17 files changed, 9 insertions, 237 deletions
diff --git a/src/doc/unstable-book/src/language-features/repr-transparent.md b/src/doc/unstable-book/src/language-features/repr-transparent.md
deleted file mode 100644
index 62202dc96fd..00000000000
--- a/src/doc/unstable-book/src/language-features/repr-transparent.md
+++ /dev/null
@@ -1,176 +0,0 @@
-# `repr_transparent`
-
-The tracking issue for this feature is: [#43036]
-
-[#43036]: https://github.com/rust-lang/rust/issues/43036
-
-------------------------
-
-This feature enables the `repr(transparent)` attribute on structs, which enables
-the use of newtypes without the usual ABI implications of wrapping the value in
-a struct.
-
-## Background
-
-It's sometimes useful to add additional type safety by introducing *newtypes*.
-For example, code that handles numeric quantities in different units such as
-millimeters, centimeters, grams, kilograms, etc. may want to use the type system
-to rule out mistakes such as adding millimeters to grams:
-
-```rust
-use std::ops::Add;
-
-struct Millimeters(f64);
-struct Grams(f64);
-
-impl Add<Millimeters> for Millimeters {
-    type Output = Millimeters;
-
-    fn add(self, other: Millimeters) -> Millimeters {
-        Millimeters(self.0 + other.0)
-    }
-}
-
-// Likewise: impl Add<Grams> for Grams {}
-```
-
-Other uses of newtypes include using `PhantomData` to add lifetimes to raw
-pointers or to implement the "phantom types" pattern. See the [PhantomData]
-documentation and [the Nomicon][nomicon-phantom] for more details.
-
-The added type safety is especially useful when interacting with C or other
-languages. However, in those cases we need to ensure the newtypes we add do not
-introduce incompatibilities with the C ABI.
-
-## Newtypes in FFI
-
-Luckily, `repr(C)` newtypes are laid out just like the type they wrap on all
-platforms which Rust currently supports, and likely on many more. For example,
-consider this C declaration:
-
-```C
-struct Object {
-    double weight; //< in grams
-    double height; //< in millimeters
-    // ...
-}
-
-void frobnicate(struct Object *);
-```
-
-While using this C code from Rust, we could add `repr(C)` to the `Grams` and
-`Millimeters` newtypes introduced above and use them to add some type safety
-while staying compatible with the memory layout of `Object`:
-
-```rust,no_run
-#[repr(C)]
-struct Grams(f64);
-
-#[repr(C)]
-struct Millimeters(f64);
-
-#[repr(C)]
-struct Object {
-    weight: Grams,
-    height: Millimeters,
-    // ...
-}
-
-extern {
-    fn frobnicate(_: *mut Object);
-}
-```
-
-This works even when adding some `PhantomData` fields, because they are
-zero-sized and therefore don't have to affect the memory layout.
-
-However, there's more to the ABI than just memory layout: there's also the
-question of how function call arguments and return values are passed. Many
-common ABI treat a struct containing a single field differently from that field
-itself, at least when the field is a scalar (e.g., integer or float or pointer).
-
-To continue the above example, suppose the C library also exposes a function
-like this:
-
-```C
-double calculate_weight(double height);
-```
-
-Using our newtypes on the Rust side like this will cause an ABI mismatch on many
-platforms:
-
-```rust,ignore
-extern {
-    fn calculate_weight(height: Millimeters) -> Grams;
-}
-```
-
-For example, on x86_64 Linux, Rust will pass the argument in an integer
-register, while the C function expects the argument to be in a floating-point
-register. Likewise, the C function will return the result in a floating-point
-register while Rust will expect it in an integer register.
-
-Note that this problem is not specific to floats: To give another example,
-32-bit x86 linux will pass and return `struct Foo(i32);` on the stack while
-`i32` is placed in registers.
-
-## Enter `repr(transparent)`
-
-So while `repr(C)` happens to do the right thing with respect to memory layout,
-it's not quite the right tool for newtypes in FFI. Instead of declaring a C
-struct, we need to communicate to the Rust compiler that our newtype is just for
-type safety on the Rust side. This is what `repr(transparent)` does.
-
-The attribute can be applied to a newtype-like structs that contains a single
-field. It indicates that the newtype should be represented exactly like that
-field's type, i.e., the newtype should be ignored for ABI purpopses: not only is
-it laid out the same in memory, it is also passed identically in function calls.
-
-In the above example, the ABI mismatches can be prevented by making the newtypes
-`Grams` and `Millimeters` transparent like this:
-
-```rust
-#![feature(repr_transparent)]
-
-#[repr(transparent)]
-struct Grams(f64);
-
-#[repr(transparent)]
-struct Millimeters(f64);
-```
-
-In addition to that single field, any number of zero-sized fields are permitted,
-including but not limited to `PhantomData`:
-
-```rust
-#![feature(repr_transparent)]
-
-use std::marker::PhantomData;
-
-struct Foo { /* ... */ }
-
-#[repr(transparent)]
-struct FooPtrWithLifetime<'a>(*const Foo, PhantomData<&'a Foo>);
-
-#[repr(transparent)]
-struct NumberWithUnit<T, U>(T, PhantomData<U>);
-
-struct CustomZst;
-
-#[repr(transparent)]
-struct PtrWithCustomZst<'a> {
-    ptr: FooPtrWithLifetime<'a>,
-    some_marker: CustomZst,
-}
-```
-
-Transparent structs can be nested: `PtrWithCustomZst` is also represented
-exactly like `*const Foo`.
-
-Because `repr(transparent)` delegates all representation concerns to another
-type, it is incompatible with all other `repr(..)` attributes. It also cannot be
-applied to enums, unions, empty structs, structs whose fields are all
-zero-sized, or structs with *multiple* non-zero-sized fields.
-
-[PhantomData]: https://doc.rust-lang.org/std/marker/struct.PhantomData.html
-[nomicon-phantom]: https://doc.rust-lang.org/nomicon/phantom-data.html
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 74bbd659246..e25742a4a61 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -105,7 +105,7 @@
 #![feature(pin)]
 #![feature(ptr_internals)]
 #![feature(ptr_offset_from)]
-#![feature(repr_transparent)]
+#![cfg_attr(stage0, feature(repr_transparent))]
 #![feature(rustc_attrs)]
 #![feature(specialization)]
 #![feature(staged_api)]
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 5ba77edee6e..40caee85541 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -100,7 +100,7 @@
 #![feature(optin_builtin_traits)]
 #![feature(prelude_import)]
 #![feature(repr_simd, platform_intrinsics)]
-#![feature(repr_transparent)]
+#![cfg_attr(stage0, feature(repr_transparent))]
 #![feature(rustc_attrs)]
 #![feature(rustc_const_unstable)]
 #![feature(simd_ffi)]
diff --git a/src/librustc/diagnostics.rs b/src/librustc/diagnostics.rs
index 7415ddd455d..1435957a5c1 100644
--- a/src/librustc/diagnostics.rs
+++ b/src/librustc/diagnostics.rs
@@ -1958,8 +1958,6 @@ representation hints.
 Erroneous code example:
 
 ```compile_fail,E0692
-#![feature(repr_transparent)]
-
 #[repr(transparent, C)] // error: incompatible representation hints
 struct Grams(f32);
 ```
@@ -1969,8 +1967,6 @@ another type, so adding more representation hints is contradictory. Remove
 either the `transparent` hint or the other hints, like this:
 
 ```
-#![feature(repr_transparent)]
-
 #[repr(transparent)]
 struct Grams(f32);
 ```
@@ -1978,8 +1974,6 @@ struct Grams(f32);
 Alternatively, move the other attributes to the contained type:
 
 ```
-#![feature(repr_transparent)]
-
 #[repr(C)]
 struct Foo {
     x: i32,
@@ -1994,8 +1988,6 @@ Note that introducing another `struct` just to have a place for the other
 attributes may have unintended side effects on the representation:
 
 ```
-#![feature(repr_transparent)]
-
 #[repr(transparent)]
 struct Grams(f32);
 
diff --git a/src/librustc_typeck/diagnostics.rs b/src/librustc_typeck/diagnostics.rs
index e4c73218de5..da54eeabdb9 100644
--- a/src/librustc_typeck/diagnostics.rs
+++ b/src/librustc_typeck/diagnostics.rs
@@ -4581,8 +4581,6 @@ on fields that were not guaranteed to be zero-sized.
 Erroneous code example:
 
 ```compile_fail,E0690
-#![feature(repr_transparent)]
-
 #[repr(transparent)]
 struct LengthWithUnit<U> { // error: transparent struct needs exactly one
     value: f32,            //        non-zero-sized field, but has 2
@@ -4602,8 +4600,6 @@ To combine `repr(transparent)` with type parameters, `PhantomData` may be
 useful:
 
 ```
-#![feature(repr_transparent)]
-
 use std::marker::PhantomData;
 
 #[repr(transparent)]
@@ -4621,7 +4617,7 @@ field that requires non-trivial alignment.
 Erroneous code example:
 
 ```compile_fail,E0691
-#![feature(repr_transparent, repr_align, attr_literals)]
+#![feature(repr_align, attr_literals)]
 
 #[repr(align(32))]
 struct ForceAlign32;
@@ -4640,8 +4636,6 @@ requirement.
 Consider removing the over-aligned zero-sized field:
 
 ```
-#![feature(repr_transparent)]
-
 #[repr(transparent)]
 struct Wrapper(f32);
 ```
@@ -4650,7 +4644,7 @@ Alternatively, `PhantomData<T>` has alignment 1 for all `T`, so you can use it
 if you need to keep the field for some reason:
 
 ```
-#![feature(repr_transparent, repr_align, attr_literals)]
+#![feature(repr_align, attr_literals)]
 
 use std::marker::PhantomData;
 
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 1535e649506..9f370672cb2 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -399,9 +399,6 @@ declare_features! (
     // `extern` in paths
     (active, extern_in_paths, "1.23.0", Some(44660), None),
 
-    // Allows `#[repr(transparent)]` attribute on newtype structs
-    (active, repr_transparent, "1.25.0", Some(43036), None),
-
     // Use `?` as the Kleene "at most one" operator
     (active, macro_at_most_once_rep, "1.25.0", Some(48075), None),
 
@@ -615,6 +612,8 @@ declare_features! (
     (accepted, termination_trait_test, "1.27.0", Some(48854), None),
     // The #[global_allocator] attribute
     (accepted, global_allocator, "1.28.0", Some(27389), None),
+    // Allows `#[repr(transparent)]` attribute on newtype structs
+    (accepted, repr_transparent, "1.28.0", Some(43036), None),
 );
 
 // If you change this, please modify src/doc/unstable-book as well. You must
@@ -1595,11 +1594,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                             gate_feature_post!(&self, repr_simd, attr.span,
                                                "SIMD types are experimental and possibly buggy");
                         }
-                        if item.check_name("transparent") {
-                            gate_feature_post!(&self, repr_transparent, attr.span,
-                                               "the `#[repr(transparent)]` attribute \
-                                               is experimental");
-                        }
                         if let Some((name, _)) = item.name_value_literal() {
                             if name == "packed" {
                                 gate_feature_post!(&self, repr_packed, attr.span,
diff --git a/src/test/codegen/repr-transparent-aggregates-1.rs b/src/test/codegen/repr-transparent-aggregates-1.rs
index 2eeed2b788c..a1185cc1e2e 100644
--- a/src/test/codegen/repr-transparent-aggregates-1.rs
+++ b/src/test/codegen/repr-transparent-aggregates-1.rs
@@ -18,7 +18,6 @@
 // See repr-transparent.rs
 
 #![crate_type="lib"]
-#![feature(repr_transparent)]
 
 
 #[repr(C)]
diff --git a/src/test/codegen/repr-transparent-aggregates-2.rs b/src/test/codegen/repr-transparent-aggregates-2.rs
index 25750a6513f..bc000bd3165 100644
--- a/src/test/codegen/repr-transparent-aggregates-2.rs
+++ b/src/test/codegen/repr-transparent-aggregates-2.rs
@@ -22,7 +22,6 @@
 // See repr-transparent.rs
 
 #![crate_type="lib"]
-#![feature(repr_transparent)]
 
 
 #[repr(C)]
diff --git a/src/test/codegen/repr-transparent-aggregates-3.rs b/src/test/codegen/repr-transparent-aggregates-3.rs
index 0c90239c9de..a292f1d70f3 100644
--- a/src/test/codegen/repr-transparent-aggregates-3.rs
+++ b/src/test/codegen/repr-transparent-aggregates-3.rs
@@ -14,7 +14,6 @@
 // See repr-transparent.rs
 
 #![crate_type="lib"]
-#![feature(repr_transparent)]
 
 
 #[repr(C)]
diff --git a/src/test/codegen/repr-transparent-sysv64.rs b/src/test/codegen/repr-transparent-sysv64.rs
index 7a30983fdd3..2e4665e22e3 100644
--- a/src/test/codegen/repr-transparent-sysv64.rs
+++ b/src/test/codegen/repr-transparent-sysv64.rs
@@ -13,7 +13,6 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type="lib"]
-#![feature(repr_transparent)]
 
 #[repr(C)]
 pub struct Rgb8 { r: u8, g: u8, b: u8 }
diff --git a/src/test/codegen/repr-transparent.rs b/src/test/codegen/repr-transparent.rs
index 087fa9b16b4..64a62fd7e88 100644
--- a/src/test/codegen/repr-transparent.rs
+++ b/src/test/codegen/repr-transparent.rs
@@ -11,7 +11,7 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type="lib"]
-#![feature(repr_transparent, repr_simd)]
+#![feature(repr_simd)]
 
 use std::marker::PhantomData;
 
diff --git a/src/test/compile-fail/repr-transparent-other-items.rs b/src/test/compile-fail/repr-transparent-other-items.rs
index cf0870866c7..685d62dc3a9 100644
--- a/src/test/compile-fail/repr-transparent-other-items.rs
+++ b/src/test/compile-fail/repr-transparent-other-items.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(repr_transparent)]
-
 // See also repr-transparent.rs
 
 #[repr(transparent)] //~ ERROR unsupported representation for zero-variant enum
diff --git a/src/test/compile-fail/repr-transparent-other-reprs.rs b/src/test/compile-fail/repr-transparent-other-reprs.rs
index 7b91a6f68e3..a391c0ae1f8 100644
--- a/src/test/compile-fail/repr-transparent-other-reprs.rs
+++ b/src/test/compile-fail/repr-transparent-other-reprs.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(repr_transparent, repr_align, attr_literals)]
+#![feature(repr_align, attr_literals)]
 
 // See also repr-transparent.rs
 
diff --git a/src/test/compile-fail/repr-transparent.rs b/src/test/compile-fail/repr-transparent.rs
index b5e6a0fa0b1..4d8ec4cdb40 100644
--- a/src/test/compile-fail/repr-transparent.rs
+++ b/src/test/compile-fail/repr-transparent.rs
@@ -14,7 +14,6 @@
 // - repr-transparent-other-items.rs
 
 #![feature(repr_align, attr_literals)]
-#![feature(repr_transparent)]
 
 use std::marker::PhantomData;
 
diff --git a/src/test/ui/feature-gate-repr_transparent.rs b/src/test/ui/feature-gate-repr_transparent.rs
deleted file mode 100644
index deadf2e535d..00000000000
--- a/src/test/ui/feature-gate-repr_transparent.rs
+++ /dev/null
@@ -1,14 +0,0 @@
-// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-#[repr(transparent)] //~ error: the `#[repr(transparent)]` attribute is experimental
-struct Foo(u64);
-
-fn main() {}
diff --git a/src/test/ui/feature-gate-repr_transparent.stderr b/src/test/ui/feature-gate-repr_transparent.stderr
deleted file mode 100644
index a4ffaa26690..00000000000
--- a/src/test/ui/feature-gate-repr_transparent.stderr
+++ /dev/null
@@ -1,11 +0,0 @@
-error[E0658]: the `#[repr(transparent)]` attribute is experimental (see issue #43036)
-  --> $DIR/feature-gate-repr_transparent.rs:11:1
-   |
-LL | #[repr(transparent)] //~ error: the `#[repr(transparent)]` attribute is experimental
-   | ^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: add #![feature(repr_transparent)] to the crate attributes to enable
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.
diff --git a/src/test/ui/lint-ctypes.rs b/src/test/ui/lint-ctypes.rs
index 85957831653..4b20001457f 100644
--- a/src/test/ui/lint-ctypes.rs
+++ b/src/test/ui/lint-ctypes.rs
@@ -9,7 +9,7 @@
 // except according to those terms.
 
 #![deny(improper_ctypes)]
-#![feature(libc, repr_transparent)]
+#![feature(libc)]
 
 extern crate libc;