//! 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.
//!
//! # 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");
//! ```

#![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,
}

/// 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(s: &str) -> Demangle {
    // 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_digit(10) {
                    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;
            }
        }
    }

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

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

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;
        let mut first = true;
        while !inner.is_empty() {
            if !first {
                try!(f.write_str("::"));
            } else {
                first = false;
            }
            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];
            while !rest.is_empty() {
                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_trans/back/symbol_names.rs for these
                    // mappings, historical ones also included.
                    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.
                        "$u7e$", => "~",
                        "$u20$", => " ",
                        "$u27$", => "'",
                        "$u5b$", => "[",
                        "$u5d$", => "]",
                        "$u7b$", => "{",
                        "$u7d$", => "}"
                    }
                } else {
                    let idx = rest.find('$').unwrap_or(rest.len());
                    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);
        })
    }

    #[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");
    }
}