tabnas/

lib.rs

// Copyright (c) 2013-2026 Richard Rodger, MIT License

#![doc = include_str!("../README.md")]
#![allow(clippy::result_large_err)]

pub const VERSION: &str = "0.12.10";

pub mod builtins;
pub mod context;
pub mod error;
pub mod grammar;
pub mod lexer;
mod merge;
pub mod options;
pub mod parser;
pub mod rule;
mod text;
pub mod token;
mod tracked;
use crate::tracked::Tracked;
pub mod utility;
pub mod value;

pub use context::{ActionError, Context, ContextSeed, InstanceInfo};
pub use error::{RecoveredAt, TabnasError};
pub use grammar::{
    GrammarError, GrammarGroups, GrammarSetting, GrammarSettingAlt, GrammarSettingRule, GrammarSpec,
};
pub use lexer::{Lexer, RelexCheckpoint};
pub use merge::MergeError;
pub use options::MAX_RULE_HISTORY;
pub use options::{
    BudgetCheck, BudgetOptions, ColorOptions, CommentDef, CommentSuffixMatcher, ConfigModifier,
    ContextParsePrepare, DebugOptions, DebugOutput, DebugPrintOptions, DebugSourceFormatter,
    ErrMsgOptions, ErrorSuffix, ErrorSuffixCallback, ErrorSuffixContext, FixedOptions, FixedToken,
    ImperativeCommentSuffixMatcher, ImperativeLexCheck, ImperativeLexMatcher,
    ImperativeTextModifier, InfoOptions, LexCheck, LexCheckResult, LexCheckToken, LexMatcher,
    LexMatcherCallback, LexMatcherFactory, ListOptions, MapMerge, MapOptions, MatchToken,
    MatchTokenCallback, MatchTokenMatcher, MatchTokenResult, MatchValue, Options, ParseOptions,
    ParsePrepare, ParsePrepareWithInstance, ParserOptions, ParserStart, ParserStartWithContext,
    ParserStartWithInstance, RecoverOptions, ResultOptions, RewindOptions, SafeOptions,
    SpaceOptions, TextModifier, ValueDef, ValueOptions, ValueTextModifier, ValueTransform,
};
pub use parser::{Continuations, ParseRecovery, Parser};
pub use rule::{
    ActionBinding, AltAction, AltActionBinding, AltBack, AltBackWithMatch, AltCondition,
    AltConditionWithLexer, AltConditionWithLexerAndMatch, AltConditionWithMatch, AltError,
    AltErrorWithMatch, AltMatch, AltModifier, AltModifierWithMatch, AltNext, AltNextWithMatch,
    AltSpec, CompareOp, Condition, Rule, RuleDone, RuleDoneAlt, RuleName, RuleSnapshot, RuleSpec,
    RuleState, StateAction,
};
pub use token::{
    name_to_tin, tin_name, Point, Site, Tin, Token, TokenCode, TokenText, TokenValFunc, TIN_AA,
    TIN_BD, TIN_CA, TIN_CB, TIN_CL, TIN_CM, TIN_CS, TIN_LN, TIN_MAX, TIN_NR, TIN_OB, TIN_OS,
    TIN_SP, TIN_ST, TIN_TX, TIN_UK, TIN_VL, TIN_ZZ,
};
pub use value::{ListRef, MapRef, Text, Value};

use indexmap::IndexMap;
use std::any::Any;
use std::collections::HashMap;
use std::fmt;
use std::panic::{catch_unwind, AssertUnwindSafe};
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::Arc;

static NEXT_INSTANCE_ID: AtomicU64 = AtomicU64::new(1);

type DecorationValue = dyn Any + Send + Sync;
type DecorationEquality = dyn Fn(&DecorationValue) -> bool + Send + Sync;

/// A type-erased value attached to a parser instance by a native plugin.
///
/// Equality-aware decorations created with [`Decoration::new`] can be
/// compared when instances merge. Opaque decorations compare by shared
/// allocation identity, which permits closures and other native handles to
/// be inherited without pretending they have value equality.
#[derive(Clone)]
pub struct Decoration {
    value: Arc<DecorationValue>,
    equals: Arc<DecorationEquality>,
    type_name: &'static str,
}

impl Decoration {
    pub fn new<T>(value: T) -> Self
    where
        T: Any + PartialEq + Send + Sync,
    {
        let value = Arc::new(value);
        let comparable = value.clone();
        Self {
            value,
            equals: Arc::new(move |other| {
                other
                    .downcast_ref::<T>()
                    .is_some_and(|other| comparable.as_ref() == other)
            }),
            type_name: std::any::type_name::<T>(),
        }
    }

    pub fn opaque<T>(value: T) -> Self
    where
        T: Any + Send + Sync,
    {
        let value = Arc::new(value);
        let identity = value.clone();
        Self {
            value,
            equals: Arc::new(move |other| {
                other
                    .downcast_ref::<T>()
                    .is_some_and(|other| std::ptr::eq(identity.as_ref(), other))
            }),
            type_name: std::any::type_name::<T>(),
        }
    }

    pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
        self.value.downcast_ref()
    }

    pub fn is<T: Any>(&self) -> bool {
        self.value.is::<T>()
    }

    pub fn type_name(&self) -> &'static str {
        self.type_name
    }

    pub(crate) fn equivalent(&self, other: &Self) -> bool {
        self.type_name == other.type_name && (self.equals)(other.value.as_ref())
    }
}

impl fmt::Debug for Decoration {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter
            .debug_struct("Decoration")
            .field("type_name", &self.type_name)
            .finish_non_exhaustive()
    }
}

pub type Action = Arc<dyn Fn(&mut Rule) + Send + Sync>;
pub type ContextAction =
    Arc<dyn Fn(&mut Rule, &mut Context) -> Result<(), ActionError> + Send + Sync>;
pub type TokenSubscriber = Arc<dyn Fn(&Token) + Send + Sync>;
pub type LexSubscriber = Arc<dyn Fn(&mut Token, &mut Rule, &mut Context) + Send + Sync>;
pub type RuleSubscriber = Arc<dyn Fn(&mut Rule, &mut Context) + Send + Sync>;
pub type RuleDoneSubscriber = Arc<dyn Fn(&Rule, &Context, &RuleDone) + Send + Sync>;
/// A check the parse loop runs at every step; see [`Tabnas::parse_guard`].
pub type ParseGuard = Arc<dyn Fn(&Context) -> bool + Send + Sync>;

pub type PluginCallback = Arc<dyn Fn(&mut Tabnas, &Value) -> Result<(), PluginError> + Send + Sync>;

/// Native Rust plugin descriptor. The explicit name replaces JavaScript's
/// `Function.name` and provides a stable namespace for plugin options.
#[derive(Clone)]
pub struct Plugin {
    pub name: String,
    pub defaults: Value,
    callback: PluginCallback,
}

impl Plugin {
    pub fn new(
        name: impl Into<String>,
        callback: impl Fn(&mut Tabnas, &Value) -> Result<(), PluginError> + Send + Sync + 'static,
    ) -> Self {
        Self {
            name: name.into(),
            defaults: Value::object(IndexMap::new()),
            callback: Arc::new(callback),
        }
    }

    pub fn with_defaults(mut self, defaults: Value) -> Self {
        self.defaults = defaults;
        self
    }
}

impl fmt::Debug for Plugin {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter
            .debug_struct("Plugin")
            .field("name", &self.name)
            .field("defaults", &self.defaults)
            .field("callback", &"<function>")
            .finish()
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct PluginError(pub String);

impl fmt::Display for PluginError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.write_str(&self.0)
    }
}

impl std::error::Error for PluginError {}

#[derive(Clone)]
pub struct Tabnas {
    pub id: String,
    /// Identifier of the instance this parser was derived from.
    pub parent_id: Option<String>,
    /// Resolved configuration used by the lexer and parser.
    ///
    /// Wrapped so that writing to it is noticed: the shared copy handed
    /// to each parse is built once and reused until something takes a
    /// mutable path to this. Reads and writes both work as they did.
    pub options: Tracked<Options>,
    /// The `options` a parse gets, prepared once. Cloning a thirty-field
    /// `Options` per `parse()` call was 7% of a small parse.
    prepared_options: PreparedOptions,
    /// The whole assembled `Parser`, prepared once. See `PreparedParser`.
    prepared_parser: PreparedParser,
    /// Accumulated option input before `config.modify` callbacks run. Keeping
    /// this separate prevents non-idempotent modifiers from compounding on
    /// each grammar overlay or derived instance.
    pub(crate) raw_options: Options,
    pub rules: Tracked<IndexMap<String, RuleSpec>>,
    pub actions: Tracked<HashMap<String, Action>>,
    pub context_actions: Tracked<HashMap<String, ContextAction>>,
    pub matched_actions: Tracked<HashMap<String, AltAction>>,
    pub state_actions: Tracked<HashMap<String, StateAction>>,
    pub token_subscribers: Tracked<Vec<TokenSubscriber>>,
    pub lex_subscribers: Tracked<Vec<LexSubscriber>>,
    pub rule_subscribers: Tracked<Vec<RuleSubscriber>>,
    pub rule_done_subscribers: Tracked<Vec<RuleDoneSubscriber>>,
    /// Checks the parse loop runs at every step, by name; see
    /// [`Tabnas::parse_guard`].
    pub parse_guards: Tracked<IndexMap<String, ParseGuard>>,
    pub plugins: Tracked<Vec<Plugin>>,
    pub plugin_options: IndexMap<String, Value>,
    /// Plugin-attached named values carried to derived instances.
    pub decorations: IndexMap<String, Decoration>,
    pub(crate) alt_conditions: HashMap<String, AltCondition>,
    pub(crate) alt_match_conditions: HashMap<String, AltConditionWithMatch>,
    pub(crate) alt_lexer_conditions: HashMap<String, AltConditionWithLexer>,
    pub(crate) alt_lexer_match_conditions: HashMap<String, AltConditionWithLexerAndMatch>,
    pub(crate) alt_modifiers: HashMap<String, AltModifier>,
    pub(crate) alt_match_modifiers: HashMap<String, AltModifierWithMatch>,
    pub(crate) alt_errors: HashMap<String, AltError>,
    pub(crate) alt_match_errors: HashMap<String, AltErrorWithMatch>,
    pub(crate) alt_pushes: HashMap<String, AltNext>,
    pub(crate) alt_match_pushes: HashMap<String, AltNextWithMatch>,
    pub(crate) alt_replaces: HashMap<String, AltNext>,
    pub(crate) alt_match_replaces: HashMap<String, AltNextWithMatch>,
    pub(crate) alt_backtracks: HashMap<String, AltBack>,
    pub(crate) alt_match_backtracks: HashMap<String, AltBackWithMatch>,
    pub(crate) match_token_refs: HashMap<String, (MatchTokenCallback, bool)>,
    pub(crate) value_transform_refs: HashMap<String, ValueTransform>,
    pub(crate) text_modifier_refs: HashMap<String, TextModifier>,
    pub(crate) lex_check_refs: HashMap<String, LexCheck>,
    pub(crate) comment_suffix_refs: HashMap<String, CommentSuffixMatcher>,
    pub(crate) match_value_refs: HashMap<String, MatchTokenCallback>,
    pub(crate) parse_prepare_refs: HashMap<String, ParsePrepare>,
    pub(crate) budget_check_refs: HashMap<String, BudgetCheck>,
    pub(crate) lex_match_refs: HashMap<String, LexMatcherCallback>,
    pub(crate) imperative_lex_match_refs: HashMap<String, ImperativeLexMatcher>,
    pub(crate) lex_match_factory_refs: HashMap<String, LexMatcherFactory>,
    pub(crate) error_suffix_refs: HashMap<String, ErrorSuffixCallback>,
    pub(crate) config_modifier_refs: HashMap<String, ConfigModifier>,
    pub(crate) parser_start_refs: HashMap<String, ParserStart>,
    pub(crate) parser_start_instance_refs: HashMap<String, ParserStartWithInstance>,
    pub(crate) parser_start_context_refs: HashMap<String, ParserStartWithContext>,
    pub(crate) map_merge_refs: HashMap<String, MapMerge>,
}

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

impl Tabnas {
    pub fn new() -> Self {
        Self::with_options(Options::default())
    }

    pub fn with_options(options: Options) -> Self {
        if let Err(error) = options.validate_comment_definitions() {
            panic!("invalid options: {error}");
        }
        let sequence = NEXT_INSTANCE_ID.fetch_add(1, Ordering::Relaxed);
        let id = format!(
            "Tabnas/{sequence}{}",
            if options.tag.is_empty() || options.tag == "-" {
                String::new()
            } else {
                format!("/{}", options.tag)
            }
        );
        let plugin_options = options.plugin.clone();
        let tabnas = Tabnas {
            id,
            parent_id: None,
            raw_options: options.clone(),
            options: Tracked::new(options),
            prepared_options: PreparedOptions::default(),
            prepared_parser: PreparedParser::default(),
            rules: Tracked::new(IndexMap::new()),
            actions: Tracked::new(HashMap::new()),
            context_actions: Tracked::new(HashMap::new()),
            matched_actions: Tracked::new(HashMap::new()),
            state_actions: Tracked::new(HashMap::new()),
            token_subscribers: Tracked::new(Vec::new()),
            lex_subscribers: Tracked::new(Vec::new()),
            rule_subscribers: Tracked::new(Vec::new()),
            rule_done_subscribers: Tracked::new(Vec::new()),
            parse_guards: Tracked::new(IndexMap::new()),
            plugins: Tracked::new(Vec::new()),
            plugin_options,
            decorations: IndexMap::new(),
            alt_conditions: HashMap::new(),
            alt_match_conditions: HashMap::new(),
            alt_lexer_conditions: HashMap::new(),
            alt_lexer_match_conditions: HashMap::new(),
            alt_modifiers: HashMap::new(),
            alt_match_modifiers: HashMap::new(),
            alt_errors: HashMap::new(),
            alt_match_errors: HashMap::new(),
            alt_pushes: HashMap::new(),
            alt_match_pushes: HashMap::new(),
            alt_replaces: HashMap::new(),
            alt_match_replaces: HashMap::new(),
            alt_backtracks: HashMap::new(),
            alt_match_backtracks: HashMap::new(),
            match_token_refs: HashMap::new(),
            value_transform_refs: HashMap::new(),
            text_modifier_refs: HashMap::new(),
            lex_check_refs: HashMap::new(),
            comment_suffix_refs: HashMap::new(),
            match_value_refs: HashMap::new(),
            parse_prepare_refs: HashMap::new(),
            budget_check_refs: HashMap::new(),
            lex_match_refs: HashMap::new(),
            imperative_lex_match_refs: HashMap::new(),
            lex_match_factory_refs: HashMap::new(),
            error_suffix_refs: HashMap::new(),
            config_modifier_refs: HashMap::new(),
            parser_start_refs: HashMap::new(),
            parser_start_instance_refs: HashMap::new(),
            parser_start_context_refs: HashMap::new(),
            map_merge_refs: HashMap::new(),
        };
        tabnas.emit_debug_config();
        tabnas
    }

    pub fn rule(&mut self, spec: RuleSpec) -> &mut Self {
        self.rules.insert(spec.name.clone(), spec);
        self
    }

    /// Create or modify a rule in place, mirroring the imperative plugin
    /// entry point in the TypeScript and Go engines.
    pub fn define_rule(
        &mut self,
        name: impl Into<String>,
        define: impl FnOnce(&mut RuleSpec),
    ) -> &mut Self {
        let name = name.into();
        let spec = self
            .rules
            .entry(name.clone())
            .or_insert_with(|| RuleSpec::new(name));
        define(spec);
        self
    }

    /// Create or modify a rule with a read-only parser snapshot. This is the
    /// Rust spelling of the canonical `RuleDefiner(rs, parser)` callback and
    /// gives a definer access to resolved options, tokens, and peer rules.
    pub fn define_rule_with_parser(
        &mut self,
        name: impl Into<String>,
        define: impl FnOnce(&mut RuleSpec, &Parser),
    ) -> &mut Self {
        let name = name.into();
        self.rules
            .entry(name.clone())
            .or_insert_with(|| RuleSpec::new(name.clone()));
        let parser = self.parser();
        let spec = self
            .rules
            .get_mut(&name)
            .expect("rule was inserted before its parser view was built");
        define(spec, &parser);
        self
    }

    /// Remove a named rule. Removing a rule that is absent is a no-op.
    pub fn remove_rule(&mut self, name: &str) -> Option<RuleSpec> {
        self.rules.shift_remove(name)
    }

    /// Apply and retain a native plugin. Defaults, previously accumulated
    /// options for the same plugin, and call-site options are deep-merged in
    /// that order. Panics are contained and returned as `PluginError`.
    pub fn use_plugin(
        &mut self,
        plugin: Plugin,
        options: Option<Value>,
    ) -> Result<&mut Self, PluginError> {
        let name = plugin.name.to_lowercase();
        if name.is_empty() {
            return Err(PluginError(
                "Tabnas::use_plugin: plugin name is empty".into(),
            ));
        }
        let current = self
            .plugin_options
            .get(&name)
            .cloned()
            .unwrap_or_else(|| Value::object(IndexMap::new()));
        let merged = merge_plugin_values(
            merge_plugin_values(current, plugin.defaults.clone()),
            options.unwrap_or(Value::Undefined),
        );
        self.plugin_options.insert(name.clone(), merged.clone());
        self.options.plugin.insert(name.clone(), merged.clone());
        self.raw_options.plugin.insert(name, merged.clone());
        self.plugins.push(plugin.clone());
        match catch_unwind(AssertUnwindSafe(|| (plugin.callback)(self, &merged))) {
            Ok(Ok(())) => Ok(self),
            Ok(Err(error)) => Err(error),
            Err(payload) => Err(PluginError(format!(
                "plugin {} panicked: {}",
                plugin.name,
                panic_message(payload)
            ))),
        }
    }

    /// Return the resolved option bag for a plugin name.
    pub fn plugin_options(&self, name: &str) -> Option<&Value> {
        self.plugin_options.get(&name.to_lowercase())
    }

    /// Deep-merge an option bag into the named plugin namespace.
    pub fn set_plugin_options(&mut self, name: impl Into<String>, options: Value) -> &mut Self {
        let name = name.into().to_lowercase();
        let current = self
            .plugin_options
            .get(&name)
            .cloned()
            .unwrap_or_else(|| Value::object(IndexMap::new()));
        let merged = merge_plugin_values(current, options);
        self.plugin_options.insert(name.clone(), merged.clone());
        self.options.plugin.insert(name.clone(), merged.clone());
        self.raw_options.plugin.insert(name, merged);
        self
    }

    /// Create a child parser from this instance's options and re-run its
    /// installed plugins so option-conditional grammar is rebuilt.
    pub fn derive(&self, modify: impl FnOnce(&mut Options)) -> Result<Self, PluginError> {
        let mut raw_options = if self.options.config_modify.is_empty() {
            // Direct typed option mutation is part of the native Rust API.
            // With no modifier-created delta, the public tree is the source.
            self.options.peek().clone()
        } else {
            self.raw_options.clone()
        };
        modify(&mut raw_options);
        let mut options = raw_options.clone();
        options.refresh_configuration().map_err(PluginError)?;
        let mut child = Self::with_options(options);
        child.parent_id = Some(self.id.clone());
        child.raw_options = raw_options;
        child.plugin_options = self.plugin_options.clone();
        child.decorations = self.decorations.clone();
        child.inherit_function_references(self);
        // The guards travel as the budget does, in the options above: a
        // plugin re-run below that installs one again under the same name
        // replaces it rather than adding a second.
        child.parse_guards = Tracked::new(self.parse_guards.peek().clone());
        for plugin in self.plugins.iter() {
            let options = child
                .plugin_options
                .get(&plugin.name.to_lowercase())
                .cloned();
            child.use_plugin(plugin.clone(), options)?;
        }
        Ok(child)
    }

    fn inherit_function_references(&mut self, parent: &Self) {
        // Rust binds serialized function names through an instance registry
        // rather than a JavaScript function-valued `GrammarSpec.ref` object.
        // A derived instance must retain that registry so later grammar
        // overlays can resolve the same names. Re-run plugins may replace an
        // entry with the same name, exactly as on the parent.
        self.actions = parent.actions.clone();
        self.context_actions = parent.context_actions.clone();
        self.matched_actions = parent.matched_actions.clone();
        self.state_actions = parent.state_actions.clone();
        self.alt_conditions = parent.alt_conditions.clone();
        self.alt_match_conditions = parent.alt_match_conditions.clone();
        self.alt_lexer_conditions = parent.alt_lexer_conditions.clone();
        self.alt_lexer_match_conditions = parent.alt_lexer_match_conditions.clone();
        self.alt_modifiers = parent.alt_modifiers.clone();
        self.alt_match_modifiers = parent.alt_match_modifiers.clone();
        self.alt_errors = parent.alt_errors.clone();
        self.alt_match_errors = parent.alt_match_errors.clone();
        self.alt_pushes = parent.alt_pushes.clone();
        self.alt_match_pushes = parent.alt_match_pushes.clone();
        self.alt_replaces = parent.alt_replaces.clone();
        self.alt_match_replaces = parent.alt_match_replaces.clone();
        self.alt_backtracks = parent.alt_backtracks.clone();
        self.alt_match_backtracks = parent.alt_match_backtracks.clone();
        self.match_token_refs = parent.match_token_refs.clone();
        self.value_transform_refs = parent.value_transform_refs.clone();
        self.text_modifier_refs = parent.text_modifier_refs.clone();
        self.lex_check_refs = parent.lex_check_refs.clone();
        self.comment_suffix_refs = parent.comment_suffix_refs.clone();
        self.match_value_refs = parent.match_value_refs.clone();
        self.parse_prepare_refs = parent.parse_prepare_refs.clone();
        self.budget_check_refs = parent.budget_check_refs.clone();
        self.lex_match_refs = parent.lex_match_refs.clone();
        self.imperative_lex_match_refs = parent.imperative_lex_match_refs.clone();
        self.lex_match_factory_refs = parent.lex_match_factory_refs.clone();
        self.error_suffix_refs = parent.error_suffix_refs.clone();
        self.config_modifier_refs = parent.config_modifier_refs.clone();
        self.parser_start_refs = parent.parser_start_refs.clone();
        self.parser_start_instance_refs = parent.parser_start_instance_refs.clone();
        self.parser_start_context_refs = parent.parser_start_context_refs.clone();
        self.map_merge_refs = parent.map_merge_refs.clone();
    }

    /// Combine two tagged parser instances without modifying either source.
    /// Options are conflict-checked against the shared defaults and rule
    /// alternates are interleaved deterministically in a fresh token space.
    pub fn merge(&self, other: &Self) -> Result<Self, MergeError> {
        merge::merge(self, other)
    }

    /// Create a fresh standalone instance. The receiver's rules, plugins,
    /// subscribers, callbacks, and custom token registrations are not copied.
    pub fn empty(&self) -> Self {
        Self::with_options(Options::empty())
    }

    /// `empty` with an explicit typed option set.
    pub fn empty_with_options(&self, options: Options) -> Self {
        Self::with_options(options)
    }

    /// Resolve or allocate a named token identity for typed matcher effects
    /// and imperative rule construction.
    pub fn token(&mut self, name: impl Into<String>) -> Tin {
        let name = name.into();
        let tin = self.options.register_token(name.clone());
        self.raw_options.register_token(name);
        tin
    }

    /// Resolve or allocate a token and bind it to a fixed source literal.
    pub fn token_with_source(&mut self, name: impl Into<String>, source: impl Into<String>) -> Tin {
        let name = name.into();
        let name = if name.starts_with('#') {
            name
        } else {
            format!("#{name}")
        };
        let source = source.into();
        let tin = self.token(name.clone());
        let token = FixedToken {
            name: name.clone(),
            tin,
            source,
        };
        self.options
            .fixed
            .tokens
            .insert(name.clone(), token.clone());
        self.raw_options.fixed.tokens.insert(name, token);
        tin
    }

    /// Return an independent snapshot of the resolved configuration.
    pub fn config(&self) -> Options {
        self.options.peek().clone()
    }

    /// Human-readable, deterministic description of this instance's public
    /// grammar and lexer configuration. This carries the intentional
    /// introspection helper provided by the mature Go runtime.
    pub fn describe(&self) -> String {
        use std::collections::BTreeSet;
        use std::fmt::Write as _;

        let mut output = String::from("=== Tabnas Instance ===\n");
        let _ = writeln!(output, "Id: {}", self.id);
        let _ = writeln!(output, "Tag: {}", self.options.tag);

        output.push_str("\n--- Tokens ---\n");
        let mut token_names = BTreeSet::new();
        token_names.extend(self.options.tokens.keys().cloned());
        token_names.extend(self.options.fixed.tokens.keys().cloned());
        token_names.extend(self.options.match_tokens.keys().cloned());
        for name in token_names {
            if let Some(tin) = self.options.token(&name) {
                let _ = writeln!(output, "  {name} = {tin}");
            }
        }

        output.push_str("\n--- Fixed Tokens ---\n");
        let mut fixed = self.options.fixed.tokens.values().collect::<Vec<_>>();
        fixed.sort_by(|left, right| {
            left.source
                .cmp(&right.source)
                .then_with(|| left.name.cmp(&right.name))
        });
        for token in fixed {
            let _ = writeln!(
                output,
                "  {:?} -> {} ({})",
                token.source, token.name, token.tin
            );
        }

        output.push_str("\n--- Rules ---\n");
        for (name, rule) in self.rules.iter() {
            let _ = writeln!(
                output,
                "  {name}: open={} close={} bo={} ao={} bc={} ac={}",
                rule.open.len(),
                rule.close.len(),
                rule.bo.len() + rule.bo_fns.len() + rule.bo_state_fns.len(),
                rule.ao.len() + rule.ao_fns.len() + rule.ao_state_fns.len(),
                rule.bc.len() + rule.bc_fns.len() + rule.bc_state_fns.len(),
                rule.ac.len() + rule.ac_fns.len() + rule.ac_state_fns.len(),
            );
        }

        if !self.options.lex.matchers.is_empty() {
            output.push_str("\n--- Custom Matchers ---\n");
            for (name, matcher) in &self.options.lex.matchers {
                let _ = writeln!(output, "  {name} (priority={})", matcher.order);
            }
        }

        let _ = writeln!(output, "\n--- Plugins: {} ---", self.plugins.len());
        for plugin in self.plugins.iter() {
            let _ = writeln!(output, "  {}", plugin.name);
        }
        output.push_str("\n--- Subscriptions ---\n");
        let _ = writeln!(
            output,
            "  Token subscribers: {}",
            self.token_subscribers.len()
        );
        let _ = writeln!(output, "  Lex subscribers: {}", self.lex_subscribers.len());
        let _ = writeln!(
            output,
            "  Rule subscribers: {}",
            self.rule_subscribers.len()
        );
        let _ = writeln!(
            output,
            "  RuleDone subscribers: {}",
            self.rule_done_subscribers.len()
        );
        let _ = writeln!(output, "  Parse guards: {}", self.parse_guards.len());

        output.push_str("\n--- Config ---\n");
        let _ = writeln!(output, "  FixedLex: {}", self.options.fixed.lex);
        let _ = writeln!(output, "  SpaceLex: {}", self.options.space.lex);
        let _ = writeln!(output, "  LineLex: {}", self.options.line.lex);
        let _ = writeln!(output, "  TextLex: {}", self.options.text.lex);
        let _ = writeln!(output, "  NumberLex: {}", self.options.number.lex);
        let _ = writeln!(output, "  CommentLex: {}", self.options.comment.lex);
        let _ = writeln!(output, "  StringLex: {}", self.options.string.lex);
        let _ = writeln!(output, "  ValueLex: {}", self.options.value.lex);
        let _ = writeln!(output, "  MapExtend: {}", self.options.map.extend);
        let _ = writeln!(output, "  ListProperty: {}", self.options.list.property);
        let _ = writeln!(output, "  SafeKey: {}", self.options.safe.key);
        let _ = writeln!(output, "  FinishRule: {}", self.options.rule.finish);
        let _ = writeln!(output, "  RuleStart: {}", self.options.rule.start);
        output
    }

    /// Install the lightweight lexer/rule trace provided by the mature Go
    /// runtime. The sink receives one complete line per event; use
    /// `enable_trace` to write those lines to the configured debug output.
    pub fn enable_trace_with(&mut self, sink: impl Fn(&str) + Send + Sync + 'static) -> &mut Self {
        let sink = Arc::new(sink);
        let lex_sink = sink.clone();
        self.subscribe_lex(move |token, _, context| {
            lex_sink(&format!(
                "[lex] {} tin={} src={:?} val={} at {}:{}",
                token.name,
                token.tin,
                token.src,
                context.options.debug.format_source(&token.val),
                token.site.ri,
                token.site.ci
            ));
        });
        self.subscribe_rules(move |rule, context| {
            sink(&format!(
                "[rule] {} state={:?} node={} ki={}",
                rule.name,
                rule.state,
                context.options.debug.format_source(&rule.node.borrow()),
                context.iteration
            ));
        });
        self
    }

    pub fn enable_trace(&mut self) -> &mut Self {
        self.subscribe_lex(|token, _, context| {
            context.options.debug.write(&format!(
                "[lex] {} tin={} src={:?} val={} at {}:{}",
                token.name,
                token.tin,
                token.src,
                context.options.debug.format_source(&token.val),
                token.site.ri,
                token.site.ci
            ));
        });
        self.subscribe_rules(|rule, context| {
            context.options.debug.write(&format!(
                "[rule] {} state={:?} node={} ki={}",
                rule.name,
                rule.state,
                context.options.debug.format_source(&rule.node.borrow()),
                context.iteration
            ));
        });
        self
    }

    pub(crate) fn emit_debug_config(&self) {
        if self.options.debug.print.config {
            self.options.debug.write(&format!("{:#?}", self.options));
        }
    }

    /// Mutate the accumulated typed options and rebuild resolved
    /// configuration without discarding installed grammar rules.
    pub fn set_options(
        &mut self,
        modify: impl FnOnce(&mut Options),
    ) -> Result<&mut Self, PluginError> {
        let mut raw_options = if self.options.config_modify.is_empty() {
            self.options.peek().clone()
        } else {
            self.raw_options.clone()
        };
        modify(&mut raw_options);
        let mut resolved = raw_options.clone();
        resolved.refresh_configuration().map_err(PluginError)?;
        self.raw_options = raw_options;
        *self.options = resolved;
        self.plugin_options = self.options.plugin.clone();
        self.emit_debug_config();
        Ok(self)
    }

    /// Installed plugins in application order.
    pub fn installed_plugins(&self) -> Vec<Plugin> {
        self.plugins.peek().clone()
    }

    /// Attach an equality-comparable native value to this instance.
    pub fn decorate<T>(&mut self, name: impl Into<String>, value: T) -> &mut Self
    where
        T: Any + PartialEq + Send + Sync,
    {
        self.decorations.insert(name.into(), Decoration::new(value));
        self
    }

    /// Attach a native value without requiring `PartialEq`. Opaque values
    /// compare by identity when instances are merged.
    pub fn decorate_opaque<T>(&mut self, name: impl Into<String>, value: T) -> &mut Self
    where
        T: Any + Send + Sync,
    {
        self.decorations
            .insert(name.into(), Decoration::opaque(value));
        self
    }

    pub fn decoration<T: Any>(&self, name: &str) -> Option<&T> {
        self.decorations
            .get(name)
            .and_then(Decoration::downcast_ref)
    }

    pub fn decoration_entry(&self, name: &str) -> Option<&Decoration> {
        self.decorations.get(name)
    }

    /// Rule specs in declaration order.
    pub fn rule_specs(&self) -> Vec<&RuleSpec> {
        self.rules.values().collect()
    }

    /// Rule names in declaration order.
    pub fn rule_names(&self) -> Vec<String> {
        self.rules.keys().cloned().collect()
    }

    pub fn token_set(&self, name: &str) -> Option<Vec<Tin>> {
        self.options
            .token_set
            .get(name.trim_start_matches('#'))
            .cloned()
    }

    pub fn set_token_set(&mut self, name: impl Into<String>, tins: Vec<Tin>) -> &mut Self {
        let name = name.into();
        let name = name.trim_start_matches('#').to_owned();
        self.options.token_set.insert(name.clone(), tins.clone());
        self.raw_options.token_set.insert(name, tins);
        self
    }

    /// Resolve the token claimed by one fixed source string.
    pub fn fixed(&self, source: &str) -> Option<Tin> {
        self.options
            .fixed
            .tokens
            .values()
            .find(|token| token.source == source)
            .map(|token| token.tin)
    }

    /// Resolve the source literal associated with a fixed token identity.
    pub fn fixed_source(&self, tin: Tin) -> Option<&str> {
        self.options
            .fixed
            .tokens
            .values()
            .find(|token| token.tin == tin)
            .map(|token| token.source.as_str())
    }

    pub fn token_name(&self, tin: Tin) -> String {
        self.options.token_name(tin)
    }

    pub fn action(
        &mut self,
        name: impl Into<String>,
        action: impl Fn(&mut Rule) + Send + Sync + 'static,
    ) -> &mut Self {
        self.actions.insert(name.into(), Arc::new(action));
        self
    }

    pub fn subscribe_tokens(
        &mut self,
        subscriber: impl Fn(&Token) + Send + Sync + 'static,
    ) -> &mut Self {
        self.token_subscribers.push(Arc::new(subscriber));
        self
    }

    /// Subscribe to every lexer token, including ignored trivia. The
    /// subscriber may annotate or replace token fields before parsing uses it.
    pub fn subscribe_lex(
        &mut self,
        subscriber: impl Fn(&mut Token, &mut Rule, &mut Context) + Send + Sync + 'static,
    ) -> &mut Self {
        self.lex_subscribers.push(Arc::new(subscriber));
        self
    }

    pub fn subscribe_rules(
        &mut self,
        subscriber: impl Fn(&mut Rule, &mut Context) + Send + Sync + 'static,
    ) -> &mut Self {
        self.rule_subscribers.push(Arc::new(subscriber));
        self
    }

    pub fn subscribe_rule_done(
        &mut self,
        subscriber: impl Fn(&Rule, &Context, &RuleDone) + Send + Sync + 'static,
    ) -> &mut Self {
        self.rule_done_subscribers.push(Arc::new(subscriber));
        self
    }

    pub fn action_with_context(
        &mut self,
        name: impl Into<String>,
        action: impl Fn(&mut Rule, &mut Context) -> Result<(), ActionError> + Send + Sync + 'static,
    ) -> &mut Self {
        self.context_actions.insert(name.into(), Arc::new(action));
        self
    }

    /// Register a named alternate action with the canonical matched-alt
    /// argument and token-error return channel.
    pub fn action_with_match_ref(
        &mut self,
        name: impl Into<String>,
        action: impl Fn(&mut Rule, &mut Context, &mut AltMatch) -> Result<Option<Token>, ActionError>
            + Send
            + Sync
            + 'static,
    ) -> &mut Self {
        self.matched_actions.insert(name.into(), Arc::new(action));
        self
    }

    /// Register a typed rule lifecycle reference such as `@top-bo`,
    /// `@top-ao/prepend`, or `@top-bc/replace`. Serialized grammar loading
    /// wires reserved names onto their matching rule phase.
    pub fn state_action_ref(
        &mut self,
        name: impl Into<String>,
        action: impl Fn(&mut Rule, &mut Context) -> Result<(), ActionError> + Send + Sync + 'static,
    ) -> &mut Self {
        self.context_actions.insert(name.into(), Arc::new(action));
        self
    }

    /// Register a lifecycle reference with canonical `next` and chained
    /// output-token arguments.
    pub fn state_action_with_next_ref(
        &mut self,
        name: impl Into<String>,
        action: impl Fn(
                &mut Rule,
                &mut Context,
                Option<&RuleSnapshot>,
                Option<Token>,
            ) -> Result<Option<Token>, ActionError>
            + Send
            + Sync
            + 'static,
    ) -> &mut Self {
        self.state_actions.insert(name.into(), Arc::new(action));
        self
    }

    /// Register a typed function reference for a serialized alternate `c`.
    pub fn alt_condition(
        &mut self,
        name: impl Into<String>,
        condition: impl Fn(&mut Rule, &mut Context) -> bool + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_conditions.insert(name.into(), Arc::new(condition));
        self
    }

    /// Register the canonical alternate condition shape, including the live
    /// effective match record.
    pub fn alt_condition_with_match(
        &mut self,
        name: impl Into<String>,
        condition: impl Fn(&mut Rule, &mut Context, &mut AltMatch) -> bool + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_match_conditions
            .insert(name.into(), Arc::new(condition));
        self
    }

    /// Register a serialized alternate condition that can re-enter the live
    /// lexer. Use `Lexer::next_raw_for_rule` when ignored tokens must remain
    /// observable, matching the canonical TypeScript lexer callback surface.
    pub fn alt_condition_with_lexer(
        &mut self,
        name: impl Into<String>,
        condition: impl for<'source> Fn(&mut Rule, &mut Context, &mut Lexer<'source>) -> bool
            + Send
            + Sync
            + 'static,
    ) -> &mut Self {
        self.alt_lexer_conditions
            .insert(name.into(), Arc::new(condition));
        self
    }

    /// Register the complete canonical alternate-condition surface, with the
    /// shared live match record and controlled access to the active lexer.
    pub fn alt_condition_with_lexer_and_match(
        &mut self,
        name: impl Into<String>,
        condition: impl for<'source> Fn(&mut Rule, &mut Context, &mut AltMatch, &mut Lexer<'source>) -> bool
            + Send
            + Sync
            + 'static,
    ) -> &mut Self {
        self.alt_lexer_match_conditions
            .insert(name.into(), Arc::new(condition));
        self
    }

    /// Register a typed function reference for a serialized alternate `h`.
    pub fn alt_modifier(
        &mut self,
        name: impl Into<String>,
        modifier: impl Fn(AltSpec, &mut Rule, &mut Context) -> AltSpec + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_modifiers.insert(name.into(), Arc::new(modifier));
        self
    }

    pub fn alt_modifier_with_match(
        &mut self,
        name: impl Into<String>,
        modifier: impl Fn(AltMatch, &mut Rule, &mut Context, Option<&RuleSnapshot>) -> AltMatch
            + Send
            + Sync
            + 'static,
    ) -> &mut Self {
        self.alt_match_modifiers
            .insert(name.into(), Arc::new(modifier));
        self
    }

    /// Register a typed function reference for a serialized alternate `e`.
    pub fn alt_error(
        &mut self,
        name: impl Into<String>,
        error: impl Fn(&mut Rule, &mut Context) -> Option<Token> + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_errors.insert(name.into(), Arc::new(error));
        self
    }

    pub fn alt_error_with_match(
        &mut self,
        name: impl Into<String>,
        error: impl Fn(&mut Rule, &mut Context, &mut AltMatch) -> Option<Token> + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_match_errors.insert(name.into(), Arc::new(error));
        self
    }

    /// Register a typed function reference for a serialized alternate `p`.
    pub fn alt_push(
        &mut self,
        name: impl Into<String>,
        route: impl Fn(&mut Rule, &mut Context) -> Option<String> + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_pushes.insert(name.into(), Arc::new(route));
        self
    }

    pub fn alt_push_with_match(
        &mut self,
        name: impl Into<String>,
        route: impl Fn(&mut Rule, &mut Context, &mut AltMatch) -> Option<String> + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_match_pushes.insert(name.into(), Arc::new(route));
        self
    }

    /// Register a typed function reference for a serialized alternate `r`.
    pub fn alt_replace(
        &mut self,
        name: impl Into<String>,
        route: impl Fn(&mut Rule, &mut Context) -> Option<String> + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_replaces.insert(name.into(), Arc::new(route));
        self
    }

    pub fn alt_replace_with_match(
        &mut self,
        name: impl Into<String>,
        route: impl Fn(&mut Rule, &mut Context, &mut AltMatch) -> Option<String> + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_match_replaces.insert(name.into(), Arc::new(route));
        self
    }

    /// Register a typed function reference for a serialized alternate `b`.
    pub fn alt_backtrack(
        &mut self,
        name: impl Into<String>,
        backtrack: impl Fn(&mut Rule, &mut Context) -> usize + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_backtracks.insert(name.into(), Arc::new(backtrack));
        self
    }

    pub fn alt_backtrack_with_match(
        &mut self,
        name: impl Into<String>,
        backtrack: impl Fn(&mut Rule, &mut Context, &mut AltMatch) -> usize + Send + Sync + 'static,
    ) -> &mut Self {
        self.alt_match_backtracks
            .insert(name.into(), Arc::new(backtrack));
        self
    }

    /// Register an effect-based function reference for
    /// `options.match.token`. The callback may consume only a non-empty prefix
    /// of the remaining source; invalid results are ignored.
    pub fn match_token_ref(
        &mut self,
        name: impl Into<String>,
        eager: bool,
        matcher: impl Fn(&str) -> Option<MatchTokenResult> + Send + Sync + 'static,
    ) -> &mut Self {
        self.match_token_refs
            .insert(name.into(), (Arc::new(matcher), eager));
        self
    }

    /// Register an effect-based high-priority value matcher for a serialized
    /// `options.match.value.<name>.match` function reference.
    pub fn match_value_ref(
        &mut self,
        name: impl Into<String>,
        matcher: impl Fn(&str) -> Option<MatchTokenResult> + Send + Sync + 'static,
    ) -> &mut Self {
        self.match_value_refs.insert(name.into(), Arc::new(matcher));
        self
    }

    /// Register a typed transformer for a regexp-backed
    /// `options.value.def.<name>.val` function reference.
    ///
    /// The slice contains the whole match followed by capture groups;
    /// unmatched optional groups are represented by empty strings, matching
    /// the Go port's cross-language callback shape.
    pub fn value_transform_ref(
        &mut self,
        name: impl Into<String>,
        transform: impl Fn(&[String]) -> Value + Send + Sync + 'static,
    ) -> &mut Self {
        self.value_transform_refs
            .insert(name.into(), Arc::new(transform));
        self
    }

    /// Register an effect-based unquoted-text value modifier for use from a
    /// serialized `options.text.modify` reference.
    pub fn text_modifier_ref(
        &mut self,
        name: impl Into<String>,
        modifier: impl Fn(Value) -> Value + Send + Sync + 'static,
    ) -> &mut Self {
        self.text_modifier_refs
            .insert(name.into(), TextModifier::new(modifier));
        self
    }

    /// Register a full canonical text modifier. It runs after the text/value
    /// matcher has produced a token and receives live lexer, rule, context,
    /// and resolved-option access.
    pub fn imperative_text_modifier_ref(
        &mut self,
        name: impl Into<String>,
        modifier: impl for<'source> Fn(Value, &mut Lexer<'source>, &mut Rule, &mut Context, &Options) -> Value
            + Send
            + Sync
            + 'static,
    ) -> &mut Self {
        self.text_modifier_refs
            .insert(name.into(), TextModifier::new_imperative(modifier));
        self
    }

    /// Register an effect-based lexer preflight hook for serialized matcher
    /// options such as `options.string.check` or `options.fixed.check`.
    pub fn lex_check_ref(
        &mut self,
        name: impl Into<String>,
        check: impl Fn(&str) -> LexCheckResult + Send + Sync + 'static,
    ) -> &mut Self {
        self.lex_check_refs
            .insert(name.into(), LexCheck::new(check));
        self
    }

    /// Register a canonical live-lexer preflight hook. It may inspect and
    /// advance the cursor and return a token built by that lexer.
    pub fn imperative_lex_check_ref(
        &mut self,
        name: impl Into<String>,
        check: impl for<'source> Fn(&mut Lexer<'source>) -> LexCheckResult + Send + Sync + 'static,
    ) -> &mut Self {
        self.lex_check_refs
            .insert(name.into(), LexCheck::new_imperative(check));
        self
    }

    /// Register an effect-based custom matcher factory reference for a
    /// serialized `options.lex.match.<name>.make` entry.
    pub fn lex_match_ref(
        &mut self,
        name: impl Into<String>,
        matcher: impl Fn(&str) -> Option<LexCheckToken> + Send + Sync + 'static,
    ) -> &mut Self {
        self.lex_match_refs.insert(name.into(), Arc::new(matcher));
        self
    }

    /// Register a full native lexer matcher for a serialized
    /// `options.lex.match.<name>.make` reference. The matcher owns cursor
    /// advancement and may inspect or modify the active rule and context.
    pub fn imperative_lex_match_ref(
        &mut self,
        name: impl Into<String>,
        matcher: impl for<'source> Fn(&mut Lexer<'source>, &mut Rule, &mut Context) -> Option<Token>
            + Send
            + Sync
            + 'static,
    ) -> &mut Self {
        self.imperative_lex_match_refs
            .insert(name.into(), Arc::new(matcher));
        self
    }

    /// Register a setup-time matcher factory for a serialized
    /// `options.lex.match.<name>.make` reference. It sees the fully resolved
    /// options and returns the persistent matcher, or `None` to disable it.
    pub fn lex_match_factory_ref(
        &mut self,
        name: impl Into<String>,
        factory: impl Fn(&Options) -> Option<ImperativeLexMatcher> + Send + Sync + 'static,
    ) -> &mut Self {
        self.lex_match_factory_refs
            .insert(name.into(), Arc::new(factory));
        self
    }

    /// Register a typed dynamic renderer for a serialized
    /// `options.errmsg.suffix` function reference.
    pub fn error_suffix_ref(
        &mut self,
        name: impl Into<String>,
        render: impl Fn(&ErrorSuffixContext) -> String + Send + Sync + 'static,
    ) -> &mut Self {
        self.error_suffix_refs.insert(name.into(), Arc::new(render));
        self
    }

    /// Register a typed load-time mutator for a serialized
    /// `options.config.modify.<name>` function reference.
    pub fn config_modifier_ref(
        &mut self,
        name: impl Into<String>,
        modifier: impl Fn(&mut Options) + Send + Sync + 'static,
    ) -> &mut Self {
        self.config_modifier_refs
            .insert(name.into(), ConfigModifier::new(modifier));
        self
    }

    /// Register the complete canonical configuration callback shape. The
    /// first argument is the mutable resolved configuration; the second is
    /// the immutable accumulated option input for this configure pass.
    pub fn config_modifier_with_options_ref(
        &mut self,
        name: impl Into<String>,
        modifier: impl Fn(&mut Options, &Options) + Send + Sync + 'static,
    ) -> &mut Self {
        self.config_modifier_refs
            .insert(name.into(), ConfigModifier::with_options(modifier));
        self
    }

    /// Register a typed replacement parse entry point for a serialized
    /// `options.parser.start` function reference.
    pub fn parser_start_ref(
        &mut self,
        name: impl Into<String>,
        start: impl Fn(&str) -> Result<Value, Box<TabnasError>> + Send + Sync + 'static,
    ) -> &mut Self {
        self.parser_start_refs.insert(name.into(), Arc::new(start));
        self
    }

    /// Register the mature parser-start shape, including the owning instance
    /// and caller metadata.
    pub fn parser_start_with_instance_ref(
        &mut self,
        name: impl Into<String>,
        start: impl Fn(&str, &Tabnas, &Value) -> Result<Value, Box<TabnasError>> + Send + Sync + 'static,
    ) -> &mut Self {
        self.parser_start_instance_refs
            .insert(name.into(), Arc::new(start));
        self
    }

    /// Register the complete canonical parser-start shape, including the
    /// optional parent-context seed supplied to `parse_with_context`.
    pub fn parser_start_with_context_ref(
        &mut self,
        name: impl Into<String>,
        start: impl Fn(&str, &Tabnas, &Value, Option<&ContextSeed>) -> Result<Value, Box<TabnasError>>
            + Send
            + Sync
            + 'static,
    ) -> &mut Self {
        self.parser_start_context_refs
            .insert(name.into(), Arc::new(start));
        self
    }

    /// Register a duplicate-map-value merger for a serialized
    /// `options.map.merge` function reference.
    pub fn map_merge_ref(
        &mut self,
        name: impl Into<String>,
        merge: impl Fn(Value, Value, &mut Rule, &mut Context) -> Value + Send + Sync + 'static,
    ) -> &mut Self {
        self.map_merge_refs.insert(name.into(), Arc::new(merge));
        self
    }

    /// Register an effect-based terminator probe for a serialized comment
    /// definition's `suffix` option.
    pub fn comment_suffix_ref(
        &mut self,
        name: impl Into<String>,
        matcher: impl Fn(&str) -> Option<String> + Send + Sync + 'static,
    ) -> &mut Self {
        self.comment_suffix_refs
            .insert(name.into(), CommentSuffixMatcher::new(matcher));
        self
    }

    /// Register a canonical live-lexer comment suffix probe. Cursor changes
    /// made while probing are rolled back; only the returned token's non-empty
    /// source prefix is consumed as the suffix.
    pub fn imperative_comment_suffix_ref(
        &mut self,
        name: impl Into<String>,
        matcher: impl for<'source> Fn(&mut Lexer<'source>) -> Option<Token> + Send + Sync + 'static,
    ) -> &mut Self {
        self.comment_suffix_refs
            .insert(name.into(), CommentSuffixMatcher::new_imperative(matcher));
        self
    }

    pub fn parse_budget(
        &mut self,
        check_every_n: usize,
        check: impl Fn(&Context) -> bool + Send + Sync + 'static,
    ) -> &mut Self {
        self.options.parse.budget.check_every_n = check_every_n;
        self.options.parse.budget.on_check = Some(Arc::new(check));
        self
    }

    /// Register a typed function reference for serialized
    /// `options.parse.budget.onCheck`.
    pub fn parse_budget_ref(
        &mut self,
        name: impl Into<String>,
        check: impl Fn(&Context) -> bool + Send + Sync + 'static,
    ) -> &mut Self {
        self.budget_check_refs.insert(name.into(), Arc::new(check));
        self
    }

    /// Install a named check that the parse loop runs at every step, ahead
    /// of the budget. A check that returns `false` stops the parse with the
    /// `cancel` code, as the budget does.
    ///
    /// A guard is the budget's counterpart for a grammar rather than for
    /// its caller. The budget is one slot: [`Tabnas::parse_budget`]
    /// replaces it in place, so a check a grammar kept there went whenever
    /// a caller set a budget of its own after installing the grammar. The
    /// grammars use that check to bound nesting, because a `Value` drops
    /// and displays by recursion, one frame per level, and a stack
    /// overflow ends the process. Guards are kept apart from the budget
    /// and from the options, so neither a budget nor a grammar document
    /// applied later removes one; a derived instance carries them, and a
    /// merge keeps both sides'. Only [`Tabnas::remove_parse_guard`] does.
    ///
    /// The name is the guard's identity: installing a second guard under
    /// a name already in use replaces the first. A grammar layered on
    /// another uses that to change the check its base installed, as JSONC
    /// raises the depth jsonic allows. Guards run in the order their names
    /// were first installed, before the budget, from the second step on,
    /// the steps the budget can run on. Each runs at every step, so it
    /// has to be cheap. A guard that panics fails the parse with an
    /// error, as a panicking budget does.
    ///
    /// Rust only: the TypeScript and Go engines have no guards, as their
    /// grammars have no depth limits to keep.
    pub fn parse_guard(
        &mut self,
        name: impl Into<String>,
        check: impl Fn(&Context) -> bool + Send + Sync + 'static,
    ) -> &mut Self {
        self.parse_guards.insert(name.into(), Arc::new(check));
        self
    }

    /// Remove the named guard, if one is installed. See
    /// [`Tabnas::parse_guard`].
    pub fn remove_parse_guard(&mut self, name: &str) -> &mut Self {
        self.parse_guards.shift_remove(name);
        self
    }

    pub fn parse_prepare(
        &mut self,
        prepare: impl Fn(&mut Context) + Send + Sync + 'static,
    ) -> &mut Self {
        self.options
            .parse
            .prepare
            .push(ParsePrepare::Context(Arc::new(prepare)));
        self
    }

    /// Add a pre-parse hook with access to the owning parser and the exact
    /// caller metadata supplied to this parse.
    pub fn parse_prepare_with_instance(
        &mut self,
        prepare: impl Fn(&Tabnas, &mut Context, &Value) + Send + Sync + 'static,
    ) -> &mut Self {
        self.options
            .parse
            .prepare
            .push(ParsePrepare::WithInstance(Arc::new(prepare)));
        self
    }

    /// Register a typed function reference for one named serialized
    /// `options.parse.prepare` callback.
    pub fn parse_prepare_ref(
        &mut self,
        name: impl Into<String>,
        prepare: impl Fn(&mut Context) + Send + Sync + 'static,
    ) -> &mut Self {
        self.parse_prepare_refs
            .insert(name.into(), ParsePrepare::Context(Arc::new(prepare)));
        self
    }

    /// Register the complete canonical pre-parse callback shape for a
    /// serialized `options.parse.prepare` function reference.
    pub fn parse_prepare_with_instance_ref(
        &mut self,
        name: impl Into<String>,
        prepare: impl Fn(&Tabnas, &mut Context, &Value) + Send + Sync + 'static,
    ) -> &mut Self {
        self.parse_prepare_refs
            .insert(name.into(), ParsePrepare::WithInstance(Arc::new(prepare)));
        self
    }

    pub fn parse(&self, src: &str) -> Result<Value, TabnasError> {
        self.parser().parse_for(self, src, Value::Undefined)
    }

    pub fn parse_with_meta(&self, src: &str, meta: Value) -> Result<Value, TabnasError> {
        self.parser().parse_for(self, src, meta)
    }

    pub fn parse_with_context(
        &self,
        src: &str,
        meta: Value,
        parent: &ContextSeed,
    ) -> Result<Value, TabnasError> {
        self.parser()
            .parse_for_with_context(self, src, meta, parent)
    }

    pub fn continuations(&self, src: &str) -> Continuations {
        self.parser().continuations_for(self, src)
    }

    pub fn parse_recover(&self, src: &str) -> ParseRecovery {
        self.parser().parse_recover_for(self, src, Value::Undefined)
    }

    pub fn parse_recover_with_meta(&self, src: &str, meta: Value) -> ParseRecovery {
        self.parser().parse_recover_for(self, src, meta)
    }

    pub fn parse_recover_with_context(
        &self,
        src: &str,
        meta: Value,
        parent: &ContextSeed,
    ) -> ParseRecovery {
        self.parser()
            .parse_recover_for_with_context(self, src, meta, parent)
    }

    /// The sum of every counter the assembled parser is built from.
    /// Each only increases, so any change moves the total.
    fn grammar_generation(&self) -> u64 {
        self.options
            .generation()
            .wrapping_add(self.rules.generation())
            .wrapping_add(self.actions.generation())
            .wrapping_add(self.context_actions.generation())
            .wrapping_add(self.matched_actions.generation())
            .wrapping_add(self.state_actions.generation())
            .wrapping_add(self.token_subscribers.generation())
            .wrapping_add(self.lex_subscribers.generation())
            .wrapping_add(self.rule_subscribers.generation())
            .wrapping_add(self.rule_done_subscribers.generation())
            .wrapping_add(self.parse_guards.generation())
            .wrapping_add(self.plugins.generation())
    }

    fn parser(&self) -> Arc<Parser> {
        self.prepared_parser
            .get(self.grammar_generation(), || self.build_parser())
    }

    fn build_parser(&self) -> Parser {
        let mut p = Parser::from_shared(self.prepared_options.get(&self.options));
        p.set_instance_info(InstanceInfo {
            id: self.id.clone(),
            parent_id: self.parent_id.clone(),
            tag: self.options.tag.clone(),
            plugins: self
                .plugins
                .iter()
                .map(|plugin| plugin.name.clone())
                .collect(),
            rule_names: self.rule_names(),
        });
        for spec in self.rules.values() {
            p.add_rule(spec.clone());
        }
        for (name, action) in self.actions.iter() {
            p.add_action(name.clone(), action.clone());
        }
        for (name, action) in self.context_actions.iter() {
            p.add_context_action(name.clone(), action.clone());
        }
        for (name, action) in self.matched_actions.iter() {
            p.add_matched_action(name.clone(), action.clone());
        }
        for (name, action) in self.state_actions.iter() {
            p.add_state_action(name.clone(), action.clone());
        }
        for subscriber in self.token_subscribers.iter() {
            p.add_token_subscriber(subscriber.clone());
        }
        for subscriber in self.lex_subscribers.iter() {
            p.add_lex_subscriber(subscriber.clone());
        }
        for subscriber in self.rule_subscribers.iter() {
            p.add_rule_subscriber(subscriber.clone());
        }
        for subscriber in self.rule_done_subscribers.iter() {
            p.add_rule_done_subscriber(subscriber.clone());
        }
        for guard in self.parse_guards.values() {
            p.add_parse_guard(guard.clone());
        }
        p
    }

    /// Strict JSON parser setup: the rule set of `ts/test/json-plugin.ts`
    /// and `go/jsonplugin_test.go`, over stricter options. Those fixtures
    /// leave `escapeStrict` off, keep the `'` and `` ` `` escapes and
    /// exclude only `00`-prefixed numbers, so they accept `\x41`,
    /// `\u{41}`, `01`, `+1`, `.5` and `1.`; this preset rejects all of
    /// them, as `JSON.parse` does. The shared fixtures pin neither way,
    /// and `ci/rust/json-fuzz.js` compares the two over generated input
    /// that stays inside strict JSON.
    pub fn make_json() -> Self {
        let mut opts = Options::default();
        opts.text.lex = false;
        opts.comment.lex = false;
        opts.map.extend = false;
        opts.lex.empty = false;
        opts.rule.finish = false;
        opts.rule.include = "json".to_string();

        opts.number.hex = false;
        opts.number.oct = false;
        opts.number.bin = false;
        opts.number.sep = None;
        // The core number matcher is intentionally lenient; reject leading
        // plus/dot forms, leading zeroes, and a trailing decimal point for
        // the strict-JSON compatibility grammar.
        opts.number.exclude = Some(r"^(?:\+|[+-]?\.|-?0\d)|\.$".to_string());

        opts.string.chars = "\"".to_string();
        opts.string.multi_chars = "".to_string();
        opts.string.allow_unknown = false;
        opts.string.escape_strict = true;
        for escape in ['v', '\'', '`'] {
            opts.string.escape.remove(&escape);
        }

        let mut tn = Tabnas::with_options(opts);

        // 1. Rule: val
        let mut val = RuleSpec::new("val");
        val.bo.push("@val-bo".to_string());
        val.bc.push("@val-bc".to_string());

        // val.open
        val.open.push(AltSpec {
            s: vec![vec![TIN_OB]],
            p: Some("map".to_string()),
            b: 1,
            g: "map,json".to_string(),
            ..Default::default()
        });
        val.open.push(AltSpec {
            s: vec![vec![TIN_OS]],
            p: Some("list".to_string()),
            b: 1,
            g: "list,json".to_string(),
            ..Default::default()
        });
        val.open.push(AltSpec {
            s: vec![vec![TIN_TX, TIN_NR, TIN_ST, TIN_VL]],
            g: "val,json".to_string(),
            ..Default::default()
        });

        // val.close
        val.close.push(AltSpec {
            s: vec![vec![TIN_ZZ]],
            g: "end,json".to_string(),
            ..Default::default()
        });
        val.close.push(AltSpec {
            s: vec![],
            b: 1,
            g: "more,json".to_string(),
            ..Default::default()
        });
        tn.rule(val);

        // 2. Rule: map
        let mut map = RuleSpec::new("map");
        map.bo.push("@map-bo".to_string());
        let mut n_pk = HashMap::new();
        n_pk.insert("pk".to_string(), 0);

        map.open.push(AltSpec {
            s: vec![vec![TIN_OB], vec![TIN_CB]],
            b: 1,
            n: n_pk.clone(),
            g: "map,json".to_string(),
            ..Default::default()
        });
        map.open.push(AltSpec {
            s: vec![vec![TIN_OB]],
            p: Some("pair".to_string()),
            n: n_pk,
            g: "map,json,pair".to_string(),
            ..Default::default()
        });

        map.close.push(AltSpec {
            s: vec![vec![TIN_CB]],
            g: "end,json".to_string(),
            ..Default::default()
        });
        tn.rule(map);

        // 3. Rule: list
        let mut list = RuleSpec::new("list");
        list.bo.push("@list-bo".to_string());

        list.open.push(AltSpec {
            s: vec![vec![TIN_OS], vec![TIN_CS]],
            b: 1,
            g: "list,json".to_string(),
            ..Default::default()
        });
        list.open.push(AltSpec {
            s: vec![vec![TIN_OS]],
            p: Some("elem".to_string()),
            g: "list,elem,json".to_string(),
            ..Default::default()
        });

        list.close.push(AltSpec {
            s: vec![vec![TIN_CS]],
            g: "end,json".to_string(),
            ..Default::default()
        });
        tn.rule(list);

        // 4. Rule: pair
        let mut pair = RuleSpec::new("pair");
        pair.bc.push("@pair-bc".to_string());

        let mut u_pair = HashMap::new();
        u_pair.insert("pair".to_string(), Value::Bool(true));

        pair.open.push(AltSpec {
            s: vec![vec![TIN_ST], vec![TIN_CL]],
            p: Some("val".to_string()),
            u: u_pair,
            a: vec!["@pairkey".to_string()],
            g: "map,pair,key,json".to_string(),
            ..Default::default()
        });

        pair.close.push(AltSpec {
            s: vec![vec![TIN_CA]],
            r: Some("pair".to_string()),
            g: "map,pair,json".to_string(),
            ..Default::default()
        });
        pair.close.push(AltSpec {
            s: vec![vec![TIN_CB]],
            b: 1,
            g: "map,pair,json".to_string(),
            ..Default::default()
        });
        tn.rule(pair);

        // 5. Rule: elem
        let mut elem = RuleSpec::new("elem");
        elem.bc.push("@elem-bc".to_string());

        elem.open.push(AltSpec {
            s: vec![],
            p: Some("val".to_string()),
            g: "list,elem,val,json".to_string(),
            ..Default::default()
        });

        elem.close.push(AltSpec {
            s: vec![vec![TIN_CA]],
            r: Some("elem".to_string()),
            g: "list,elem,json".to_string(),
            ..Default::default()
        });
        elem.close.push(AltSpec {
            s: vec![vec![TIN_CS]],
            b: 1,
            g: "list,elem,json".to_string(),
            ..Default::default()
        });
        tn.rule(elem);

        tn
    }
}

impl fmt::Display for Tabnas {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.write_str(&self.id)
    }
}

fn panic_message(payload: Box<dyn std::any::Any + Send>) -> String {
    if let Some(message) = payload.downcast_ref::<&str>() {
        (*message).to_string()
    } else if let Some(message) = payload.downcast_ref::<String>() {
        message.clone()
    } else {
        "non-string panic payload".into()
    }
}

pub(crate) fn merge_plugin_values(base: Value, overlay: Value) -> Value {
    const DANGEROUS: [&str; 3] = ["__proto__", "constructor", "prototype"];
    match (base, overlay) {
        (base, Value::Undefined) => base,
        (Value::Object(base), Value::Object(overlay)) => {
            let mut base = crate::value::unwrap_arc(base);
            for (key, value) in crate::value::unwrap_arc(overlay) {
                if DANGEROUS.contains(&key.as_str()) {
                    continue;
                }
                let previous = base.shift_remove(&key).unwrap_or(Value::Undefined);
                base.insert(key, merge_plugin_values(previous, value));
            }
            Value::object(base)
        }
        (Value::Array(base), Value::Array(overlay)) => {
            let length = base.len().max(overlay.len());
            let mut base = crate::value::unwrap_arc(base).into_iter();
            let mut overlay = crate::value::unwrap_arc(overlay).into_iter();
            Value::array(
                (0..length)
                    .map(|_| match (base.next(), overlay.next()) {
                        (Some(base), Some(overlay)) => merge_plugin_values(base, overlay),
                        (Some(base), None) => base,
                        (None, Some(overlay)) => overlay,
                        (None, None) => unreachable!("length comes from both iterators"),
                    })
                    .collect(),
            )
        }
        (_, overlay) => overlay,
    }
}

/// One shared `Options` per configuration, rebuilt when the
/// configuration changes and shared by every parse until it does.
///
/// A `Mutex` rather than a `RefCell` because `Tabnas` is `Send + Sync`
/// and should stay that way, and `Arc` rather than `Rc` for the same
/// reason. Both are per `parse()` call, not per token, which is why
/// the atomics do not show up.
#[derive(Default)]
struct PreparedOptions(std::sync::Mutex<Option<(u64, Arc<Options>)>>);

impl PreparedOptions {
    fn get(&self, options: &crate::tracked::Tracked<Options>) -> Arc<Options> {
        let generation = options.generation();
        let mut slot = self.0.lock().expect("prepared options lock");
        if let Some((prepared_at, ref prepared)) = *slot {
            if prepared_at == generation {
                return Arc::clone(prepared);
            }
        }
        let mut prepared_value = options.peek().clone();
        prepared_value.sort_for_lexing();
        let prepared = Arc::new(prepared_value);
        *slot = Some((generation, Arc::clone(&prepared)));
        prepared
    }
}

/// A cloned instance prepares its own; it does not inherit the
/// original's, which may already be stale for it.
impl Clone for PreparedOptions {
    fn clone(&self) -> Self {
        PreparedOptions::default()
    }
}

/// The assembled `Parser` for a configuration, prepared once and shared
/// by every parse until the configuration changes.
///
/// This is only possible because a `Parser` is `Send + Sync`: it holds
/// `Arc<Options>` and `Arc<RuleSpec>`, and its actions are already
/// `Arc<dyn Fn .. + Send + Sync>`. An earlier attempt at this was
/// abandoned when the parser still held `Rc`s, because caching one
/// would have cost `Tabnas` its own `Sync` without saying so.
///
/// The key is the sum of the generations of every `Tracked` field the
/// parser is built from. Summing is enough because each counter only
/// ever increases, so any change moves the total.
#[derive(Default)]
struct PreparedParser(std::sync::Mutex<Option<(u64, Arc<Parser>)>>);

impl PreparedParser {
    fn get(&self, generation: u64, build: impl FnOnce() -> Parser) -> Arc<Parser> {
        let mut slot = self.0.lock().expect("prepared parser lock");
        if let Some((prepared_at, ref prepared)) = *slot {
            if prepared_at == generation {
                return Arc::clone(prepared);
            }
        }
        let prepared = Arc::new(build());
        *slot = Some((generation, Arc::clone(&prepared)));
        prepared
    }
}

impl Clone for PreparedParser {
    fn clone(&self) -> Self {
        PreparedParser::default()
    }
}