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    use std::fmt;
    #[cfg(not(feature = "cpp_demangle"))]
    use std::marker::PhantomData;
    use std::os::raw::c_void;
    use std::path::Path;
    use std::str;
    use rustc_demangle::{try_demangle, Demangle};

    /// Resolve an address to a symbol, passing the symbol to the specified
    /// closure.
    ///
    /// This function will look up the given address in areas such as the local
    /// symbol table, dynamic symbol table, or DWARF debug info (depending on the
    /// activated implementation) to find symbols to yield.
    ///
    /// The closure may not be called if resolution could not be performed, and it
    /// also may be called more than once in the case of inlined functions.
    ///
    /// Symbols yielded represent the execution at the specified `addr`, returning
    /// file/line pairs for that address (if available).
    ///
    /// # Example
    ///
    /// ```
    /// extern crate backtrace;
    ///
    /// fn main() {
    ///     backtrace::trace(|frame| {
    ///         let ip = frame.ip();
    ///
    ///         backtrace::resolve(ip, |symbol| {
    ///             // ...
    ///         });
    ///
    ///         false // only look at the top frame
    ///     });
    /// }
    /// ```
    pub fn resolve<F: FnMut(&Symbol)>(addr: *mut c_void, mut cb: F) {
        resolve_imp(addr, &mut cb)
    }

    /// A trait representing the resolution of a symbol in a file.
    ///
    /// This trait is yielded as a trait object to the closure given to the
    /// `backtrace::resolve` function, and it is virtually dispatched as it's
    /// unknown which implementation is behind it.
    ///
    /// A symbol can give contextual information about a function, for example the
    /// name, filename, line number, precise address, etc. Not all information is
    /// always available in a symbol, however, so all methods return an `Option`.
    pub struct Symbol {
        inner: SymbolImp,
    }

    impl Symbol {
        /// Returns the name of this function.
        ///
        /// The returned structure can be used to query various properties about the
        /// symbol name:
        ///
        /// * The `Display` implementation will print out the demangled symbol.
        /// * The raw `str` value of the symbol can be accessed (if it's valid
        ///   utf-8).
        /// * The raw bytes for the symbol name can be accessed.
        pub fn name(&self) -> Option<SymbolName> {
            self.inner.name()
        }

        /// Returns the starting address of this function.
        pub fn addr(&self) -> Option<*mut c_void> {
            self.inner.addr()
        }

        /// Returns the file name where this function was defined.
        ///
        /// This is currently only available when libbacktrace is being used (e.g.
        /// unix platforms other than OSX) and when a binary is compiled with
        /// debuginfo. If neither of these conditions is met then this will likely
        /// return `None`.
        pub fn filename(&self) -> Option<&Path> {
            self.inner.filename()
        }

        /// Returns the line number for where this symbol is currently executing.
        ///
        /// This return value is typically `Some` if `filename` returns `Some`, and
        /// is consequently subject to similar caveats.
        pub fn lineno(&self) -> Option<u32> {
            self.inner.lineno()
        }
    }

    impl fmt::Debug for Symbol {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            let mut d = f.debug_struct("Symbol");
            if let Some(name) = self.name() {
                d.field("name", &name);
            }
            if let Some(addr) = self.addr() {
                d.field("addr", &addr);
            }
            if let Some(filename) = self.filename() {
                d.field("filename", &filename);
            }
            if let Some(lineno) = self.lineno() {
                d.field("lineno", &lineno);
            }
            d.finish()
        }
    }

    cfg_if! {
        if #[cfg(feature = "cpp_demangle")] {
            // Maybe a parsed C++ symbol, if parsing the mangled symbol as Rust
            // failed.
            struct OptionCppSymbol<'a>(Option<::cpp_demangle::BorrowedSymbol<'a>>);

            impl<'a> OptionCppSymbol<'a> {
                fn parse(input: &'a [u8]) -> OptionCppSymbol<'a> {
                    OptionCppSymbol(::cpp_demangle::BorrowedSymbol::new(input).ok())
                }

                fn none() -> OptionCppSymbol<'a> {
                    OptionCppSymbol(None)
                }
            }
        } else {
            // Make sure to keep this zero-sized, so that the `cpp_demangle` feature
            // has no cost when disabled.
            struct OptionCppSymbol<'a>(PhantomData<&'a ()>);

            impl<'a> OptionCppSymbol<'a> {
                fn parse(_: &'a [u8]) -> OptionCppSymbol<'a> {
                    OptionCppSymbol(PhantomData)
                }

                fn none() -> OptionCppSymbol<'a> {
                    OptionCppSymbol(PhantomData)
                }
            }
        }
    }

    /// A wrapper around a symbol name to provide ergonomic accessors to the
    /// demangled name, the raw bytes, the raw string, etc.
    // Allow dead code for when the `cpp_demangle` feature is not enabled.
    #[allow(dead_code)]
    pub struct SymbolName<'a> {
        bytes: &'a [u8],
        demangled: Option<Demangle<'a>>,
        cpp_demangled: OptionCppSymbol<'a>,
    }

    impl<'a> SymbolName<'a> {
        /// Creates a new symbol name from the raw underlying bytes.
        pub fn new(bytes: &'a [u8]) -> SymbolName<'a> {
            let str_bytes = str::from_utf8(bytes).ok();
            let demangled = str_bytes.and_then(|s| try_demangle(s).ok());

            let cpp = if demangled.is_none() {
                OptionCppSymbol::parse(bytes)
            } else {
                OptionCppSymbol::none()
            };

            SymbolName {
                bytes: bytes,
                demangled: demangled,
                cpp_demangled: cpp,
            }
        }

        /// Returns the raw symbol name as a `str` if the symbols is valid utf-8.
        pub fn as_str(&self) -> Option<&'a str> {
            self.demangled
                .as_ref()
                .map(|s| s.as_str())
                .or_else(|| {
                    str::from_utf8(self.bytes).ok()
                })
        }

        /// Returns the raw symbol name as a list of bytes
        pub fn as_bytes(&self) -> &'a [u8] {
            self.bytes
        }
    }

    cfg_if! {
        if #[cfg(feature = "cpp_demangle")] {
            impl<'a> fmt::Display for SymbolName<'a> {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    if let Some(ref s) = self.demangled {
                        s.fmt(f)
                    } else if let Some(ref cpp) = self.cpp_demangled.0 {
                        cpp.fmt(f)
                    } else {
                        String::from_utf8_lossy(self.bytes).fmt(f)
                    }
                }
            }
        } else {
            impl<'a> fmt::Display for SymbolName<'a> {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    if let Some(ref s) = self.demangled {
                        s.fmt(f)
                    } else {
                        String::from_utf8_lossy(self.bytes).fmt(f)
                    }
                }
            }
        }
    }

    cfg_if! {
        if #[cfg(feature = "cpp_demangle")] {
            impl<'a> fmt::Debug for SymbolName<'a> {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    use std::fmt::Write;

                    if let Some(ref s) = self.demangled {
                        return s.fmt(f)
                    }

                    // This may to print if the demangled symbol isn't actually
                    // valid, so handle the error here gracefully by not propagating
                    // it outwards.
                    if let Some(ref cpp) = self.cpp_demangled.0 {
                        let mut s = String::new();
                        if write!(s, "{}", cpp).is_ok() {
                            return s.fmt(f)
                        }
                    }

                    String::from_utf8_lossy(self.bytes).fmt(f)
                }
            }
        } else {
            impl<'a> fmt::Debug for SymbolName<'a> {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    if let Some(ref s) = self.demangled {
                        s.fmt(f)
                    } else {
                        String::from_utf8_lossy(self.bytes).fmt(f)
                    }
                }
            }
        }
    }

    cfg_if! {
        if #[cfg(all(windows, feature = "dbghelp"))] {
            mod dbghelp;
            use self::dbghelp::resolve as resolve_imp;
            use self::dbghelp::Symbol as SymbolImp;
        } else if #[cfg(all(feature = "gimli-symbolize",
                            unix,
                            target_os = "linux"))] {
            mod gimli;
            use self::gimli::resolve as resolve_imp;
            use self::gimli::Symbol as SymbolImp;
        } else if #[cfg(all(feature = "libbacktrace",
                            unix,
                            not(target_os = "fuchsia"),
                            not(target_os = "emscripten"),
                            not(target_os = "macos"),
                            not(target_os = "ios")))] {
            mod libbacktrace;
            use self::libbacktrace::resolve as resolve_imp;
            use self::libbacktrace::Symbol as SymbolImp;
        } else if #[cfg(all(feature = "coresymbolication",
                            any(target_os = "macos",
                                target_os = "ios")))] {
            mod coresymbolication;
            use self::coresymbolication::resolve as resolve_imp;
            use self::coresymbolication::Symbol as SymbolImp;
        } else if #[cfg(all(unix,
                            not(target_os = "emscripten"),
                            feature = "dladdr"))] {
            mod dladdr;
            use self::dladdr::resolve as resolve_imp;
            use self::dladdr::Symbol as SymbolImp;
        } else {
            mod noop;
            use self::noop::resolve as resolve_imp;
            use self::noop::Symbol as SymbolImp;
        }
    }

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