retex_engine/

error.rs

//! Error reporting and recovery (*TeX: The Program* §71–§98, §311–§320).
//!
//! Errors print `! message.`, the input context and help text exactly as
//! TeX does. Fatal errors end the run by unwinding to the top-level driver
//! with a [`JumpOut`] payload (TeX's `jump_out`). `std::panic::resume_unwind`
//! is used, so no panic hook runs and nothing is printed. This is the only
//! non-local exit in the engine.

use crate::Engine;
use crate::input::{Level, LineSource, TokKind};
use crate::print::Selector;

/// Interaction level (`interaction`).
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
pub enum Interaction {
    /// `\batchmode`.
    Batch = 0,
    /// `\nonstopmode`.
    NonStop = 1,
    /// `\scrollmode`.
    Scroll = 2,
    /// `\errorstopmode`.
    ErrorStop = 3,
}

impl Interaction {
    /// The level with numeric value `n` (0–3).
    pub fn from_i32(n: i32) -> Interaction {
        match n {
            0 => Interaction::Batch,
            1 => Interaction::NonStop,
            2 => Interaction::Scroll,
            _ => Interaction::ErrorStop,
        }
    }
}

/// How bad things are (`history`).
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
pub enum History {
    /// No problems.
    Spotless,
    /// `begin_diagnostic` was called with warnings.
    WarningIssued,
    /// An error was reported.
    ErrorMessageIssued,
    /// The run was aborted.
    FatalErrorStop,
}

/// Payload of the unwind that ends a run (TeX's `jump_out`).
#[derive(Debug, Clone, Copy)]
pub struct JumpOut;

/// Error-handling state.
#[derive(Debug)]
pub struct ErrorState {
    /// The interaction level.
    pub interaction: Interaction,
    /// The run's history.
    pub history: History,
    /// Number of errors since the last paragraph end (`error_count`).
    pub error_count: i32,
    /// Help lines for the next error, top line first.
    pub help: Vec<&'static str>,
    /// Owned help lines (used instead of `help` when non-empty).
    pub help_owned: Vec<String>,
    /// Whether `\errhelp` should be shown instead of the help lines.
    pub use_err_help: bool,
    /// Whether deletions are allowed in error recovery.
    pub deletions_allowed: bool,
    /// Whether `\setbox` is allowed here.
    pub set_box_allowed: bool,
    /// `no_new_control_sequence`: lookups must not create new names.
    pub no_new_control_sequence: bool,
    /// The selector saved by `begin_diagnostic`.
    pub old_setting: Option<Selector>,
    /// Whether `file:line:error` style messages are requested.
    pub file_line_error: bool,
    /// Whether a `\par` should not be inserted (`OK_to_interrupt`).
    pub interrupt: bool,
}

impl Default for ErrorState {
    fn default() -> Self {
        ErrorState {
            interaction: Interaction::ErrorStop,
            history: History::FatalErrorStop,
            error_count: 0,
            help: Vec::new(),
            help_owned: Vec::new(),
            use_err_help: false,
            deletions_allowed: true,
            set_box_allowed: true,
            no_new_control_sequence: true,
            old_setting: None,
            file_line_error: false,
            interrupt: false,
        }
    }
}

impl Engine {
    /// Starts an error message (`print_err`).
    pub fn print_err(&mut self, msg: &str) {
        self.printer.begin_line();
        if !(self.err.file_line_error && self.print_file_line()) {
            self.printer.print_str("! ");
        }
        if self.diagnostics.is_some() {
            self.printer.capture = Some(Vec::new());
        }
        self.printer.print_str(msg);
    }

    /// Starts collecting a warning message (default output mode).
    pub fn diag_capture_start(&mut self) {
        if self.diagnostics.is_some() {
            self.printer.capture = Some(Vec::new());
        }
    }

    /// The innermost input file: name, line number, line text and the
    /// reading position in it.
    pub fn source_location(&self) -> Option<(String, u32, String, usize)> {
        let elc = self
            .eqtb
            .int(crate::primitives_gen::assign_int::ENDLINECHAR);
        self.input.stack.iter().rev().find_map(|l| match l {
            crate::input::Level::Text(t) if t.is_input_file => {
                let mut chars: &[u32] = &t.buf;
                if let Some((&last, rest)) = chars.split_last()
                    && i64::from(last) == i64::from(elc)
                {
                    chars = rest;
                }
                let text: String = chars.iter().filter_map(|&c| char::from_u32(c)).collect();
                Some((
                    String::from_utf8_lossy(&t.name).into_owned(),
                    t.line.max(0) as u32,
                    text,
                    t.loc.min(chars.len()),
                ))
            }
            _ => None,
        })
    }

    /// Records the captured warning text as a diagnostic located at `line`
    /// of the current file (or its current line).
    pub fn diag_capture_warning(&mut self, line: Option<u32>) {
        let Some(text) = self.printer.capture.take() else {
            return;
        };
        let message = String::from_utf8_lossy(&text).trim().replace('\n', " ");
        let mut d = crate::diag::Diagnostic::new(crate::diag::Severity::Warning, message);
        if let Some((file, cur, _, _)) = self.source_location() {
            d.file = Some(file);
            d.line = Some(line.unwrap_or(cur));
        }
        if let Some(list) = self.diagnostics.as_mut() {
            list.push(d);
        }
    }

    /// Records the error being reported (default output mode).
    fn record_error(&mut self) {
        let Some(text) = self.printer.capture.take() else {
            return;
        };
        let mut message = String::from_utf8_lossy(&text).trim().replace('\n', " ");
        if message == "Undefined control sequence" && self.cur_cs != crate::hash::NO_CS {
            let name = self.print_to_string(|e| e.print_cs(e.cur_cs));
            message = format!(
                "Undefined control sequence {}",
                String::from_utf8_lossy(&name).trim_end()
            );
        }
        let mut d = crate::diag::Diagnostic::new(crate::diag::Severity::Error, message);
        if let Some((file, line, source, column)) = self.source_location() {
            d.file = Some(file);
            d.line = Some(line);
            d.source = Some(source);
            d.column = Some(column);
        }
        d.help = if self.err.help_owned.is_empty() {
            self.err.help.iter().map(|s| (*s).to_owned()).collect()
        } else {
            self.err.help_owned.clone()
        };
        if let Some(list) = self.diagnostics.as_mut() {
            list.push(d);
        }
    }

    /// Starts an error message given as bytes.
    pub fn print_err_bytes(&mut self, msg: &[u8]) {
        self.print_err("");
        self.printer.print_bytes(msg);
    }

    /// Prints `file:line: ` for `-file-line-error`; returns `false` if no
    /// file is open.
    fn print_file_line(&mut self) -> bool {
        let found = self.input.stack.iter().rev().find_map(|l| match l {
            Level::Text(t) if t.is_input_file => Some((t.name.clone(), t.line)),
            _ => None,
        });
        match found {
            Some((name, line)) => {
                self.printer.print_bytes(&name);
                self.printer.print_char(':' as u32);
                self.printer.print_int(line.into());
                self.printer.print_str(": ");
                true
            }
            None => false,
        }
    }

    /// Sets the help lines for the next error (top line first).
    pub fn help(&mut self, lines: &[&'static str]) {
        self.err.help.clear();
        self.err.help.extend_from_slice(lines);
        self.err.help_owned.clear();
    }

    /// Sets owned help lines.
    pub fn help_owned(&mut self, lines: Vec<String>) {
        self.err.help.clear();
        self.err.help_owned = lines;
    }

    /// Completes an error message: prints the context and help, and
    /// interacts with the user if appropriate (`error`, §82).
    pub fn error(&mut self) {
        self.record_error();
        if self.err.history < History::ErrorMessageIssued {
            self.err.history = History::ErrorMessageIssued;
        }
        self.printer.print_char('.' as u32);
        self.show_context();
        if self.err.interaction == Interaction::ErrorStop {
            // No interactive terminal support: behave like scroll mode, but
            // a real terminal session would ask the user here.
            self.terminal_error_stop();
        }
        self.err.error_count += 1;
        if self.err.error_count == 100 {
            self.printer
                .print_nl("(That makes 100 errors; please try again.)");
            self.err.history = History::FatalErrorStop;
            self.jump_out();
        }
        // Put the help message on the transcript file.
        let sel = self.printer.selector;
        if self.err.interaction > Interaction::Batch {
            self.printer.selector = match sel {
                Selector::TermAndLog => Selector::LogOnly,
                Selector::TermOnly => Selector::NoPrint,
                s => s,
            };
        }
        if self.err.use_err_help {
            self.printer.print_ln();
            self.give_err_help();
        } else {
            let lines: Vec<String> = if self.err.help_owned.is_empty() {
                self.err.help.iter().map(|s| s.to_string()).collect()
            } else {
                self.err.help_owned.clone()
            };
            let empty = lines.is_empty();
            for l in lines {
                self.printer.print_nl(&l);
            }
            // LuaTeX does not add an empty line when there is no help and
            // the context line was wrapped at max_print_line.
            if empty {
                self.printer.begin_line();
            } else {
                self.printer.print_ln();
            }
        }
        if self.err.use_err_help {
            self.printer.print_ln();
        }
        self.err.help.clear();
        self.err.help_owned.clear();
        if self.err.interaction > Interaction::Batch {
            self.printer.selector = sel;
        }
        self.printer.print_ln();
    }

    /// Reads a line from the terminal, echoing it to the log
    /// (`term_input`, §71). End of input is fatal, as in TeX.
    pub fn term_input(&mut self) -> Vec<u32> {
        self.printer.update_terminal();
        let mut line = String::new();
        match std::io::stdin().read_line(&mut line) {
            Ok(0) | Err(_) => self.fatal_error("End of file on the terminal!"),
            Ok(_) => {}
        }
        let chars = crate::input::decode_line(line.trim_end_matches(['\n', '\r']).as_bytes());
        self.printer.term_offset = 0;
        let old = self.printer.selector;
        self.printer.selector = match old {
            Selector::TermAndLog => Selector::LogOnly,
            Selector::TermOnly => Selector::NoPrint,
            s => s,
        };
        for &c in &chars {
            self.printer.print_char(c);
        }
        self.printer.print_ln();
        self.printer.selector = old;
        chars
    }

    /// Prints a prompt and reads a line (`prompt_input`).
    pub fn prompt_input(&mut self, prompt: &str) -> Vec<u32> {
        self.printer.print_str(prompt);
        self.term_input()
    }

    /// Asks the user what to do about an error (§84–§93).
    fn terminal_error_stop(&mut self) {
        loop {
            if self.err.interaction != Interaction::ErrorStop {
                return;
            }
            self.clear_for_error_prompt();
            let line = self.prompt_input("? ");
            let Some(&c0) = line.first() else {
                return;
            };
            let c = char::from_u32(c0).unwrap_or(' ').to_ascii_uppercase();
            match c {
                '0'..='9' if self.err.deletions_allowed => {
                    let mut n = c as u32 - '0' as u32;
                    if let Some(&d) = line.get(1)
                        && (0x30..=0x39).contains(&d)
                    {
                        n = n * 10 + (d - 0x30);
                    }
                    let (s1, s2, s3, s4) = (
                        self.cur_tok,
                        self.cur_cmd,
                        self.cur_chr,
                        self.input.align_state,
                    );
                    self.input.align_state = 1_000_000;
                    for _ in 0..n {
                        self.get_token();
                    }
                    self.cur_tok = s1;
                    self.cur_cmd = s2;
                    self.cur_chr = s3;
                    self.input.align_state = s4;
                    self.help(&[
                        "I have just deleted some text, as you asked.",
                        "You can now delete more, or insert, or whatever.",
                    ]);
                    self.show_context();
                    continue;
                }
                'E' => {
                    let file = self.input.stack.iter().rev().find_map(|l| match l {
                        Level::Text(t) if t.is_input_file => Some((t.name.clone(), t.line)),
                        _ => None,
                    });
                    if let Some((name, line)) = file {
                        self.printer.print_nl("You want to edit file ");
                        self.printer.print_bytes(&name);
                        self.printer.print_str(" at line ");
                        self.printer.print_int(line.into());
                        self.err.interaction = Interaction::Scroll;
                        self.jump_out();
                    }
                }
                'H' => {
                    if self.err.use_err_help {
                        self.give_err_help();
                        self.err.use_err_help = false;
                    } else {
                        let lines: Vec<String> = if !self.err.help_owned.is_empty() {
                            self.err.help_owned.clone()
                        } else if !self.err.help.is_empty() {
                            self.err.help.iter().map(|s| s.to_string()).collect()
                        } else {
                            vec![
                                "Sorry, I don't know how to help in this situation.".into(),
                                "Maybe you should try asking a human?".into(),
                            ]
                        };
                        for l in lines {
                            self.printer.print_str(&l);
                            self.printer.print_ln();
                        }
                    }
                    self.help(&[
                        "Sorry, I already gave what help I could...",
                        "Maybe you should try asking a human?",
                        "An error might have occurred before I noticed any problems.",
                        "``If all else fails, read the instructions.''",
                    ]);
                    continue;
                }
                'I' => {
                    // Insert material from the terminal.
                    let text: Vec<u32> = if line.len() > 1 {
                        let mut v = vec![' ' as u32];
                        v.extend_from_slice(&line[1..]);
                        v
                    } else {
                        self.prompt_input("insert>")
                    };
                    self.begin_file_reading(crate::input::LineSource::Terminal, Vec::new(), false);
                    if let Some(Level::Text(t)) = self.input.stack.last_mut() {
                        t.buf = text;
                        t.loc = 0;
                        t.state = crate::input::LexState::MidLine;
                    }
                    return;
                }
                'Q' | 'R' | 'S' => {
                    self.err.error_count = 0;
                    self.printer.print_str("OK, entering ");
                    match c {
                        'Q' => {
                            self.err.interaction = Interaction::Batch;
                            self.print_esc_str("batchmode");
                            self.printer.selector = match self.printer.selector {
                                Selector::TermAndLog => Selector::LogOnly,
                                _ => Selector::NoPrint,
                            };
                        }
                        'R' => {
                            self.err.interaction = Interaction::NonStop;
                            self.print_esc_str("nonstopmode");
                        }
                        _ => {
                            self.err.interaction = Interaction::Scroll;
                            self.print_esc_str("scrollmode");
                        }
                    }
                    self.printer.print_str("...");
                    self.printer.print_ln();
                    self.printer.update_terminal();
                    return;
                }
                'X' => {
                    self.err.interaction = Interaction::Scroll;
                    self.jump_out();
                }
                _ => {}
            }
            // Print the menu of available options.
            self.printer
                .print_str("Type <return> to proceed, S to scroll future error messages,");
            self.printer
                .print_nl("R to run without stopping, Q to run quietly,");
            self.printer.print_nl("I to insert something, ");
            if self
                .input
                .stack
                .iter()
                .any(|l| matches!(l, Level::Text(t) if t.is_input_file))
            {
                self.printer.print_str("E to edit your file,");
            }
            if self.err.deletions_allowed {
                self.printer
                    .print_nl("1 or ... or 9 to ignore the next 1 to 9 tokens of input,");
            }
            self.printer.print_nl("H for help, X to quit.");
        }
    }

    /// Pops finished terminal levels before prompting
    /// (`clear_for_error_prompt`, §330).
    fn clear_for_error_prompt(&mut self) {
        while self.input.stack.len() > 1 {
            match self.input.stack.last() {
                Some(Level::Text(t))
                    if matches!(t.source, LineSource::Terminal) && t.loc >= t.buf.len() =>
                {
                    self.end_file_reading();
                }
                _ => break,
            }
        }
        self.printer.print_ln();
    }

    /// Prints `\errhelp` (`give_err_help`).
    pub fn give_err_help(&mut self) {
        let list = self
            .eqtb
            .toks_param(crate::primitives_gen::assign_toks::ERRHELP)
            .clone();
        self.token_show_list(&list, 0, list.len(), 10_000_000);
    }

    /// Reports a fatal error and ends the run (`fatal_error`).
    pub fn fatal_error(&mut self, s: &str) -> ! {
        self.normalize_selector();
        self.print_err("Emergency stop");
        self.help_owned(vec![s.to_owned()]);
        self.succumb();
    }

    /// A LuaTeX fatal error of category `category` (as LuaTeX prints them:
    /// `! error:  (category): message`, then `!  ==> Fatal error
    /// occurred, …`); ends the run without the transcript line.
    pub fn luatex_fatal(&mut self, category: &str, msg: &str) -> ! {
        self.normalize_selector();
        self.printer.print_nl("! error:  (");
        self.printer.print_str(category);
        self.printer.print_str("): ");
        self.printer.print_str(msg);
        let pdf = self.eqtb.int(crate::primitives_gen::assign_int::OUTPUTMODE) > 0;
        self.printer.print_nl(if pdf {
            "!  ==> Fatal error occurred, bad output PDF file produced!"
        } else {
            "!  ==> Fatal error occurred, bad output DVI file produced!"
        });
        self.printer.print_ln();
        self.err.history = History::FatalErrorStop;
        for n in 0..128u32 {
            if self.printer.write_open(n) {
                self.printer.close_write(n);
            }
        }
        if self.total_pages == 0 {
            self.printer.print_str("No pages of output.");
            self.printer.print_ln();
        }
        if self.printer.log_opened() {
            self.printer.close_log();
        }
        self.printer.selector = Selector::TermOnly;
        self.printer.flush();
        std::panic::resume_unwind(Box::new(JumpOut));
    }

    /// Reports that a capacity was exceeded and ends the run (`overflow`).
    pub fn overflow(&mut self, s: &str, n: i64) -> ! {
        self.normalize_selector();
        self.print_err("TeX capacity exceeded, sorry [");
        self.printer.print_str(s);
        self.printer.print_char('=' as u32);
        self.printer.print_int(n);
        self.printer.print_char(']' as u32);
        self.help(&[
            "If you really absolutely need more capacity,",
            "you can ask a wizard to enlarge me.",
        ]);
        self.succumb();
    }

    /// Reports an internal inconsistency (`confusion`).
    pub fn confusion(&mut self, s: &str) -> ! {
        self.normalize_selector();
        if self.err.history < History::ErrorMessageIssued {
            self.print_err("This can't happen (");
            self.printer.print_str(s);
            self.printer.print_char(')' as u32);
            self.help(&["I'm broken. Please show this to someone who can fix can fix"]);
        } else {
            self.print_err("I can't go on meeting you like this");
            self.help(&[
                "One of your faux pas seems to have wounded me deeply...",
                "in fact, I'm barely conscious. Please fix it and try again.",
            ]);
        }
        self.succumb();
    }

    fn succumb(&mut self) -> ! {
        if self.err.interaction == Interaction::ErrorStop {
            self.err.interaction = Interaction::Scroll;
        }
        if self.printer.log_opened() {
            self.error();
        }
        self.err.history = History::FatalErrorStop;
        self.jump_out();
    }

    /// Ends the run (`jump_out`): closes files and unwinds to the driver.
    pub fn jump_out(&mut self) -> ! {
        self.close_files_and_terminate();
        std::panic::resume_unwind(Box::new(JumpOut));
    }

    /// Makes sure output goes somewhere sensible (`normalize_selector`).
    pub fn normalize_selector(&mut self) {
        self.printer.selector = if self.printer.log_opened() {
            Selector::TermAndLog
        } else {
            Selector::TermOnly
        };
        if self.job_name.is_none() {
            self.open_log_file();
        }
        if self.err.interaction == Interaction::Batch {
            self.printer.selector = match self.printer.selector {
                Selector::TermAndLog => Selector::LogOnly,
                _ => Selector::NoPrint,
            };
        }
    }

    /// Hook for user interrupts; retex does not support them.
    pub fn check_interrupt(&mut self) {}

    /// `back_error`: backs up the current token and reports an error.
    pub fn back_error(&mut self) {
        self.err.interrupt = false;
        self.back_input();
        self.err.interrupt = true;
        self.error();
    }

    /// `ins_error`: like `back_error` but the token is marked inserted.
    pub fn ins_error(&mut self) {
        self.err.interrupt = false;
        self.back_input_inserted();
        self.err.interrupt = true;
        self.error();
    }

    /// A LuaTeX warning (`warning  (category): message` on a line of its
    /// own); it counts as a warning for the final "see the transcript"
    /// note.
    pub fn luatex_warning(&mut self, category: &str, msg: &str) {
        self.printer.luatex_warning(category, msg);
        if self.err.history == History::Spotless {
            self.err.history = History::WarningIssued;
        }
    }

    /// Starts diagnostic output (`begin_diagnostic`): goes to the log only
    /// unless `\tracingonline > 0`.
    pub fn begin_diagnostic(&mut self) {
        self.err.old_setting = Some(self.printer.selector);
        let online = self
            .eqtb
            .int(crate::primitives_gen::assign_int::TRACINGONLINE);
        if online <= 0 && self.printer.selector == Selector::TermAndLog {
            self.printer.selector = Selector::LogOnly;
            if self.err.history == History::Spotless {
                self.err.history = History::WarningIssued;
            }
        }
    }

    /// Ends diagnostic output (`end_diagnostic`).
    pub fn end_diagnostic(&mut self, blank_line: bool) {
        self.printer.print_nl("");
        if blank_line {
            self.printer.print_ln();
        }
        if let Some(s) = self.err.old_setting.take() {
            self.printer.selector = s;
        }
    }

    /// Shows where the scanner is (`show_context`, §311).
    pub fn show_context(&mut self) {
        let error_context_lines = self
            .eqtb
            .int(crate::primitives_gen::assign_int::ERRORCONTEXTLINES);
        let input_ptr = self.input.stack.len().saturating_sub(1);
        let mut base_ptr = input_ptr;
        let mut nn: i32 = -1;
        loop {
            let (is_text, bottom) = match &self.input.stack.get(base_ptr) {
                Some(Level::Text(t)) => (
                    true,
                    t.is_input_file || matches!(t.source, LineSource::File { .. }) || base_ptr == 0,
                ),
                Some(Level::Tokens(_)) => (false, false),
                None => (true, true),
            };
            let bottom_line = is_text && bottom;
            if base_ptr == input_ptr || bottom_line || nn < error_context_lines {
                // Display the current context, omitting backed-up token
                // lists that have already been read.
                let show = match self.input.stack.get(base_ptr) {
                    Some(Level::Tokens(t)) => {
                        base_ptr == input_ptr
                            || !matches!(t.kind, TokKind::BackedUp | TokKind::BackedUpChar)
                            || t.loc < t.list.len()
                    }
                    _ => true,
                };
                if show {
                    self.printer.term_just_wrapped = false;
                    self.display_context(base_ptr);
                    nn += 1;
                    // LuaTeX's terminal shows an empty line after a context
                    // line that filled the terminal line exactly, when more
                    // context follows (the log does not).
                    if self.printer.term_just_wrapped
                        && !(bottom_line || base_ptr == 0)
                        && matches!(
                            self.printer.selector,
                            crate::print::Selector::TermAndLog | crate::print::Selector::TermOnly
                        )
                    {
                        self.printer.term_raw(b"\n");
                    }
                }
            } else if nn == error_context_lines {
                self.printer.print_nl("...");
                nn += 1;
            }
            if bottom_line || base_ptr == 0 {
                break;
            }
            base_ptr -= 1;
        }
    }

    fn display_context(&mut self, base_ptr: usize) {
        let old_setting = self.printer.selector;
        self.printer.tally = 0;
        let level = self.input.stack[base_ptr].clone();
        let l: usize;
        match &level {
            Level::Text(t) => {
                match &t.source {
                    LineSource::Terminal => {
                        if base_ptr == 0 {
                            self.printer.print_nl("<*>");
                        } else {
                            self.printer.print_nl("<insert> ");
                        }
                    }
                    LineSource::Read(n) => {
                        self.printer.print_nl("<read ");
                        if *n == 16 {
                            self.printer.print_char('*' as u32);
                        } else {
                            self.printer.print_int(i64::from(*n));
                        }
                        self.printer.print_char('>' as u32);
                    }
                    _ => {
                        self.printer.print_nl("l.");
                        self.printer.print_int(t.line.into());
                    }
                }
                self.printer.print_char(' ' as u32);
                // Pseudoprint the line.
                l = self.begin_pseudoprint();
                let end_line_char = self
                    .eqtb
                    .int(crate::primitives_gen::assign_int::ENDLINECHAR);
                let mut j = t.buf.len();
                if j > 0 && t.buf[j - 1] as i32 == end_line_char {
                    j -= 1;
                }
                for i in 0..j {
                    if i == t.loc {
                        self.set_trick_count();
                    }
                    self.printer.print_char(t.buf[i]);
                }
            }
            Level::Tokens(t) => {
                match t.kind {
                    TokKind::Parameter => self.printer.print_nl("<argument> "),
                    TokKind::UTemplate | TokKind::VTemplate => self.printer.print_nl("<template> "),
                    TokKind::BackedUp | TokKind::BackedUpChar => {
                        if t.loc >= t.list.len() {
                            self.printer.print_nl("<recently read> ")
                        } else {
                            self.printer.print_nl("<to be read again> ")
                        }
                    }
                    TokKind::Inserted => self.printer.print_nl("<inserted text> "),
                    TokKind::Macro => {
                        self.printer.print_ln();
                        self.print_cs(t.name);
                    }
                    TokKind::OutputText => self.printer.print_nl("<output> "),
                    TokKind::EveryParText => self.printer.print_nl("<everypar> "),
                    TokKind::EveryMathText => self.printer.print_nl("<everymath> "),
                    TokKind::EveryDisplayText => self.printer.print_nl("<everydisplay> "),
                    TokKind::EveryHboxText => self.printer.print_nl("<everyhbox> "),
                    TokKind::EveryVboxText => self.printer.print_nl("<everyvbox> "),
                    TokKind::EveryJobText => self.printer.print_nl("<everyjob> "),
                    TokKind::EveryCrText => self.printer.print_nl("<everycr> "),
                    TokKind::MarkText => self.printer.print_nl("<mark> "),
                    TokKind::EveryEofText => self.printer.print_nl("<everyeof> "),
                    TokKind::WriteText => self.printer.print_nl("<write> "),
                    TokKind::LocalText => self.printer.print_nl("<local> "),
                }
                l = self.begin_pseudoprint();
                // For macros the list starts with the parameter text; TeX
                // shows the whole definition (parameters and body).
                self.show_token_list_ctx(&t.list, t.loc, 100_000);
            }
        }
        self.printer.selector = old_setting;
        self.print_two_lines(l);
    }

    fn begin_pseudoprint(&mut self) -> usize {
        let l = self.printer.tally;
        self.printer.tally = 0;
        self.printer.selector = Selector::Pseudo;
        self.printer.trick_count = 1_000_000;
        self.printer.trick_buf.clear();
        self.printer.trick_buf.resize(self.printer.error_line, b' ');
        l
    }

    /// TeX's `set_trick_count`.
    pub fn set_trick_count(&mut self) {
        let p = &mut self.printer;
        p.first_count = p.tally;
        p.trick_count = p.tally + 1 + p.error_line - p.half_error_line;
        if p.trick_count < p.error_line {
            p.trick_count = p.error_line;
        }
    }

    fn print_two_lines(&mut self, l: usize) {
        if self.printer.trick_count == 1_000_000 {
            self.set_trick_count();
        }
        let p = &self.printer;
        let (tally, first_count, trick_count, half, error_line) = (
            p.tally,
            p.first_count,
            p.trick_count,
            p.half_error_line,
            p.error_line,
        );
        let m = if tally < trick_count {
            tally - first_count
        } else {
            trick_count - first_count
        };
        let (start, n) = if l + first_count <= half {
            (0, l + first_count)
        } else {
            self.printer.print_plain("...");
            (l + first_count - half + 3, half)
        };
        let buf = self.printer.trick_buf.clone();
        let mut bytes = Vec::new();
        for q in start..first_count {
            bytes.push(buf[q % error_line]);
        }
        self.print_raw_bytes(&bytes);
        self.printer.print_ln();
        for _ in 0..n {
            self.printer.print_char(' ' as u32);
        }
        let p_end = if m + n <= error_line {
            first_count + m
        } else {
            first_count + (error_line - n - 3)
        };
        bytes.clear();
        for q in first_count..p_end {
            bytes.push(buf[q % error_line]);
        }
        self.print_raw_bytes(&bytes);
        if m + n > error_line {
            self.printer.print_plain("...");
        }
    }

    /// Prints already-converted bytes from the pseudo buffer, decoding
    /// complete UTF-8 sequences so that line lengths stay correct.
    fn print_raw_bytes(&mut self, bytes: &[u8]) {
        let mut i = 0;
        while i < bytes.len() {
            let (c, n) = crate::utf8x::decode(bytes, i);
            if c < 32 && c != 9 && c != 10 && c != 13 {
                // A raw control byte inside the buffer: print as is.
                self.printer.print_char(c);
            } else {
                self.printer.print_char(c);
            }
            i += n;
        }
    }
}