retex_engine/

expand.rs

//! Expansion (*TeX: The Program* §366–§401, with e-TeX and LuaTeX
//! additions): `expand`, macro calls, `\csname`, `\noexpand`, `\input`.

use std::rc::Rc;

use crate::Engine;
use crate::cmd::Cmd;
use crate::hash::{CsId, NO_CS};
use crate::input::{Level, ScannerStatus, TokKind};
use crate::primitives_gen::assign_int as ip;
use crate::token::{Token, TokenList};

/// Maximum expansion nesting before LuaTeX gives up.
pub const EXPAND_DEPTH: u32 = 10000;

/// `cs_name` modifiers.
pub mod cs_name_codes {
    /// `\csname`.
    pub const CSNAME: u32 = 0;
    /// `\lastnamedcs`.
    pub const LAST_NAMED_CS: u32 = 1;
    /// `\begincsname`.
    pub const BEGIN_CSNAME: u32 = 2;
}

/// Whether `t` is a `match` or `end_match` token.
#[inline]
fn is_match_or_end(t: Token) -> bool {
    !t.is_cs() && (t.cmd_code() == Cmd::ParEnd as u32 || t.cmd_code() == Cmd::Stop as u32)
}

/// Whether `t` is a left or right brace character token
/// (`cur_tok < right_brace_limit`).
#[inline]
fn is_brace(t: Token) -> bool {
    !t.is_cs() && (t.cmd_code() == Cmd::LeftBrace as u32 || t.cmd_code() == Cmd::RightBrace as u32)
}

#[inline]
fn is_left_brace(t: Token) -> bool {
    !t.is_cs() && t.cmd_code() == Cmd::LeftBrace as u32
}

impl Engine {
    /// Gets the next token, expanding macros and other expandable commands
    /// (`get_x_token`).
    pub fn get_x_token(&mut self) {
        self.get_next();
        if self.cur_cmd > Cmd::MAX_COMMAND {
            self.get_x_token_expanding();
        } else {
            self.cur_tok = self.make_cur_tok();
        }
    }

    /// [`get_x_token`](Self::get_x_token) once an expandable token has been
    /// read.
    #[inline(never)]
    fn get_x_token_expanding(&mut self) {
        loop {
            if self.cur_cmd >= Cmd::Call {
                if self.cur_cmd < Cmd::EndTemplate {
                    self.macro_call();
                } else {
                    self.cur_cs = self.cs.frozen_endv;
                    self.cur_cmd = Cmd::Endv;
                    break;
                }
            } else {
                self.expand();
            }
            self.get_next();
            if self.cur_cmd <= Cmd::MAX_COMMAND {
                break;
            }
        }
        self.cur_tok = self.make_cur_tok();
    }

    /// Expands the current token while it is expandable (`x_token`).
    pub fn x_token(&mut self) {
        while self.cur_cmd > Cmd::MAX_COMMAND {
            if self.cur_cmd == Cmd::EndTemplate {
                // LuaTeX converts `\endtemplate` in place (as
                // `get_x_token` does) instead of backing up `\endv`.
                self.cur_cs = self.cs.frozen_endv;
                self.cur_cmd = Cmd::Endv;
                break;
            }
            self.expand();
            self.get_next();
        }
        self.cur_tok = self.make_cur_tok();
    }

    /// Expands the current (expandable) command (`expand`).
    pub fn expand(&mut self) {
        let cv = self.cur_val;
        let cvl = self.cur_val_level;
        let cg = self.cur_glue;
        self.expand_depth += 1;
        if self.expand_depth >= EXPAND_DEPTH {
            self.overflow("expansion depth", i64::from(EXPAND_DEPTH));
        }
        loop {
            if self.cur_cmd < Cmd::Call {
                if self.eqtb.int(ip::TRACINGCOMMANDS) > 1 {
                    self.show_cur_cmd_chr();
                }
                match self.cur_cmd {
                    Cmd::TopBotMark => self.insert_mark_text(),
                    Cmd::ExpandAfter => {
                        if self.cur_chr == 0 {
                            // \expandafter
                            self.get_token();
                            let t = self.cur_tok;
                            self.get_token();
                            if self.cur_cmd > Cmd::MAX_COMMAND {
                                self.expand();
                            } else {
                                self.back_input();
                            }
                            self.cur_tok = t;
                            self.back_input();
                        } else {
                            // \unless
                            self.get_token();
                            if self.cur_cmd == Cmd::IfTest
                                && self.cur_chr != crate::cond::if_codes::IF_CASE
                            {
                                self.cur_chr += crate::cond::UNLESS_CODE;
                                continue; // reswitch
                            }
                            self.print_err("You can't use `");
                            self.print_esc_str("unless");
                            self.printer.print_str("' before `");
                            self.print_cmd_chr(self.cur_cmd, self.cur_chr);
                            self.printer.print_char('\'' as u32);
                            self.help(&["Continue, and I'll forget that it ever happened."]);
                            self.back_error();
                        }
                    }
                    Cmd::NoExpand => {
                        if self.cur_chr == 0 {
                            self.no_expand();
                        } else {
                            self.primitive_cmd();
                            if self.cur_cmd > Cmd::MAX_COMMAND && self.cur_cmd != Cmd::NoExpand {
                                continue;
                            }
                            if self.cur_cmd <= Cmd::MAX_COMMAND {
                                self.back_input();
                            }
                        }
                    }
                    Cmd::CsName => self.manufacture_cs_name(),
                    Cmd::Convert => self.conv_toks(),
                    Cmd::The => self.ins_the_toks(),
                    Cmd::IfTest => self.conditional(),
                    Cmd::FiOrElse => self.fi_or_else(),
                    Cmd::Input => self.input_command(),
                    Cmd::LuaExpandableCall | Cmd::LuaLocalCall => self.lua_expandable_call(),
                    Cmd::Variable | Cmd::Feedback => self.backend_expandable(),
                    _ => {
                        self.print_err("Undefined control sequence");
                        self.help(&[
                            "The control sequence at the end of the top line",
                            "of your error message was never \\def'ed. If you have",
                            "misspelled it (e.g., `\\hobx'), type `I' and the correct",
                            "spelling (e.g., `I\\hbox'). Otherwise just continue,",
                            "and I'll forget about whatever was undefined.",
                        ]);
                        self.error();
                    }
                }
            } else if self.cur_cmd < Cmd::EndTemplate {
                self.macro_call();
            } else {
                self.cur_tok = Token::cs(self.cs.frozen_endv);
                self.back_input();
            }
            break;
        }
        self.expand_depth -= 1;
        self.cur_val = cv;
        self.cur_val_level = cvl;
        self.cur_glue = cg;
    }

    /// `\noexpand`: makes the next token unexpandable once (§369).
    fn no_expand(&mut self) {
        let save = self.input.scanner_status;
        self.input.scanner_status = ScannerStatus::Normal;
        self.get_token();
        self.input.scanner_status = save;
        let t = self.cur_tok;
        if t.is_cs() {
            // Pop exhausted lists as back_input would.
            while let Some(Level::Tokens(l)) = self.input.stack.last() {
                if l.loc < l.list.len() || l.kind == TokKind::VTemplate {
                    break;
                }
                self.end_token_list();
            }
            let list: TokenList = Rc::from(vec![Token::cs(self.cs.frozen_dont_expand), t]);
            self.begin_token_list(list, TokKind::BackedUp);
        } else {
            self.back_input();
        }
    }

    /// `\primitive`: replaces the next control sequence by the primitive of
    /// that name, if there is one (LuaTeX).
    fn primitive_cmd(&mut self) {
        let save = self.input.scanner_status;
        self.input.scanner_status = ScannerStatus::Normal;
        self.get_token();
        self.input.scanner_status = save;
        if self.cur_cs != NO_CS
            && let Some(p) = crate::primitives::lookup(self.hash.name(self.cur_cs))
        {
            self.cur_cmd = p.cmd;
            self.cur_chr = p.chr;
            // The frozen copy carries the primitive meaning.
            let frozen = self.frozen_primitive(self.cur_cs);
            self.cur_cs = frozen;
            self.cur_tok = Token::cs(frozen);
            if self.cur_cmd > Cmd::MAX_COMMAND {
                return;
            }
            return;
        }
        self.cur_cmd = Cmd::Relax;
        self.cur_chr = 0;
        self.back_input();
        self.cur_cmd = Cmd::NoExpand;
    }

    /// Looks up the control sequence named by `\ifcsname` or
    /// `\begincsname` and records it for `\lastnamedcs`: an undefined
    /// name gives the undefined control sequence, an empty name none.
    pub(crate) fn lookup_named_cs(&mut self, name: &[u8]) -> CsId {
        let cs = if name.is_empty() {
            NO_CS
        } else {
            match self.hash.lookup(name) {
                Some(cs) if self.eqtb.meaning(cs).cmd != Cmd::UndefinedCs => cs,
                _ => crate::hash::UNDEFINED_CS,
            }
        };
        self.last_cs_name = cs;
        cs
    }

    /// Builds the control sequence for `\csname…\endcsname` (§372).
    fn manufacture_cs_name(&mut self) {
        if self.cur_chr == cs_name_codes::LAST_NAMED_CS {
            if self.last_cs_name != NO_CS {
                self.cur_tok = Token::cs(self.last_cs_name);
                self.back_input();
            }
            return;
        }
        let begin = self.cur_chr == cs_name_codes::BEGIN_CSNAME;
        let e = self.cond.is_in_csname;
        self.cond.is_in_csname = true;
        let mut name: Vec<u8> = Vec::new();
        loop {
            self.get_x_token();
            if self.cur_cs != NO_CS {
                break;
            }
            crate::utf8x::push(&mut name, self.cur_chr);
        }
        if self.cur_cmd != Cmd::EndCsName {
            self.complain_missing_endcsname();
        }
        self.cond.is_in_csname = e;
        if begin {
            let cs = self.lookup_named_cs(&name);
            if cs != NO_CS && cs != crate::hash::UNDEFINED_CS {
                self.cur_tok = Token::cs(cs);
                self.back_input();
            }
            return;
        }
        let cs = self.hash.lookup_or_insert(&name);
        self.last_cs_name = cs;
        if self.eqtb.meaning(cs).cmd == Cmd::UndefinedCs {
            self.eq_define(
                crate::eqtb::Loc::Cs(cs),
                crate::eqtb::Val::Meaning(crate::eqtb::Meaning::prim(Cmd::Relax, RELAX_CHR)),
            );
        }
        self.cur_tok = Token::cs(cs);
        self.back_input();
    }

    /// Reports a missing `\endcsname`.
    pub fn complain_missing_endcsname(&mut self) {
        self.print_err("Missing ");
        self.print_esc_str("endcsname");
        self.printer.print_str(" inserted");
        self.help(&[
            "The control sequence marked <to be read again> should",
            "not appear between \\csname and \\endcsname.",
        ]);
        self.back_error();
    }

    /// Inserts `\relax` after the current token (`insert_relax`).
    pub fn insert_relax(&mut self) {
        self.cur_tok = Token::cs(self.cur_cs);
        self.back_input();
        self.cur_tok = Token::cs(self.cs.frozen_relax);
        self.back_input();
        if let Some(Level::Tokens(t)) = self.input.stack.last_mut() {
            t.kind = TokKind::Inserted;
        }
    }

    /// `\input`, `\endinput`, `\scantokens`, `\scantextokens`.
    fn input_command(&mut self) {
        match self.cur_chr {
            1 => self.input.force_eof = true,
            2 | 3 => self.pseudo_start(self.cur_chr == 3),
            _ => {
                if self.files.name_in_progress {
                    self.insert_relax();
                } else {
                    self.start_input();
                }
            }
        }
    }

    /// Inserts the text of a mark (`top_bot_mark`, §386).
    fn insert_mark_text(&mut self) {
        let mut code = self.cur_chr;
        let class = if code >= 5 {
            code -= 5;
            self.scan_register_num();
            self.cur_val as u32
        } else {
            0
        };
        if let Some(list) = self.marks.get(class, code)
            && !list.is_empty()
        {
            self.begin_token_list(list, TokKind::MarkText);
        }
    }

    /// Calls a user macro (`macro_call`, §389).
    pub fn macro_call(&mut self) {
        self.check_snapshot();
        // Fast path: a macro without parameters, not traced.
        if let Some(mac) = &self.eqtb.meaning(self.cur_cs).mac
            && mac.tokens[0] == Token::END_MATCH
            && self.eqtb.int(ip::TRACINGMACROS) <= 0
        {
            let tokens = mac.tokens.clone();
            while let Some(Level::Tokens(t)) = self.input.stack.last() {
                if t.loc < t.list.len() || t.kind == TokKind::VTemplate {
                    break;
                }
                self.end_token_list();
            }
            let param_start = self.input.param_stack.len();
            self.begin_macro(tokens, 1, self.cur_cs, param_start);
            return;
        }
        // The argument being scanned is kept in `runaway_list` while
        // tokens are read, to be shown if it runs away; an enclosing
        // scan's list is put back afterwards.
        let saved_runaway = std::mem::take(&mut self.runaway_list);
        self.macro_call_with_args();
        self.runaway_list = saved_runaway;
    }

    /// [`macro_call`](Self::macro_call) for a macro with parameters or
    /// traced.
    fn macro_call_with_args(&mut self) {
        let save_scanner_status = self.input.scanner_status;
        let save_warning_index = self.input.warning_index;
        self.input.warning_index = self.cur_cs;
        let Some(mac) = self.eqtb.meaning(self.cur_cs).mac.clone() else {
            self.input.scanner_status = save_scanner_status;
            self.input.warning_index = save_warning_index;
            return;
        };
        let tokens = mac.tokens.clone();
        if self.eqtb.int(ip::TRACINGMACROS) > 0 {
            self.begin_diagnostic();
            self.printer.print_ln();
            self.print_input_level();
            self.print_cs(self.input.warning_index);
            self.token_show_list(&tokens, 0, tokens.len(), 10_000_000);
            self.end_diagnostic(false);
        }
        let mut r = 0usize;
        // The arguments, in a buffer reused from call to call.
        let mut pstack: Vec<TokenList> = std::mem::take(&mut self.param_scratch);
        pstack.clear();
        if tokens[0] != Token::END_MATCH {
            self.input.scanner_status = ScannerStatus::Matching;
            let mut unbalance: i32 = 0;
            self.long_state = self.cur_cmd;
            if self.long_state >= Cmd::OuterCall {
                self.long_state = if self.long_state == Cmd::OuterCall {
                    Cmd::Call
                } else {
                    Cmd::LongCall
                };
            }
            let par_token = Token::cs(self.cs.par);
            loop {
                // One parameter (or the leading compulsory delimiter). The
                // scratch buffer is reused from call to call.
                // The argument is built in `runaway_list`, where a runaway
                // error (in get_token) shows it.
                self.runaway_list = std::mem::take(&mut self.arg_scratch);
                self.runaway_list.clear();
                let s: Option<usize>;
                let mut match_chr = 0u32;
                let mut m = 0i32;
                let mut rbrace_ptr = 0usize;
                if !is_match_or_end(tokens[r]) || tokens[r] == Token::END_MATCH {
                    s = None;
                } else {
                    match_chr = tokens[r].chr();
                    s = Some(r + 1);
                    r += 1;
                }
                'cont: loop {
                    self.get_token();
                    if self.cur_tok == tokens[r] {
                        r += 1;
                        if is_match_or_end(tokens[r]) {
                            if is_left_brace(self.cur_tok) {
                                self.input.align_state -= 1;
                            }
                            break 'cont; // found
                        }
                        continue 'cont;
                    }
                    // Contribute recently matched tokens.
                    if s != Some(r) {
                        match s {
                            None => {
                                self.print_err("Use of ");
                                self.sprint_cs(self.input.warning_index);
                                self.printer.print_str(" doesn't match its definition");
                                self.help(&[
                                    "If you say, e.g., `\\def\\a1{...}', then you must always",
                                    "put `1' after `\\a', since control sequence names are",
                                    "made up of letters only. The macro here has not been",
                                    "followed by the required stuff, so I'm ignoring it.",
                                ]);
                                self.error();
                                self.runaway_list.clear();
                                self.input.scanner_status = save_scanner_status;
                                self.input.warning_index = save_warning_index;
                                return;
                            }
                            Some(s) => {
                                let mut t = s;
                                loop {
                                    self.runaway_list.push(tokens[t]);
                                    m += 1;
                                    let mut u = t + 1;
                                    let mut v = s;
                                    let mut resumed = false;
                                    loop {
                                        if u == r {
                                            if self.cur_tok != tokens[v] {
                                                break;
                                            }
                                            r = v + 1;
                                            resumed = true;
                                            break;
                                        }
                                        if tokens[u] != tokens[v] {
                                            break;
                                        }
                                        u += 1;
                                        v += 1;
                                    }
                                    if resumed {
                                        continue 'cont;
                                    }
                                    t += 1;
                                    if t == r {
                                        break;
                                    }
                                }
                                r = s;
                            }
                        }
                    }
                    if self.cur_tok == par_token && self.long_state != Cmd::LongCall {
                        self.report_runaway_argument();
                        self.input.align_state -= unbalance;
                        self.input.scanner_status = save_scanner_status;
                        self.input.warning_index = save_warning_index;
                        return;
                    }
                    if is_brace(self.cur_tok) {
                        if is_left_brace(self.cur_tok) {
                            // Contribute an entire group.
                            unbalance = 1;
                            loop {
                                self.runaway_list.push(self.cur_tok);
                                self.get_token();
                                if self.cur_tok == par_token && self.long_state != Cmd::LongCall {
                                    self.report_runaway_argument();
                                    self.input.align_state -= unbalance;
                                    self.input.scanner_status = save_scanner_status;
                                    self.input.warning_index = save_warning_index;
                                    return;
                                }
                                if is_brace(self.cur_tok) {
                                    if is_left_brace(self.cur_tok) {
                                        unbalance += 1;
                                    } else {
                                        unbalance -= 1;
                                        if unbalance == 0 {
                                            break;
                                        }
                                    }
                                }
                            }
                            rbrace_ptr = self.runaway_list.len();
                            self.runaway_list.push(self.cur_tok);
                        } else {
                            // An extra right brace.
                            self.back_input();
                            self.print_err("Argument of ");
                            self.sprint_cs(self.input.warning_index);
                            self.printer.print_str(" has an extra }");
                            self.help(&[
                                "I've run across a `}' that doesn't seem to match anything.",
                                "For example, `\\def\\a#1{...}' and `\\a}' would produce",
                                "this error. If you simply proceed now, the `\\par' that",
                                "I've just inserted will cause me to report a runaway",
                                "argument that might be the root of the problem. But if",
                                "your `}' was spurious, just type `2' and it will go away.",
                            ]);
                            self.input.align_state += 1;
                            self.long_state = Cmd::Call;
                            self.cur_tok = par_token;
                            self.ins_error();
                            continue 'cont;
                        }
                    } else {
                        if self.cur_tok == Token::SPACE && is_match_or_end(tokens[r]) {
                            continue 'cont;
                        }
                        self.runaway_list.push(self.cur_tok);
                    }
                    m += 1;
                    if !is_match_or_end(tokens[r]) {
                        continue 'cont;
                    }
                    break 'cont;
                }
                // found:
                if s.is_some() {
                    // Tidy up the parameter just scanned.
                    let param: TokenList = if m == 1
                        && self.runaway_list.last().is_some_and(|&t| is_brace(t))
                        && rbrace_ptr > 0
                    {
                        Rc::from(&self.runaway_list[1..rbrace_ptr])
                    } else {
                        Rc::from(&self.runaway_list[..])
                    };
                    pstack.push(param);
                    let param = &pstack[pstack.len() - 1];
                    if self.eqtb.int(ip::TRACINGMACROS) > 0 {
                        self.begin_diagnostic();
                        if !self.print_input_level() {
                            self.printer.begin_line();
                        }
                        self.printer.print_char(match_chr);
                        self.printer.print_int(pstack.len() as i64);
                        self.printer.print_str("<-");
                        self.show_token_list(param, 0, param.len(), 1000);
                        self.end_diagnostic(false);
                    }
                }
                self.arg_scratch = std::mem::take(&mut self.runaway_list);
                if tokens[r] == Token::END_MATCH {
                    break;
                }
            }
        }
        // Feed the macro body and its parameters to the scanner.
        while let Some(Level::Tokens(t)) = self.input.stack.last() {
            if t.loc < t.list.len() || t.kind == TokKind::VTemplate {
                break;
            }
            self.end_token_list();
        }
        let param_start = self.input.param_stack.len();
        self.input.param_stack.append(&mut pstack);
        self.param_scratch = pstack;
        self.begin_macro(tokens, r + 1, self.input.warning_index, param_start);
        self.input.scanner_status = save_scanner_status;
        self.input.warning_index = save_warning_index;
    }

    /// Reports a runaway argument ("Paragraph ended before …").
    fn report_runaway_argument(&mut self) {
        if self.long_state == Cmd::Call {
            self.runaway();
            self.print_err("Paragraph ended before ");
            self.sprint_cs(self.input.warning_index);
            self.printer.print_str(" was complete");
            self.help(&[
                "I suspect you've forgotten a `}', causing me to apply this",
                "control sequence to too much text. How can we recover?",
                "My plan is to forget the whole thing and hope for the best.",
            ]);
            self.back_error();
        }
    }

    /// Prints the text that has run away (`runaway`).
    pub fn runaway(&mut self) {
        let what = match self.input.scanner_status {
            ScannerStatus::Defining => "definition",
            ScannerStatus::Matching => "argument",
            ScannerStatus::Aligning => "preamble",
            ScannerStatus::Absorbing => "text",
            _ => return,
        };
        self.printer.print_nl("Runaway ");
        self.printer.print_str(what);
        self.printer.print_char('?' as u32);
        self.printer.print_ln();
        let list = std::mem::take(&mut self.runaway_list);
        let limit = self.printer.error_line.saturating_sub(10);
        self.show_token_list(&list, 0, list.len(), limit as i64);
        self.runaway_list = list;
    }

    /// Checks whether an `\outer` macro or end of file is allowed here
    /// (`check_outer_validity`, §336).
    pub fn check_outer_validity(&mut self) {
        if self.input.scanner_status == ScannerStatus::Normal {
            return;
        }
        if self.eqtb.int(ip::SUPPRESSOUTERERROR) > 0 && self.cur_cs != NO_CS {
            return;
        }
        self.err.deletions_allowed = false;
        // Back up an outer control sequence so that it can be reread.
        if self.cur_cs != NO_CS {
            let reread = match self.input.stack.last() {
                Some(Level::Tokens(_)) => true,
                Some(Level::Text(t)) => !matches!(
                    t.source,
                    crate::input::LineSource::Terminal | crate::input::LineSource::Read(_)
                ),
                None => true,
            };
            if reread {
                let list: TokenList = Rc::from(vec![Token::cs(self.cur_cs)]);
                self.back_list(list);
            }
            self.cur_cmd = Cmd::Spacer;
            self.cur_chr = ' ' as u32;
        }
        if self.input.scanner_status > ScannerStatus::Skipping {
            self.runaway();
            if self.cur_cs == NO_CS {
                self.print_err("File ended");
            } else {
                self.cur_cs = NO_CS;
                self.print_err("Forbidden control sequence found");
            }
            self.printer.print_str(" while scanning ");
            let mut ins: Vec<Token> = Vec::new();
            match self.input.scanner_status {
                ScannerStatus::Defining => {
                    self.printer.print_str("definition");
                    ins.push(Token::RIGHT_BRACE);
                }
                ScannerStatus::Matching => {
                    self.printer.print_str("use");
                    ins.push(Token::cs(self.cs.par));
                    self.long_state = Cmd::OuterCall;
                }
                ScannerStatus::Aligning => {
                    self.printer.print_str("preamble");
                    ins.push(Token::cs(self.cs.frozen_cr));
                    ins.push(Token::RIGHT_BRACE);
                    self.input.align_state = -1_000_000;
                }
                _ => {
                    self.printer.print_str("text");
                    ins.push(Token::RIGHT_BRACE);
                }
            }
            self.ins_list(Rc::from(ins));
            self.printer.print_str(" of ");
            self.sprint_cs(self.input.warning_index);
            self.help(&[
                "I suspect you have forgotten a `}', causing me",
                "to read past where you wanted me to stop.",
                "I'll try to recover; but if the error is serious,",
                "you'd better type `E' or `X' now and fix your file.",
            ]);
            self.error();
        } else {
            self.print_err("Incomplete ");
            self.print_cmd_chr(Cmd::IfTest, self.cond.cur_if);
            self.printer.print_str("; all text was ignored after line ");
            self.printer.print_int(self.cond.skip_line.into());
            let third = if self.cur_cs != NO_CS {
                self.cur_cs = NO_CS;
                "the matching `\\fi'. I've inserted a `\\fi'; this might work."
            } else {
                "The file ended while I was skipping conditional text."
            };
            self.help(&[
                "A forbidden control sequence occurred in skipped text.",
                "This kind of error happens when you say `\\if...' and forget",
                third,
            ]);
            self.cur_tok = Token::cs(self.cs.frozen_fi);
            self.ins_error();
        }
        self.err.deletions_allowed = true;
    }

    /// Returns the frozen control sequence that carries the primitive
    /// meaning of the primitive named like `cs` (for `\primitive`).
    fn frozen_primitive(&mut self, cs: CsId) -> CsId {
        let name = self.hash.name(cs).to_vec();
        if let Some(&f) = self.frozen_prims.get(&name) {
            return f;
        }
        let f = self.hash.new_frozen(&name);
        if let Some(p) = crate::primitives::lookup(&name) {
            self.eqtb.ensure_cs(f);
            self.eqtb.cs[f.0 as usize].val = crate::eqtb::Meaning::prim(p.cmd, p.chr);
        }
        self.frozen_prims.insert(name, f);
        f
    }
}

/// The modifier of `\relax` (LuaTeX uses one past the largest character).
pub const RELAX_CHR: u32 = 0x11_0000;