librustc: Implement a lint mode for default methods. r=brson

src/librustc/middle/lint.rs

@@ -65,6 +65,7 @@ enum lint {
     non_camel_case_types,
     structural_records,
     type_limits,
+    default_methods,
 
     managed_heap_memory,
     owned_heap_memory,
@@ -200,7 +201,12 @@ fn get_lint_dict() -> lint_dict {
         (~"type_limits",
          @{lint: type_limits,
            desc: ~"comparisons made useless by limits of the types involved",
-           default: warn})
+           default: warn}),
+
+        (~"default_methods",
+         @{lint: default_methods,
+           desc: ~"allow default methods",
+           default: forbid}),
 
         /* FIXME(#3266)--make liveness warnings lintable
         (~"unused_variable",
@@ -414,6 +420,7 @@ fn check_item(i: @ast::item, cx: ty::ctxt) {
     check_item_structural_records(cx, i);
     check_item_deprecated_modes(cx, i);
     check_item_type_limits(cx, i);
+    check_item_default_methods(cx, i);
 }
 
 // Take a visitor, and modify it so that it will not proceed past subitems.
@@ -563,6 +570,27 @@ fn check_limits(cx: ty::ctxt, binop: ast::binop, l: &ast::expr,
     visit::visit_item(it, (), visit);
 }
 
+fn check_item_default_methods(cx: ty::ctxt, item: @ast::item) {
+    match item.node {
+        ast::item_trait(_, _, methods) => {
+            for methods.each |method| {
+                match *method {
+                    ast::required(*) => {}
+                    ast::provided(*) => {
+                        cx.sess.span_lint(
+                            default_methods,
+                            item.id,
+                            item.id,
+                            item.span,
+                            ~"default methods are experimental");
+                    }
+                }
+            }
+        }
+        _ => {}
+    }
+}
+
 fn check_item_structural_records(cx: ty::ctxt, it: @ast::item) {
     let visit = item_stopping_visitor(visit::mk_simple_visitor(@{
         visit_expr: fn@(e: @ast::expr) {

src/test/compile-fail/lint-default-methods.rs

+#[forbid(default_methods)];
+
+trait Foo {
+    fn bar() { io::println("hi"); } //~ ERROR default methods are experimental
+}
+
+fn main() {}
+