Fix feature gate only being checked on first repr attr.

src/libsyntax/attr/mod.rs

@@ -455,6 +455,11 @@ pub fn find_by_name<'a>(attrs: &'a [Attribute], name: &str) -> Option<&'a Attrib
     attrs.iter().find(|attr| attr.check_name(name))
 }
 
+pub fn filter_by_name<'a>(attrs: &'a [Attribute], name: &'a str)
+    -> impl Iterator<Item = &'a Attribute> {
+    attrs.iter().filter(move |attr| attr.check_name(name))
+}
+
 pub fn first_attr_value_str_by_name(attrs: &[Attribute], name: &str) -> Option<Symbol> {
     attrs.iter()
         .find(|at| at.check_name(name))

src/libsyntax/feature_gate.rs

@@ -1625,7 +1625,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             }
 
             ast::ItemKind::Struct(..) => {
-                if let Some(attr) = attr::find_by_name(&i.attrs[..], "repr") {
+                for attr in attr::filter_by_name(&i.attrs[..], "repr") {
                     for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
                         if item.check_name("simd") {
                             gate_feature_post!(&self, repr_simd, attr.span,

src/test/ui/feature-gates/feature-gate-repr-simd.rs

@@ -11,4 +11,8 @@
 #[repr(simd)] //~ error: SIMD types are experimental
 struct Foo(u64, u64);
 
+#[repr(C)]
+#[repr(simd)] //~ error: SIMD types are experimental
+struct Bar(u64, u64);
+
 fn main() {}

src/test/ui/feature-gates/feature-gate-repr-simd.stderr

@@ -6,6 +6,14 @@ LL | #[repr(simd)] //~ error: SIMD types are experimental
    |
    = help: add #![feature(repr_simd)] to the crate attributes to enable
 
-error: aborting due to previous error
+error[E0658]: SIMD types are experimental and possibly buggy (see issue #27731)
+  --> $DIR/feature-gate-repr-simd.rs:15:1
+   |
+LL | #[repr(simd)] //~ error: SIMD types are experimental
+   | ^^^^^^^^^^^^^
+   |
+   = help: add #![feature(repr_simd)] to the crate attributes to enable
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0658`.

src/test/ui/feature-gates/feature-gate-repr_packed.rs

@@ -11,4 +11,8 @@
 #[repr(packed(1))] //~ error: the `#[repr(packed(n))]` attribute is experimental
 struct Foo(u64);
 
+#[repr(C)]
+#[repr(packed(1))] //~ error: the `#[repr(packed(n))]` attribute is experimental
+struct Bar(u64);
+
 fn main() {}

src/test/ui/feature-gates/feature-gate-repr_packed.stderr

@@ -6,6 +6,14 @@ LL | #[repr(packed(1))] //~ error: the `#[repr(packed(n))]` attribute is experim
    |
    = help: add #![feature(repr_packed)] to the crate attributes to enable
 
-error: aborting due to previous error
+error[E0658]: the `#[repr(packed(n))]` attribute is experimental (see issue #33158)
+  --> $DIR/feature-gate-repr_packed.rs:15:1
+   |
+LL | #[repr(packed(1))] //~ error: the `#[repr(packed(n))]` attribute is experimental
+   | ^^^^^^^^^^^^^^^^^^
+   |
+   = help: add #![feature(repr_packed)] to the crate attributes to enable
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0658`.