core: Remove the cast module

This commit revisits the `cast` module in libcore and libstd, and scrutinizes
all functions inside of it. The result was to remove the `cast` module entirely,
folding all functionality into the `mem` module. Specifically, this is the fate
of each function in the `cast` module.

* transmute - This function was moved to `mem`, but it is now marked as
              #[unstable]. This is due to planned changes to the `transmute`
              function and how it can be invoked (see the #[unstable] comment).
              For more information, see RFC 5 and #12898

* transmute_copy - This function was moved to `mem`, with clarification that is
                   is not an error to invoke it with T/U that are different
                   sizes, but rather that it is strongly discouraged. This
                   function is now #[stable]

* forget - This function was moved to `mem` and marked #[stable]

* bump_box_refcount - This function was removed due to the deprecation of
                      managed boxes as well as its questionable utility.

* transmute_mut - This function was previously deprecated, and removed as part
                  of this commit.

* transmute_mut_unsafe - This function doesn't serve much of a purpose when it
                         can be achieved with an `as` in safe code, so it was
                         removed.

* transmute_lifetime - This function was removed because it is likely a strong
                       indication that code is incorrect in the first place.

* transmute_mut_lifetime - This function was removed for the same reasons as
                           `transmute_lifetime`

* copy_lifetime - This function was moved to `mem`, but it is marked
                  `#[unstable]` now due to the likelihood of being removed in
                  the future if it is found to not be very useful.

* copy_mut_lifetime - This function was also moved to `mem`, but had the same
                      treatment as `copy_lifetime`.

* copy_lifetime_vec - This function was removed because it is not used today,
                      and its existence is not necessary with DST
                      (copy_lifetime will suffice).

In summary, the cast module was stripped down to these functions, and then the
functions were moved to the `mem` module.

    transmute - #[unstable]
    transmute_copy - #[stable]
    forget - #[stable]
    copy_lifetime - #[unstable]
    copy_mut_lifetime - #[unstable]

[breaking-change]

2 files changed, 7 insertions, 7 deletions

diff --git a/src/test/debuginfo/nil-enum.rs b/src/test/debuginfo/nil-enum.rs
index 67c7eb30da6..43d82e75c4d 100644
--- a/src/test/debuginfo/nil-enum.rs
+++ b/src/test/debuginfo/nil-enum.rs
@@ -32,8 +32,8 @@ enum AnotherNilEnum {}
 // 2. That gdb prints the string "{<No data fields>}" for empty structs (which may change some time)
 fn main() {
     unsafe {
-        let first: ANilEnum = std::cast::transmute(());
-        let second: AnotherNilEnum = std::cast::transmute(());
+        let first: ANilEnum = std::mem::transmute(());
+        let second: AnotherNilEnum = std::mem::transmute(());
 
         zzz();
     }
diff --git a/src/test/debuginfo/option-like-enum.rs b/src/test/debuginfo/option-like-enum.rs
index b60c9c4a4b9..5c44703f6f2 100644
--- a/src/test/debuginfo/option-like-enum.rs
+++ b/src/test/debuginfo/option-like-enum.rs
@@ -69,21 +69,21 @@ struct NamedFieldsRepr<'a> {
 
 fn main() {
 
-    let some: Option<&u32> = Some(unsafe { std::cast::transmute(0x12345678) });
+    let some: Option<&u32> = Some(unsafe { std::mem::transmute(0x12345678) });
     let none: Option<&u32> = None;
 
-    let full = Full(454545, unsafe { std::cast::transmute(0x87654321) }, 9988);
+    let full = Full(454545, unsafe { std::mem::transmute(0x87654321) }, 9988);
 
     let int_val = 0;
-    let empty: &MoreFieldsRepr = unsafe { std::cast::transmute(&Empty) };
+    let empty: &MoreFieldsRepr = unsafe { std::mem::transmute(&Empty) };
 
     let droid = Droid {
         id: 675675,
         range: 10000001,
-        internals: unsafe { std::cast::transmute(0x43218765) }
+        internals: unsafe { std::mem::transmute(0x43218765) }
     };
 
-    let void_droid: &NamedFieldsRepr = unsafe { std::cast::transmute(&Void) };
+    let void_droid: &NamedFieldsRepr = unsafe { std::mem::transmute(&Void) };
 
     zzz();
 }