Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1530 insertions, 0 deletions

diff --git a/third_party/rust/rustc-demangle/src/v0.rs b/third_party/rust/rustc-demangle/src/v0.rs
new file mode 100644
index 0000000000..3e88fa64de
--- /dev/null
+++ b/third_party/rust/rustc-demangle/src/v0.rs
@@ -0,0 +1,1530 @@
+use core::convert::TryFrom;
+use core::{char, fmt, iter, mem, str};
+
+#[allow(unused_macros)]
+macro_rules! write {
+    ($($ignored:tt)*) => {
+        compile_error!(
+            "use `self.print(value)` or `fmt::Trait::fmt(&value, self.out)`, \
+             instead of `write!(self.out, \"{...}\", value)`"
+        )
+    };
+}
+
+// Maximum recursion depth when parsing symbols before we just bail out saying
+// "this symbol is invalid"
+const MAX_DEPTH: u32 = 500;
+
+/// Representation of a demangled symbol name.
+pub struct Demangle<'a> {
+    inner: &'a str,
+}
+
+#[derive(PartialEq, Eq, Debug)]
+pub enum ParseError {
+    /// Symbol doesn't match the expected `v0` grammar.
+    Invalid,
+
+    /// Parsing the symbol crossed the recursion limit (see `MAX_DEPTH`).
+    RecursedTooDeep,
+}
+
+/// De-mangles a Rust symbol into a more readable version
+///
+/// This function will take a **mangled** symbol and return a value. When printed,
+/// the de-mangled version will be written. If the symbol does not look like
+/// a mangled symbol, the original value will be written instead.
+pub fn demangle(s: &str) -> Result<(Demangle, &str), ParseError> {
+    // First validate the symbol. If it doesn't look like anything we're
+    // expecting, we just print it literally. Note that we must handle non-Rust
+    // symbols because we could have any function in the backtrace.
+    let inner;
+    if s.len() > 2 && s.starts_with("_R") {
+        inner = &s[2..];
+    } else if s.len() > 1 && s.starts_with('R') {
+        // On Windows, dbghelp strips leading underscores, so we accept "R..."
+        // form too.
+        inner = &s[1..];
+    } else if s.len() > 3 && s.starts_with("__R") {
+        // On OSX, symbols are prefixed with an extra _
+        inner = &s[3..];
+    } else {
+        return Err(ParseError::Invalid);
+    }
+
+    // Paths always start with uppercase characters.
+    match inner.as_bytes()[0] {
+        b'A'..=b'Z' => {}
+        _ => return Err(ParseError::Invalid),
+    }
+
+    // only work with ascii text
+    if inner.bytes().any(|c| c & 0x80 != 0) {
+        return Err(ParseError::Invalid);
+    }
+
+    // Verify that the symbol is indeed a valid path.
+    let try_parse_path = |parser| {
+        let mut dummy_printer = Printer {
+            parser: Ok(parser),
+            out: None,
+            bound_lifetime_depth: 0,
+        };
+        dummy_printer
+            .print_path(false)
+            .expect("`fmt::Error`s should be impossible without a `fmt::Formatter`");
+        dummy_printer.parser
+    };
+    let mut parser = Parser {
+        sym: inner,
+        next: 0,
+        depth: 0,
+    };
+    parser = try_parse_path(parser)?;
+
+    // Instantiating crate (paths always start with uppercase characters).
+    if let Some(&(b'A'..=b'Z')) = parser.sym.as_bytes().get(parser.next) {
+        parser = try_parse_path(parser)?;
+    }
+
+    Ok((Demangle { inner }, &parser.sym[parser.next..]))
+}
+
+impl<'s> fmt::Display for Demangle<'s> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut printer = Printer {
+            parser: Ok(Parser {
+                sym: self.inner,
+                next: 0,
+                depth: 0,
+            }),
+            out: Some(f),
+            bound_lifetime_depth: 0,
+        };
+        printer.print_path(true)
+    }
+}
+
+struct Ident<'s> {
+    /// ASCII part of the identifier.
+    ascii: &'s str,
+    /// Punycode insertion codes for Unicode codepoints, if any.
+    punycode: &'s str,
+}
+
+const SMALL_PUNYCODE_LEN: usize = 128;
+
+impl<'s> Ident<'s> {
+    /// Attempt to decode punycode on the stack (allocation-free),
+    /// and pass the char slice to the closure, if successful.
+    /// This supports up to `SMALL_PUNYCODE_LEN` characters.
+    fn try_small_punycode_decode<F: FnOnce(&[char]) -> R, R>(&self, f: F) -> Option<R> {
+        let mut out = ['\0'; SMALL_PUNYCODE_LEN];
+        let mut out_len = 0;
+        let r = self.punycode_decode(|i, c| {
+            // Check there's space left for another character.
+            out.get(out_len).ok_or(())?;
+
+            // Move the characters after the insert position.
+            let mut j = out_len;
+            out_len += 1;
+
+            while j > i {
+                out[j] = out[j - 1];
+                j -= 1;
+            }
+
+            // Insert the new character.
+            out[i] = c;
+
+            Ok(())
+        });
+        if r.is_ok() {
+            Some(f(&out[..out_len]))
+        } else {
+            None
+        }
+    }
+
+    /// Decode punycode as insertion positions and characters
+    /// and pass them to the closure, which can return `Err(())`
+    /// to stop the decoding process.
+    fn punycode_decode<F: FnMut(usize, char) -> Result<(), ()>>(
+        &self,
+        mut insert: F,
+    ) -> Result<(), ()> {
+        let mut punycode_bytes = self.punycode.bytes().peekable();
+        if punycode_bytes.peek().is_none() {
+            return Err(());
+        }
+
+        let mut len = 0;
+
+        // Populate initial output from ASCII fragment.
+        for c in self.ascii.chars() {
+            insert(len, c)?;
+            len += 1;
+        }
+
+        // Punycode parameters and initial state.
+        let base = 36;
+        let t_min = 1;
+        let t_max = 26;
+        let skew = 38;
+        let mut damp = 700;
+        let mut bias = 72;
+        let mut i: usize = 0;
+        let mut n: usize = 0x80;
+
+        loop {
+            // Read one delta value.
+            let mut delta: usize = 0;
+            let mut w = 1;
+            let mut k: usize = 0;
+            loop {
+                use core::cmp::{max, min};
+
+                k += base;
+                let t = min(max(k.saturating_sub(bias), t_min), t_max);
+
+                let d = match punycode_bytes.next() {
+                    Some(d @ b'a'..=b'z') => d - b'a',
+                    Some(d @ b'0'..=b'9') => 26 + (d - b'0'),
+                    _ => return Err(()),
+                };
+                let d = d as usize;
+                delta = delta.checked_add(d.checked_mul(w).ok_or(())?).ok_or(())?;
+                if d < t {
+                    break;
+                }
+                w = w.checked_mul(base - t).ok_or(())?;
+            }
+
+            // Compute the new insert position and character.
+            len += 1;
+            i = i.checked_add(delta).ok_or(())?;
+            n = n.checked_add(i / len).ok_or(())?;
+            i %= len;
+
+            let n_u32 = n as u32;
+            let c = if n_u32 as usize == n {
+                char::from_u32(n_u32).ok_or(())?
+            } else {
+                return Err(());
+            };
+
+            // Insert the new character and increment the insert position.
+            insert(i, c)?;
+            i += 1;
+
+            // If there are no more deltas, decoding is complete.
+            if punycode_bytes.peek().is_none() {
+                return Ok(());
+            }
+
+            // Perform bias adaptation.
+            delta /= damp;
+            damp = 2;
+
+            delta += delta / len;
+            let mut k = 0;
+            while delta > ((base - t_min) * t_max) / 2 {
+                delta /= base - t_min;
+                k += base;
+            }
+            bias = k + ((base - t_min + 1) * delta) / (delta + skew);
+        }
+    }
+}
+
+impl<'s> fmt::Display for Ident<'s> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.try_small_punycode_decode(|chars| {
+            for &c in chars {
+                c.fmt(f)?;
+            }
+            Ok(())
+        })
+        .unwrap_or_else(|| {
+            if !self.punycode.is_empty() {
+                f.write_str("punycode{")?;
+
+                // Reconstruct a standard Punycode encoding,
+                // by using `-` as the separator.
+                if !self.ascii.is_empty() {
+                    f.write_str(self.ascii)?;
+                    f.write_str("-")?;
+                }
+                f.write_str(self.punycode)?;
+
+                f.write_str("}")
+            } else {
+                f.write_str(self.ascii)
+            }
+        })
+    }
+}
+
+/// Sequence of lowercase hexadecimal nibbles (`0-9a-f`), used by leaf consts.
+struct HexNibbles<'s> {
+    nibbles: &'s str,
+}
+
+impl<'s> HexNibbles<'s> {
+    /// Decode an integer value (with the "most significant nibble" first),
+    /// returning `None` if it can't fit in an `u64`.
+    // FIXME(eddyb) should this "just" use `u128` instead?
+    fn try_parse_uint(&self) -> Option<u64> {
+        let nibbles = self.nibbles.trim_start_matches("0");
+
+        if nibbles.len() > 16 {
+            return None;
+        }
+
+        let mut v = 0;
+        for nibble in nibbles.chars() {
+            v = (v << 4) | (nibble.to_digit(16).unwrap() as u64);
+        }
+        Some(v)
+    }
+
+    /// Decode a UTF-8 byte sequence (with each byte using a pair of nibbles)
+    /// into individual `char`s, returning `None` for invalid UTF-8.
+    fn try_parse_str_chars(&self) -> Option<impl Iterator<Item = char> + 's> {
+        if self.nibbles.len() % 2 != 0 {
+            return None;
+        }
+
+        // FIXME(eddyb) use `array_chunks` instead, when that becomes stable.
+        let mut bytes = self
+            .nibbles
+            .as_bytes()
+            .chunks_exact(2)
+            .map(|slice| match slice {
+                [a, b] => [a, b],
+                _ => unreachable!(),
+            })
+            .map(|[&hi, &lo]| {
+                let half = |nibble: u8| (nibble as char).to_digit(16).unwrap() as u8;
+                (half(hi) << 4) | half(lo)
+            });
+
+        let chars = iter::from_fn(move || {
+            // As long as there are any bytes left, there's at least one more
+            // UTF-8-encoded `char` to decode (or the possibility of error).
+            bytes.next().map(|first_byte| -> Result<char, ()> {
+                // FIXME(eddyb) this `enum` and `fn` should be somewhere in `core`.
+                enum Utf8FirstByteError {
+                    ContinuationByte,
+                    TooLong,
+                }
+                fn utf8_len_from_first_byte(byte: u8) -> Result<usize, Utf8FirstByteError> {
+                    match byte {
+                        0x00..=0x7f => Ok(1),
+                        0x80..=0xbf => Err(Utf8FirstByteError::ContinuationByte),
+                        0xc0..=0xdf => Ok(2),
+                        0xe0..=0xef => Ok(3),
+                        0xf0..=0xf7 => Ok(4),
+                        0xf8..=0xff => Err(Utf8FirstByteError::TooLong),
+                    }
+                }
+
+                // Collect the appropriate amount of bytes (up to 4), according
+                // to the UTF-8 length implied by the first byte.
+                let utf8_len = utf8_len_from_first_byte(first_byte).map_err(|_| ())?;
+                let utf8 = &mut [first_byte, 0, 0, 0][..utf8_len];
+                for i in 1..utf8_len {
+                    utf8[i] = bytes.next().ok_or(())?;
+                }
+
+                // Fully validate the UTF-8 sequence.
+                let s = str::from_utf8(utf8).map_err(|_| ())?;
+
+                // Since we included exactly one UTF-8 sequence, and validation
+                // succeeded, `str::chars` should return exactly one `char`.
+                let mut chars = s.chars();
+                match (chars.next(), chars.next()) {
+                    (Some(c), None) => Ok(c),
+                    _ => unreachable!(
+                        "str::from_utf8({:?}) = {:?} was expected to have 1 char, \
+                         but {} chars were found",
+                        utf8,
+                        s,
+                        s.chars().count()
+                    ),
+                }
+            })
+        });
+
+        // HACK(eddyb) doing a separate validation iteration like this might be
+        // wasteful, but it's easier to avoid starting to print a string literal
+        // in the first place, than to abort it mid-string.
+        if chars.clone().any(|r| r.is_err()) {
+            None
+        } else {
+            Some(chars.map(Result::unwrap))
+        }
+    }
+}
+
+fn basic_type(tag: u8) -> Option<&'static str> {
+    Some(match tag {
+        b'b' => "bool",
+        b'c' => "char",
+        b'e' => "str",
+        b'u' => "()",
+        b'a' => "i8",
+        b's' => "i16",
+        b'l' => "i32",
+        b'x' => "i64",
+        b'n' => "i128",
+        b'i' => "isize",
+        b'h' => "u8",
+        b't' => "u16",
+        b'm' => "u32",
+        b'y' => "u64",
+        b'o' => "u128",
+        b'j' => "usize",
+        b'f' => "f32",
+        b'd' => "f64",
+        b'z' => "!",
+        b'p' => "_",
+        b'v' => "...",
+
+        _ => return None,
+    })
+}
+
+struct Parser<'s> {
+    sym: &'s str,
+    next: usize,
+    depth: u32,
+}
+
+impl<'s> Parser<'s> {
+    fn push_depth(&mut self) -> Result<(), ParseError> {
+        self.depth += 1;
+        if self.depth > MAX_DEPTH {
+            Err(ParseError::RecursedTooDeep)
+        } else {
+            Ok(())
+        }
+    }
+
+    fn pop_depth(&mut self) {
+        self.depth -= 1;
+    }
+
+    fn peek(&self) -> Option<u8> {
+        self.sym.as_bytes().get(self.next).cloned()
+    }
+
+    fn eat(&mut self, b: u8) -> bool {
+        if self.peek() == Some(b) {
+            self.next += 1;
+            true
+        } else {
+            false
+        }
+    }
+
+    fn next(&mut self) -> Result<u8, ParseError> {
+        let b = self.peek().ok_or(ParseError::Invalid)?;
+        self.next += 1;
+        Ok(b)
+    }
+
+    fn hex_nibbles(&mut self) -> Result<HexNibbles<'s>, ParseError> {
+        let start = self.next;
+        loop {
+            match self.next()? {
+                b'0'..=b'9' | b'a'..=b'f' => {}
+                b'_' => break,
+                _ => return Err(ParseError::Invalid),
+            }
+        }
+        Ok(HexNibbles {
+            nibbles: &self.sym[start..self.next - 1],
+        })
+    }
+
+    fn digit_10(&mut self) -> Result<u8, ParseError> {
+        let d = match self.peek() {
+            Some(d @ b'0'..=b'9') => d - b'0',
+            _ => return Err(ParseError::Invalid),
+        };
+        self.next += 1;
+        Ok(d)
+    }
+
+    fn digit_62(&mut self) -> Result<u8, ParseError> {
+        let d = match self.peek() {
+            Some(d @ b'0'..=b'9') => d - b'0',
+            Some(d @ b'a'..=b'z') => 10 + (d - b'a'),
+            Some(d @ b'A'..=b'Z') => 10 + 26 + (d - b'A'),
+            _ => return Err(ParseError::Invalid),
+        };
+        self.next += 1;
+        Ok(d)
+    }
+
+    fn integer_62(&mut self) -> Result<u64, ParseError> {
+        if self.eat(b'_') {
+            return Ok(0);
+        }
+
+        let mut x: u64 = 0;
+        while !self.eat(b'_') {
+            let d = self.digit_62()? as u64;
+            x = x.checked_mul(62).ok_or(ParseError::Invalid)?;
+            x = x.checked_add(d).ok_or(ParseError::Invalid)?;
+        }
+        x.checked_add(1).ok_or(ParseError::Invalid)
+    }
+
+    fn opt_integer_62(&mut self, tag: u8) -> Result<u64, ParseError> {
+        if !self.eat(tag) {
+            return Ok(0);
+        }
+        self.integer_62()?.checked_add(1).ok_or(ParseError::Invalid)
+    }
+
+    fn disambiguator(&mut self) -> Result<u64, ParseError> {
+        self.opt_integer_62(b's')
+    }
+
+    fn namespace(&mut self) -> Result<Option<char>, ParseError> {
+        match self.next()? {
+            // Special namespaces, like closures and shims.
+            ns @ b'A'..=b'Z' => Ok(Some(ns as char)),
+
+            // Implementation-specific/unspecified namespaces.
+            b'a'..=b'z' => Ok(None),
+
+            _ => Err(ParseError::Invalid),
+        }
+    }
+
+    fn backref(&mut self) -> Result<Parser<'s>, ParseError> {
+        let s_start = self.next - 1;
+        let i = self.integer_62()?;
+        if i >= s_start as u64 {
+            return Err(ParseError::Invalid);
+        }
+        let mut new_parser = Parser {
+            sym: self.sym,
+            next: i as usize,
+            depth: self.depth,
+        };
+        new_parser.push_depth()?;
+        Ok(new_parser)
+    }
+
+    fn ident(&mut self) -> Result<Ident<'s>, ParseError> {
+        let is_punycode = self.eat(b'u');
+        let mut len = self.digit_10()? as usize;
+        if len != 0 {
+            while let Ok(d) = self.digit_10() {
+                len = len.checked_mul(10).ok_or(ParseError::Invalid)?;
+                len = len.checked_add(d as usize).ok_or(ParseError::Invalid)?;
+            }
+        }
+
+        // Skip past the optional `_` separator.
+        self.eat(b'_');
+
+        let start = self.next;
+        self.next = self.next.checked_add(len).ok_or(ParseError::Invalid)?;
+        if self.next > self.sym.len() {
+            return Err(ParseError::Invalid);
+        }
+
+        let ident = &self.sym[start..self.next];
+
+        if is_punycode {
+            let ident = match ident.bytes().rposition(|b| b == b'_') {
+                Some(i) => Ident {
+                    ascii: &ident[..i],
+                    punycode: &ident[i + 1..],
+                },
+                None => Ident {
+                    ascii: "",
+                    punycode: ident,
+                },
+            };
+            if ident.punycode.is_empty() {
+                return Err(ParseError::Invalid);
+            }
+            Ok(ident)
+        } else {
+            Ok(Ident {
+                ascii: ident,
+                punycode: "",
+            })
+        }
+    }
+}
+
+struct Printer<'a, 'b: 'a, 's> {
+    /// The input parser to demangle from, or `Err` if any (parse) error was
+    /// encountered (in order to disallow further likely-incorrect demangling).
+    ///
+    /// See also the documentation on the `invalid!` and `parse!` macros below.
+    parser: Result<Parser<'s>, ParseError>,
+
+    /// The output formatter to demangle to, or `None` while skipping printing.
+    out: Option<&'a mut fmt::Formatter<'b>>,
+
+    /// Cumulative number of lifetimes bound by `for<...>` binders ('G'),
+    /// anywhere "around" the current entity (e.g. type) being demangled.
+    /// This value is not tracked while skipping printing, as it'd be unused.
+    ///
+    /// See also the documentation on the `Printer::in_binder` method.
+    bound_lifetime_depth: u32,
+}
+
+impl ParseError {
+    /// Snippet to print when the error is initially encountered.
+    fn message(&self) -> &str {
+        match self {
+            ParseError::Invalid => "{invalid syntax}",
+            ParseError::RecursedTooDeep => "{recursion limit reached}",
+        }
+    }
+}
+
+/// Mark the parser as errored (with `ParseError::Invalid`), print the
+/// appropriate message (see `ParseError::message`) and return early.
+macro_rules! invalid {
+    ($printer:ident) => {{
+        let err = ParseError::Invalid;
+        $printer.print(err.message())?;
+        $printer.parser = Err(err);
+        return Ok(());
+    }};
+}
+
+/// Call a parser method (if the parser hasn't errored yet),
+/// and mark the parser as errored if it returns `Err`.
+///
+/// If the parser errored, before or now, this returns early,
+/// from the current function, after printing either:
+/// * for a new error, the appropriate message (see `ParseError::message`)
+/// * for an earlier error, only `?` -  this allows callers to keep printing
+///   the approximate syntax of the path/type/const, despite having errors,
+///   e.g. `Vec<[(A, ?); ?]>` instead of `Vec<[(A, ?`
+macro_rules! parse {
+    ($printer:ident, $method:ident $(($($arg:expr),*))*) => {
+        match $printer.parser {
+            Ok(ref mut parser) => match parser.$method($($($arg),*)*) {
+                Ok(x) => x,
+                Err(err) => {
+                    $printer.print(err.message())?;
+                    $printer.parser = Err(err);
+                    return Ok(());
+                }
+            }
+            Err(_) => return $printer.print("?"),
+        }
+    };
+}
+
+impl<'a, 'b, 's> Printer<'a, 'b, 's> {
+    /// Eat the given character from the parser,
+    /// returning `false` if the parser errored.
+    fn eat(&mut self, b: u8) -> bool {
+        self.parser.as_mut().map(|p| p.eat(b)) == Ok(true)
+    }
+
+    /// Skip printing (i.e. `self.out` will be `None`) for the duration of the
+    /// given closure. This should not change parsing behavior, only disable the
+    /// output, but there may be optimizations (such as not traversing backrefs).
+    fn skipping_printing<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut Self) -> fmt::Result,
+    {
+        let orig_out = self.out.take();
+        f(self).expect("`fmt::Error`s should be impossible without a `fmt::Formatter`");
+        self.out = orig_out;
+    }
+
+    /// Print the target of a backref, using the given closure.
+    /// When printing is being skipped, the backref will only be parsed,
+    /// ignoring the backref's target completely.
+    fn print_backref<F>(&mut self, f: F) -> fmt::Result
+    where
+        F: FnOnce(&mut Self) -> fmt::Result,
+    {
+        let backref_parser = parse!(self, backref);
+
+        if self.out.is_none() {
+            return Ok(());
+        }
+
+        let orig_parser = mem::replace(&mut self.parser, Ok(backref_parser));
+        let r = f(self);
+        self.parser = orig_parser;
+        r
+    }
+
+    fn pop_depth(&mut self) {
+        if let Ok(ref mut parser) = self.parser {
+            parser.pop_depth();
+        }
+    }
+
+    /// Output the given value to `self.out` (using `fmt::Display` formatting),
+    /// if printing isn't being skipped.
+    fn print(&mut self, x: impl fmt::Display) -> fmt::Result {
+        if let Some(out) = &mut self.out {
+            fmt::Display::fmt(&x, out)?;
+        }
+        Ok(())
+    }
+
+    /// Output the given `char`s (escaped using `char::escape_debug`), with the
+    /// whole sequence wrapped in quotes, for either a `char` or `&str` literal,
+    /// if printing isn't being skipped.
+    fn print_quoted_escaped_chars(
+        &mut self,
+        quote: char,
+        chars: impl Iterator<Item = char>,
+    ) -> fmt::Result {
+        if let Some(out) = &mut self.out {
+            use core::fmt::Write;
+
+            out.write_char(quote)?;
+            for c in chars {
+                // Special-case not escaping a single/double quote, when
+                // inside the opposite kind of quote.
+                if matches!((quote, c), ('\'', '"') | ('"', '\'')) {
+                    out.write_char(c)?;
+                    continue;
+                }
+
+                for escaped in c.escape_debug() {
+                    out.write_char(escaped)?;
+                }
+            }
+            out.write_char(quote)?;
+        }
+        Ok(())
+    }
+
+    /// Print the lifetime according to the previously decoded index.
+    /// An index of `0` always refers to `'_`, but starting with `1`,
+    /// indices refer to late-bound lifetimes introduced by a binder.
+    fn print_lifetime_from_index(&mut self, lt: u64) -> fmt::Result {
+        // Bound lifetimes aren't tracked when skipping printing.
+        if self.out.is_none() {
+            return Ok(());
+        }
+
+        self.print("'")?;
+        if lt == 0 {
+            return self.print("_");
+        }
+        match (self.bound_lifetime_depth as u64).checked_sub(lt) {
+            Some(depth) => {
+                // Try to print lifetimes alphabetically first.
+                if depth < 26 {
+                    let c = (b'a' + depth as u8) as char;
+                    self.print(c)
+                } else {
+                    // Use `'_123` after running out of letters.
+                    self.print("_")?;
+                    self.print(depth)
+                }
+            }
+            None => invalid!(self),
+        }
+    }
+
+    /// Optionally enter a binder ('G') for late-bound lifetimes,
+    /// printing e.g. `for<'a, 'b> ` before calling the closure,
+    /// and make those lifetimes visible to it (via depth level).
+    fn in_binder<F>(&mut self, f: F) -> fmt::Result
+    where
+        F: FnOnce(&mut Self) -> fmt::Result,
+    {
+        let bound_lifetimes = parse!(self, opt_integer_62(b'G'));
+
+        // Don't track bound lifetimes when skipping printing.
+        if self.out.is_none() {
+            return f(self);
+        }
+
+        if bound_lifetimes > 0 {
+            self.print("for<")?;
+            for i in 0..bound_lifetimes {
+                if i > 0 {
+                    self.print(", ")?;
+                }
+                self.bound_lifetime_depth += 1;
+                self.print_lifetime_from_index(1)?;
+            }
+            self.print("> ")?;
+        }
+
+        let r = f(self);
+
+        // Restore `bound_lifetime_depth` to the previous value.
+        self.bound_lifetime_depth -= bound_lifetimes as u32;
+
+        r
+    }
+
+    /// Print list elements using the given closure and separator,
+    /// until the end of the list ('E') is found, or the parser errors.
+    /// Returns the number of elements printed.
+    fn print_sep_list<F>(&mut self, f: F, sep: &str) -> Result<usize, fmt::Error>
+    where
+        F: Fn(&mut Self) -> fmt::Result,
+    {
+        let mut i = 0;
+        while self.parser.is_ok() && !self.eat(b'E') {
+            if i > 0 {
+                self.print(sep)?;
+            }
+            f(self)?;
+            i += 1;
+        }
+        Ok(i)
+    }
+
+    fn print_path(&mut self, in_value: bool) -> fmt::Result {
+        parse!(self, push_depth);
+
+        let tag = parse!(self, next);
+        match tag {
+            b'C' => {
+                let dis = parse!(self, disambiguator);
+                let name = parse!(self, ident);
+
+                self.print(name)?;
+                if let Some(out) = &mut self.out {
+                    if !out.alternate() {
+                        out.write_str("[")?;
+                        fmt::LowerHex::fmt(&dis, out)?;
+                        out.write_str("]")?;
+                    }
+                }
+            }
+            b'N' => {
+                let ns = parse!(self, namespace);
+
+                self.print_path(in_value)?;
+
+                // HACK(eddyb) if the parser is already marked as having errored,
+                // `parse!` below will print a `?` without its preceding `::`
+                // (because printing the `::` is skipped in certain conditions,
+                // i.e. a lowercase namespace with an empty identifier),
+                // so in order to get `::?`, the `::` has to be printed here.
+                if self.parser.is_err() {
+                    self.print("::")?;
+                }
+
+                let dis = parse!(self, disambiguator);
+                let name = parse!(self, ident);
+
+                match ns {
+                    // Special namespaces, like closures and shims.
+                    Some(ns) => {
+                        self.print("::{")?;
+                        match ns {
+                            'C' => self.print("closure")?,
+                            'S' => self.print("shim")?,
+                            _ => self.print(ns)?,
+                        }
+                        if !name.ascii.is_empty() || !name.punycode.is_empty() {
+                            self.print(":")?;
+                            self.print(name)?;
+                        }
+                        self.print("#")?;
+                        self.print(dis)?;
+                        self.print("}")?;
+                    }
+
+                    // Implementation-specific/unspecified namespaces.
+                    None => {
+                        if !name.ascii.is_empty() || !name.punycode.is_empty() {
+                            self.print("::")?;
+                            self.print(name)?;
+                        }
+                    }
+                }
+            }
+            b'M' | b'X' | b'Y' => {
+                if tag != b'Y' {
+                    // Ignore the `impl`'s own path.
+                    parse!(self, disambiguator);
+                    self.skipping_printing(|this| this.print_path(false));
+                }
+
+                self.print("<")?;
+                self.print_type()?;
+                if tag != b'M' {
+                    self.print(" as ")?;
+                    self.print_path(false)?;
+                }
+                self.print(">")?;
+            }
+            b'I' => {
+                self.print_path(in_value)?;
+                if in_value {
+                    self.print("::")?;
+                }
+                self.print("<")?;
+                self.print_sep_list(Self::print_generic_arg, ", ")?;
+                self.print(">")?;
+            }
+            b'B' => {
+                self.print_backref(|this| this.print_path(in_value))?;
+            }
+            _ => invalid!(self),
+        }
+
+        self.pop_depth();
+        Ok(())
+    }
+
+    fn print_generic_arg(&mut self) -> fmt::Result {
+        if self.eat(b'L') {
+            let lt = parse!(self, integer_62);
+            self.print_lifetime_from_index(lt)
+        } else if self.eat(b'K') {
+            self.print_const(false)
+        } else {
+            self.print_type()
+        }
+    }
+
+    fn print_type(&mut self) -> fmt::Result {
+        let tag = parse!(self, next);
+
+        if let Some(ty) = basic_type(tag) {
+            return self.print(ty);
+        }
+
+        parse!(self, push_depth);
+
+        match tag {
+            b'R' | b'Q' => {
+                self.print("&")?;
+                if self.eat(b'L') {
+                    let lt = parse!(self, integer_62);
+                    if lt != 0 {
+                        self.print_lifetime_from_index(lt)?;
+                        self.print(" ")?;
+                    }
+                }
+                if tag != b'R' {
+                    self.print("mut ")?;
+                }
+                self.print_type()?;
+            }
+
+            b'P' | b'O' => {
+                self.print("*")?;
+                if tag != b'P' {
+                    self.print("mut ")?;
+                } else {
+                    self.print("const ")?;
+                }
+                self.print_type()?;
+            }
+
+            b'A' | b'S' => {
+                self.print("[")?;
+                self.print_type()?;
+                if tag == b'A' {
+                    self.print("; ")?;
+                    self.print_const(true)?;
+                }
+                self.print("]")?;
+            }
+            b'T' => {
+                self.print("(")?;
+                let count = self.print_sep_list(Self::print_type, ", ")?;
+                if count == 1 {
+                    self.print(",")?;
+                }
+                self.print(")")?;
+            }
+            b'F' => self.in_binder(|this| {
+                let is_unsafe = this.eat(b'U');
+                let abi = if this.eat(b'K') {
+                    if this.eat(b'C') {
+                        Some("C")
+                    } else {
+                        let abi = parse!(this, ident);
+                        if abi.ascii.is_empty() || !abi.punycode.is_empty() {
+                            invalid!(this);
+                        }
+                        Some(abi.ascii)
+                    }
+                } else {
+                    None
+                };
+
+                if is_unsafe {
+                    this.print("unsafe ")?;
+                }
+
+                if let Some(abi) = abi {
+                    this.print("extern \"")?;
+
+                    // If the ABI had any `-`, they were replaced with `_`,
+                    // so the parts between `_` have to be re-joined with `-`.
+                    let mut parts = abi.split('_');
+                    this.print(parts.next().unwrap())?;
+                    for part in parts {
+                        this.print("-")?;
+                        this.print(part)?;
+                    }
+
+                    this.print("\" ")?;
+                }
+
+                this.print("fn(")?;
+                this.print_sep_list(Self::print_type, ", ")?;
+                this.print(")")?;
+
+                if this.eat(b'u') {
+                    // Skip printing the return type if it's 'u', i.e. `()`.
+                } else {
+                    this.print(" -> ")?;
+                    this.print_type()?;
+                }
+
+                Ok(())
+            })?,
+            b'D' => {
+                self.print("dyn ")?;
+                self.in_binder(|this| {
+                    this.print_sep_list(Self::print_dyn_trait, " + ")?;
+                    Ok(())
+                })?;
+
+                if !self.eat(b'L') {
+                    invalid!(self);
+                }
+                let lt = parse!(self, integer_62);
+                if lt != 0 {
+                    self.print(" + ")?;
+                    self.print_lifetime_from_index(lt)?;
+                }
+            }
+            b'B' => {
+                self.print_backref(Self::print_type)?;
+            }
+            _ => {
+                // Go back to the tag, so `print_path` also sees it.
+                let _ = self.parser.as_mut().map(|p| p.next -= 1);
+                self.print_path(false)?;
+            }
+        }
+
+        self.pop_depth();
+        Ok(())
+    }
+
+    /// A trait in a trait object may have some "existential projections"
+    /// (i.e. associated type bindings) after it, which should be printed
+    /// in the `<...>` of the trait, e.g. `dyn Trait<T, U, Assoc=X>`.
+    /// To this end, this method will keep the `<...>` of an 'I' path
+    /// open, by omitting the `>`, and return `Ok(true)` in that case.
+    fn print_path_maybe_open_generics(&mut self) -> Result<bool, fmt::Error> {
+        if self.eat(b'B') {
+            // NOTE(eddyb) the closure may not run if printing is being skipped,
+            // but in that case the returned boolean doesn't matter.
+            let mut open = false;
+            self.print_backref(|this| {
+                open = this.print_path_maybe_open_generics()?;
+                Ok(())
+            })?;
+            Ok(open)
+        } else if self.eat(b'I') {
+            self.print_path(false)?;
+            self.print("<")?;
+            self.print_sep_list(Self::print_generic_arg, ", ")?;
+            Ok(true)
+        } else {
+            self.print_path(false)?;
+            Ok(false)
+        }
+    }
+
+    fn print_dyn_trait(&mut self) -> fmt::Result {
+        let mut open = self.print_path_maybe_open_generics()?;
+
+        while self.eat(b'p') {
+            if !open {
+                self.print("<")?;
+                open = true;
+            } else {
+                self.print(", ")?;
+            }
+
+            let name = parse!(self, ident);
+            self.print(name)?;
+            self.print(" = ")?;
+            self.print_type()?;
+        }
+
+        if open {
+            self.print(">")?;
+        }
+
+        Ok(())
+    }
+
+    fn print_const(&mut self, in_value: bool) -> fmt::Result {
+        let tag = parse!(self, next);
+
+        parse!(self, push_depth);
+
+        // Only literals (and the names of `const` generic parameters, but they
+        // don't get mangled at all), can appear in generic argument position
+        // without any disambiguation, all other expressions require braces.
+        // To avoid duplicating the mapping between `tag` and what syntax gets
+        // used (especially any special-casing), every case that needs braces
+        // has to call `open_brace(self)?` (and the closing brace is automatic).
+        let mut opened_brace = false;
+        let mut open_brace_if_outside_expr = |this: &mut Self| {
+            // If this expression is nested in another, braces aren't required.
+            if in_value {
+                return Ok(());
+            }
+
+            opened_brace = true;
+            this.print("{")
+        };
+
+        match tag {
+            b'p' => self.print("_")?,
+
+            // Primitive leaves with hex-encoded values (see `basic_type`).
+            b'h' | b't' | b'm' | b'y' | b'o' | b'j' => self.print_const_uint(tag)?,
+            b'a' | b's' | b'l' | b'x' | b'n' | b'i' => {
+                if self.eat(b'n') {
+                    self.print("-")?;
+                }
+
+                self.print_const_uint(tag)?;
+            }
+            b'b' => match parse!(self, hex_nibbles).try_parse_uint() {
+                Some(0) => self.print("false")?,
+                Some(1) => self.print("true")?,
+                _ => invalid!(self),
+            },
+            b'c' => {
+                let valid_char = parse!(self, hex_nibbles)
+                    .try_parse_uint()
+                    .and_then(|v| u32::try_from(v).ok())
+                    .and_then(char::from_u32);
+                match valid_char {
+                    Some(c) => self.print_quoted_escaped_chars('\'', iter::once(c))?,
+                    None => invalid!(self),
+                }
+            }
+            b'e' => {
+                // NOTE(eddyb) a string literal `"..."` has type `&str`, so
+                // to get back the type `str`, `*"..."` syntax is needed
+                // (even if that may not be valid in Rust itself).
+                open_brace_if_outside_expr(self)?;
+                self.print("*")?;
+
+                self.print_const_str_literal()?;
+            }
+
+            b'R' | b'Q' => {
+                // NOTE(eddyb) this prints `"..."` instead of `&*"..."`, which
+                // is what `Re..._` would imply (see comment for `str` above).
+                if tag == b'R' && self.eat(b'e') {
+                    self.print_const_str_literal()?;
+                } else {
+                    open_brace_if_outside_expr(self)?;
+                    self.print("&")?;
+                    if tag != b'R' {
+                        self.print("mut ")?;
+                    }
+                    self.print_const(true)?;
+                }
+            }
+            b'A' => {
+                open_brace_if_outside_expr(self)?;
+                self.print("[")?;
+                self.print_sep_list(|this| this.print_const(true), ", ")?;
+                self.print("]")?;
+            }
+            b'T' => {
+                open_brace_if_outside_expr(self)?;
+                self.print("(")?;
+                let count = self.print_sep_list(|this| this.print_const(true), ", ")?;
+                if count == 1 {
+                    self.print(",")?;
+                }
+                self.print(")")?;
+            }
+            b'V' => {
+                open_brace_if_outside_expr(self)?;
+                self.print_path(true)?;
+                match parse!(self, next) {
+                    b'U' => {}
+                    b'T' => {
+                        self.print("(")?;
+                        self.print_sep_list(|this| this.print_const(true), ", ")?;
+                        self.print(")")?;
+                    }
+                    b'S' => {
+                        self.print(" { ")?;
+                        self.print_sep_list(
+                            |this| {
+                                parse!(this, disambiguator);
+                                let name = parse!(this, ident);
+                                this.print(name)?;
+                                this.print(": ")?;
+                                this.print_const(true)
+                            },
+                            ", ",
+                        )?;
+                        self.print(" }")?;
+                    }
+                    _ => invalid!(self),
+                }
+            }
+            b'B' => {
+                self.print_backref(|this| this.print_const(in_value))?;
+            }
+            _ => invalid!(self),
+        }
+
+        if opened_brace {
+            self.print("}")?;
+        }
+
+        self.pop_depth();
+        Ok(())
+    }
+
+    fn print_const_uint(&mut self, ty_tag: u8) -> fmt::Result {
+        let hex = parse!(self, hex_nibbles);
+
+        match hex.try_parse_uint() {
+            Some(v) => self.print(v)?,
+
+            // Print anything that doesn't fit in `u64` verbatim.
+            None => {
+                self.print("0x")?;
+                self.print(hex.nibbles)?;
+            }
+        }
+
+        if let Some(out) = &mut self.out {
+            if !out.alternate() {
+                let ty = basic_type(ty_tag).unwrap();
+                self.print(ty)?;
+            }
+        }
+
+        Ok(())
+    }
+
+    fn print_const_str_literal(&mut self) -> fmt::Result {
+        match parse!(self, hex_nibbles).try_parse_str_chars() {
+            Some(chars) => self.print_quoted_escaped_chars('"', chars),
+            None => invalid!(self),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::prelude::v1::*;
+
+    macro_rules! t {
+        ($a:expr, $b:expr) => {{
+            assert_eq!(format!("{}", ::demangle($a)), $b);
+        }};
+    }
+    macro_rules! t_nohash {
+        ($a:expr, $b:expr) => {{
+            assert_eq!(format!("{:#}", ::demangle($a)), $b);
+        }};
+    }
+    macro_rules! t_nohash_type {
+        ($a:expr, $b:expr) => {
+            t_nohash!(concat!("_RMC0", $a), concat!("<", $b, ">"))
+        };
+    }
+    macro_rules! t_const {
+        ($mangled:expr, $value:expr) => {
+            t_nohash!(
+                concat!("_RIC0K", $mangled, "E"),
+                concat!("::<", $value, ">")
+            )
+        };
+    }
+    macro_rules! t_const_suffixed {
+        ($mangled:expr, $value:expr, $value_ty_suffix:expr) => {{
+            t_const!($mangled, $value);
+            t!(
+                concat!("_RIC0K", $mangled, "E"),
+                concat!("[0]::<", $value, $value_ty_suffix, ">")
+            );
+        }};
+    }
+
+    #[test]
+    fn demangle_crate_with_leading_digit() {
+        t_nohash!("_RNvC6_123foo3bar", "123foo::bar");
+    }
+
+    #[test]
+    fn demangle_utf8_idents() {
+        t_nohash!(
+            "_RNqCs4fqI2P2rA04_11utf8_identsu30____7hkackfecea1cbdathfdh9hlq6y",
+            "utf8_idents::საჭმელად_გემრიელი_სადილი"
+        );
+    }
+
+    #[test]
+    fn demangle_closure() {
+        t_nohash!(
+            "_RNCNCNgCs6DXkGYLi8lr_2cc5spawn00B5_",
+            "cc::spawn::{closure#0}::{closure#0}"
+        );
+        t_nohash!(
+            "_RNCINkXs25_NgCsbmNqQUJIY6D_4core5sliceINyB9_4IterhENuNgNoBb_4iter8iterator8Iterator9rpositionNCNgNpB9_6memchr7memrchrs_0E0Bb_",
+            "<core::slice::Iter<u8> as core::iter::iterator::Iterator>::rposition::<core::slice::memchr::memrchr::{closure#1}>::{closure#0}"
+        );
+    }
+
+    #[test]
+    fn demangle_dyn_trait() {
+        t_nohash!(
+            "_RINbNbCskIICzLVDPPb_5alloc5alloc8box_freeDINbNiB4_5boxed5FnBoxuEp6OutputuEL_ECs1iopQbuBiw2_3std",
+            "alloc::alloc::box_free::<dyn alloc::boxed::FnBox<(), Output = ()>>"
+        );
+    }
+
+    #[test]
+    fn demangle_const_generics_preview() {
+        // NOTE(eddyb) this was hand-written, before rustc had working
+        // const generics support (but the mangling format did include them).
+        t_nohash_type!(
+            "INtC8arrayvec8ArrayVechKj7b_E",
+            "arrayvec::ArrayVec<u8, 123>"
+        );
+        t_const_suffixed!("j7b_", "123", "usize");
+    }
+
+    #[test]
+    fn demangle_min_const_generics() {
+        t_const!("p", "_");
+        t_const_suffixed!("hb_", "11", "u8");
+        t_const_suffixed!("off00ff00ff00ff00ff_", "0xff00ff00ff00ff00ff", "u128");
+        t_const_suffixed!("s98_", "152", "i16");
+        t_const_suffixed!("anb_", "-11", "i8");
+        t_const!("b0_", "false");
+        t_const!("b1_", "true");
+        t_const!("c76_", "'v'");
+        t_const!("c22_", r#"'"'"#);
+        t_const!("ca_", "'\\n'");
+        t_const!("c2202_", "'∂'");
+    }
+
+    #[test]
+    fn demangle_const_str() {
+        t_const!("e616263_", "{*\"abc\"}");
+        t_const!("e27_", r#"{*"'"}"#);
+        t_const!("e090a_", "{*\"\\t\\n\"}");
+        t_const!("ee28882c3bc_", "{*\"∂ü\"}");
+        t_const!(
+            "ee183a1e18390e183ade1839be18394e1839ae18390e183935fe18392e18394e1839b\
+              e183a0e18398e18394e1839ae183985fe183a1e18390e18393e18398e1839ae18398_",
+            "{*\"საჭმელად_გემრიელი_სადილი\"}"
+        );
+        t_const!(
+            "ef09f908af09fa688f09fa686f09f90ae20c2a720f09f90b6f09f9192e298\
+              95f09f94a520c2a720f09fa7a1f09f929bf09f929af09f9299f09f929c_",
+            "{*\"🐊🦈🦆🐮 § 🐶👒☕🔥 § 🧡💛💚💙💜\"}"
+        );
+    }
+
+    // NOTE(eddyb) this uses the same strings as `demangle_const_str` and should
+    // be kept in sync with it - while a macro could be used to generate both
+    // `str` and `&str` tests, from a single list of strings, this seems clearer.
+    #[test]
+    fn demangle_const_ref_str() {
+        t_const!("Re616263_", "\"abc\"");
+        t_const!("Re27_", r#""'""#);
+        t_const!("Re090a_", "\"\\t\\n\"");
+        t_const!("Ree28882c3bc_", "\"∂ü\"");
+        t_const!(
+            "Ree183a1e18390e183ade1839be18394e1839ae18390e183935fe18392e18394e1839b\
+               e183a0e18398e18394e1839ae183985fe183a1e18390e18393e18398e1839ae18398_",
+            "\"საჭმელად_გემრიელი_სადილი\""
+        );
+        t_const!(
+            "Ref09f908af09fa688f09fa686f09f90ae20c2a720f09f90b6f09f9192e298\
+               95f09f94a520c2a720f09fa7a1f09f929bf09f929af09f9299f09f929c_",
+            "\"🐊🦈🦆🐮 § 🐶👒☕🔥 § 🧡💛💚💙💜\""
+        );
+    }
+
+    #[test]
+    fn demangle_const_ref() {
+        t_const!("Rp", "{&_}");
+        t_const!("Rh7b_", "{&123}");
+        t_const!("Rb0_", "{&false}");
+        t_const!("Rc58_", "{&'X'}");
+        t_const!("RRRh0_", "{&&&0}");
+        t_const!("RRRe_", "{&&\"\"}");
+        t_const!("QAE", "{&mut []}");
+    }
+
+    #[test]
+    fn demangle_const_array() {
+        t_const!("AE", "{[]}");
+        t_const!("Aj0_E", "{[0]}");
+        t_const!("Ah1_h2_h3_E", "{[1, 2, 3]}");
+        t_const!("ARe61_Re62_Re63_E", "{[\"a\", \"b\", \"c\"]}");
+        t_const!("AAh1_h2_EAh3_h4_EE", "{[[1, 2], [3, 4]]}");
+    }
+
+    #[test]
+    fn demangle_const_tuple() {
+        t_const!("TE", "{()}");
+        t_const!("Tj0_E", "{(0,)}");
+        t_const!("Th1_b0_E", "{(1, false)}");
+        t_const!(
+            "TRe616263_c78_RAh1_h2_h3_EE",
+            "{(\"abc\", 'x', &[1, 2, 3])}"
+        );
+    }
+
+    #[test]
+    fn demangle_const_adt() {
+        t_const!(
+            "VNvINtNtC4core6option6OptionjE4NoneU",
+            "{core::option::Option::<usize>::None}"
+        );
+        t_const!(
+            "VNvINtNtC4core6option6OptionjE4SomeTj0_E",
+            "{core::option::Option::<usize>::Some(0)}"
+        );
+        t_const!(
+            "VNtC3foo3BarS1sRe616263_2chc78_5sliceRAh1_h2_h3_EE",
+            "{foo::Bar { s: \"abc\", ch: 'x', slice: &[1, 2, 3] }}"
+        );
+    }
+
+    #[test]
+    fn demangle_exponential_explosion() {
+        // NOTE(eddyb) because of the prefix added by `t_nohash_type!` is
+        // 3 bytes long, `B2_` refers to the start of the type, not `B_`.
+        // 6 backrefs (`B8_E` through `B3_E`) result in 2^6 = 64 copies of `_`.
+        // Also, because the `p` (`_`) type is after all of the starts of the
+        // backrefs, it can be replaced with any other type, independently.
+        t_nohash_type!(
+            concat!("TTTTTT", "p", "B8_E", "B7_E", "B6_E", "B5_E", "B4_E", "B3_E"),
+            "((((((_, _), (_, _)), ((_, _), (_, _))), (((_, _), (_, _)), ((_, _), (_, _)))), \
+             ((((_, _), (_, _)), ((_, _), (_, _))), (((_, _), (_, _)), ((_, _), (_, _))))), \
+             (((((_, _), (_, _)), ((_, _), (_, _))), (((_, _), (_, _)), ((_, _), (_, _)))), \
+             ((((_, _), (_, _)), ((_, _), (_, _))), (((_, _), (_, _)), ((_, _), (_, _))))))"
+        );
+    }
+
+    #[test]
+    fn demangle_thinlto() {
+        t_nohash!("_RC3foo.llvm.9D1C9369", "foo");
+        t_nohash!("_RC3foo.llvm.9D1C9369@@16", "foo");
+        t_nohash!("_RNvC9backtrace3foo.llvm.A5310EB9", "backtrace::foo");
+    }
+
+    #[test]
+    fn demangle_extra_suffix() {
+        // From alexcrichton/rustc-demangle#27:
+        t_nohash!(
+            "_RNvNtNtNtNtCs92dm3009vxr_4rand4rngs7adapter9reseeding4fork23FORK_HANDLER_REGISTERED.0.0",
+            "rand::rngs::adapter::reseeding::fork::FORK_HANDLER_REGISTERED.0.0"
+        );
+    }
+
+    #[test]
+    fn demangling_limits() {
+        // Stress tests found via fuzzing.
+
+        for sym in include_str!("v0-large-test-symbols/early-recursion-limit")
+            .lines()
+            .filter(|line| !line.is_empty() && !line.starts_with('#'))
+        {
+            assert_eq!(
+                super::demangle(sym).map(|_| ()),
+                Err(super::ParseError::RecursedTooDeep)
+            );
+        }
+
+        assert_contains!(
+            ::demangle(
+                "RIC20tRYIMYNRYFG05_EB5_B_B6_RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR\
+        RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRB_E",
+            )
+            .to_string(),
+            "{recursion limit reached}"
+        );
+    }
+
+    #[test]
+    fn recursion_limit_leaks() {
+        // NOTE(eddyb) this test checks that both paths and types support the
+        // recursion limit correctly, i.e. matching `push_depth` and `pop_depth`,
+        // and don't leak "recursion levels" and trip the limit.
+        // The test inputs are generated on the fly, using a repeated pattern,
+        // as hardcoding the actual strings would be too verbose.
+        // Also, `MAX_DEPTH` can be directly used, instead of assuming its value.
+        for &(sym_leaf, expected_leaf) in &[("p", "_"), ("Rp", "&_"), ("C1x", "x")] {
+            let mut sym = format!("_RIC0p");
+            let mut expected = format!("::<_");
+            for _ in 0..(super::MAX_DEPTH * 2) {
+                sym.push_str(sym_leaf);
+                expected.push_str(", ");
+                expected.push_str(expected_leaf);
+            }
+            sym.push('E');
+            expected.push('>');
+
+            t_nohash!(&sym, expected);
+        }
+    }
+
+    #[test]
+    fn recursion_limit_backref_free_bypass() {
+        // NOTE(eddyb) this test checks that long symbols cannot bypass the
+        // recursion limit by not using backrefs, and cause a stack overflow.
+
+        // This value was chosen to be high enough that stack overflows were
+        // observed even with `cargo test --release`.
+        let depth = 100_000;
+
+        // In order to hide the long mangling from the initial "shallow" parse,
+        // it's nested in an identifier (crate name), preceding its use.
+        let mut sym = format!("_RIC{}", depth);
+        let backref_start = sym.len() - 2;
+        for _ in 0..depth {
+            sym.push('R');
+        }
+
+        // Write a backref to just after the length of the identifier.
+        sym.push('B');
+        sym.push(char::from_digit((backref_start - 1) as u32, 36).unwrap());
+        sym.push('_');
+
+        // Close the `I` at the start.
+        sym.push('E');
+
+        assert_contains!(::demangle(&sym).to_string(), "{recursion limit reached}");
+    }
+}