std: Redesign c_str and c_vec

This commit is an implementation of [RFC 494][rfc] which removes the entire
`std::c_vec` module and redesigns the `std::c_str` module as `std::ffi`.

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0494-c_str-and-c_vec-stability.md

The interface of the new `CString` is outlined in the linked RFC, the primary
changes being:

* The `ToCStr` trait is gone, meaning the `with_c_str` and `to_c_str` methods
  are now gone. These two methods are replaced with a `CString::from_slice`
  method.
* The `CString` type is now just a wrapper around `Vec<u8>` with a static
  guarantee that there is a trailing nul byte with no internal nul bytes. This
  means that `CString` now implements `Deref<Target = [c_char]>`, which is where
  it gains most of its methods from. A few helper methods are added to acquire a
  slice of `u8` instead of `c_char`, as well as including a slice with the
  trailing nul byte if necessary.
* All usage of non-owned `CString` values is now done via two functions inside
  of `std::ffi`, called `c_str_to_bytes` and `c_str_to_bytes_with_nul`. These
  functions are now the one method used to convert a `*const c_char` to a Rust
  slice of `u8`.

Many more details, including newly deprecated methods, can be found linked in
the RFC. This is a:

[breaking-change]
Closes #20444

src/libstd/path/mod.rs

@@ -62,7 +62,7 @@
 #![experimental]
 
 use core::kinds::Sized;
-use c_str::CString;
+use ffi::CString;
 use clone::Clone;
 use fmt;
 use iter::IteratorExt;
@@ -892,7 +892,7 @@ impl BytesContainer for Vec<u8> {
 impl BytesContainer for CString {
     #[inline]
     fn container_as_bytes<'a>(&'a self) -> &'a [u8] {
-        self.as_bytes_no_nul()
+        self.as_bytes()
     }
 }
 
@@ -913,21 +913,3 @@ impl<'a, Sized? T: BytesContainer> BytesContainer for &'a T {
 fn contains_nul<T: BytesContainer>(v: &T) -> bool {
     v.container_as_bytes().iter().any(|&x| x == 0)
 }
-
-#[cfg(test)]
-mod tests {
-    use prelude::v1::*;
-    use c_str::ToCStr;
-    use path::{WindowsPath, PosixPath};
-
-    #[test]
-    fn test_cstring() {
-        let input = "/foo/bar/baz";
-        let path: PosixPath = PosixPath::new(input.to_c_str());
-        assert_eq!(path.as_vec(), input.as_bytes());
-
-        let input = r"\foo\bar\baz";
-        let path: WindowsPath = WindowsPath::new(input.to_c_str());
-        assert_eq!(path.as_str().unwrap(), input);
-    }
-}

src/libstd/path/posix.rs

@@ -10,19 +10,16 @@
 
 //! POSIX file path handling
 
-use c_str::{CString, ToCStr};
 use clone::Clone;
-use cmp::{PartialEq, Eq, PartialOrd, Ord, Ordering};
+use cmp::{Ordering, Eq, Ord, PartialEq, PartialOrd};
 use hash;
 use io::Writer;
 use iter::{AdditiveIterator, Extend};
 use iter::{Iterator, IteratorExt, Map};
-use option::Option;
-use option::Option::{None, Some};
 use kinds::Sized;
-use str::{FromStr, Str};
-use str;
-use slice::{Split, AsSlice, SliceConcatExt, SliceExt};
+use option::Option::{self, Some, None};
+use slice::{AsSlice, Split, SliceExt, SliceConcatExt};
+use str::{self, FromStr, StrExt};
 use vec::Vec;
 
 use super::{BytesContainer, GenericPath, GenericPathUnsafe};
@@ -86,26 +83,6 @@ impl FromStr for Path {
     }
 }
 
-// FIXME (#12938): Until DST lands, we cannot decompose &str into & and str, so
-// we cannot usefully take ToCStr arguments by reference (without forcing an
-// additional & around &str). So we are instead temporarily adding an instance
-// for &Path, so that we can take ToCStr as owned. When DST lands, the &Path
-// instance should be removed, and arguments bound by ToCStr should be passed by
-// reference.
-
-impl ToCStr for Path {
-    #[inline]
-    fn to_c_str(&self) -> CString {
-        // The Path impl guarantees no internal NUL
-        unsafe { self.to_c_str_unchecked() }
-    }
-
-    #[inline]
-    unsafe fn to_c_str_unchecked(&self) -> CString {
-        self.as_vec().to_c_str_unchecked()
-    }
-}
-
 impl<S: hash::Writer> hash::Hash<S> for Path {
     #[inline]
     fn hash(&self, state: &mut S) {

src/libstd/path/windows.rs

@@ -15,17 +15,15 @@
 use self::PathPrefix::*;
 
 use ascii::AsciiExt;
-use c_str::{CString, ToCStr};
 use char::CharExt;
 use clone::Clone;
-use cmp::{PartialEq, Eq, PartialOrd, Ord, Ordering};
+use cmp::{Ordering, Eq, Ord, PartialEq, PartialOrd};
 use hash;
 use io::Writer;
 use iter::{AdditiveIterator, Extend};
 use iter::{Iterator, IteratorExt, Map, repeat};
 use mem;
-use option::Option;
-use option::Option::{Some, None};
+use option::Option::{self, Some, None};
 use slice::{SliceExt, SliceConcatExt};
 use str::{SplitTerminator, FromStr, StrExt};
 use string::{String, ToString};
@@ -112,26 +110,6 @@ impl FromStr for Path {
     }
 }
 
-// FIXME (#12938): Until DST lands, we cannot decompose &str into & and str, so
-// we cannot usefully take ToCStr arguments by reference (without forcing an
-// additional & around &str). So we are instead temporarily adding an instance
-// for &Path, so that we can take ToCStr as owned. When DST lands, the &Path
-// instance should be removed, and arguments bound by ToCStr should be passed by
-// reference.
-
-impl ToCStr for Path {
-    #[inline]
-    fn to_c_str(&self) -> CString {
-        // The Path impl guarantees no internal NUL
-        unsafe { self.to_c_str_unchecked() }
-    }
-
-    #[inline]
-    unsafe fn to_c_str_unchecked(&self) -> CString {
-        self.as_vec().to_c_str_unchecked()
-    }
-}
-
 impl<S: hash::Writer> hash::Hash<S> for Path {
     #[cfg(not(test))]
     #[inline]