Forbid use Trait::*

Author: jseyfried

src/librustc_resolve/resolve_imports.rs

@@ -586,6 +586,10 @@ impl<'a, 'b:'a, 'tcx:'b> ImportResolver<'a, 'b, 'tcx> {
                            target_module: Module<'b>,
                            directive: &'b ImportDirective)
                            -> ResolveResult<()> {
+        if let Some(Def::Trait(_)) = target_module.def {
+            self.resolver.session.span_err(directive.span, "items in traits are not importable.");
+        }
+
         if module_.def_id() == target_module.def_id() {
             // This means we are trying to glob import a module into itself, and it is a no-go
             let msg = "Cannot glob-import a module into itself.".into();

src/test/compile-fail/issue-30560.rs

@@ -12,4 +12,7 @@ type Alias = ();
 use Alias::*; //~ ERROR Not a module
 use std::io::Result::*; //~ ERROR Not a module
 
+trait T {}
+use T::*; //~ ERROR items in traits are not importable
+
 fn main() {}