std: Tweak String implementations

This commit performs a pass over the implementations of the new `String` trait
in the formatting module. Some implementations were removed as a conservative
move pending an upcoming convention about `String` implementations, and some
were added in order to retain consistency across the libraries. Specifically:

* All "smart pointers" implement `String` now, adding missing implementations
  for `Arc` and `Rc`.
* The `Vec<T>` and `[T]` types no longer implement `String`.
* The `*const T` and `*mut T` type no longer implement `String`.
* The `()` type no longer implements `String`.
* The `Path` type's `Show` implementation does not surround itself with `Path
  {}` (a minor tweak).

All implementations of `String` in this PR were also marked `#[stable]` to
indicate that the types will continue to implement the `String` trait regardless
of what it looks like.

src/test/compile-fail/borrowck-borrowed-uniq-rvalue-2.rs

@@ -18,7 +18,7 @@ struct defer<'a> {
 impl<'a> Drop for defer<'a> {
     fn drop(&mut self) {
         unsafe {
-            println!("{}", self.x);
+            println!("{:?}", self.x);
         }
     }
 }

src/test/compile-fail/drop-with-active-borrows-2.rs

@@ -15,5 +15,5 @@ fn read_lines_borrowed<'a>() -> Vec<&'a str> {
 }
 
 fn main() {
-    println!("{}", read_lines_borrowed());
+    println!("{:?}", read_lines_borrowed());
 }

src/test/compile-fail/no-capture-arc.rs

@@ -23,5 +23,5 @@ fn main() {
 
     assert_eq!((*arc_v)[2], 3);
 
-    println!("{}", *arc_v);
+    println!("{:?}", *arc_v);
 }

src/test/compile-fail/no-reuse-move-arc.rs

@@ -21,5 +21,5 @@ fn main() {
 
     assert_eq!((*arc_v)[2], 3); //~ ERROR use of moved value: `arc_v`
 
-    println!("{}", *arc_v); //~ ERROR use of moved value: `arc_v`
+    println!("{:?}", *arc_v); //~ ERROR use of moved value: `arc_v`
 }

src/test/compile-fail/packed-struct-generic-transmute.rs

@@ -34,6 +34,6 @@ fn main() {
     let foo = Foo { bar: [1u8, 2, 3, 4, 5], baz: 10i32 };
     unsafe {
         let oof: Oof<[u8; 5], i32> = mem::transmute(foo);
-        println!("{} {}", &oof.rab[], oof.zab);
+        println!("{:?} {:?}", &oof.rab[], oof.zab);
     }
 }

src/test/run-pass/evec-slice.rs

@@ -22,7 +22,7 @@ pub fn main() {
     let c : &[int] = &[2,2,2,2,3];
     let cc : &[int] = &[2,2,2,2,2,2];
 
-    println!("{}", a);
+    println!("{:?}", a);
 
     assert!(a < b);
     assert!(a <= b);
@@ -30,7 +30,7 @@ pub fn main() {
     assert!(b >= a);
     assert!(b > a);
 
-    println!("{}", b);
+    println!("{:?}", b);
 
     assert!(b < c);
     assert!(b <= c);
@@ -44,7 +44,7 @@ pub fn main() {
     assert!(c >= a);
     assert!(c > a);
 
-    println!("{}", c);
+    println!("{:?}", c);
 
     assert!(a < cc);
     assert!(a <= cc);
@@ -52,5 +52,5 @@ pub fn main() {
     assert!(cc >= a);
     assert!(cc > a);
 
-    println!("{}", cc);
+    println!("{:?}", cc);
 }

src/test/run-pass/ifmt.rs

@@ -183,7 +183,7 @@ fn test_write() {
 // can do with them just yet (to test the output)
 fn test_print() {
     print!("hi");
-    print!("{}", vec!(0u8));
+    print!("{:?}", vec!(0u8));
     println!("hello");
     println!("this is a {}", "test");
     println!("{foo}", foo="bar");

src/test/run-pass/issue-17503.rs

@@ -15,7 +15,7 @@ fn main() {
     let ss: &&[int] = &s;
     let sss: &&&[int] = &ss;
 
-    println!("{}", &s[0..3]);
-    println!("{}", &ss[3..]);
-    println!("{}", &sss[2..4]);
+    println!("{:?}", &s[0..3]);
+    println!("{:?}", &ss[3..]);
+    println!("{:?}", &sss[2..4]);
 }

src/test/run-pass/issue-5688.rs

@@ -25,6 +25,6 @@ static V: &'static [X] = &[X { vec: &[1, 2, 3] }];
 
 pub fn main() {
     for &v in V.iter() {
-        println!("{}", v.vec);
+        println!("{:?}", v.vec);
     }
 }

src/test/run-pass/repeated-vector-syntax.rs

@@ -16,8 +16,8 @@ pub fn main() {
 
     print!("[");
     for xi in x.iter() {
-        print!("{}, ", &xi[]);
+        print!("{:?}, ", &xi[]);
     }
     println!("]");
-    println!("{}", &y[]);
+    println!("{:?}", &y[]);
 }

src/test/run-pass/vec-to_str.rs

@@ -9,11 +9,11 @@
 // except according to those terms.
 
 pub fn main() {
-    assert_eq!((vec!(0i, 1)).to_string(), "[0, 1]".to_string());
+    assert_eq!(format!("{:?}", vec!(0i, 1)), "[0i, 1i]".to_string());
 
     let foo = vec!(3i, 4);
     let bar: &[int] = &[4, 5];
 
-    assert_eq!(foo.to_string(), "[3, 4]".to_string());
-    assert_eq!(bar.to_string(), "[4, 5]".to_string());
+    assert_eq!(format!("{:?}", foo), "[3i, 4i]");
+    assert_eq!(format!("{:?}", bar), "[4i, 5i]");
 }