std: Implement CString-related RFCs

This commit is an implementation of [RFC 592][r592] and [RFC 840][r840]. These
two RFCs tweak the behavior of `CString` and add a new `CStr` unsized slice type
to the module.

[r592]: https://github.com/rust-lang/rfcs/blob/master/text/0592-c-str-deref.md
[r840]: https://github.com/rust-lang/rfcs/blob/master/text/0840-no-panic-in-c-string.md

The new `CStr` type is only constructable via two methods:

1. By `deref`'ing from a `CString`
2. Unsafely via `CStr::from_ptr`

The purpose of `CStr` is to be an unsized type which is a thin pointer to a
`libc::c_char` (currently it is a fat pointer slice due to implementation
limitations). Strings from C can be safely represented with a `CStr` and an
appropriate lifetime as well. Consumers of `&CString` should now consume `&CStr`
instead to allow producers to pass in C-originating strings instead of just
Rust-allocated strings.

A new constructor was added to `CString`, `new`, which takes `T: IntoBytes`
instead of separate `from_slice` and `from_vec` methods (both have been
deprecated in favor of `new`). The `new` method returns a `Result` instead of
panicking.  The error variant contains the relevant information about where the
error happened and bytes (if present). Conversions are provided to the
`io::Error` and `old_io::IoError` types via the `FromError` trait which
translate to `InvalidInput`.

This is a breaking change due to the modification of existing `#[unstable]` APIs
and new deprecation, and more detailed information can be found in the two RFCs.
Notable breakage includes:

* All construction of `CString` now needs to use `new` and handle the outgoing
  `Result`.
* Usage of `CString` as a byte slice now explicitly needs a `.as_bytes()` call.
* The `as_slice*` methods have been removed in favor of just having the
  `as_bytes*` methods.

Closes #22469
Closes #22470
[breaking-change]

src/libstd/sys/unix/fs.rs

@@ -12,7 +12,7 @@
 
 use prelude::v1::*;
 
-use ffi::{self, CString};
+use ffi::{CString, CStr};
 use old_io::{FilePermission, Write, UnstableFileStat, Open, FileAccess, FileMode};
 use old_io::{IoResult, FileStat, SeekStyle};
 use old_io::{Read, Truncate, SeekCur, SeekSet, ReadWrite, SeekEnd, Append};
@@ -151,8 +151,8 @@ impl Drop for FileDesc {
     }
 }
 
-fn cstr(path: &Path) -> CString {
-    CString::from_slice(path.as_vec())
+fn cstr(path: &Path) -> IoResult<CString> {
+    Ok(try!(CString::new(path.as_vec())))
 }
 
 pub fn open(path: &Path, fm: FileMode, fa: FileAccess) -> IoResult<FileDesc> {
@@ -170,7 +170,7 @@ pub fn open(path: &Path, fm: FileMode, fa: FileAccess) -> IoResult<FileDesc> {
                             libc::S_IRUSR | libc::S_IWUSR),
     };
 
-    let path = cstr(path);
+    let path = try!(cstr(path));
     match retry(|| unsafe { libc::open(path.as_ptr(), flags, mode) }) {
         -1 => Err(super::last_error()),
         fd => Ok(FileDesc::new(fd, true)),
@@ -178,7 +178,7 @@ pub fn open(path: &Path, fm: FileMode, fa: FileAccess) -> IoResult<FileDesc> {
 }
 
 pub fn mkdir(p: &Path, mode: uint) -> IoResult<()> {
-    let p = cstr(p);
+    let p = try!(cstr(p));
     mkerr_libc(unsafe { libc::mkdir(p.as_ptr(), mode as libc::mode_t) })
 }
 
@@ -203,7 +203,7 @@ pub fn readdir(p: &Path) -> IoResult<Vec<Path>> {
     let mut buf = Vec::<u8>::with_capacity(size as uint);
     let ptr = buf.as_mut_ptr() as *mut dirent_t;
 
-    let p = CString::from_slice(p.as_vec());
+    let p = try!(CString::new(p.as_vec()));
     let dir_ptr = unsafe {opendir(p.as_ptr())};
 
     if dir_ptr as uint != 0 {
@@ -212,7 +212,7 @@ pub fn readdir(p: &Path) -> IoResult<Vec<Path>> {
         while unsafe { readdir_r(dir_ptr, ptr, &mut entry_ptr) == 0 } {
             if entry_ptr.is_null() { break }
             paths.push(unsafe {
-                Path::new(ffi::c_str_to_bytes(&rust_list_dir_val(entry_ptr)))
+                Path::new(CStr::from_ptr(rust_list_dir_val(entry_ptr)).to_bytes())
             });
         }
         assert_eq!(unsafe { closedir(dir_ptr) }, 0);
@@ -223,39 +223,39 @@ pub fn readdir(p: &Path) -> IoResult<Vec<Path>> {
 }
 
 pub fn unlink(p: &Path) -> IoResult<()> {
-    let p = cstr(p);
+    let p = try!(cstr(p));
     mkerr_libc(unsafe { libc::unlink(p.as_ptr()) })
 }
 
 pub fn rename(old: &Path, new: &Path) -> IoResult<()> {
-    let old = cstr(old);
-    let new = cstr(new);
+    let old = try!(cstr(old));
+    let new = try!(cstr(new));
     mkerr_libc(unsafe {
         libc::rename(old.as_ptr(), new.as_ptr())
     })
 }
 
 pub fn chmod(p: &Path, mode: uint) -> IoResult<()> {
-    let p = cstr(p);
+    let p = try!(cstr(p));
     mkerr_libc(retry(|| unsafe {
         libc::chmod(p.as_ptr(), mode as libc::mode_t)
     }))
 }
 
 pub fn rmdir(p: &Path) -> IoResult<()> {
-    let p = cstr(p);
+    let p = try!(cstr(p));
     mkerr_libc(unsafe { libc::rmdir(p.as_ptr()) })
 }
 
 pub fn chown(p: &Path, uid: int, gid: int) -> IoResult<()> {
-    let p = cstr(p);
+    let p = try!(cstr(p));
     mkerr_libc(retry(|| unsafe {
         libc::chown(p.as_ptr(), uid as libc::uid_t, gid as libc::gid_t)
     }))
 }
 
 pub fn readlink(p: &Path) -> IoResult<Path> {
-    let c_path = cstr(p);
+    let c_path = try!(cstr(p));
     let p = c_path.as_ptr();
     let mut len = unsafe { libc::pathconf(p as *mut _, libc::_PC_NAME_MAX) };
     if len == -1 {
@@ -276,14 +276,14 @@ pub fn readlink(p: &Path) -> IoResult<Path> {
 }
 
 pub fn symlink(src: &Path, dst: &Path) -> IoResult<()> {
-    let src = cstr(src);
-    let dst = cstr(dst);
+    let src = try!(cstr(src));
+    let dst = try!(cstr(dst));
     mkerr_libc(unsafe { libc::symlink(src.as_ptr(), dst.as_ptr()) })
 }
 
 pub fn link(src: &Path, dst: &Path) -> IoResult<()> {
-    let src = cstr(src);
-    let dst = cstr(dst);
+    let src = try!(cstr(src));
+    let dst = try!(cstr(dst));
     mkerr_libc(unsafe { libc::link(src.as_ptr(), dst.as_ptr()) })
 }
 
@@ -331,7 +331,7 @@ fn mkstat(stat: &libc::stat) -> FileStat {
 }
 
 pub fn stat(p: &Path) -> IoResult<FileStat> {
-    let p = cstr(p);
+    let p = try!(cstr(p));
     let mut stat: libc::stat = unsafe { mem::zeroed() };
     match unsafe { libc::stat(p.as_ptr(), &mut stat) } {
         0 => Ok(mkstat(&stat)),
@@ -340,7 +340,7 @@ pub fn stat(p: &Path) -> IoResult<FileStat> {
 }
 
 pub fn lstat(p: &Path) -> IoResult<FileStat> {
-    let p = cstr(p);
+    let p = try!(cstr(p));
     let mut stat: libc::stat = unsafe { mem::zeroed() };
     match unsafe { libc::lstat(p.as_ptr(), &mut stat) } {
         0 => Ok(mkstat(&stat)),
@@ -349,7 +349,7 @@ pub fn lstat(p: &Path) -> IoResult<FileStat> {
 }
 
 pub fn utime(p: &Path, atime: u64, mtime: u64) -> IoResult<()> {
-    let p = cstr(p);
+    let p = try!(cstr(p));
     let buf = libc::utimbuf {
         actime: (atime / 1000) as libc::time_t,
         modtime: (mtime / 1000) as libc::time_t,