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    // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    #![cfg_attr(target_os = "nacl", allow(dead_code))]

    use env;
    use io::prelude::*;
    use io;
    use libc;
    use str;
    use sync::atomic::{self, Ordering};

    pub use sys::backtrace::write;

    #[cfg(target_pointer_width = "64")]
    pub const HEX_WIDTH: usize = 18;

    #[cfg(target_pointer_width = "32")]
    pub const HEX_WIDTH: usize = 10;

    // For now logging is turned off by default, and this function checks to see
    // whether the magical environment variable is present to see if it's turned on.
    pub fn log_enabled() -> bool {
        static ENABLED: atomic::AtomicIsize = atomic::AtomicIsize::new(0);
        match ENABLED.load(Ordering::SeqCst) {
            1 => return false,
            2 => return true,
            _ => {}
        }

        let val = match env::var_os("RUST_BACKTRACE") {
            Some(x) => if &x == "0" { 1 } else { 2 },
            None => 1,
        };
        ENABLED.store(val, Ordering::SeqCst);
        val == 2
    }

    // These output functions should now be used everywhere to ensure consistency.
    pub fn output(w: &mut Write, idx: isize, addr: *mut libc::c_void,
                  s: Option<&[u8]>) -> io::Result<()> {
        write!(w, "  {:2}: {:2$?} - ", idx, addr, HEX_WIDTH)?;
        match s.and_then(|s| str::from_utf8(s).ok()) {
            Some(string) => demangle(w, string)?,
            None => write!(w, "<unknown>")?,
        }
        w.write_all(&['\n' as u8])
    }

    #[allow(dead_code)]
    pub fn output_fileline(w: &mut Write, file: &[u8], line: libc::c_int,
                           more: bool) -> io::Result<()> {
        let file = str::from_utf8(file).unwrap_or("<unknown>");
        // prior line: "  ##: {:2$} - func"
        write!(w, "      {:3$}at {}:{}", "", file, line, HEX_WIDTH)?;
        if more {
            write!(w, " <... and possibly more>")?;
        }
        w.write_all(&['\n' as u8])
    }

    // 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(writer: &mut Write, s: &str) -> io::Result<()> {
        // 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];
        // On Windows, dbghelp strips leading underscores, so we accept "ZN...E" form too.
        } else if s.len() > 3 && s.starts_with("ZN") && s.ends_with("E") {
            inner = &s[2 .. s.len() - 1];
        } else {
            valid = false;
        }

        if valid {
            let mut chars = inner.chars();
            while valid {
                let mut i = 0;
                for c in chars.by_ref() {
                    if c.is_numeric() {
                        i = i * 10 + c as usize - '0' as usize;
                    } else {
                        break
                    }
                }
                if i == 0 {
                    valid = chars.next().is_none();
                    break
                } else if chars.by_ref().take(i - 1).count() != i - 1 {
                    valid = false;
                }
            }
        }

        // Alright, let's do this.
        if !valid {
            writer.write_all(s.as_bytes())?;
        } else {
            let mut first = true;
            while !inner.is_empty() {
                if !first {
                    writer.write_all(b"::")?;
                } else {
                    first = false;
                }
                let mut rest = inner;
                while rest.chars().next().unwrap().is_numeric() {
                    rest = &rest[1..];
                }
                let i: usize = inner[.. (inner.len() - rest.len())].parse().unwrap();
                inner = &rest[i..];
                rest = &rest[..i];
                while !rest.is_empty() {
                    if rest.starts_with("$") {
                        macro_rules! demangle {
                            ($($pat:expr, => $demangled:expr),*) => ({
                                $(if rest.starts_with($pat) {
                                    try!(writer.write_all($demangled));
                                    rest = &rest[$pat.len()..];
                                  } else)*
                                {
                                    try!(writer.write_all(rest.as_bytes()));
                                    break;
                                }

                            })
                        }

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

                            // in theory we can demangle any Unicode code point, but
                            // for simplicity we just catch the common ones.
                            "$u7e$", => b"~",
                            "$u20$", => b" ",
                            "$u27$", => b"'",
                            "$u5b$", => b"[",
                            "$u5d$", => b"]"
                        )
                    } else {
                        let idx = match rest.find('$') {
                            None => rest.len(),
                            Some(i) => i,
                        };
                        writer.write_all(rest[..idx].as_bytes())?;
                        rest = &rest[idx..];
                    }
                }
            }
        }

        Ok(())
    }

    #[cfg(test)]
    mod tests {
        use prelude::v1::*;
        use sys_common;
        macro_rules! t { ($a:expr, $b:expr) => ({
            let mut m = Vec::new();
            sys_common::backtrace::demangle(&mut m, $a).unwrap();
            assert_eq!(String::from_utf8(m).unwrap(), $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");
        }

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

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

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