nsstring/src/lib.rs

//! This module provides rust bindings for the XPCOM string types.
//!
//! # TL;DR (what types should I use)
//!
//! Use `&{mut,} nsA[C]String` for functions in rust which wish to take or
//! mutate XPCOM strings. The other string types `Deref` to this type.
//!
//! Use `ns[C]String<'a>` for string struct members which don't leave rust, and
//! as an intermediate between rust string data structures (such as `String`,
//! `Vec<u16>`, `&str`, and `&[u16]`) and `&{mut,} nsA[C]String` (using
//! `ns[C]String::from(value)`). These conversions, when possible, will not
//! perform any allocations.
//!
//! Use `nsFixed[C]String` or `ns_auto_[c]string!` for dynamic stack allocated
//! strings which are expected to hold short string values.
//!
//! Use `*{const,mut} nsA[C]String` (`{const,} nsA[C]String*` in C++) for
//! function arguments passed across the rust/C++ language boundary.
//!
//! Use `ns[C]StringRepr` for string struct members which are shared between
//! rust and C++, but be careful, because this type lacks a `Drop`
//! implementation.
//!
//! # String Types
//!
//! ## `nsA[C]String`
//!
//! The core types in this module are `nsAString` and `nsACString`. These types
//! are zero-sized as far as rust is concerned, and are safe to pass around
//! behind both references (in rust code), and pointers (in C++ code). They
//! represent a handle to a XPCOM string which holds either `u16` or `u8`
//! characters respectively. The backing character buffer is guaranteed to live
//! as long as the reference to the `nsAString` or `nsACString`.
//!
//! These types in rust are simply used as dummy types. References to them
//! represent a pointer to the beginning of a variable-sized `#[repr(C)]` struct
//! which is common between both C++ and Rust implementations. In C++, their
//! corresponding types are also named `nsAString` or `nsACString`, and they are
//! defined within the `nsTSubstring.{cpp,h}` file.
//!
//! ### Valid Operations
//!
//! An `&nsA[C]String` acts like rust's `&str`, in that it is a borrowed
//! reference to the backing data. When used as an argument to other functions
//! on `&mut nsA[C]String`, optimizations can be performed to avoid copying
//! buffers, as information about the backing storage is preserved.
//!
//! An `&mut nsA[C]String` acts like rust's `&mut Cow<str>`, in that it is a
//! mutable reference to a potentially borrowed string, which when modified will
//! ensure that it owns its own backing storage. This type can be appended to
//! with the methods `.append`, `.append_utf{8,16}`, and with the `write!`
//! macro, and can be assigned to with `.assign`.
//!
//! ## `ns[C]String<'a>`
//!
//! This type is an maybe-owned string type. It acts similarially to a
//! `Cow<[{u8,u16}]>`. This type provides `Deref` and `DerefMut` implementations
//! to `nsA[C]String`, which provides the methods for manipulating this type.
//! This type's lifetime parameter, `'a`, represents the lifetime of the backing
//! storage. When modified this type may re-allocate in order to ensure that it
//! does not mutate its backing storage.
//!
//! `ns[C]String`s can be constructed either with `ns[C]String::new()`, which
//! creates an empty `ns[C]String<'static>`, or through one of the provided
//! `From` implementations. Both string types may be constructed `From<&'a
//! str>`, with `nsCString` having a `'a` lifetime, as the storage is shared
//! with the `str`, while `nsString` has a `'static` lifetime, as its storage
//! has to be transcoded.
//!
//! When passing this type by reference, prefer passing a `&nsA[C]String` or
//! `&mut nsA[C]String`. to passing this type.
//!
//! This type is _not_ `#[repr(C)]`, as it has a `Drop` impl, which in versions
//! of `rustc < 1.13` adds drop flags to the struct, which messes up the layout,
//! making it unsafe to pass across the FFI boundary. The rust compiler will
//! warn if this type appears in `extern "C"` function definitions.
//!
//! When passing this type across the language boundary, pass it as `*const
//! nsA[C]String` for an immutable reference, or `*mut nsA[C]String` for a
//! mutable reference.
//!
//! This type is similar to the C++ type of the same name.
//!
//! ## `nsFixed[C]String<'a>`
//!
//! This type is a string type with fixed backing storage. It is created with
//! `nsFixed[C]String::new(buffer)`, passing a mutable reference to a buffer as
//! the argument. This buffer will be used as backing storage whenever the
//! resulting string will fit within it, falling back to heap allocations only
//! when the string size exceeds that of the backing buffer.
//!
//! Like `ns[C]String`, this type dereferences to `nsA[C]String` which provides
//! the methods for manipulating the type, and is not `#[repr(C)]`.
//!
//! When passing this type by reference, prefer passing a `&nsA[C]String` or
//! `&mut nsA[C]String`. to passing this type.
//!
//! This type is _not_ `#[repr(C)]`, as it has a `Drop` impl, which in versions
//! of `rustc < 1.13` adds drop flags to the struct, which messes up the layout,
//! making it unsafe to pass across the FFI boundary. The rust compiler will
//! warn if this type appears in `extern "C"` function definitions.
//!
//! When passing this type across the language boundary, pass it as `*const
//! nsA[C]String` for an immutable reference, or `*mut nsA[C]String` for a
//! mutable reference.
//!
//! This type is similar to the C++ type of the same name.
//!
//! ## `ns_auto_[c]string!($name)`
//!
//! This is a helper macro which defines a fixed size, (currently 64 character),
//! backing array on the stack, and defines a local variable with name `$name`
//! which is a `nsFixed[C]String` using this buffer as its backing storage.
//!
//! Usage of this macro is similar to the C++ type `nsAuto[C]String`, but could
//! not be implemented as a basic type due to the differences between rust and
//! C++'s move semantics.
//!
//! ## `ns[C]StringRepr`
//!
//! This type represents a C++ `ns[C]String`. This type is `#[repr(C)]` and is
//! safe to use in struct definitions which are shared across the language
//! boundary. It automatically dereferences to `&{mut,} nsA[C]String`, and thus
//! can be treated similarially to `ns[C]String`.
//!
//! If this type is dropped in rust, it will not free its backing storage. This
//! is because types implementing `Drop` have a drop flag added, which messes up
//! the layout of this type. When drop flags are removed, which should happen in
//! `rustc 1.13` (see rust-lang/rust#35764), this type will likely be removed,
//! and replaced with direct usage of `ns[C]String<'a>`, as its layout may be
//! identical. This module provides rust bindings to our xpcom ns[C]String
//! types.

#![allow(non_camel_case_types)]

use std::ops::{Deref, DerefMut};
use std::marker::PhantomData;
use std::slice;
use std::ptr;
use std::mem;
use std::fmt;
use std::cmp;
use std::str;
use std::u32;

//////////////////////////////////
// Internal Implemenation Flags //
//////////////////////////////////

const F_NONE: u32 = 0; // no flags

// data flags are in the lower 16-bits
const F_TERMINATED: u32 = 1 << 0; // IsTerminated returns true
const F_VOIDED: u32 = 1 << 1; // IsVoid returns true
const F_SHARED: u32 = 1 << 2; // mData points to a heap-allocated, shared buffer
const F_OWNED: u32 = 1 << 3; // mData points to a heap-allocated, raw buffer
const F_FIXED: u32 = 1 << 4; // mData points to a fixed-size writable, dependent buffer
const F_LITERAL: u32 = 1 << 5; // mData points to a string literal; F_TERMINATED will also be set

// class flags are in the upper 16-bits
const F_CLASS_FIXED: u32 = 1 << 16; // indicates that |this| is of type nsTFixedString

////////////////////////////////////
// Generic String Bindings Macros //
////////////////////////////////////

macro_rules! define_string_types {
    {
        char_t = $char_t: ty;
        AString = $AString: ident;
        String = $String: ident;
        FixedString = $FixedString: ident;

        StringRepr = $StringRepr: ident;
        FixedStringRepr = $FixedStringRepr: ident;
        AutoStringRepr = $AutoStringRepr: ident;
    } => {
        /// The representation of a ns[C]String type in C++. This type is
        /// used internally by our definition of ns[C]String to ensure layout
        /// compatibility with the C++ ns[C]String type.
        ///
        /// This type may also be used in place of a C++ ns[C]String inside of
        /// struct definitions which are shared with C++, as it has identical
        /// layout to our ns[C]String type. Due to drop flags, our ns[C]String
        /// type does not have identical layout. When drop flags are removed,
        /// this type will likely be made a private implementation detail, and
        /// its uses will be replaced with `ns[C]String`.
        ///
        /// This struct will leak its data if dropped from rust. See the module
        /// documentation for more information on this type.
        #[repr(C)]
        pub struct $StringRepr {
            data: *const $char_t,
            length: u32,
            flags: u32,
        }

        impl Deref for $StringRepr {
            type Target = $AString;
            fn deref(&self) -> &$AString {
                unsafe {
                    mem::transmute(self)
                }
            }
        }

        impl DerefMut for $StringRepr {
            fn deref_mut(&mut self) -> &mut $AString {
                unsafe {
                    mem::transmute(self)
                }
            }
        }

        /// The representation of a nsFixed[C]String type in C++. This type is
        /// used internally by our definition of nsFixed[C]String to ensure layout
        /// compatibility with the C++ nsFixed[C]String type.
        #[repr(C)]
        struct $FixedStringRepr {
            base: $StringRepr,
            capacity: u32,
            buffer: *mut $char_t,
        }

        /// This type is the abstract type which is used for interacting with
        /// strings in rust. Each string type can derefence to an instance of
        /// this type, which provides the useful operations on strings.
        ///
        /// NOTE: Rust thinks this type has a size of 0, because the data
        /// associated with it is not necessarially safe to move. It is not safe
        /// to construct a nsAString yourself, unless it is received by
        /// dereferencing one of these types.
        ///
        /// NOTE: The `[u8; 0]` member is zero sized, and only exists to prevent
        /// the construction by code outside of this module. It is used instead
        /// of a private `()` member because the `improper_ctypes` lint complains
        /// about some ZST members in `extern "C"` function declarations.
        #[repr(C)]
        pub struct $AString {
            _prohibit_constructor: [u8; 0],
        }

        impl Deref for $AString {
            type Target = [$char_t];
            fn deref(&self) -> &[$char_t] {
                unsafe {
                    // This is legal, as all $AString values actually point to a
                    // $StringRepr
                    let this: &$StringRepr = mem::transmute(self);
                    if this.data.is_null() {
                        debug_assert!(this.length == 0);
                        // Use an arbitrary non-null value as the pointer
                        slice::from_raw_parts(0x1 as *const $char_t, 0)
                    } else {
                        slice::from_raw_parts(this.data, this.length as usize)
                    }
                }
            }
        }

        impl cmp::PartialEq for $AString {
            fn eq(&self, other: &$AString) -> bool {
                &self[..] == &other[..]
            }
        }

        impl cmp::PartialEq<[$char_t]> for $AString {
            fn eq(&self, other: &[$char_t]) -> bool {
                &self[..] == other
            }
        }

        impl<'a> cmp::PartialEq<$String<'a>> for $AString {
            fn eq(&self, other: &$String<'a>) -> bool {
                self.eq(&**other)
            }
        }

        impl<'a> cmp::PartialEq<$FixedString<'a>> for $AString {
            fn eq(&self, other: &$FixedString<'a>) -> bool {
                self.eq(&**other)
            }
        }

        pub struct $String<'a> {
            hdr: $StringRepr,
            _marker: PhantomData<&'a [$char_t]>,
        }

        impl $String<'static> {
            pub fn new() -> $String<'static> {
                $String {
                    hdr: $StringRepr {
                        data: ptr::null(),
                        length: 0,
                        flags: F_NONE,
                    },
                    _marker: PhantomData,
                }
            }
        }

        impl<'a> Deref for $String<'a> {
            type Target = $AString;
            fn deref(&self) -> &$AString {
                &self.hdr
            }
        }

        impl<'a> DerefMut for $String<'a> {
            fn deref_mut(&mut self) -> &mut $AString {
                &mut self.hdr
            }
        }

        impl<'a> From<&'a String> for $String<'a> {
            fn from(s: &'a String) -> $String<'a> {
                $String::from(&s[..])
            }
        }

        impl<'a> From<&'a Vec<$char_t>> for $String<'a> {
            fn from(s: &'a Vec<$char_t>) -> $String<'a> {
                $String::from(&s[..])
            }
        }

        impl<'a> From<&'a [$char_t]> for $String<'a> {
            fn from(s: &'a [$char_t]) -> $String<'a> {
                assert!(s.len() < (u32::MAX as usize));
                $String {
                    hdr: $StringRepr {
                        data: s.as_ptr(),
                        length: s.len() as u32,
                        flags: F_NONE,
                    },
                    _marker: PhantomData,
                }
            }
        }

        impl From<Box<[$char_t]>> for $String<'static> {
            fn from(s: Box<[$char_t]>) -> $String<'static> {
                assert!(s.len() < (u32::MAX as usize));
                // SAFETY NOTE: This method produces an F_OWNED ns[C]String from
                // a Box<[$char_t]>. this is only safe because in the Gecko
                // tree, we use the same allocator for Rust code as for C++
                // code, meaning that our box can be legally freed with
                // libc::free().
                let length = s.len() as u32;
                let ptr = s.as_ptr();
                mem::forget(s);
                $String {
                    hdr: $StringRepr {
                        data: ptr,
                        length: length,
                        flags: F_OWNED,
                    },
                    _marker: PhantomData,
                }
            }
        }

        impl From<Vec<$char_t>> for $String<'static> {
            fn from(s: Vec<$char_t>) -> $String<'static> {
                s.into_boxed_slice().into()
            }
        }

        impl<'a> From<&'a $AString> for $String<'static> {
            fn from(s: &'a $AString) -> $String<'static> {
                let mut string = $String::new();
                string.assign(s);
                string
            }
        }

        impl<'a> fmt::Write for $String<'a> {
            fn write_str(&mut self, s: &str) -> Result<(), fmt::Error> {
                $AString::write_str(self, s)
            }
        }

        impl<'a> fmt::Display for $String<'a> {
            fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
                <$AString as fmt::Display>::fmt(self, f)
            }
        }

        impl<'a> fmt::Debug for $String<'a> {
            fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
                <$AString as fmt::Debug>::fmt(self, f)
            }
        }

        impl<'a> cmp::PartialEq for $String<'a> {
            fn eq(&self, other: &$String<'a>) -> bool {
                $AString::eq(self, other)
            }
        }

        impl<'a> cmp::PartialEq<[$char_t]> for $String<'a> {
            fn eq(&self, other: &[$char_t]) -> bool {
                $AString::eq(self, other)
            }
        }

        impl<'a, 'b> cmp::PartialEq<&'b [$char_t]> for $String<'a> {
            fn eq(&self, other: &&'b [$char_t]) -> bool {
                $AString::eq(self, *other)
            }
        }

        impl<'a> cmp::PartialEq<str> for $String<'a> {
            fn eq(&self, other: &str) -> bool {
                $AString::eq(self, other)
            }
        }

        impl<'a, 'b> cmp::PartialEq<&'b str> for $String<'a> {
            fn eq(&self, other: &&'b str) -> bool {
                $AString::eq(self, *other)
            }
        }

        impl<'a> Drop for $String<'a> {
            fn drop(&mut self) {
                unsafe {
                    self.finalize();
                }
            }
        }

        /// A nsFixed[C]String is a string which uses a fixed size mutable
        /// backing buffer for storing strings which will fit within that
        /// buffer, rather than using heap allocations.
        pub struct $FixedString<'a> {
            hdr: $FixedStringRepr,
            _marker: PhantomData<&'a mut [$char_t]>,
        }

        impl<'a> $FixedString<'a> {
            pub fn new(buf: &'a mut [$char_t]) -> $FixedString<'a> {
                let len = buf.len();
                assert!(len < (u32::MAX as usize));
                let buf_ptr = buf.as_mut_ptr();
                $FixedString {
                    hdr: $FixedStringRepr {
                        base: $StringRepr {
                            data: ptr::null(),
                            length: 0,
                            flags: F_CLASS_FIXED,
                        },
                        capacity: len as u32,
                        buffer: buf_ptr,
                    },
                    _marker: PhantomData,
                }
            }
        }

        impl<'a> Deref for $FixedString<'a> {
            type Target = $AString;
            fn deref(&self) -> &$AString {
                &self.hdr.base
            }
        }

        impl<'a> DerefMut for $FixedString<'a> {
            fn deref_mut(&mut self) -> &mut $AString {
                &mut self.hdr.base
            }
        }

        impl<'a> fmt::Write for $FixedString<'a> {
            fn write_str(&mut self, s: &str) -> Result<(), fmt::Error> {
                $AString::write_str(self, s)
            }
        }

        impl<'a> fmt::Display for $FixedString<'a> {
            fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
                <$AString as fmt::Display>::fmt(self, f)
            }
        }

        impl<'a> fmt::Debug for $FixedString<'a> {
            fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
                <$AString as fmt::Debug>::fmt(self, f)
            }
        }

        impl<'a> cmp::PartialEq for $FixedString<'a> {
            fn eq(&self, other: &$FixedString<'a>) -> bool {
                $AString::eq(self, other)
            }
        }

        impl<'a> cmp::PartialEq<[$char_t]> for $FixedString<'a> {
            fn eq(&self, other: &[$char_t]) -> bool {
                $AString::eq(self, other)
            }
        }

        impl<'a, 'b> cmp::PartialEq<&'b [$char_t]> for $FixedString<'a> {
            fn eq(&self, other: &&'b [$char_t]) -> bool {
                $AString::eq(self, *other)
            }
        }

        impl<'a> cmp::PartialEq<str> for $FixedString<'a> {
            fn eq(&self, other: &str) -> bool {
                $AString::eq(self, other)
            }
        }

        impl<'a, 'b> cmp::PartialEq<&'b str> for $FixedString<'a> {
            fn eq(&self, other: &&'b str) -> bool {
                $AString::eq(self, *other)
            }
        }

        impl<'a> Drop for $FixedString<'a> {
            fn drop(&mut self) {
                unsafe {
                    self.finalize();
                }
            }
        }
    }
}

///////////////////////////////////////////
// Bindings for nsCString (u8 char type) //
///////////////////////////////////////////

define_string_types! {
    char_t = u8;

    AString = nsACString;
    String = nsCString;
    FixedString = nsFixedCString;

    StringRepr = nsCStringRepr;
    FixedStringRepr = nsFixedCStringRepr;
    AutoStringRepr = nsAutoCStringRepr;
}

impl nsACString {
    /// Leaves the nsACString in an unstable state with a dangling data pointer.
    /// Should only be used in drop implementations of rust types which wrap
    /// this type.
    unsafe fn finalize(&mut self) {
        Gecko_FinalizeCString(self);
    }

    pub fn assign(&mut self, other: &nsACString) {
        unsafe {
            Gecko_AssignCString(self as *mut _, other as *const _);
        }
    }

    pub fn assign_utf16(&mut self, other: &nsAString) {
        self.assign(&nsCString::new());
        self.append_utf16(other);
    }

    pub fn append(&mut self, other: &nsACString) {
        unsafe {
            Gecko_AppendCString(self as *mut _, other as *const _);
        }
    }

    pub fn append_utf16(&mut self, other: &nsAString) {
        unsafe {
            Gecko_AppendUTF16toCString(self as *mut _, other as *const _);
        }
    }

    pub unsafe fn as_str_unchecked(&self) -> &str {
        str::from_utf8_unchecked(self)
    }
}

impl<'a> From<&'a str> for nsCString<'a> {
    fn from(s: &'a str) -> nsCString<'a> {
        s.as_bytes().into()
    }
}

impl From<Box<str>> for nsCString<'static> {
    fn from(s: Box<str>) -> nsCString<'static> {
        s.into_string().into()
    }
}

impl From<String> for nsCString<'static> {
    fn from(s: String) -> nsCString<'static> {
        s.into_bytes().into()
    }
}

// Support for the write!() macro for appending to nsACStrings
impl fmt::Write for nsACString {
    fn write_str(&mut self, s: &str) -> Result<(), fmt::Error> {
        self.append(&nsCString::from(s));
        Ok(())
    }
}

impl fmt::Display for nsACString {
    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        fmt::Display::fmt(&String::from_utf8_lossy(&self[..]), f)
    }
}

impl fmt::Debug for nsACString {
    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        fmt::Debug::fmt(&String::from_utf8_lossy(&self[..]), f)
    }
}

impl cmp::PartialEq<str> for nsACString {
    fn eq(&self, other: &str) -> bool {
        &self[..] == other.as_bytes()
    }
}

#[macro_export]
macro_rules! ns_auto_cstring {
    ($name:ident) => {
        let mut buf: [u8; 64] = [0; 64];
        let mut $name = $crate::nsFixedCString::new(&mut buf);
    }
}

///////////////////////////////////////////
// Bindings for nsString (u16 char type) //
///////////////////////////////////////////

define_string_types! {
    char_t = u16;

    AString = nsAString;
    String = nsString;
    FixedString = nsFixedString;

    StringRepr = nsStringRepr;
    FixedStringRepr = nsFixedStringRepr;
    AutoStringRepr = nsAutoStringRepr;
}

impl nsAString {
    /// Leaves the nsAString in an unstable state with a dangling data pointer.
    /// Should only be used in drop implementations of rust types which wrap
    /// this type.
    unsafe fn finalize(&mut self) {
        Gecko_FinalizeString(self);
    }

    pub fn assign(&mut self, other: &nsAString) {
        unsafe {
            Gecko_AssignString(self as *mut _, other as *const _);
        }
    }

    pub fn assign_utf8(&mut self, other: &nsACString) {
        self.assign(&nsString::new());
        self.append_utf8(other);
    }

    pub fn append(&mut self, other: &nsAString) {
        unsafe {
            Gecko_AppendString(self as *mut _, other as *const _);
        }
    }

    pub fn append_utf8(&mut self, other: &nsACString) {
        unsafe {
            Gecko_AppendUTF8toString(self as *mut _, other as *const _);
        }
    }
}

// NOTE: The From impl for a string slice for nsString produces a <'static>
// lifetime, as it allocates.
impl<'a> From<&'a str> for nsString<'static> {
    fn from(s: &'a str) -> nsString<'static> {
        s.encode_utf16().collect::<Vec<u16>>().into()
    }
}

// Support for the write!() macro for writing to nsStrings
impl fmt::Write for nsAString {
    fn write_str(&mut self, s: &str) -> Result<(), fmt::Error> {
        // Directly invoke gecko's routines for appending utf8 strings to
        // nsAString values, to avoid as much overhead as possible
        self.append_utf8(&nsCString::from(s));
        Ok(())
    }
}

impl fmt::Display for nsAString {
    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        fmt::Display::fmt(&String::from_utf16_lossy(&self[..]), f)
    }
}

impl fmt::Debug for nsAString {
    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        fmt::Debug::fmt(&String::from_utf16_lossy(&self[..]), f)
    }
}

impl cmp::PartialEq<str> for nsAString {
    fn eq(&self, other: &str) -> bool {
        other.encode_utf16().eq(self.iter().cloned())
    }
}

#[macro_export]
macro_rules! ns_auto_string {
    ($name:ident) => {
        let mut buf: [u16; 64] = [0; 64];
        let mut $name = $crate::nsFixedString::new(&mut buf);
    }
}

// NOTE: These bindings currently only expose infallible operations. Perhaps
// consider allowing for fallible methods?
extern "C" {
    // Gecko implementation in nsSubstring.cpp
    fn Gecko_FinalizeCString(this: *mut nsACString);
    fn Gecko_AssignCString(this: *mut nsACString, other: *const nsACString);
    fn Gecko_AppendCString(this: *mut nsACString, other: *const nsACString);

    fn Gecko_FinalizeString(this: *mut nsAString);
    fn Gecko_AssignString(this: *mut nsAString, other: *const nsAString);
    fn Gecko_AppendString(this: *mut nsAString, other: *const nsAString);

    // Gecko implementation in nsReadableUtils.cpp
    fn Gecko_AppendUTF16toCString(this: *mut nsACString, other: *const nsAString);
    fn Gecko_AppendUTF8toString(this: *mut nsAString, other: *const nsACString);
}

//////////////////////////////////////
// Repr Validation Helper Functions //
//////////////////////////////////////

pub mod test_helpers {
    //! This module only exists to help with ensuring that the layout of the
    //! structs inside of rust and C++ are identical.
    //!
    //! It is public to ensure that these testing functions are avaliable to
    //! gtest code.

    use super::{
        nsFixedCStringRepr,
        nsFixedStringRepr,
        nsCStringRepr,
        nsStringRepr,
        F_NONE,
        F_TERMINATED,
        F_VOIDED,
        F_SHARED,
        F_OWNED,
        F_FIXED,
        F_LITERAL,
        F_CLASS_FIXED,
    };
    use std::mem;

    /// Generates an #[no_mangle] extern "C" function which returns the size and
    /// alignment of the given type with the given name.
    macro_rules! size_align_check {
        ($T:ty, $fname:ident) => {
            #[no_mangle]
            #[allow(non_snake_case)]
            pub extern fn $fname(size: *mut usize, align: *mut usize) {
                unsafe {
                    *size = mem::size_of::<$T>();
                    *align = mem::align_of::<$T>();
                }
            }
        }
    }

    size_align_check!(nsStringRepr, Rust_Test_ReprSizeAlign_nsString);
    size_align_check!(nsCStringRepr, Rust_Test_ReprSizeAlign_nsCString);
    size_align_check!(nsFixedStringRepr, Rust_Test_ReprSizeAlign_nsFixedString);
    size_align_check!(nsFixedCStringRepr, Rust_Test_ReprSizeAlign_nsFixedCString);

    /// Generates a $[no_mangle] extern "C" function which returns the size,
    /// alignment and offset in the parent struct of a given member, with the
    /// given name.
    ///
    /// This method can trigger Undefined Behavior if the accessing the member
    /// $member on a given type would use that type's `Deref` implementation.
    macro_rules! member_check {
        ($T:ty, $member:ident, $method:ident) => {
            #[no_mangle]
            #[allow(non_snake_case)]
            pub extern fn $method(size: *mut usize,
                                  align: *mut usize,
                                  offset: *mut usize) {
                unsafe {
                    // Create a temporary value of type T to get offsets, sizes
                    // and aligns off of
                    let tmp: $T = mem::zeroed();
                    *size = mem::size_of_val(&tmp.$member);
                    *align = mem::align_of_val(&tmp.$member);
                    *offset =
                        (&tmp.$member as *const _ as usize) -
                        (&tmp as *const _ as usize);
                    mem::forget(tmp);
                }
            }
        }
    }

    member_check!(nsStringRepr, data, Rust_Test_Member_nsString_mData);
    member_check!(nsStringRepr, length, Rust_Test_Member_nsString_mLength);
    member_check!(nsStringRepr, flags, Rust_Test_Member_nsString_mFlags);
    member_check!(nsCStringRepr, data, Rust_Test_Member_nsCString_mData);
    member_check!(nsCStringRepr, length, Rust_Test_Member_nsCString_mLength);
    member_check!(nsCStringRepr, flags, Rust_Test_Member_nsCString_mFlags);
    member_check!(nsFixedStringRepr, capacity, Rust_Test_Member_nsFixedString_mFixedCapacity);
    member_check!(nsFixedStringRepr, buffer, Rust_Test_Member_nsFixedString_mFixedBuf);
    member_check!(nsFixedCStringRepr, capacity, Rust_Test_Member_nsFixedCString_mFixedCapacity);
    member_check!(nsFixedCStringRepr, buffer, Rust_Test_Member_nsFixedCString_mFixedBuf);

    #[no_mangle]
    #[allow(non_snake_case)]
    pub extern fn Rust_Test_NsStringFlags(f_none: *mut u32,
                                          f_terminated: *mut u32,
                                          f_voided: *mut u32,
                                          f_shared: *mut u32,
                                          f_owned: *mut u32,
                                          f_fixed: *mut u32,
                                          f_literal: *mut u32,
                                          f_class_fixed: *mut u32) {
        unsafe {
            *f_none = F_NONE;
            *f_terminated = F_TERMINATED;
            *f_voided = F_VOIDED;
            *f_shared = F_SHARED;
            *f_owned = F_OWNED;
            *f_fixed = F_FIXED;
            *f_literal = F_LITERAL;
            *f_class_fixed = F_CLASS_FIXED;
        }
    }
}