Add tests for calling trait methods on concrete types

src/test/ui/rfc-2632-const-trait-impl/call-const-trait-method.rs

@@ -0,0 +1,30 @@
+#![allow(incomplete_features)]
+#![feature(const_trait_impl)]
+#![feature(const_fn)]
+
+pub trait Plus {
+    fn plus(self, rhs: Self) -> Self;
+}
+
+impl const Plus for i32 {
+    fn plus(self, rhs: Self) -> Self {
+        self + rhs
+    }
+}
+
+impl Plus for u32 {
+    fn plus(self, rhs: Self) -> Self {
+        self + rhs
+    }
+}
+
+pub const fn add_i32(a: i32, b: i32) -> i32 {
+    a.plus(b)
+}
+
+pub const fn add_u32(a: u32, b: u32) -> u32 {
+    a.plus(b)
+    //~^ ERROR calls in constant functions are limited to constant functions
+}
+
+fn main() {}