Emit parentheses in suggestion for global paths

Author: Manishearth

src/librustc/hir/lowering.rs

@@ -914,7 +914,7 @@ impl<'a> LoweringContext<'a> {
                 let qpath = self.lower_qpath(t.id, qself, path, ParamMode::Explicit, itctx);
                 let ty = self.ty_path(id, t.span, qpath);
                 if let hir::TyTraitObject(..) = ty.node {
-                    self.maybe_lint_bare_trait(t.span, t.id);
+                    self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
                 }
                 return ty;
             }
@@ -955,7 +955,7 @@ impl<'a> LoweringContext<'a> {
                     self.elided_lifetime(t.span)
                 });
                 if kind != TraitObjectSyntax::Dyn {
-                    self.maybe_lint_bare_trait(t.span, t.id);
+                    self.maybe_lint_bare_trait(t.span, t.id, false);
                 }
                 hir::TyTraitObject(bounds, lifetime_bound)
             }
@@ -3710,12 +3710,12 @@ impl<'a> LoweringContext<'a> {
         }
     }
 
-    fn maybe_lint_bare_trait(&self, span: Span, id: NodeId) {
+    fn maybe_lint_bare_trait(&self, span: Span, id: NodeId, is_global: bool) {
         if self.sess.features.borrow().dyn_trait {
             self.sess.buffer_lint_with_diagnostic(
                 builtin::BARE_TRAIT_OBJECT, id, span,
                 "trait objects without an explicit `dyn` are deprecated",
-                builtin::BuiltinLintDiagnostics::BareTraitObject(span)
+                builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global)
             )
         }
     }

src/librustc/lint/builtin.rs

@@ -320,15 +320,16 @@ impl LintPass for HardwiredLints {
 #[derive(PartialEq, RustcEncodable, RustcDecodable, Debug)]
 pub enum BuiltinLintDiagnostics {
     Normal,
-    BareTraitObject(Span)
+    BareTraitObject(Span, /* is_global */ bool)
 }
 
 impl BuiltinLintDiagnostics {
     pub fn run(self, sess: &Session, db: &mut DiagnosticBuilder) {
         match self {
             BuiltinLintDiagnostics::Normal => (),
-            BuiltinLintDiagnostics::BareTraitObject(span) => {
+            BuiltinLintDiagnostics::BareTraitObject(span, is_global) => {
                 let sugg = match sess.codemap().span_to_snippet(span) {
+                    Ok(ref s) if is_global => format!("dyn ({})", s),
                     Ok(s) => format!("dyn {}", s),
                     Err(_) => format!("dyn <type>")
                 };