Added feature gate, updated error messages and tests.

Author: bitshifter

src/doc/unstable-book/src/SUMMARY.md

@@ -72,6 +72,7 @@
     - [proc_macro](language-features/proc-macro.md)
     - [quote](language-features/quote.md)
     - [relaxed_adts](language-features/relaxed-adts.md)
+    - [repr_align](language-features/repr-align.md)
     - [repr_simd](language-features/repr-simd.md)
     - [rustc_attrs](language-features/rustc-attrs.md)
     - [rustc_diagnostic_macros](language-features/rustc-diagnostic-macros.md)

src/doc/unstable-book/src/language-features/repr-align.md

@@ -0,0 +1,11 @@
+# `repr_align`
+
+The tracking issue for this feature is: [#33626]
+
+[#33626]: https://github.com/rust-lang/rust/issues/33626
+
+------------------------
+
+
+
+

src/libsyntax/attr.rs

@@ -972,19 +972,24 @@ pub fn find_repr_attrs(diagnostic: &Handler, attr: &Attribute) -> Vec<ReprAttr>
                 } else if let Some((name, value)) = item.name_value_literal() {
                     if name == "align" {
                         recognised = true;
-                        let mut valid_align = false;
+                        let mut align_error = None;
                         if let ast::LitKind::Int(align, ast::LitIntType::Unsuffixed) = value.node {
                             if align.is_power_of_two() {
                                 // rustc::ty::layout::Align restricts align to <= 32768
                                 if align <= 32768 {
                                     acc.push(ReprAlign(align as u16));
-                                    valid_align = true;
+                                } else {
+                                    align_error = Some("larger than 32768");
                                 }
+                            } else {
+                                align_error = Some("not a power of two");
                             }
+                        } else {
+                            align_error = Some("not an unsuffixed integer");
                         }
-                        if !valid_align {
+                        if let Some(align_error) = align_error {
                             span_err!(diagnostic, item.span, E0589,
-                                      "align representation must be a u16 power of two");
+                                      "invalid `repr(align)` attribute: {}", align_error);
                         }
                     }
                 }

src/libsyntax/diagnostic_list.rs

@@ -292,5 +292,5 @@ register_diagnostics! {
     E0556, // malformed feature, expected just one word
     E0557, // feature has been removed
     E0584, // file for module `..` found at both .. and ..
-    E0589, // align representation must be a u16 power of two
+    E0589, // invalid `repr(align)` attribute
 }

src/libsyntax/feature_gate.rs

@@ -338,6 +338,9 @@ declare_features! (
     // Allows the `catch {...}` expression
     (active, catch_expr, "1.17.0", Some(31436)),
 
+    // Allows `repr(align(u16))` struct attribute (RFC 1358)
+    (active, repr_align, "1.17.0", Some(33626)),
+
     // See rust-lang/rfcs#1414. Allows code like `let x: &'static u32 = &42` to work.
     (active, rvalue_static_promotion, "1.15.1", Some(38865)),
 
@@ -1189,6 +1192,11 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                                                     and possibly buggy");
 
                             }
+                            if item.check_name("align") {
+                                gate_feature_post!(&self, repr_align, i.span,
+                                                   "the struct `#[repr(align(u16))]` attribute \
+                                                    is experimental");
+                            }
                         }
                     }
                 }

src/test/compile-fail/conflicting-repr-hints.rs

@@ -10,6 +10,7 @@
 
 #![allow(dead_code)]
 #![feature(attr_literals)]
+#![feature(repr_align)]
 
 #[repr(C)]
 enum A { A }

src/test/compile-fail/feature-gate-repr_align.rs

@@ -0,0 +1,15 @@
+// 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.
+#![feature(attr_literals)]
+
+#[repr(align(64))]
+struct Foo(u64, u64); //~ error: the struct `#[repr(align(u16))]` attribute is experimental
+
+fn main() {}

src/test/compile-fail/repr-align.rs

@@ -9,14 +9,15 @@
 // except according to those terms.
 #![allow(dead_code)]
 #![feature(attr_literals)]
+#![feature(repr_align)]
 
-#[repr(align(16.0))] //~ ERROR: align representation must be a u16 power of two
+#[repr(align(16.0))] //~ ERROR: invalid `repr(align)` attribute: not an unsuffixed integer
 struct A(i32);
 
-#[repr(align(15))] //~ ERROR: align representation must be a u16 power of two
+#[repr(align(15))] //~ ERROR: invalid `repr(align)` attribute: not a power of two
 struct B(i32);
 
-#[repr(align(65536))] //~ ERROR: align representation must be a u16 power of tw
+#[repr(align(65536))] //~ ERROR: invalid `repr(align)` attribute: larger than 32768
 struct C(i32);
 
 fn main() {}

src/test/compile-fail/repr-packed-contains-align.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 #![feature(attr_literals)]
+#![feature(repr_align)]
 #![allow(dead_code)]
 
 #[repr(align(16))]

src/test/run-pass/align-struct.rs

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