + 0x180).to_signal(&system, true),
            Some(("TERM".into(), SIGTERM))
        );
    }
}