Fix incorrect unused import warnings on cfg_attred path attributes

src/librustc_passes/ast_validation.rs

@@ -19,6 +19,7 @@
 use rustc::lint;
 use rustc::session::Session;
 use syntax::ast::*;
+use syntax::attr;
 use syntax::parse::token::{self, keywords};
 use syntax::visit::{self, Visitor};
 use syntax_pos::Span;
@@ -168,6 +169,10 @@ impl<'a> Visitor for AstValidator<'a> {
                     }
                 }
             }
+            ItemKind::Mod(_) => {
+                // Ensure that `path` attributes on modules are recorded as used (c.f. #35584).
+                attr::first_attr_value_str_by_name(&item.attrs, "path");
+            }
             _ => {}
         }
 

src/test/compile-fail/cfg_attr_path.rs

@@ -8,5 +8,17 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#[cfg_attr(all(), path = "nonexistent_file.rs")] mod foo;
-//~^ ERROR nonexistent_file.rs
+#![feature(rustc_attrs)]
+#![allow(dead_code)]
+#![deny(unused_attributes)] // c.f #35584
+
+mod auxiliary {
+    #[cfg_attr(any(), path = "nonexistent_file.rs")] pub mod namespaced_enums;
+    #[cfg_attr(all(), path = "namespaced_enums.rs")] pub mod nonexistent_file;
+}
+
+#[rustc_error]
+fn main() { //~ ERROR compilation successful
+    let _ = auxiliary::namespaced_enums::Foo::A;
+    let _ = auxiliary::nonexistent_file::Foo::A;
+}