1 files changed, 33 insertions, 2 deletions
diff --git a/compiler/rustc_builtin_macros/src/util.rs b/compiler/rustc_builtin_macros/src/util.rs
index 01ea80c4c8a..527fe50eff0 100644
--- a/compiler/rustc_builtin_macros/src/util.rs
+++ b/compiler/rustc_builtin_macros/src/util.rs
@@ -1,6 +1,7 @@
-use rustc_ast::MetaItem;
-use rustc_expand::base::ExtCtxt;
+use rustc_ast::{Attribute, MetaItem};
+use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_feature::AttributeTemplate;
+use rustc_lint_defs::builtin::DUPLICATE_MACRO_ATTRIBUTES;
 use rustc_parse::validate_attr;
 use rustc_span::Symbol;
 
@@ -10,3 +11,33 @@ pub fn check_builtin_macro_attribute(ecx: &ExtCtxt<'_>, meta_item: &MetaItem, na
     let attr = ecx.attribute(meta_item.clone());
     validate_attr::check_builtin_attribute(&ecx.sess.parse_sess, &attr, name, template);
 }
+
+/// Emit a warning if the item is annotated with the given attribute. This is used to diagnose when
+/// an attribute may have been mistakenly duplicated.
+pub fn warn_on_duplicate_attribute(ecx: &ExtCtxt<'_>, item: &Annotatable, name: Symbol) {
+    let attrs: Option<&[Attribute]> = match item {
+        Annotatable::Item(item) => Some(&item.attrs),
+        Annotatable::TraitItem(item) => Some(&item.attrs),
+        Annotatable::ImplItem(item) => Some(&item.attrs),
+        Annotatable::ForeignItem(item) => Some(&item.attrs),
+        Annotatable::Expr(expr) => Some(&expr.attrs),
+        Annotatable::Arm(arm) => Some(&arm.attrs),
+        Annotatable::ExprField(field) => Some(&field.attrs),
+        Annotatable::PatField(field) => Some(&field.attrs),
+        Annotatable::GenericParam(param) => Some(&param.attrs),
+        Annotatable::Param(param) => Some(&param.attrs),
+        Annotatable::FieldDef(def) => Some(&def.attrs),
+        Annotatable::Variant(variant) => Some(&variant.attrs),
+        _ => None,
+    };
+    if let Some(attrs) = attrs {
+        if let Some(attr) = ecx.sess.find_by_name(attrs, name) {
+            ecx.parse_sess().buffer_lint(
+                DUPLICATE_MACRO_ATTRIBUTES,
+                attr.span,
+                ecx.current_expansion.lint_node_id,
+                "duplicated attribute",
+            );
+        }
+    }
+}