Add test

src/test/ui/rfc-2632-const-trait-impl/default-method-body-is-const-same-trait-ck.rs

@@ -0,0 +1,17 @@
+#![feature(const_fn_trait_bound)]
+#![feature(const_trait_impl)]
+
+pub trait Tr {
+    #[default_method_body_is_const]
+    fn a(&self) {}
+
+    #[default_method_body_is_const]
+    fn b(&self) {
+        ().a()
+        //~^ ERROR calls in constant functions are limited
+    }
+}
+
+impl Tr for () {}
+
+fn main() {}

src/test/ui/rfc-2632-const-trait-impl/default-method-body-is-const-same-trait-ck.stderr

@@ -0,0 +1,9 @@
+error[E0015]: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+  --> $DIR/default-method-body-is-const-same-trait-ck.rs:10:9
+   |
+LL |         ().a()
+   |         ^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0015`.