Added feature gate, updated error messages and tests.

3 files changed, 18 insertions, 5 deletions

diff --git a/src/libsyntax/attr.rs b/src/libsyntax/attr.rs
index 442345ceb3c..82492d97627 100644
--- a/src/libsyntax/attr.rs
+++ b/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);
                         }
                     }
                 }
diff --git a/src/libsyntax/diagnostic_list.rs b/src/libsyntax/diagnostic_list.rs
index 775775875a4..01d1277ea62 100644
--- a/src/libsyntax/diagnostic_list.rs
+++ b/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
 }
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 175447e1112..9b55a860b35 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/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");
+                            }
                         }
                     }
                 }