Implement fmt::Pointer for pointers to unsized types

This allows printing pointers to unsized types with the {:p} formatting
directive. The following impls are extended to unsized types:
 - impl<'a, T: ?Sized> Pointer for &'a T
 - impl<'a, T: ?Sized> Pointer for &'a mut T
 - impl<T: ?Sized> Pointer for *const T
 - impl<T: ?Sized> Pointer for *mut T
 - impl<T: ?Sized> fmt::Pointer for Box<T>
 - impl<T: ?Sized> fmt::Pointer for Rc<T>
 - impl<T: ?Sized> fmt::Pointer for Arc<T>

Author: kamalmarhubi

src/liballoc/arc.rs

@@ -879,7 +879,7 @@ impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> fmt::Pointer for Arc<T> {
+impl<T: ?Sized> fmt::Pointer for Arc<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Pointer::fmt(&*self._ptr, f)
     }

src/liballoc/boxed.rs

@@ -442,7 +442,7 @@ impl<T: fmt::Debug + ?Sized> fmt::Debug for Box<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> fmt::Pointer for Box<T> {
+impl<T: ?Sized> fmt::Pointer for Box<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         // It's not possible to extract the inner Uniq directly from the Box,
         // instead we cast it to a *const which aliases the Unique

src/liballoc/rc.rs

@@ -688,7 +688,7 @@ impl<T: ?Sized + fmt::Debug> fmt::Debug for Rc<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> fmt::Pointer for Rc<T> {
+impl<T: ?Sized> fmt::Pointer for Rc<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Pointer::fmt(&*self._ptr, f)
     }

src/libcore/fmt/mod.rs

@@ -1384,7 +1384,7 @@ impl Display for char {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Pointer for *const T {
+impl<T: ?Sized> Pointer for *const T {
     fn fmt(&self, f: &mut Formatter) -> Result {
         let old_width = f.width;
         let old_flags = f.flags;
@@ -1402,7 +1402,7 @@ impl<T> Pointer for *const T {
         }
         f.flags |= 1 << (FlagV1::Alternate as u32);
 
-        let ret = LowerHex::fmt(&(*self as usize), f);
+        let ret = LowerHex::fmt(&(*self as *const () as usize), f);
 
         f.width = old_width;
         f.flags = old_flags;
@@ -1412,7 +1412,7 @@ impl<T> Pointer for *const T {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Pointer for *mut T {
+impl<T: ?Sized> Pointer for *mut T {
     fn fmt(&self, f: &mut Formatter) -> Result {
         // FIXME(#23542) Replace with type ascription.
         #![allow(trivial_casts)]
@@ -1421,7 +1421,7 @@ impl<T> Pointer for *mut T {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T> Pointer for &'a T {
+impl<'a, T: ?Sized> Pointer for &'a T {
     fn fmt(&self, f: &mut Formatter) -> Result {
         // FIXME(#23542) Replace with type ascription.
         #![allow(trivial_casts)]
@@ -1430,7 +1430,7 @@ impl<'a, T> Pointer for &'a T {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T> Pointer for &'a mut T {
+impl<'a, T: ?Sized> Pointer for &'a mut T {
     fn fmt(&self, f: &mut Formatter) -> Result {
         // FIXME(#23542) Replace with type ascription.
         #![allow(trivial_casts)]

src/libcoretest/fmt/mod.rs

@@ -20,3 +20,11 @@ fn test_format_flags() {
 
     assert_eq!(format!("{: >3}", 'a'), "  a");
 }
+
+#[test]
+fn test_pointer_formats_data_pointer() {
+    let b: &[u8] = b"";
+    let s: &str = "";
+    assert_eq!(format!("{:p}", s), format!("{:p}", s.as_ptr()));
+    assert_eq!(format!("{:p}", b), format!("{:p}", b.as_ptr()));
+}