Add rust_2018_idioms lint group

src/librustc_lint/lib.rs

@@ -43,6 +43,7 @@ extern crate rustc_mir;
 extern crate syntax_pos;
 
 use rustc::lint;
+use rustc::lint::builtin::BARE_TRAIT_OBJECT;
 use rustc::session;
 use rustc::util;
 
@@ -177,6 +178,11 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
                     UNUSED_FEATURES,
                     UNUSED_PARENS);
 
+    add_lint_group!(sess,
+                    "rust_2018_idioms",
+                    BARE_TRAIT_OBJECT,
+                    UNREACHABLE_PUB);
+
     // Guidelines for creating a future incompatibility lint:
     //
     // - Create a lint defaulting to warn as normal, with ideally the same error