Add ToCStr impl for &Path and ~str

This is a stopgap until DST (rust-lang#12938) lands.

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 and ~str, so that we can take ToCStr as owned. When
DST lands, the &Path instance should be removed, the string instances
should be revisted, and arguments bound by ToCStr should be passed by
reference.

FIXMEs have been added accordingly.

src/libstd/c_str.rs

@@ -293,6 +293,13 @@ pub trait ToCStr {
     }
 }
 
+// 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 ~str, so that we can take ToCStr as owned. When DST lands, the string
+// instances should be revisted, and arguments bound by ToCStr should be passed
+// by reference.
+
 impl<'a> ToCStr for &'a str {
     #[inline]
     fn to_c_str(&self) -> CString {
@@ -315,6 +322,28 @@ impl<'a> ToCStr for &'a str {
     }
 }
 
+impl ToCStr for ~str {
+    #[inline]
+    fn to_c_str(&self) -> CString {
+        self.as_bytes().to_c_str()
+    }
+
+    #[inline]
+    unsafe fn to_c_str_unchecked(&self) -> CString {
+        self.as_bytes().to_c_str_unchecked()
+    }
+
+    #[inline]
+    fn with_c_str<T>(&self, f: |*libc::c_char| -> T) -> T {
+        self.as_bytes().with_c_str(f)
+    }
+
+    #[inline]
+    unsafe fn with_c_str_unchecked<T>(&self, f: |*libc::c_char| -> T) -> T {
+        self.as_bytes().with_c_str_unchecked(f)
+    }
+}
+
 // The length of the stack allocated buffer for `vec.with_c_str()`
 static BUF_LEN: uint = 128;
 

src/libstd/path/posix.rs

@@ -79,11 +79,18 @@ 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.as_vec().to_c_str_unchecked() }
+        unsafe { self.to_c_str_unchecked() }
     }
 
     #[inline]
@@ -92,6 +99,18 @@ impl ToCStr for Path {
     }
 }
 
+impl<'a> ToCStr for &'a Path {
+    #[inline]
+    fn to_c_str(&self) -> CString {
+        (*self).to_c_str()
+    }
+
+    #[inline]
+    unsafe fn to_c_str_unchecked(&self) -> CString {
+        (*self).to_c_str_unchecked()
+    }
+}
+
 impl<S: Writer> ::hash::Hash<S> for Path {
     #[inline]
     fn hash(&self, state: &mut S) {

src/libstd/path/windows.rs

@@ -103,11 +103,18 @@ 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 embedded NULs
-        unsafe { self.as_vec().to_c_str_unchecked() }
+        // The Path impl guarantees no internal NUL
+        unsafe { self.to_c_str_unchecked() }
     }
 
     #[inline]
@@ -116,6 +123,18 @@ impl ToCStr for Path {
     }
 }
 
+impl<'a> ToCStr for &'a Path {
+    #[inline]
+    fn to_c_str(&self) -> CString {
+        (*self).to_c_str()
+    }
+
+    #[inline]
+    unsafe fn to_c_str_unchecked(&self) -> CString {
+        (*self).to_c_str_unchecked()
+    }
+}
+
 impl<S: Writer> ::hash::Hash<S> for Path {
     #[inline]
     fn hash(&self, state: &mut S) {