vendor/rustc-demangle-0.1.21/src/lib.rs - toolchain/rustc - Git at Google

 //! Demangle Rust compiler symbol names.
 //!
 //! This crate provides a `demangle` function which will return a `Demangle`
 //! sentinel value that can be used to learn about the demangled version of a
 //! symbol name. The demangled representation will be the same as the original
 //! if it doesn't look like a mangled symbol name.
 //!
 //! `Demangle` can be formatted with the `Display` trait. The alternate
 //! modifier (`#`) can be used to format the symbol name without the
 //! trailing hash value.
 //!
 //! # Examples
 //!
 //! ```
 //! use rustc_demangle::demangle;
 //!
 //! assert_eq!(demangle("_ZN4testE").to_string(), "test");
 //! assert_eq!(demangle("_ZN3foo3barE").to_string(), "foo::bar");
 //! assert_eq!(demangle("foo").to_string(), "foo");
 //! // With hash
 //! assert_eq!(format!("{}", demangle("_ZN3foo17h05af221e174051e9E")), "foo::h05af221e174051e9");
 //! // Without hash
 //! assert_eq!(format!("{:#}", demangle("_ZN3foo17h05af221e174051e9E")), "foo");
 //! ```

 #![no_std]
 #![deny(missing_docs)]

 #[cfg(test)]
 #[macro_use]
 extern crate std;

 // HACK(eddyb) helper macros for tests.
 #[cfg(test)]
 macro_rules! assert_contains {
     ($s:expr, $needle:expr) => {{
         let (s, needle) = ($s, $needle);
         assert!(
             s.contains(needle),
             "{:?} should've contained {:?}",
             s,
             needle
         );
     }};
 }
 #[cfg(test)]
 macro_rules! assert_ends_with {
     ($s:expr, $suffix:expr) => {{
         let (s, suffix) = ($s, $suffix);
         assert!(
             s.ends_with(suffix),
             "{:?} should've ended in {:?}",
             s,
             suffix
         );
     }};
 }

 mod legacy;
 mod v0;

 use core::fmt::{self, Write as _};

 /// Representation of a demangled symbol name.
 pub struct Demangle<'a> {
     style: Option<DemangleStyle<'a>>,
     original: &'a str,
     suffix: &'a str,
 }

 enum DemangleStyle<'a> {
     Legacy(legacy::Demangle<'a>),
     V0(v0::Demangle<'a>),
 }

 /// 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.
 ///
 /// # Examples
 ///
 /// ```
 /// use rustc_demangle::demangle;
 ///
 /// assert_eq!(demangle("_ZN4testE").to_string(), "test");
 /// assert_eq!(demangle("_ZN3foo3barE").to_string(), "foo::bar");
 /// assert_eq!(demangle("foo").to_string(), "foo");
 /// ```
 pub fn demangle(mut s: &str) -> Demangle {
     // During ThinLTO LLVM may import and rename internal symbols, so strip out
     // those endings first as they're one of the last manglings applied to symbol
     // names.
     let llvm = ".llvm.";
     if let Some(i) = s.find(llvm) {
         let candidate = &s[i + llvm.len()..];
         let all_hex = candidate.chars().all(|c| match c {
             'A'..='F' | '0'..='9' | '@' => true,
             _ => false,
         });

         if all_hex {
             s = &s[..i];
         }
     }

     let mut suffix = "";
     let mut style = match legacy::demangle(s) {
         Ok((d, s)) => {
             suffix = s;
             Some(DemangleStyle::Legacy(d))
         }
         Err(()) => match v0::demangle(s) {
             Ok((d, s)) => {
                 suffix = s;
                 Some(DemangleStyle::V0(d))
             }
             // FIXME(eddyb) would it make sense to treat an unknown-validity
             // symbol (e.g. one that errored with `RecursedTooDeep`) as
             // v0-mangled, and have the error show up in the demangling?
             // (that error already gets past this initial check, and therefore
             // will show up in the demangling, if hidden behind a backref)
             Err(v0::ParseError::Invalid) | Err(v0::ParseError::RecursedTooDeep) => None,
         },
     };

     // Output like LLVM IR adds extra period-delimited words. See if
     // we are in that case and save the trailing words if so.
     if !suffix.is_empty() {
         if suffix.starts_with('.') && is_symbol_like(suffix) {
             // Keep the suffix.
         } else {
             // Reset the suffix and invalidate the demangling.
             suffix = "";
             style = None;
         }
     }

     Demangle {
         style,
         original: s,
         suffix,
     }
 }

 /// Error returned from the `try_demangle` function below when demangling fails.
 #[derive(Debug, Clone)]
 pub struct TryDemangleError {
     _priv: (),
 }

 /// The same as `demangle`, except return an `Err` if the string does not appear
 /// to be a Rust symbol, rather than "demangling" the given string as a no-op.
 ///
 /// ```
 /// extern crate rustc_demangle;
 ///
 /// let not_a_rust_symbol = "la la la";
 ///
 /// // The `try_demangle` function will reject strings which are not Rust symbols.
 /// assert!(rustc_demangle::try_demangle(not_a_rust_symbol).is_err());
 ///
 /// // While `demangle` will just pass the non-symbol through as a no-op.
 /// assert_eq!(rustc_demangle::demangle(not_a_rust_symbol).as_str(), not_a_rust_symbol);
 /// ```
 pub fn try_demangle(s: &str) -> Result<Demangle, TryDemangleError> {
     let sym = demangle(s);
     if sym.style.is_some() {
         Ok(sym)
     } else {
         Err(TryDemangleError { _priv: () })
     }
 }

 impl<'a> Demangle<'a> {
     /// Returns the underlying string that's being demangled.
     pub fn as_str(&self) -> &'a str {
         self.original
     }
 }

 fn is_symbol_like(s: &str) -> bool {
     s.chars().all(|c| {
         // Once `char::is_ascii_punctuation` and `char::is_ascii_alphanumeric`
         // have been stable for long enough, use those instead for clarity
         is_ascii_alphanumeric(c) || is_ascii_punctuation(c)
     })
 }

 // Copied from the documentation of `char::is_ascii_alphanumeric`
 fn is_ascii_alphanumeric(c: char) -> bool {
     match c {
         '\u{0041}'..='\u{005A}' | '\u{0061}'..='\u{007A}' | '\u{0030}'..='\u{0039}' => true,
         _ => false,
     }
 }

 // Copied from the documentation of `char::is_ascii_punctuation`
 fn is_ascii_punctuation(c: char) -> bool {
     match c {
         '\u{0021}'..='\u{002F}'
         | '\u{003A}'..='\u{0040}'
         | '\u{005B}'..='\u{0060}'
         | '\u{007B}'..='\u{007E}' => true,
         _ => false,
     }
 }

 impl<'a> fmt::Display for DemangleStyle<'a> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             DemangleStyle::Legacy(ref d) => fmt::Display::fmt(d, f),
             DemangleStyle::V0(ref d) => fmt::Display::fmt(d, f),
         }
     }
 }

 // Maximum size of the symbol that we'll print.
 const MAX_SIZE: usize = 1_000_000;

 #[derive(Copy, Clone, Debug)]
 struct SizeLimitExhausted;

 struct SizeLimitedFmtAdapter<F> {
     remaining: Result<usize, SizeLimitExhausted>,
     inner: F,
 }

 impl<F: fmt::Write> fmt::Write for SizeLimitedFmtAdapter<F> {
     fn write_str(&mut self, s: &str) -> fmt::Result {
         self.remaining = self
             .remaining
             .and_then(|r| r.checked_sub(s.len()).ok_or(SizeLimitExhausted));

         match self.remaining {
             Ok(_) => self.inner.write_str(s),
             Err(SizeLimitExhausted) => Err(fmt::Error),
         }
     }
 }

 impl<'a> fmt::Display for Demangle<'a> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.style {
             None => f.write_str(self.original)?,
             Some(ref d) => {
                 let alternate = f.alternate();
                 let mut size_limited_fmt = SizeLimitedFmtAdapter {
                     remaining: Ok(MAX_SIZE),
                     inner: &mut *f,
                 };
                 let fmt_result = if alternate {
                     write!(size_limited_fmt, "{:#}", d)
                 } else {
                     write!(size_limited_fmt, "{}", d)
                 };
                 let size_limit_result = size_limited_fmt.remaining.map(|_| ());

                 // Translate a `fmt::Error` generated by `SizeLimitedFmtAdapter`
                 // into an error message, instead of propagating it upwards
                 // (which could cause panicking from inside e.g. `std::io::print`).
                 match (fmt_result, size_limit_result) {
                     (Err(_), Err(SizeLimitExhausted)) => f.write_str("{size limit reached}")?,

                     _ => {
                         fmt_result?;
                         size_limit_result
                             .expect("`fmt::Error` from `SizeLimitedFmtAdapter` was discarded");
                     }
                 }
             }
         }
         f.write_str(self.suffix)
     }
 }

 impl<'a> fmt::Debug for Demangle<'a> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Display::fmt(self, f)
     }
 }

 #[cfg(test)]
 mod tests {
     use std::prelude::v1::*;

     macro_rules! t {
         ($a:expr, $b:expr) => {
             assert!(ok($a, $b))
         };
     }

     macro_rules! t_err {
         ($a:expr) => {
             assert!(ok_err($a))
         };
     }

     macro_rules! t_nohash {
         ($a:expr, $b:expr) => {{
             assert_eq!(format!("{:#}", super::demangle($a)), $b);
         }};
     }

     fn ok(sym: &str, expected: &str) -> bool {
         match super::try_demangle(sym) {
             Ok(s) => {
                 if s.to_string() == expected {
                     true
                 } else {
                     println!("\n{}\n!=\n{}\n", s, expected);
                     false
                 }
             }
             Err(_) => {
                 println!("error demangling");
                 false
             }
         }
     }

     fn ok_err(sym: &str) -> bool {
         match super::try_demangle(sym) {
             Ok(_) => {
                 println!("succeeded in demangling");
                 false
             }
             Err(_) => super::demangle(sym).to_string() == sym,
         }
     }

     #[test]
     fn demangle() {
         t_err!("test");
         t!("_ZN4testE", "test");
         t_err!("_ZN4test");
         t!("_ZN4test1a2bcE", "test::a::bc");
     }

     #[test]
     fn demangle_dollars() {
         t!("_ZN4$RP$E", ")");
         t!("_ZN8$RF$testE", "&test");
         t!("_ZN8$BP$test4foobE", "*test::foob");
         t!("_ZN9$u20$test4foobE", " test::foob");
         t!("_ZN35Bar$LT$$u5b$u32$u3b$$u20$4$u5d$$GT$E", "Bar<[u32; 4]>");
     }

     #[test]
     fn demangle_many_dollars() {
         t!("_ZN13test$u20$test4foobE", "test test::foob");
         t!("_ZN12test$BP$test4foobE", "test*test::foob");
     }

     #[test]
     fn demangle_osx() {
         t!(
             "__ZN5alloc9allocator6Layout9for_value17h02a996811f781011E",
             "alloc::allocator::Layout::for_value::h02a996811f781011"
         );
         t!("__ZN38_$LT$core..option..Option$LT$T$GT$$GT$6unwrap18_MSG_FILE_LINE_COL17haf7cb8d5824ee659E", "<core::option::Option<T>>::unwrap::_MSG_FILE_LINE_COL::haf7cb8d5824ee659");
         t!("__ZN4core5slice89_$LT$impl$u20$core..iter..traits..IntoIterator$u20$for$u20$$RF$$u27$a$u20$$u5b$T$u5d$$GT$9into_iter17h450e234d27262170E", "core::slice::<impl core::iter::traits::IntoIterator for &'a [T]>::into_iter::h450e234d27262170");
     }

     #[test]
     fn demangle_windows() {
         t!("ZN4testE", "test");
         t!("ZN13test$u20$test4foobE", "test test::foob");
         t!("ZN12test$RF$test4foobE", "test&test::foob");
     }

     #[test]
     fn demangle_elements_beginning_with_underscore() {
         t!("_ZN13_$LT$test$GT$E", "<test>");
         t!("_ZN28_$u7b$$u7b$closure$u7d$$u7d$E", "{{closure}}");
         t!("_ZN15__STATIC_FMTSTRE", "__STATIC_FMTSTR");
     }

     #[test]
     fn demangle_trait_impls() {
         t!(
             "_ZN71_$LT$Test$u20$$u2b$$u20$$u27$static$u20$as$u20$foo..Bar$LT$Test$GT$$GT$3barE",
             "<Test + 'static as foo::Bar<Test>>::bar"
         );
     }

     #[test]
     fn demangle_without_hash() {
         let s = "_ZN3foo17h05af221e174051e9E";
         t!(s, "foo::h05af221e174051e9");
         t_nohash!(s, "foo");
     }

     #[test]
     fn demangle_without_hash_edgecases() {
         // One element, no hash.
         t_nohash!("_ZN3fooE", "foo");
         // Two elements, no hash.
         t_nohash!("_ZN3foo3barE", "foo::bar");
         // Longer-than-normal hash.
         t_nohash!("_ZN3foo20h05af221e174051e9abcE", "foo");
         // Shorter-than-normal hash.
         t_nohash!("_ZN3foo5h05afE", "foo");
         // Valid hash, but not at the end.
         t_nohash!("_ZN17h05af221e174051e93fooE", "h05af221e174051e9::foo");
         // Not a valid hash, missing the 'h'.
         t_nohash!("_ZN3foo16ffaf221e174051e9E", "foo::ffaf221e174051e9");
         // Not a valid hash, has a non-hex-digit.
         t_nohash!("_ZN3foo17hg5af221e174051e9E", "foo::hg5af221e174051e9");
     }

     #[test]
     fn demangle_thinlto() {
         // One element, no hash.
         t!("_ZN3fooE.llvm.9D1C9369", "foo");
         t!("_ZN3fooE.llvm.9D1C9369@@16", "foo");
         t_nohash!(
             "_ZN9backtrace3foo17hbb467fcdaea5d79bE.llvm.A5310EB9",
             "backtrace::foo"
         );
     }

     #[test]
     fn demangle_llvm_ir_branch_labels() {
         t!("_ZN4core5slice77_$LT$impl$u20$core..ops..index..IndexMut$LT$I$GT$$u20$for$u20$$u5b$T$u5d$$GT$9index_mut17haf9727c2edfbc47bE.exit.i.i", "core::slice::<impl core::ops::index::IndexMut<I> for [T]>::index_mut::haf9727c2edfbc47b.exit.i.i");
         t_nohash!("_ZN4core5slice77_$LT$impl$u20$core..ops..index..IndexMut$LT$I$GT$$u20$for$u20$$u5b$T$u5d$$GT$9index_mut17haf9727c2edfbc47bE.exit.i.i", "core::slice::<impl core::ops::index::IndexMut<I> for [T]>::index_mut.exit.i.i");
     }

     #[test]
     fn demangle_ignores_suffix_that_doesnt_look_like_a_symbol() {
         t_err!("_ZN3fooE.llvm moocow");
     }

     #[test]
     fn dont_panic() {
         super::demangle("_ZN2222222222222222222222EE").to_string();
         super::demangle("_ZN5*70527e27.ll34csaғE").to_string();
         super::demangle("_ZN5*70527a54.ll34_$b.1E").to_string();
         super::demangle(
             "\
              _ZN5~saäb4e\n\
              2734cOsbE\n\
              5usage20h)3\0\0\0\0\0\0\07e2734cOsbE\
              ",
         )
         .to_string();
     }

     #[test]
     fn invalid_no_chop() {
         t_err!("_ZNfooE");
     }

     #[test]
     fn handle_assoc_types() {
         t!("_ZN151_$LT$alloc..boxed..Box$LT$alloc..boxed..FnBox$LT$A$C$$u20$Output$u3d$R$GT$$u20$$u2b$$u20$$u27$a$GT$$u20$as$u20$core..ops..function..FnOnce$LT$A$GT$$GT$9call_once17h69e8f44b3723e1caE", "<alloc::boxed::Box<alloc::boxed::FnBox<A, Output=R> + 'a> as core::ops::function::FnOnce<A>>::call_once::h69e8f44b3723e1ca");
     }

     #[test]
     fn handle_bang() {
         t!(
             "_ZN88_$LT$core..result..Result$LT$$u21$$C$$u20$E$GT$$u20$as$u20$std..process..Termination$GT$6report17hfc41d0da4a40b3e8E",
             "<core::result::Result<!, E> as std::process::Termination>::report::hfc41d0da4a40b3e8"
         );
     }

     #[test]
     fn limit_recursion() {
         assert_contains!(
             super::demangle("_RNvB_1a").to_string(),
             "{recursion limit reached}"
         );
         assert_contains!(
             super::demangle("_RMC0RB2_").to_string(),
             "{recursion limit reached}"
         );
     }

     #[test]
     fn limit_output() {
         assert_ends_with!(
             super::demangle("RYFG_FGyyEvRYFF_EvRYFFEvERLB_B_B_ERLRjB_B_B_").to_string(),
             "{size limit reached}"
         );
         // NOTE(eddyb) somewhat reduced version of the above, effectively
         // `<for<...> fn()>` with a larger number of lifetimes in `...`.
         assert_ends_with!(
             super::demangle("_RMC0FGZZZ_Eu").to_string(),
             "{size limit reached}"
         );
     }
 }
	//! Demangle Rust compiler symbol names.
	//!
	//! This crate provides a `demangle` function which will return a `Demangle`
	//! sentinel value that can be used to learn about the demangled version of a
	//! symbol name. The demangled representation will be the same as the original
	//! if it doesn't look like a mangled symbol name.
	//!
	//! `Demangle` can be formatted with the `Display` trait. The alternate
	//! modifier (`#`) can be used to format the symbol name without the
	//! trailing hash value.
	//!
	//! # Examples
	//!
	//! ```
	//! use rustc_demangle::demangle;
	//!
	//! assert_eq!(demangle("_ZN4testE").to_string(), "test");
	//! assert_eq!(demangle("_ZN3foo3barE").to_string(), "foo::bar");
	//! assert_eq!(demangle("foo").to_string(), "foo");
	//! // With hash
	//! assert_eq!(format!("{}", demangle("_ZN3foo17h05af221e174051e9E")), "foo::h05af221e174051e9");
	//! // Without hash
	//! assert_eq!(format!("{:#}", demangle("_ZN3foo17h05af221e174051e9E")), "foo");
	//! ```

	#![no_std]
	#![deny(missing_docs)]

	#[cfg(test)]
	#[macro_use]
	extern crate std;

	// HACK(eddyb) helper macros for tests.
	#[cfg(test)]
	macro_rules! assert_contains {
	($s:expr, $needle:expr) => {{
	let (s, needle) = ($s, $needle);
	assert!(
	s.contains(needle),
	"{:?} should've contained {:?}",
	s,
	needle
	);
	}};
	}
	#[cfg(test)]
	macro_rules! assert_ends_with {
	($s:expr, $suffix:expr) => {{
	let (s, suffix) = ($s, $suffix);
	assert!(
	s.ends_with(suffix),
	"{:?} should've ended in {:?}",
	s,
	suffix
	);
	}};
	}

	mod legacy;
	mod v0;

	use core::fmt::{self, Write as _};

	/// Representation of a demangled symbol name.
	pub struct Demangle<'a> {
	style: Option<DemangleStyle<'a>>,
	original: &'a str,
	suffix: &'a str,
	}

	enum DemangleStyle<'a> {
	Legacy(legacy::Demangle<'a>),
	V0(v0::Demangle<'a>),
	}

	/// 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.
	///
	/// # Examples
	///
	/// ```
	/// use rustc_demangle::demangle;
	///
	/// assert_eq!(demangle("_ZN4testE").to_string(), "test");
	/// assert_eq!(demangle("_ZN3foo3barE").to_string(), "foo::bar");
	/// assert_eq!(demangle("foo").to_string(), "foo");
	/// ```
	pub fn demangle(mut s: &str) -> Demangle {
	// During ThinLTO LLVM may import and rename internal symbols, so strip out
	// those endings first as they're one of the last manglings applied to symbol
	// names.
	let llvm = ".llvm.";
	if let Some(i) = s.find(llvm) {
	let candidate = &s[i + llvm.len()..];
	let all_hex = candidate.chars().all(\|c\| match c {
	'A'..='F' \| '0'..='9' \| '@' => true,
	_ => false,
	});

	if all_hex {
	s = &s[..i];
	}
	}

	let mut suffix = "";
	let mut style = match legacy::demangle(s) {
	Ok((d, s)) => {
	suffix = s;
	Some(DemangleStyle::Legacy(d))
	}
	Err(()) => match v0::demangle(s) {
	Ok((d, s)) => {
	suffix = s;
	Some(DemangleStyle::V0(d))
	}
	// FIXME(eddyb) would it make sense to treat an unknown-validity
	// symbol (e.g. one that errored with `RecursedTooDeep`) as
	// v0-mangled, and have the error show up in the demangling?
	// (that error already gets past this initial check, and therefore
	// will show up in the demangling, if hidden behind a backref)
	Err(v0::ParseError::Invalid) \| Err(v0::ParseError::RecursedTooDeep) => None,
	},
	};

	// Output like LLVM IR adds extra period-delimited words. See if
	// we are in that case and save the trailing words if so.
	if !suffix.is_empty() {
	if suffix.starts_with('.') && is_symbol_like(suffix) {
	// Keep the suffix.
	} else {
	// Reset the suffix and invalidate the demangling.
	suffix = "";
	style = None;
	}
	}

	Demangle {
	style,
	original: s,
	suffix,
	}
	}

	/// Error returned from the `try_demangle` function below when demangling fails.
	#[derive(Debug, Clone)]
	pub struct TryDemangleError {
	_priv: (),
	}

	/// The same as `demangle`, except return an `Err` if the string does not appear
	/// to be a Rust symbol, rather than "demangling" the given string as a no-op.
	///
	/// ```
	/// extern crate rustc_demangle;
	///
	/// let not_a_rust_symbol = "la la la";
	///
	/// // The `try_demangle` function will reject strings which are not Rust symbols.
	/// assert!(rustc_demangle::try_demangle(not_a_rust_symbol).is_err());
	///
	/// // While `demangle` will just pass the non-symbol through as a no-op.
	/// assert_eq!(rustc_demangle::demangle(not_a_rust_symbol).as_str(), not_a_rust_symbol);
	/// ```
	pub fn try_demangle(s: &str) -> Result<Demangle, TryDemangleError> {
	let sym = demangle(s);
	if sym.style.is_some() {
	Ok(sym)
	} else {
	Err(TryDemangleError { _priv: () })
	}
	}

	impl<'a> Demangle<'a> {
	/// Returns the underlying string that's being demangled.
	pub fn as_str(&self) -> &'a str {
	self.original
	}
	}

	fn is_symbol_like(s: &str) -> bool {
	s.chars().all(\|c\| {
	// Once `char::is_ascii_punctuation` and `char::is_ascii_alphanumeric`
	// have been stable for long enough, use those instead for clarity
	is_ascii_alphanumeric(c) \|\| is_ascii_punctuation(c)
	})
	}

	// Copied from the documentation of `char::is_ascii_alphanumeric`
	fn is_ascii_alphanumeric(c: char) -> bool {
	match c {
	'\u{0041}'..='\u{005A}' \| '\u{0061}'..='\u{007A}' \| '\u{0030}'..='\u{0039}' => true,
	_ => false,
	}
	}

	// Copied from the documentation of `char::is_ascii_punctuation`
	fn is_ascii_punctuation(c: char) -> bool {
	match c {
	'\u{0021}'..='\u{002F}'
	\| '\u{003A}'..='\u{0040}'
	\| '\u{005B}'..='\u{0060}'
	\| '\u{007B}'..='\u{007E}' => true,
	_ => false,
	}
	}

	impl<'a> fmt::Display for DemangleStyle<'a> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	match *self {
	DemangleStyle::Legacy(ref d) => fmt::Display::fmt(d, f),
	DemangleStyle::V0(ref d) => fmt::Display::fmt(d, f),
	}
	}
	}

	// Maximum size of the symbol that we'll print.
	const MAX_SIZE: usize = 1_000_000;

	#[derive(Copy, Clone, Debug)]
	struct SizeLimitExhausted;

	struct SizeLimitedFmtAdapter<F> {
	remaining: Result<usize, SizeLimitExhausted>,
	inner: F,
	}

	impl<F: fmt::Write> fmt::Write for SizeLimitedFmtAdapter<F> {
	fn write_str(&mut self, s: &str) -> fmt::Result {
	self.remaining = self
	.remaining
	.and_then(\|r\| r.checked_sub(s.len()).ok_or(SizeLimitExhausted));

	match self.remaining {
	Ok(_) => self.inner.write_str(s),
	Err(SizeLimitExhausted) => Err(fmt::Error),
	}
	}
	}

	impl<'a> fmt::Display for Demangle<'a> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	match self.style {
	None => f.write_str(self.original)?,
	Some(ref d) => {
	let alternate = f.alternate();
	let mut size_limited_fmt = SizeLimitedFmtAdapter {
	remaining: Ok(MAX_SIZE),
	inner: &mut *f,
	};
	let fmt_result = if alternate {
	write!(size_limited_fmt, "{:#}", d)
	} else {
	write!(size_limited_fmt, "{}", d)
	};
	let size_limit_result = size_limited_fmt.remaining.map(\|_\| ());

	// Translate a `fmt::Error` generated by `SizeLimitedFmtAdapter`
	// into an error message, instead of propagating it upwards
	// (which could cause panicking from inside e.g. `std::io::print`).
	match (fmt_result, size_limit_result) {
	(Err(_), Err(SizeLimitExhausted)) => f.write_str("{size limit reached}")?,

	_ => {
	fmt_result?;
	size_limit_result
	.expect("`fmt::Error` from `SizeLimitedFmtAdapter` was discarded");
	}
	}
	}
	}
	f.write_str(self.suffix)
	}
	}

	impl<'a> fmt::Debug for Demangle<'a> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	fmt::Display::fmt(self, f)
	}
	}

	#[cfg(test)]
	mod tests {
	use std::prelude::v1::*;

	macro_rules! t {
	($a:expr, $b:expr) => {
	assert!(ok($a, $b))
	};
	}

	macro_rules! t_err {
	($a:expr) => {
	assert!(ok_err($a))
	};
	}

	macro_rules! t_nohash {
	($a:expr, $b:expr) => {{
	assert_eq!(format!("{:#}", super::demangle($a)), $b);
	}};
	}

	fn ok(sym: &str, expected: &str) -> bool {
	match super::try_demangle(sym) {
	Ok(s) => {
	if s.to_string() == expected {
	true
	} else {
	println!("\n{}\n!=\n{}\n", s, expected);
	false
	}
	}
	Err(_) => {
	println!("error demangling");
	false
	}
	}
	}

	fn ok_err(sym: &str) -> bool {
	match super::try_demangle(sym) {
	Ok(_) => {
	println!("succeeded in demangling");
	false
	}
	Err(_) => super::demangle(sym).to_string() == sym,
	}
	}

	#[test]
	fn demangle() {
	t_err!("test");
	t!("_ZN4testE", "test");
	t_err!("_ZN4test");
	t!("_ZN4test1a2bcE", "test::a::bc");
	}

	#[test]
	fn demangle_dollars() {
	t!("_ZN4$RP$E", ")");
	t!("_ZN8$RF$testE", "&test");
	t!("_ZN8$BP$test4foobE", "*test::foob");
	t!("_ZN9$u20$test4foobE", " test::foob");
	t!("_ZN35Bar$LT$$u5b$u32$u3b$$u20$4$u5d$$GT$E", "Bar<[u32; 4]>");
	}

	#[test]
	fn demangle_many_dollars() {
	t!("_ZN13test$u20$test4foobE", "test test::foob");
	t!("_ZN12test$BP$test4foobE", "test*test::foob");
	}

	#[test]
	fn demangle_osx() {
	t!(
	"__ZN5alloc9allocator6Layout9for_value17h02a996811f781011E",
	"alloc::allocator::Layout::for_value::h02a996811f781011"
	);
	t!("__ZN38_$LT$core..option..Option$LT$T$GT$$GT$6unwrap18_MSG_FILE_LINE_COL17haf7cb8d5824ee659E", "<core::option::Option<T>>::unwrap::_MSG_FILE_LINE_COL::haf7cb8d5824ee659");
	t!("__ZN4core5slice89_$LT$impl$u20$core..iter..traits..IntoIterator$u20$for$u20$$RF$$u27$a$u20$$u5b$T$u5d$$GT$9into_iter17h450e234d27262170E", "core::slice::<impl core::iter::traits::IntoIterator for &'a [T]>::into_iter::h450e234d27262170");
	}

	#[test]
	fn demangle_windows() {
	t!("ZN4testE", "test");
	t!("ZN13test$u20$test4foobE", "test test::foob");
	t!("ZN12test$RF$test4foobE", "test&test::foob");
	}

	#[test]
	fn demangle_elements_beginning_with_underscore() {
	t!("_ZN13_$LT$test$GT$E", "<test>");
	t!("_ZN28_$u7b$$u7b$closure$u7d$$u7d$E", "{{closure}}");
	t!("_ZN15__STATIC_FMTSTRE", "__STATIC_FMTSTR");
	}

	#[test]
	fn demangle_trait_impls() {
	t!(
	"_ZN71_$LT$Test$u20$$u2b$$u20$$u27$static$u20$as$u20$foo..Bar$LT$Test$GT$$GT$3barE",
	"<Test + 'static as foo::Bar<Test>>::bar"
	);
	}

	#[test]
	fn demangle_without_hash() {
	let s = "_ZN3foo17h05af221e174051e9E";
	t!(s, "foo::h05af221e174051e9");
	t_nohash!(s, "foo");
	}

	#[test]
	fn demangle_without_hash_edgecases() {
	// One element, no hash.
	t_nohash!("_ZN3fooE", "foo");
	// Two elements, no hash.
	t_nohash!("_ZN3foo3barE", "foo::bar");
	// Longer-than-normal hash.
	t_nohash!("_ZN3foo20h05af221e174051e9abcE", "foo");
	// Shorter-than-normal hash.
	t_nohash!("_ZN3foo5h05afE", "foo");
	// Valid hash, but not at the end.
	t_nohash!("_ZN17h05af221e174051e93fooE", "h05af221e174051e9::foo");
	// Not a valid hash, missing the 'h'.
	t_nohash!("_ZN3foo16ffaf221e174051e9E", "foo::ffaf221e174051e9");
	// Not a valid hash, has a non-hex-digit.
	t_nohash!("_ZN3foo17hg5af221e174051e9E", "foo::hg5af221e174051e9");
	}

	#[test]
	fn demangle_thinlto() {
	// One element, no hash.
	t!("_ZN3fooE.llvm.9D1C9369", "foo");
	t!("_ZN3fooE.llvm.9D1C9369@@16", "foo");
	t_nohash!(
	"_ZN9backtrace3foo17hbb467fcdaea5d79bE.llvm.A5310EB9",
	"backtrace::foo"
	);
	}

	#[test]
	fn demangle_llvm_ir_branch_labels() {
	t!("_ZN4core5slice77_$LT$impl$u20$core..ops..index..IndexMut$LT$I$GT$$u20$for$u20$$u5b$T$u5d$$GT$9index_mut17haf9727c2edfbc47bE.exit.i.i", "core::slice::<impl core::ops::index::IndexMut<I> for [T]>::index_mut::haf9727c2edfbc47b.exit.i.i");
	t_nohash!("_ZN4core5slice77_$LT$impl$u20$core..ops..index..IndexMut$LT$I$GT$$u20$for$u20$$u5b$T$u5d$$GT$9index_mut17haf9727c2edfbc47bE.exit.i.i", "core::slice::<impl core::ops::index::IndexMut<I> for [T]>::index_mut.exit.i.i");
	}

	#[test]
	fn demangle_ignores_suffix_that_doesnt_look_like_a_symbol() {
	t_err!("_ZN3fooE.llvm moocow");
	}

	#[test]
	fn dont_panic() {
	super::demangle("_ZN2222222222222222222222EE").to_string();
	super::demangle("_ZN5*70527e27.ll34csaғE").to_string();
	super::demangle("_ZN5*70527a54.ll34_$b.1E").to_string();
	super::demangle(
	"\
	_ZN5~saäb4e\n\
	2734cOsbE\n\
	5usage20h)3\0\0\0\0\0\0\07e2734cOsbE\
	",
	)
	.to_string();
	}

	#[test]
	fn invalid_no_chop() {
	t_err!("_ZNfooE");
	}

	#[test]
	fn handle_assoc_types() {
	t!("_ZN151_$LT$alloc..boxed..Box$LT$alloc..boxed..FnBox$LT$A$C$$u20$Output$u3d$R$GT$$u20$$u2b$$u20$$u27$a$GT$$u20$as$u20$core..ops..function..FnOnce$LT$A$GT$$GT$9call_once17h69e8f44b3723e1caE", "<alloc::boxed::Box<alloc::boxed::FnBox<A, Output=R> + 'a> as core::ops::function::FnOnce<A>>::call_once::h69e8f44b3723e1ca");
	}

	#[test]
	fn handle_bang() {
	t!(
	"_ZN88_$LT$core..result..Result$LT$$u21$$C$$u20$E$GT$$u20$as$u20$std..process..Termination$GT$6report17hfc41d0da4a40b3e8E",
	"<core::result::Result<!, E> as std::process::Termination>::report::hfc41d0da4a40b3e8"
	);
	}

	#[test]
	fn limit_recursion() {
	assert_contains!(
	super::demangle("_RNvB_1a").to_string(),
	"{recursion limit reached}"
	);
	assert_contains!(
	super::demangle("_RMC0RB2_").to_string(),
	"{recursion limit reached}"
	);
	}

	#[test]
	fn limit_output() {
	assert_ends_with!(
	super::demangle("RYFG_FGyyEvRYFF_EvRYFFEvERLB_B_B_ERLRjB_B_B_").to_string(),
	"{size limit reached}"
	);
	// NOTE(eddyb) somewhat reduced version of the above, effectively
	// `<for<...> fn()>` with a larger number of lifetimes in `...`.
	assert_ends_with!(
	super::demangle("_RMC0FGZZZ_Eu").to_string(),
	"{size limit reached}"
	);
	}
	}