Auto merge of #42313 - pnkfelix:allocator-integration, r=alexcrichton

Allocator integration

Lets start getting some feedback on `trait Alloc`.

Here is:
 *  the `trait Alloc` itself,
 * the `struct Layout` and `enum AllocErr` that its API relies on
 * a `struct HeapAlloc` that exposes the system allocator as an instance of `Alloc`
 * an integration of `Alloc` with `RawVec`
 * ~~an integration of `Alloc` with `Vec`~~

 TODO
 * [x] split `fn realloc_in_place` into `grow` and `shrink` variants
 * [x] add `# Unsafety` and `# Errors` sections to documentation for all relevant methods
 * [x] remove `Vec` integration with `Allocator`
 * [x] add `allocate_zeroed` impl to `HeapAllocator`
 * [x] remove typedefs e.g. `type Size = usize;`
 * [x] impl `trait Error` for all error types in PR
 * [x] make `Layout::from_size_align` public
 * [x] clarify docs of `fn padding_needed_for`.
 * [x] revise `Layout` constructors to ensure that [size+align combination is valid](https://github.com/rust-lang/rust/pull/42313#issuecomment-306845446)
 * [x] resolve mismatch re requirements of align on dealloc. See [comment](https://github.com/rust-lang/rust/pull/42313#issuecomment-306202489).

2 files changed, 20 insertions, 0 deletions

diff --git a/src/libstd/error.rs b/src/libstd/error.rs
index f56e3a5d780..3d203429e7b 100644
--- a/src/libstd/error.rs
+++ b/src/libstd/error.rs
@@ -51,6 +51,7 @@
 // coherence challenge (e.g., specialization, neg impls, etc) we can
 // reconsider what crate these items belong in.
 
+use alloc::allocator;
 use any::TypeId;
 use cell;
 use char;
@@ -221,6 +222,24 @@ impl Error for ! {
     fn description(&self) -> &str { *self }
 }
 
+#[unstable(feature = "allocator_api",
+           reason = "the precise API and guarantees it provides may be tweaked.",
+           issue = "27700")]
+impl Error for allocator::AllocErr {
+    fn description(&self) -> &str {
+        allocator::AllocErr::description(self)
+    }
+}
+
+#[unstable(feature = "allocator_api",
+           reason = "the precise API and guarantees it provides may be tweaked.",
+           issue = "27700")]
+impl Error for allocator::CannotReallocInPlace {
+    fn description(&self) -> &str {
+        allocator::CannotReallocInPlace::description(self)
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Error for str::ParseBoolError {
     fn description(&self) -> &str { "failed to parse bool" }
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 105f4026ec8..7c843711dbe 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -245,6 +245,7 @@
 // std is implemented with unstable features, many of which are internal
 // compiler details that will never be stable
 #![feature(alloc)]
+#![feature(allocator_api)]
 #![feature(allow_internal_unstable)]
 #![feature(asm)]
 #![feature(associated_consts)]