Add rust_2018_idioms lint group

Author: Manishearth

Diff for: src/librustc_lint/builtin.rs

@@ -1263,7 +1263,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnionsWithDropFields {
 pub struct UnreachablePub;
 
 declare_lint! {
-    UNREACHABLE_PUB,
+    pub UNREACHABLE_PUB,
     Allow,
     "`pub` items not reachable from crate root"
 }

Diff for: 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

Diff for: src/test/ui/inference-variable-behind-raw-pointer.stderr

@@ -5,6 +5,6 @@ LL |     if data.is_null() {}
    |             ^^^^^^^
    |
    = note: #[warn(tyvar_behind_raw_pointer)] on by default
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2018 epoch!
    = note: for more information, see issue #46906 <https://github.com/rust-lang/rust/issues/46906>