feature error span on attr. for fn_must_use, SIMD/align, macro reëxport

There were several feature-gated attributes for which the
feature-not-available error spans would point to the item annotated with
the gated attribute, when it would make more sense for the span to point
to the attribute itself: if the attribute is removed, the
function/struct/&c. likely still makes sense and the program will
compile. (Note that we decline to make the analogous change for the
`main`, `start`, and `plugin_registrar` features, for in those cases it
makes sense for the span to implicate the entire function, of which
there is little hope of using without the gated attribute.)

2 files changed, 23 insertions, 23 deletions

diff --git a/src/libsyntax/attr.rs b/src/libsyntax/attr.rs
index ca87c807103..f97a8f67e22 100644
--- a/src/libsyntax/attr.rs
+++ b/src/libsyntax/attr.rs
@@ -490,6 +490,10 @@ pub fn contains_name(attrs: &[Attribute], name: &str) -> bool {
     })
 }
 
+pub fn find_by_name<'a>(attrs: &'a [Attribute], name: &str) -> Option<&'a Attribute> {
+    attrs.iter().find(|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))
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 09574d5ba12..2526ac3021a 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -1248,8 +1248,8 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
     fn visit_item(&mut self, i: &'a ast::Item) {
         match i.node {
             ast::ItemKind::ExternCrate(_) => {
-                if attr::contains_name(&i.attrs[..], "macro_reexport") {
-                    gate_feature_post!(&self, macro_reexport, i.span,
+                if let Some(attr) = attr::find_by_name(&i.attrs[..], "macro_reexport") {
+                    gate_feature_post!(&self, macro_reexport, attr.span,
                                        "macros reexports are experimental \
                                         and possibly buggy");
                 }
@@ -1276,36 +1276,32 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                                         function may change over time, for now \
                                         a top-level `fn main()` is required");
                 }
-                if attr::contains_name(&i.attrs[..], "must_use") {
-                    gate_feature_post!(&self, fn_must_use, i.span,
+                if let Some(attr) = attr::find_by_name(&i.attrs[..], "must_use") {
+                    gate_feature_post!(&self, fn_must_use, attr.span,
                                        "`#[must_use]` on functions is experimental",
                                        GateStrength::Soft);
                 }
             }
 
             ast::ItemKind::Struct(..) => {
-                if attr::contains_name(&i.attrs[..], "simd") {
-                    gate_feature_post!(&self, simd, i.span,
+                if let Some(attr) = attr::find_by_name(&i.attrs[..], "simd") {
+                    gate_feature_post!(&self, simd, attr.span,
                                        "SIMD types are experimental and possibly buggy");
-                    self.context.parse_sess.span_diagnostic.span_warn(i.span,
+                    self.context.parse_sess.span_diagnostic.span_warn(attr.span,
                                                                       "the `#[simd]` attribute \
                                                                        is deprecated, use \
                                                                        `#[repr(simd)]` instead");
                 }
-                for attr in &i.attrs {
-                    if attr.path == "repr" {
-                        for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
-                            if item.check_name("simd") {
-                                gate_feature_post!(&self, repr_simd, i.span,
-                                                   "SIMD types are experimental \
-                                                    and possibly buggy");
-
-                            }
-                            if item.check_name("align") {
-                                gate_feature_post!(&self, repr_align, i.span,
-                                                   "the struct `#[repr(align(u16))]` attribute \
-                                                    is experimental");
-                            }
+                if let Some(attr) = attr::find_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,
+                                               "SIMD types are experimental and possibly buggy");
+                        }
+                        if item.check_name("align") {
+                            gate_feature_post!(&self, repr_align, attr.span,
+                                               "the struct `#[repr(align(u16))]` attribute \
+                                                is experimental");
                         }
                     }
                 }
@@ -1334,8 +1330,8 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 
                 for impl_item in impl_items {
                     if let ast::ImplItemKind::Method(..) = impl_item.node {
-                        if attr::contains_name(&impl_item.attrs[..], "must_use") {
-                            gate_feature_post!(&self, fn_must_use, impl_item.span,
+                        if let Some(attr) = attr::find_by_name(&impl_item.attrs[..], "must_use") {
+                            gate_feature_post!(&self, fn_must_use, attr.span,
                                                "`#[must_use]` on methods is experimental",
                                                GateStrength::Soft);
                         }