nushell/crates/nu-protocol/src/engine/engine_state.rs

use fancy_regex::Regex;
use lru::LruCache;

use super::{usage::build_usage, usage::Usage, StateDelta};
use super::{Command, EnvVars, OverlayFrame, ScopeFrame, Stack, Visibility, DEFAULT_OVERLAY_NAME};
use crate::ast::Block;
use crate::debugger::{Debugger, NoopDebugger};
use crate::{
    BlockId, Config, DeclId, Example, FileId, HistoryConfig, Module, ModuleId, OverlayId,
    ShellError, Signature, Span, Type, VarId, Variable, VirtualPathId,
};
use crate::{Category, Value};
use std::borrow::Borrow;
use std::collections::HashMap;
use std::num::NonZeroUsize;
use std::path::Path;
use std::path::PathBuf;
use std::sync::atomic::Ordering;
use std::sync::{
    atomic::{AtomicBool, AtomicU32},
    Arc, Mutex, MutexGuard, PoisonError,
};

type PoisonDebuggerError<'a> = PoisonError<MutexGuard<'a, Box<dyn Debugger>>>;

pub static PWD_ENV: &str = "PWD";

#[derive(Clone, Debug)]
pub enum VirtualPath {
    File(FileId),
    Dir(Vec<VirtualPathId>),
}

pub struct ReplState {
    pub buffer: String,
    // A byte position, as `EditCommand::MoveToPosition` is also a byte position
    pub cursor_pos: usize,
}

pub struct IsDebugging(AtomicBool);

impl IsDebugging {
    pub fn new(val: bool) -> Self {
        IsDebugging(AtomicBool::new(val))
    }
}

impl Clone for IsDebugging {
    fn clone(&self) -> Self {
        IsDebugging(AtomicBool::new(self.0.load(Ordering::Relaxed)))
    }
}

/// The core global engine state. This includes all global definitions as well as any global state that
/// will persist for the whole session.
///
/// Declarations, variables, blocks, and other forms of data are held in the global state and referenced
/// elsewhere using their IDs. These IDs are simply their index into the global state. This allows us to
/// more easily handle creating blocks, binding variables and callsites, and more, because each of these
/// will refer to the corresponding IDs rather than their definitions directly. At runtime, this means
/// less copying and smaller structures.
///
/// Note that the runtime stack is not part of this global state. Runtime stacks are handled differently,
/// but they also rely on using IDs rather than full definitions.
///
/// A note on implementation:
///
/// Much of the global definitions are built on the Bodil's 'im' crate. This gives us a way of working with
/// lists of definitions in a way that is very cheap to access, while also allowing us to update them at
/// key points in time (often, the transition between parsing and evaluation).
///
/// Over the last two years we tried a few different approaches to global state like this. I'll list them
/// here for posterity, so we can more easily know how we got here:
///
/// * `Rc` - Rc is cheap, but not thread-safe. The moment we wanted to work with external processes, we
/// needed a way send to stdin/stdout. In Rust, the current practice is to spawn a thread to handle both.
/// These threads would need access to the global state, as they'll need to process data as it streams out
/// of the data pipeline. Because Rc isn't thread-safe, this breaks.
///
/// * `Arc` - Arc is the thread-safe version of the above. Often Arc is used in combination with a Mutex or
/// RwLock, but you can use Arc by itself. We did this a few places in the original Nushell. This *can* work
/// but because of Arc's nature of not allowing mutation if there's a second copy of the Arc around, this
/// ultimately becomes limiting.
///
/// * `Arc` + `Mutex/RwLock` - the standard practice for thread-safe containers. Unfortunately, this would
/// have meant we would incur a lock penalty every time we needed to access any declaration or block. As we
/// would be reading far more often than writing, it made sense to explore solutions that favor large amounts
/// of reads.
///
/// * `im` - the `im` crate was ultimately chosen because it has some very nice properties: it gives the
/// ability to cheaply clone these structures, which is nice as EngineState may need to be cloned a fair bit
/// to follow ownership rules for closures and iterators. It also is cheap to access. Favoring reads here fits
/// more closely to what we need with Nushell. And, of course, it's still thread-safe, so we get the same
/// benefits as above.
///
#[derive(Clone)]
pub struct EngineState {
    files: Vec<(String, usize, usize)>,
    file_contents: Vec<(Vec<u8>, usize, usize)>,
    pub(super) virtual_paths: Vec<(String, VirtualPath)>,
    vars: Vec<Variable>,
    decls: Vec<Box<dyn Command + 'static>>,
    pub(super) blocks: Vec<Block>,
    pub(super) modules: Vec<Module>,
    usage: Usage,
    pub scope: ScopeFrame,
    pub ctrlc: Option<Arc<AtomicBool>>,
    pub env_vars: EnvVars,
    pub previous_env_vars: HashMap<String, Value>,
    pub config: Config,
    pub pipeline_externals_state: Arc<(AtomicU32, AtomicU32)>,
    pub repl_state: Arc<Mutex<ReplState>>,
    pub table_decl_id: Option<usize>,
    #[cfg(feature = "plugin")]
    pub plugin_signatures: Option<PathBuf>,
    config_path: HashMap<String, PathBuf>,
    pub history_enabled: bool,
    pub history_session_id: i64,
    // If Nushell was started, e.g., with `nu spam.nu`, the file's parent is stored here
    pub(super) currently_parsed_cwd: Option<PathBuf>,
    pub regex_cache: Arc<Mutex<LruCache<String, Regex>>>,
    pub is_interactive: bool,
    pub is_login: bool,
    startup_time: i64,
    is_debugging: IsDebugging,
    pub debugger: Arc<Mutex<Box<dyn Debugger>>>,
}

// The max number of compiled regexes to keep around in a LRU cache, arbitrarily chosen
const REGEX_CACHE_SIZE: usize = 100; // must be nonzero, otherwise will panic

pub const NU_VARIABLE_ID: usize = 0;
pub const IN_VARIABLE_ID: usize = 1;
pub const ENV_VARIABLE_ID: usize = 2;
// NOTE: If you add more to this list, make sure to update the > checks based on the last in the list

impl EngineState {
    pub fn new() -> Self {
        Self {
            files: vec![],
            file_contents: vec![],
            virtual_paths: vec![],
            vars: vec![
                Variable::new(Span::new(0, 0), Type::Any, false),
                Variable::new(Span::new(0, 0), Type::Any, false),
                Variable::new(Span::new(0, 0), Type::Any, false),
                Variable::new(Span::new(0, 0), Type::Any, false),
                Variable::new(Span::new(0, 0), Type::Any, false),
            ],
            decls: vec![],
            blocks: vec![],
            modules: vec![Module::new(DEFAULT_OVERLAY_NAME.as_bytes().to_vec())],
            usage: Usage::new(),
            // make sure we have some default overlay:
            scope: ScopeFrame::with_empty_overlay(
                DEFAULT_OVERLAY_NAME.as_bytes().to_vec(),
                0,
                false,
            ),
            ctrlc: None,
            env_vars: [(DEFAULT_OVERLAY_NAME.to_string(), HashMap::new())]
                .into_iter()
                .collect(),
            previous_env_vars: HashMap::new(),
            config: Config::default(),
            pipeline_externals_state: Arc::new((AtomicU32::new(0), AtomicU32::new(0))),
            repl_state: Arc::new(Mutex::new(ReplState {
                buffer: "".to_string(),
                cursor_pos: 0,
            })),
            table_decl_id: None,
            #[cfg(feature = "plugin")]
            plugin_signatures: None,
            config_path: HashMap::new(),
            history_enabled: true,
            history_session_id: 0,
            currently_parsed_cwd: None,
            regex_cache: Arc::new(Mutex::new(LruCache::new(
                NonZeroUsize::new(REGEX_CACHE_SIZE).expect("tried to create cache of size zero"),
            ))),
            is_interactive: false,
            is_login: false,
            startup_time: -1,
            is_debugging: IsDebugging::new(false),
            debugger: Arc::new(Mutex::new(Box::new(NoopDebugger))),
        }
    }

    /// Merges a `StateDelta` onto the current state. These deltas come from a system, like the parser, that
    /// creates a new set of definitions and visible symbols in the current scope. We make this transactional
    /// as there are times when we want to run the parser and immediately throw away the results (namely:
    /// syntax highlighting and completions).
    ///
    /// When we want to preserve what the parser has created, we can take its output (the `StateDelta`) and
    /// use this function to merge it into the global state.
    pub fn merge_delta(&mut self, mut delta: StateDelta) -> Result<(), ShellError> {
        // Take the mutable reference and extend the permanent state from the working set
        self.files.extend(delta.files);
        self.file_contents.extend(delta.file_contents);
        self.virtual_paths.extend(delta.virtual_paths);
        self.decls.extend(delta.decls);
        self.vars.extend(delta.vars);
        self.blocks.extend(delta.blocks);
        self.modules.extend(delta.modules);
        self.usage.merge_with(delta.usage);

        let first = delta.scope.remove(0);

        for (delta_name, delta_overlay) in first.clone().overlays {
            if let Some((_, existing_overlay)) = self
                .scope
                .overlays
                .iter_mut()
                .find(|(name, _)| name == &delta_name)
            {
                // Updating existing overlay
                for item in delta_overlay.decls.into_iter() {
                    existing_overlay.decls.insert(item.0, item.1);
                }
                for item in delta_overlay.vars.into_iter() {
                    existing_overlay.vars.insert(item.0, item.1);
                }
                for item in delta_overlay.modules.into_iter() {
                    existing_overlay.modules.insert(item.0, item.1);
                }

                existing_overlay
                    .visibility
                    .merge_with(delta_overlay.visibility);
            } else {
                // New overlay was added to the delta
                self.scope.overlays.push((delta_name, delta_overlay));
            }
        }

        let mut activated_ids = self.translate_overlay_ids(&first);

        let mut removed_ids = vec![];

        for name in &first.removed_overlays {
            if let Some(overlay_id) = self.find_overlay(name) {
                removed_ids.push(overlay_id);
            }
        }

        // Remove overlays removed in delta
        self.scope
            .active_overlays
            .retain(|id| !removed_ids.contains(id));

        // Move overlays activated in the delta to be first
        self.scope
            .active_overlays
            .retain(|id| !activated_ids.contains(id));
        self.scope.active_overlays.append(&mut activated_ids);

        #[cfg(feature = "plugin")]
        if delta.plugins_changed {
            let result = self.update_plugin_file();

            if result.is_ok() {
                delta.plugins_changed = false;
            }

            return result;
        }

        Ok(())
    }

    /// Merge the environment from the runtime Stack into the engine state
    pub fn merge_env(
        &mut self,
        stack: &mut Stack,
        cwd: impl AsRef<Path>,
    ) -> Result<(), ShellError> {
        for mut scope in stack.env_vars.drain(..) {
            for (overlay_name, mut env) in scope.drain() {
                if let Some(env_vars) = self.env_vars.get_mut(&overlay_name) {
                    // Updating existing overlay
                    for (k, v) in env.drain() {
                        if k == "config" {
                            // Don't insert the record as the "config" env var as-is.
                            // Instead, mutate a clone of it with into_config(), and put THAT in env_vars.
                            let mut new_record = v.clone();
                            let (config, error) = new_record.into_config(&self.config);
                            self.config = config;
                            env_vars.insert(k, new_record);
                            if let Some(e) = error {
                                return Err(e);
                            }
                        } else {
                            env_vars.insert(k, v);
                        }
                    }
                } else {
                    // Pushing a new overlay
                    self.env_vars.insert(overlay_name, env);
                }
            }
        }

        // TODO: better error
        std::env::set_current_dir(cwd)?;

        Ok(())
    }

    /// Mark a starting point if it is a script (e.g., nu spam.nu)
    pub fn start_in_file(&mut self, file_path: Option<&str>) {
        self.currently_parsed_cwd = if let Some(path) = file_path {
            Path::new(path).parent().map(PathBuf::from)
        } else {
            None
        };
    }

    pub fn has_overlay(&self, name: &[u8]) -> bool {
        self.scope
            .overlays
            .iter()
            .any(|(overlay_name, _)| name == overlay_name)
    }

    pub fn active_overlay_ids<'a, 'b>(
        &'b self,
        removed_overlays: &'a [Vec<u8>],
    ) -> impl DoubleEndedIterator<Item = &OverlayId> + 'a
    where
        'b: 'a,
    {
        self.scope.active_overlays.iter().filter(|id| {
            !removed_overlays
                .iter()
                .any(|name| name == self.get_overlay_name(**id))
        })
    }

    pub fn active_overlays<'a, 'b>(
        &'b self,
        removed_overlays: &'a [Vec<u8>],
    ) -> impl DoubleEndedIterator<Item = &OverlayFrame> + 'a
    where
        'b: 'a,
    {
        self.active_overlay_ids(removed_overlays)
            .map(|id| self.get_overlay(*id))
    }

    pub fn active_overlay_names<'a, 'b>(
        &'b self,
        removed_overlays: &'a [Vec<u8>],
    ) -> impl DoubleEndedIterator<Item = &[u8]> + 'a
    where
        'b: 'a,
    {
        self.active_overlay_ids(removed_overlays)
            .map(|id| self.get_overlay_name(*id))
    }

    /// Translate overlay IDs from other to IDs in self
    pub fn translate_overlay_ids(&self, other: &ScopeFrame) -> Vec<OverlayId> {
        let other_names = other.active_overlays.iter().map(|other_id| {
            &other
                .overlays
                .get(*other_id)
                .expect("internal error: missing overlay")
                .0
        });

        other_names
            .map(|other_name| {
                self.find_overlay(other_name)
                    .expect("internal error: missing overlay")
            })
            .collect()
    }

    pub fn last_overlay_name(&self, removed_overlays: &[Vec<u8>]) -> &[u8] {
        self.active_overlay_names(removed_overlays)
            .last()
            .expect("internal error: no active overlays")
    }

    pub fn last_overlay(&self, removed_overlays: &[Vec<u8>]) -> &OverlayFrame {
        self.active_overlay_ids(removed_overlays)
            .last()
            .map(|id| self.get_overlay(*id))
            .expect("internal error: no active overlays")
    }

    pub fn get_overlay_name(&self, overlay_id: OverlayId) -> &[u8] {
        &self
            .scope
            .overlays
            .get(overlay_id)
            .expect("internal error: missing overlay")
            .0
    }

    pub fn get_overlay(&self, overlay_id: OverlayId) -> &OverlayFrame {
        &self
            .scope
            .overlays
            .get(overlay_id)
            .expect("internal error: missing overlay")
            .1
    }

    pub fn render_env_vars(&self) -> HashMap<&String, &Value> {
        let mut result = HashMap::new();

        for overlay_name in self.active_overlay_names(&[]) {
            let name = String::from_utf8_lossy(overlay_name);
            if let Some(env_vars) = self.env_vars.get(name.as_ref()) {
                result.extend(env_vars);
            }
        }

        result
    }

    pub fn add_env_var(&mut self, name: String, val: Value) {
        let overlay_name = String::from_utf8_lossy(self.last_overlay_name(&[])).to_string();

        if let Some(env_vars) = self.env_vars.get_mut(&overlay_name) {
            env_vars.insert(name, val);
        } else {
            self.env_vars
                .insert(overlay_name, [(name, val)].into_iter().collect());
        }
    }

    pub fn get_env_var(&self, name: &str) -> Option<&Value> {
        for overlay_id in self.scope.active_overlays.iter().rev() {
            let overlay_name = String::from_utf8_lossy(self.get_overlay_name(*overlay_id));
            if let Some(env_vars) = self.env_vars.get(overlay_name.as_ref()) {
                if let Some(val) = env_vars.get(name) {
                    return Some(val);
                }
            }
        }

        None
    }

    // Get the path environment variable in a platform agnostic way
    pub fn get_path_env_var(&self) -> Option<&Value> {
        let env_path_name_windows: &str = "Path";
        let env_path_name_nix: &str = "PATH";

        for overlay_id in self.scope.active_overlays.iter().rev() {
            let overlay_name = String::from_utf8_lossy(self.get_overlay_name(*overlay_id));
            if let Some(env_vars) = self.env_vars.get(overlay_name.as_ref()) {
                if let Some(val) = env_vars.get(env_path_name_nix) {
                    return Some(val);
                } else if let Some(val) = env_vars.get(env_path_name_windows) {
                    return Some(val);
                } else {
                    return None;
                }
            }
        }

        None
    }

    #[cfg(feature = "plugin")]
    pub fn update_plugin_file(&self) -> Result<(), ShellError> {
        use std::io::Write;

        use crate::{PluginExample, PluginSignature};

        // Updating the signatures plugin file with the added signatures
        self.plugin_signatures
            .as_ref()
            .ok_or_else(|| ShellError::PluginFailedToLoad {
                msg: "Plugin file not found".into(),
            })
            .and_then(|plugin_path| {
                // Always create the file, which will erase previous signatures
                std::fs::File::create(plugin_path.as_path()).map_err(|err| {
                    ShellError::PluginFailedToLoad {
                        msg: err.to_string(),
                    }
                })
            })
            .and_then(|mut plugin_file| {
                // Plugin definitions with parsed signature
                self.plugin_decls().try_for_each(|decl| {
                    // A successful plugin registration already includes the plugin filename
                    // No need to check the None option
                    let (path, shell) = decl.is_plugin().expect("plugin should have file name");
                    let mut file_name = path
                        .to_str()
                        .expect("path was checked during registration as a str")
                        .to_string();

                    // Fix files or folders with quotes
                    if file_name.contains('\'')
                        || file_name.contains('"')
                        || file_name.contains(' ')
                    {
                        file_name = format!("`{file_name}`");
                    }

                    let sig = decl.signature();
                    let examples = decl
                        .examples()
                        .into_iter()
                        .map(|eg| PluginExample {
                            example: eg.example.into(),
                            description: eg.description.into(),
                            result: eg.result,
                        })
                        .collect();
                    let sig_with_examples = PluginSignature::new(sig, examples);
                    serde_json::to_string_pretty(&sig_with_examples)
                        .map(|signature| {
                            // Extracting the possible path to the shell used to load the plugin
                            let shell_str = shell
                                .as_ref()
                                .map(|path| {
                                    format!(
                                        "-s {}",
                                        path.to_str().expect(
                                            "shell path was checked during registration as a str"
                                        )
                                    )
                                })
                                .unwrap_or_default();

                            // Each signature is stored in the plugin file with the shell and signature
                            // This information will be used when loading the plugin
                            // information when nushell starts
                            format!("register {file_name} {shell_str} {signature}\n\n")
                        })
                        .map_err(|err| ShellError::PluginFailedToLoad {
                            msg: err.to_string(),
                        })
                        .and_then(|line| {
                            plugin_file.write_all(line.as_bytes()).map_err(|err| {
                                ShellError::PluginFailedToLoad {
                                    msg: err.to_string(),
                                }
                            })
                        })
                        .and_then(|_| {
                            plugin_file.flush().map_err(|err| ShellError::GenericError {
                                error: "Error flushing plugin file".into(),
                                msg: format! {"{err}"},
                                span: None,
                                help: None,
                                inner: vec![],
                            })
                        })
                })
            })
    }

    pub fn num_files(&self) -> usize {
        self.files.len()
    }

    pub fn num_virtual_paths(&self) -> usize {
        self.virtual_paths.len()
    }

    pub fn num_vars(&self) -> usize {
        self.vars.len()
    }

    pub fn num_decls(&self) -> usize {
        self.decls.len()
    }

    pub fn num_blocks(&self) -> usize {
        self.blocks.len()
    }

    pub fn num_modules(&self) -> usize {
        self.modules.len()
    }

    pub fn print_vars(&self) {
        for var in self.vars.iter().enumerate() {
            println!("var{}: {:?}", var.0, var.1);
        }
    }

    pub fn print_decls(&self) {
        for decl in self.decls.iter().enumerate() {
            println!("decl{}: {:?}", decl.0, decl.1.signature());
        }
    }

    pub fn print_blocks(&self) {
        for block in self.blocks.iter().enumerate() {
            println!("block{}: {:?}", block.0, block.1);
        }
    }

    pub fn print_contents(&self) {
        for (contents, _, _) in self.file_contents.iter() {
            let string = String::from_utf8_lossy(contents);
            println!("{string}");
        }
    }

    pub fn find_decl(&self, name: &[u8], removed_overlays: &[Vec<u8>]) -> Option<DeclId> {
        let mut visibility: Visibility = Visibility::new();

        for overlay_frame in self.active_overlays(removed_overlays).rev() {
            visibility.append(&overlay_frame.visibility);

            if let Some(decl_id) = overlay_frame.get_decl(name) {
                if visibility.is_decl_id_visible(&decl_id) {
                    return Some(decl_id);
                }
            }
        }

        None
    }

    pub fn find_decl_name(&self, decl_id: DeclId, removed_overlays: &[Vec<u8>]) -> Option<&[u8]> {
        let mut visibility: Visibility = Visibility::new();

        for overlay_frame in self.active_overlays(removed_overlays).rev() {
            visibility.append(&overlay_frame.visibility);

            if visibility.is_decl_id_visible(&decl_id) {
                for (name, id) in overlay_frame.decls.iter() {
                    if id == &decl_id {
                        return Some(name);
                    }
                }
            }
        }

        None
    }

    pub fn get_module_comments(&self, module_id: ModuleId) -> Option<&[Span]> {
        self.usage.get_module_comments(module_id)
    }

    #[cfg(feature = "plugin")]
    pub fn plugin_decls(&self) -> impl Iterator<Item = &Box<dyn Command + 'static>> {
        let mut unique_plugin_decls = HashMap::new();

        // Make sure there are no duplicate decls: Newer one overwrites the older one
        for decl in self.decls.iter().filter(|d| d.is_plugin().is_some()) {
            unique_plugin_decls.insert(decl.name(), decl);
        }

        let mut plugin_decls: Vec<(&str, &Box<dyn Command>)> =
            unique_plugin_decls.into_iter().collect();

        // Sort the plugins by name so we don't end up with a random plugin file each time
        plugin_decls.sort_by(|a, b| a.0.cmp(b.0));
        plugin_decls.into_iter().map(|(_, decl)| decl)
    }

    pub fn find_module(&self, name: &[u8], removed_overlays: &[Vec<u8>]) -> Option<ModuleId> {
        for overlay_frame in self.active_overlays(removed_overlays).rev() {
            if let Some(module_id) = overlay_frame.modules.get(name) {
                return Some(*module_id);
            }
        }

        None
    }

    pub fn which_module_has_decl(
        &self,
        decl_name: &[u8],
        removed_overlays: &[Vec<u8>],
    ) -> Option<&[u8]> {
        for overlay_frame in self.active_overlays(removed_overlays).rev() {
            for (module_name, module_id) in overlay_frame.modules.iter() {
                let module = self.get_module(*module_id);
                if module.has_decl(decl_name) {
                    return Some(module_name);
                }
            }
        }

        None
    }

    pub fn find_overlay(&self, name: &[u8]) -> Option<OverlayId> {
        self.scope.find_overlay(name)
    }

    pub fn find_active_overlay(&self, name: &[u8]) -> Option<OverlayId> {
        self.scope.find_active_overlay(name)
    }

    pub fn find_commands_by_predicate(
        &self,
        predicate: impl Fn(&[u8]) -> bool,
        ignore_deprecated: bool,
    ) -> Vec<(Vec<u8>, Option<String>)> {
        let mut output = vec![];

        for overlay_frame in self.active_overlays(&[]).rev() {
            for decl in &overlay_frame.decls {
                if overlay_frame.visibility.is_decl_id_visible(decl.1) && predicate(decl.0) {
                    let command = self.get_decl(*decl.1);
                    if ignore_deprecated && command.signature().category == Category::Removed {
                        continue;
                    }
                    output.push((decl.0.clone(), Some(command.usage().to_string())));
                }
            }
        }

        output
    }

    pub fn get_span_contents(&self, span: Span) -> &[u8] {
        for (contents, start, finish) in &self.file_contents {
            if span.start >= *start && span.end <= *finish {
                return &contents[(span.start - start)..(span.end - start)];
            }
        }
        &[0u8; 0]
    }

    pub fn get_config(&self) -> &Config {
        &self.config
    }

    pub fn set_config(&mut self, conf: Config) {
        self.config = conf;
    }

    /// Fetch the configuration for a plugin
    ///
    /// The `plugin` must match the registered name of a plugin.  For `register nu_plugin_example`
    /// the plugin name to use will be `"example"`
    pub fn get_plugin_config(&self, plugin: &str) -> Option<&Value> {
        self.config.plugins.get(plugin)
    }

    /// Returns the configuration settings for command history or `None` if history is disabled
    pub fn history_config(&self) -> Option<HistoryConfig> {
        if self.history_enabled {
            Some(self.config.history)
        } else {
            None
        }
    }

    pub fn get_var(&self, var_id: VarId) -> &Variable {
        self.vars
            .get(var_id)
            .expect("internal error: missing variable")
    }

    pub fn get_constant(&self, var_id: VarId) -> Option<&Value> {
        let var = self.get_var(var_id);
        var.const_val.as_ref()
    }

    pub fn set_variable_const_val(&mut self, var_id: VarId, val: Value) {
        self.vars[var_id].const_val = Some(val);
    }

    #[allow(clippy::borrowed_box)]
    pub fn get_decl(&self, decl_id: DeclId) -> &Box<dyn Command> {
        self.decls
            .get(decl_id)
            .expect("internal error: missing declaration")
    }

    /// Get all commands within scope, sorted by the commands' names
    pub fn get_decls_sorted(
        &self,
        include_hidden: bool,
    ) -> impl Iterator<Item = (Vec<u8>, DeclId)> {
        let mut decls_map = HashMap::new();

        for overlay_frame in self.active_overlays(&[]) {
            let new_decls = if include_hidden {
                overlay_frame.decls.clone()
            } else {
                overlay_frame
                    .decls
                    .clone()
                    .into_iter()
                    .filter(|(_, id)| overlay_frame.visibility.is_decl_id_visible(id))
                    .collect()
            };

            decls_map.extend(new_decls);
        }

        let mut decls: Vec<(Vec<u8>, DeclId)> = decls_map.into_iter().collect();

        decls.sort_by(|a, b| a.0.cmp(&b.0));
        decls.into_iter()
    }

    #[allow(clippy::borrowed_box)]
    pub fn get_signature(&self, decl: &Box<dyn Command>) -> Signature {
        if let Some(block_id) = decl.get_block_id() {
            *self.blocks[block_id].signature.clone()
        } else {
            decl.signature()
        }
    }

    /// Get signatures of all commands within scope.
    pub fn get_signatures(&self, include_hidden: bool) -> Vec<Signature> {
        self.get_decls_sorted(include_hidden)
            .map(|(_, id)| {
                let decl = self.get_decl(id);

                self.get_signature(decl).update_from_command(decl.borrow())
            })
            .collect()
    }

    /// Get signatures of all commands within scope.
    ///
    /// In addition to signatures, it returns whether each command is:
    ///     a) a plugin
    ///     b) custom
    pub fn get_signatures_with_examples(
        &self,
        include_hidden: bool,
    ) -> Vec<(Signature, Vec<Example>, bool, bool, bool)> {
        self.get_decls_sorted(include_hidden)
            .map(|(_, id)| {
                let decl = self.get_decl(id);

                let signature = self.get_signature(decl).update_from_command(decl.borrow());

                (
                    signature,
                    decl.examples(),
                    decl.is_plugin().is_some(),
                    decl.get_block_id().is_some(),
                    decl.is_parser_keyword(),
                )
            })
            .collect()
    }

    pub fn get_block(&self, block_id: BlockId) -> &Block {
        self.blocks
            .get(block_id)
            .expect("internal error: missing block")
    }

    /// Optionally get a block by id, if it exists
    ///
    /// Prefer to use [`.get_block()`] in most cases - `BlockId`s that don't exist are normally a
    /// compiler error. This only exists to stop plugins from crashing the engine if they send us
    /// something invalid.
    pub fn try_get_block(&self, block_id: BlockId) -> Option<&Block> {
        self.blocks.get(block_id)
    }

    pub fn get_module(&self, module_id: ModuleId) -> &Module {
        self.modules
            .get(module_id)
            .expect("internal error: missing module")
    }

    pub fn get_virtual_path(&self, virtual_path_id: VirtualPathId) -> &(String, VirtualPath) {
        self.virtual_paths
            .get(virtual_path_id)
            .expect("internal error: missing virtual path")
    }

    pub fn next_span_start(&self) -> usize {
        if let Some((_, _, last)) = self.file_contents.last() {
            *last
        } else {
            0
        }
    }

    pub fn files(&self) -> impl Iterator<Item = &(String, usize, usize)> {
        self.files.iter()
    }

    pub fn add_file(&mut self, filename: String, contents: Vec<u8>) -> usize {
        let next_span_start = self.next_span_start();
        let next_span_end = next_span_start + contents.len();

        self.file_contents
            .push((contents, next_span_start, next_span_end));

        self.files.push((filename, next_span_start, next_span_end));

        self.num_files() - 1
    }

    pub fn get_cwd(&self) -> Option<String> {
        if let Some(pwd_value) = self.get_env_var(PWD_ENV) {
            pwd_value.coerce_string().ok()
        } else {
            None
        }
    }

    pub fn set_config_path(&mut self, key: &str, val: PathBuf) {
        self.config_path.insert(key.to_string(), val);
    }

    pub fn get_config_path(&self, key: &str) -> Option<&PathBuf> {
        self.config_path.get(key)
    }

    pub fn build_usage(&self, spans: &[Span]) -> (String, String) {
        let comment_lines: Vec<&[u8]> = spans
            .iter()
            .map(|span| self.get_span_contents(*span))
            .collect();
        build_usage(&comment_lines)
    }

    pub fn build_module_usage(&self, module_id: ModuleId) -> Option<(String, String)> {
        self.get_module_comments(module_id)
            .map(|comment_spans| self.build_usage(comment_spans))
    }

    pub fn current_work_dir(&self) -> String {
        self.get_env_var("PWD")
            .map(|d| d.coerce_string().unwrap_or_default())
            .unwrap_or_default()
    }

    pub fn get_file_contents(&self) -> &[(Vec<u8>, usize, usize)] {
        &self.file_contents
    }

    pub fn get_startup_time(&self) -> i64 {
        self.startup_time
    }

    pub fn set_startup_time(&mut self, startup_time: i64) {
        self.startup_time = startup_time;
    }

    pub fn activate_debugger(
        &self,
        debugger: Box<dyn Debugger>,
    ) -> Result<(), PoisonDebuggerError> {
        let mut locked_debugger = self.debugger.lock()?;
        *locked_debugger = debugger;
        locked_debugger.activate();
        self.is_debugging.0.store(true, Ordering::Relaxed);
        Ok(())
    }

    pub fn deactivate_debugger(&self) -> Result<Box<dyn Debugger>, PoisonDebuggerError> {
        let mut locked_debugger = self.debugger.lock()?;
        locked_debugger.deactivate();
        let ret = std::mem::replace(&mut *locked_debugger, Box::new(NoopDebugger));
        self.is_debugging.0.store(false, Ordering::Relaxed);
        Ok(ret)
    }

    pub fn is_debugging(&self) -> bool {
        self.is_debugging.0.load(Ordering::Relaxed)
    }

    pub fn recover_from_panic(&mut self) {
        if Mutex::is_poisoned(&self.repl_state) {
            self.repl_state = Arc::new(Mutex::new(ReplState {
                buffer: "".to_string(),
                cursor_pos: 0,
            }));
        }
        if Mutex::is_poisoned(&self.regex_cache) {
            self.regex_cache = Arc::new(Mutex::new(LruCache::new(
                NonZeroUsize::new(REGEX_CACHE_SIZE).expect("tried to create cache of size zero"),
            )));
        }
    }
}

impl Default for EngineState {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
mod engine_state_tests {
    use crate::engine::StateWorkingSet;
    use std::str::{from_utf8, Utf8Error};

    use super::*;

    #[test]
    fn add_file_gives_id() {
        let engine_state = EngineState::new();
        let mut engine_state = StateWorkingSet::new(&engine_state);
        let id = engine_state.add_file("test.nu".into(), &[]);

        assert_eq!(id, 0);
    }

    #[test]
    fn add_file_gives_id_including_parent() {
        let mut engine_state = EngineState::new();
        let parent_id = engine_state.add_file("test.nu".into(), vec![]);

        let mut working_set = StateWorkingSet::new(&engine_state);
        let working_set_id = working_set.add_file("child.nu".into(), &[]);

        assert_eq!(parent_id, 0);
        assert_eq!(working_set_id, 1);
    }

    #[test]
    fn merge_states() -> Result<(), ShellError> {
        let mut engine_state = EngineState::new();
        engine_state.add_file("test.nu".into(), vec![]);

        let delta = {
            let mut working_set = StateWorkingSet::new(&engine_state);
            let _ = working_set.add_file("child.nu".into(), &[]);
            working_set.render()
        };

        engine_state.merge_delta(delta)?;

        assert_eq!(engine_state.num_files(), 2);
        assert_eq!(&engine_state.files[0].0, "test.nu");
        assert_eq!(&engine_state.files[1].0, "child.nu");

        Ok(())
    }

    #[test]
    fn list_variables() -> Result<(), Utf8Error> {
        let varname = "something";
        let varname_with_sigil = "$".to_owned() + varname;
        let engine_state = EngineState::new();
        let mut working_set = StateWorkingSet::new(&engine_state);
        working_set.add_variable(
            varname.as_bytes().into(),
            Span { start: 0, end: 1 },
            Type::Int,
            false,
        );
        let variables = working_set
            .list_variables()
            .into_iter()
            .map(from_utf8)
            .collect::<Result<Vec<&str>, Utf8Error>>()?;
        assert_eq!(variables, vec![varname_with_sigil]);
        Ok(())
    }

    #[test]
    fn get_plugin_config() {
        let mut engine_state = EngineState::new();

        assert!(
            engine_state.get_plugin_config("example").is_none(),
            "Unexpected plugin configuration"
        );

        let mut plugins = HashMap::new();
        plugins.insert("example".into(), Value::string("value", Span::test_data()));

        let mut config = engine_state.get_config().clone();
        config.plugins = plugins;

        engine_state.set_config(config);

        assert!(
            engine_state.get_plugin_config("example").is_some(),
            "Plugin configuration not found"
        );
    }
}