# lib.rs.html -- source
Source to the Rust file `/Users/travis/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-demangle-0.1.7/src/lib.rs`.
Keywords: rust, rustlang, rust-lang

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    //! 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;

    use core::fmt;

    /// Representation of a demangled symbol name.
    pub struct Demangle<'a> {
        original: &'a str,
        inner: &'a str,
        valid: bool,
        /// The number of ::-separated elements in the original name.
        elements: usize,
    }

    /// De-mangles a Rust symbol into a more readable version
    ///
    /// All rust symbols by default are mangled as they contain characters that
    /// cannot be represented in all object files. The mangling mechanism is similar
    /// to C++'s, but Rust has a few specifics to handle items like lifetimes in
    /// symbols.
    ///
    /// This function will take a **mangled** symbol (typically acquired from a
    /// `Symbol` which is in turn resolved from a `Frame`) and then writes the
    /// de-mangled version into the given `writer`. If the symbol does not look like
    /// a mangled symbol, it is still written to `writer`.
    ///
    /// # 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");
    /// ```

    // All rust symbols are in theory lists of "::"-separated identifiers. Some
    // assemblers, however, can't handle these characters in symbol names. To get
    // around this, we use C++-style mangling. The mangling method is:
    //
    // 1. Prefix the symbol with "_ZN"
    // 2. For each element of the path, emit the length plus the element
    // 3. End the path with "E"
    //
    // For example, "_ZN4testE" => "test" and "_ZN3foo3barE" => "foo::bar".
    //
    // We're the ones printing our backtraces, so we can't rely on anything else to
    // demangle our symbols. It's *much* nicer to look at demangled symbols, so
    // this function is implemented to give us nice pretty output.
    //
    // Note that this demangler isn't quite as fancy as it could be. We have lots
    // of other information in our symbols like hashes, version, type information,
    // etc. Additionally, this doesn't handle glue symbols at all.
    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 on 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];
            }
        }

        // 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 mut valid = true;
        let mut inner = s;
        if s.len() > 4 && s.starts_with("_ZN") && s.ends_with('E') {
            inner = &s[3..s.len() - 1];
        } else if s.len() > 3 && s.starts_with("ZN") && s.ends_with('E') {
            // On Windows, dbghelp strips leading underscores, so we accept "ZN...E"
            // form too.
            inner = &s[2..s.len() - 1];
        } else if s.len() > 5 && s.starts_with("__ZN") && s.ends_with('E') {
            // On OSX, symbols are prefixed with an extra _
            inner = &s[4..s.len() - 1];
        } else {
            valid = false;
        }

        // only work with ascii text
        if inner.bytes().any(|c| c & 0x80 != 0) {
            valid = false;
        }

        let mut elements = 0;
        if valid {
            let mut chars = inner.chars().peekable();
            while valid {
                let mut i = 0usize;
                while let Some(&c) = chars.peek() {
                    if !c.is_digit(10) {
                        break
                    }
                    chars.next();
                    let next = i.checked_mul(10)
                        .and_then(|i| i.checked_add(c as usize - '0' as usize));
                    i = match next {
                        Some(i) => i,
                        None => {
                            valid = false;
                            break
                        }
                    };
                }

                if i == 0 {
                    valid = chars.next().is_none();
                    break;
                } else if chars.by_ref().take(i).count() != i {
                    valid = false;
                } else {
                    elements += 1;
                }
            }
        }

        Demangle {
            inner: inner,
            valid: valid,
            elements: elements,
            original: s,
        }
    }

    /// 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.valid {
            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
        }
    }

    // Rust hashes are hex digits with an `h` prepended.
    fn is_rust_hash(s: &str) -> bool {
        s.starts_with('h') && s[1..].chars().all(|c| c.is_digit(16))
    }

    impl<'a> fmt::Display for Demangle<'a> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            // Alright, let's do this.
            if !self.valid {
                return f.write_str(self.inner);
            }

            let mut inner = self.inner;
            for element in 0..self.elements {
                let mut rest = inner;
                while rest.chars().next().unwrap().is_digit(10) {
                    rest = &rest[1..];
                }
                let i: usize = inner[..(inner.len() - rest.len())].parse().unwrap();
                inner = &rest[i..];
                rest = &rest[..i];
                // Skip printing the hash if alternate formatting
                // was requested.
                if f.alternate() && element+1 == self.elements && is_rust_hash(&rest) {
                    break;
                }
                if element != 0 {
                    try!(f.write_str("::"));
                }
                if rest.starts_with("_$") {
                    rest = &rest[1..];
                }
                while !rest.is_empty() {
                    if rest.starts_with('.') {
                        if let Some('.') = rest[1..].chars().next() {
                            try!(f.write_str("::"));
                            rest = &rest[2..];
                        } else {
                            try!(f.write_str("."));
                            rest = &rest[1..];
                        }
                    } else if rest.starts_with('$') {
                        macro_rules! demangle {
                            ($($pat:expr => $demangled:expr),*) => ({
                                $(if rest.starts_with($pat) {
                                    try!(f.write_str($demangled));
                                    rest = &rest[$pat.len()..];
                                  } else)*
                                {
                                    try!(f.write_str(rest));
                                    break;
                                }

                            })
                        }

                        // see src/librustc/back/link.rs for these mappings
                        demangle! {
                            "$SP$" => "@",
                            "$BP$" => "*",
                            "$RF$" => "&",
                            "$LT$" => "<",
                            "$GT$" => ">",
                            "$LP$" => "(",
                            "$RP$" => ")",
                            "$C$" => ",",

                            // in theory we can demangle any Unicode code point, but
                            // for simplicity we just catch the common ones.
                            "$u7e$" => "~",
                            "$u20$" => " ",
                            "$u27$" => "'",
                            "$u5b$" => "[",
                            "$u5d$" => "]",
                            "$u7b$" => "{",
                            "$u7d$" => "}",
                            "$u3b$" => ";",
                            "$u2b$" => "+",
                            "$u22$" => "\""
                        }
                    } else {
                        let idx = match rest.char_indices().find(|&(_, c)| c == '$' || c == '.') {
                            None => rest.len(),
                            Some((i, _)) => i,
                        };
                        try!(f.write_str(&rest[..idx]));
                        rest = &rest[idx..];
                    }
                }
            }

            Ok(())
        }
    }

    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, $b:expr) => ({
                assert_eq!(super::demangle($a).to_string(), $b);
            })
        }

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

        #[test]
        fn demangle() {
            t!("test", "test");
            t!("_ZN4testE", "test");
            t!("_ZN4test", "_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 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();
        }
    }

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