Feature gate repr(packed).

There are some correctness issues due to unaligned internal fields and
references. cc rust-lang#27060.

Author: huonw

src/libsyntax/feature_gate.rs

@@ -158,6 +158,9 @@ const KNOWN_FEATURES: &'static [(&'static str, &'static str, Status)] = &[
 
     // Allows using #[prelude_import] on glob `use` items.
     ("prelude_import", "1.2.0", Active),
+
+    // Allows use of repr(packed)
+    ("repr_packed", "1.3.0", Active),
 ];
 // (changing above list without updating src/doc/reference.md makes @cmr sad)
 
@@ -564,6 +567,17 @@ impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
                     self.gate_feature("simd", i.span,
                                       "SIMD types are experimental and possibly buggy");
                 }
+
+                for attr in &i.attrs {
+                    if attr.name() == "repr" {
+                        for item in attr.meta_item_list().unwrap_or(&[]) {
+                            if item.name() == "packed" {
+                                self.gate_feature("repr_packed", item.span,
+                                                  "packed types are experimental and buggy");
+                            }
+                        }
+                    }
+                }
             }
 
             ast::ItemDefaultImpl(..) => {

src/test/auxiliary/packed.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(repr_packed)]
+
 #[repr(packed)]
 pub struct S {
     a: u8,

src/test/compile-fail/feature-gate-repr-packed.rs

@@ -0,0 +1,19 @@
+// Copyright 2015 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(packed)] //~ ERROR packed types are experimental
+struct Foo { x: u8 }
+#[repr(packed, C)] //~ ERROR packed types are experimental
+struct Bar { x: u8 }
+#[repr(C, packed)] //~ ERROR packed types are experimental
+struct Baz { x: u8 }
+
+fn main() {}

src/test/compile-fail/issue-14309.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(repr_packed)]
 #![deny(improper_ctypes)]
 #![allow(dead_code)]
 

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

@@ -15,6 +15,8 @@
 
 // error-pattern: transmute called on types with different size
 
+#![feature(repr_packed)]
+
 use std::mem;
 
 #[repr(packed)]

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

@@ -15,6 +15,8 @@
 
 // error-pattern: transmute called on types with different size
 
+#![feature(repr_packed)]
+
 use std::mem;
 
 #[repr(packed)]

src/test/debuginfo/c-style-enum-in-composite.rs

@@ -65,6 +65,7 @@
 
 #![allow(unused_variables)]
 #![omit_gdb_pretty_printer_section]
+#![feature(repr_packed)]
 
 use self::AnEnum::{OneHundred, OneThousand, OneMillion};
 use self::AnotherEnum::{MountainView, Toronto, Vienna};

src/test/debuginfo/packed-struct-with-destructor.rs

@@ -74,6 +74,7 @@
 
 #![allow(unused_variables)]
 #![omit_gdb_pretty_printer_section]
+#![feature(repr_packed)]
 
 #[repr(packed)]
 struct Packed {

src/test/debuginfo/packed-struct.rs

@@ -60,6 +60,7 @@
 
 #![allow(unused_variables)]
 #![omit_gdb_pretty_printer_section]
+#![feature(repr_packed)]
 
 #[repr(packed)]
 struct Packed {

src/test/run-make/extern-fn-with-packed-struct/test.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(repr_packed)]
+
 #[repr(packed)]
 #[derive(Copy, Clone, PartialEq, Debug)]
 struct Foo {

src/test/run-pass/issue-26646.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(repr_packed)]
 #![deny(unused_attributes)]
 
 #[repr(C)]

src/test/run-pass/packed-struct-borrow-element.rs

@@ -9,6 +9,8 @@
 // except according to those terms.
 
 
+#![feature(repr_packed)]
+
 #[repr(packed)]
 struct Foo {
     bar: u8,

src/test/run-pass/packed-struct-generic-layout.rs

@@ -9,6 +9,8 @@
 // except according to those terms.
 
 
+#![feature(repr_packed)]
+
 use std::mem;
 
 #[repr(packed)]

src/test/run-pass/packed-struct-generic-size.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(repr_packed)]
 
 use std::mem;
 

src/test/run-pass/packed-struct-layout.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(repr_packed)]
 
 use std::mem;
 

src/test/run-pass/packed-struct-match.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(repr_packed)]
 
 #[repr(packed)]
 struct Foo {

src/test/run-pass/packed-struct-size.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 
+#![feature(repr_packed)]
 
 use std::mem;
 

src/test/run-pass/packed-struct-vec.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(repr_packed)]
+
 use std::mem;
 
 #[repr(packed)]

src/test/run-pass/packed-tuple-struct-layout.rs

@@ -9,6 +9,8 @@
 // except according to those terms.
 
 
+#![feature(repr_packed)]
+
 use std::mem;
 
 #[repr(packed)]

src/test/run-pass/packed-tuple-struct-size.rs

@@ -10,6 +10,8 @@
 
 
 
+#![feature(repr_packed)]
+
 use std::mem;
 
 #[repr(packed)]