auto merge of #19252 : japaric/rust/cow, r=aturon

- Add `IntoCow` trait, and put it in the prelude
- Add `is_owned`/`is_borrowed` methods to `Cow`
- Add `CowString`/`CowVec` type aliases (to `Cow<'_, String, str>`/`Cow<'_, Vec, [T]>` respectively)
- `Cow` implements: `Show`, `Hash`, `[Partial]{Eq,Ord}`
- `impl BorrowFrom<Cow<'a, T, B>> for B`

[breaking-change]s:

- `IntoMaybeOwned` has been removed from the prelude
- libcollections: `SendStr` is now an alias to `CowString<'static>` (it was aliased to `MaybeOwned<'static>`)
- libgraphviz:
  - `LabelText` variants now wrap `CowString` instead of `MaybeOwned`
  - `Nodes` and `Edges` are now type aliases to `CowVec` (they were aliased to `MaybeOwnedVec`)
- libstd/path: `Display::as_maybe_owned` has been renamed to `Display::as_cow` and now returns a `CowString`
- These functions now accept/return `Cow` instead of `MaybeOwned[Vector]`:
  - libregex: `Replacer::reg_replace`
  - libcollections: `str::from_utf8_lossy`
  - libgraphviz: `Id::new`, `Id::name`, `LabelText::pre_escaped_content`
  - libstd: `TaskBuilder::named`

r? @aturon 

3 files changed, 7 insertions, 7 deletions

diff --git a/src/libstd/path/mod.rs b/src/libstd/path/mod.rs
index a185a29a700..ce3440ead40 100644
--- a/src/libstd/path/mod.rs
+++ b/src/libstd/path/mod.rs
@@ -74,7 +74,7 @@ use fmt;
 use iter::Iterator;
 use option::{Option, None, Some};
 use str;
-use str::{MaybeOwned, Str, StrPrelude};
+use str::{CowString, MaybeOwned, Str, StrPrelude};
 use string::String;
 use slice::{AsSlice, CloneSliceAllocPrelude};
 use slice::{PartialEqSlicePrelude, SlicePrelude};
@@ -830,7 +830,7 @@ pub struct Display<'a, P:'a> {
 
 impl<'a, P: GenericPath> fmt::Show for Display<'a, P> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        self.as_maybe_owned().as_slice().fmt(f)
+        self.as_cow().fmt(f)
     }
 }
 
@@ -840,7 +840,7 @@ impl<'a, P: GenericPath> Display<'a, P> {
     /// If the path is not UTF-8, invalid sequences will be replaced with the
     /// Unicode replacement char. This involves allocation.
     #[inline]
-    pub fn as_maybe_owned(&self) -> MaybeOwned<'a> {
+    pub fn as_cow(&self) -> CowString<'a> {
         String::from_utf8_lossy(if self.filename {
             match self.path.filename() {
                 None => {
diff --git a/src/libstd/path/posix.rs b/src/libstd/path/posix.rs
index 2b444fdc32b..bdce759a1df 100644
--- a/src/libstd/path/posix.rs
+++ b/src/libstd/path/posix.rs
@@ -551,14 +551,14 @@ mod tests {
             ($path:expr, $exp:expr) => (
                 {
                     let path = Path::new($path);
-                    let mo = path.display().as_maybe_owned();
+                    let mo = path.display().as_cow();
                     assert!(mo.as_slice() == $exp);
                 }
             );
             ($path:expr, $exp:expr, filename) => (
                 {
                     let path = Path::new($path);
-                    let mo = path.filename_display().as_maybe_owned();
+                    let mo = path.filename_display().as_cow();
                     assert!(mo.as_slice() == $exp);
                 }
             )
diff --git a/src/libstd/path/windows.rs b/src/libstd/path/windows.rs
index 9f81de72980..fc367710131 100644
--- a/src/libstd/path/windows.rs
+++ b/src/libstd/path/windows.rs
@@ -1326,10 +1326,10 @@ mod tests {
         assert_eq!(path.filename_display().to_string(), "".to_string());
 
         let path = Path::new("foo");
-        let mo = path.display().as_maybe_owned();
+        let mo = path.display().as_cow();
         assert_eq!(mo.as_slice(), "foo");
         let path = Path::new(b"\\");
-        let mo = path.filename_display().as_maybe_owned();
+        let mo = path.filename_display().as_cow();
         assert_eq!(mo.as_slice(), "");
     }