1 files changed, 65 insertions, 0 deletions
diff --git a/tests/ui/consts/trait_specialization.rs b/tests/ui/consts/trait_specialization.rs
new file mode 100644
index 00000000000..c581ef6b0f7
--- /dev/null
+++ b/tests/ui/consts/trait_specialization.rs
@@ -0,0 +1,65 @@
+// ignore-wasm32-bare which doesn't support `std::process:exit()`
+// compile-flags: -Zmir-opt-level=3
+// run-pass
+
+// Tests that specialization does not cause optimizations running on polymorphic MIR to resolve
+// to a `default` implementation.
+
+#![feature(specialization)] //~ WARN the feature `specialization` is incomplete
+
+trait Marker {}
+
+trait SpecializedTrait {
+    const CONST_BOOL: bool;
+    const CONST_STR: &'static str;
+    fn method() -> &'static str;
+}
+impl <T> SpecializedTrait for T {
+    default const CONST_BOOL: bool = false;
+    default const CONST_STR: &'static str = "in default impl";
+    #[inline(always)]
+    default fn method() -> &'static str {
+        "in default impl"
+    }
+}
+impl <T: Marker> SpecializedTrait for T {
+    const CONST_BOOL: bool = true;
+    const CONST_STR: &'static str = "in specialized impl";
+    fn method() -> &'static str {
+        "in specialized impl"
+    }
+}
+
+fn const_bool<T>() -> &'static str {
+    if <T as SpecializedTrait>::CONST_BOOL {
+        "in specialized impl"
+    } else {
+        "in default impl"
+    }
+}
+fn const_str<T>() -> &'static str {
+    <T as SpecializedTrait>::CONST_STR
+}
+fn run_method<T>() -> &'static str {
+    <T as SpecializedTrait>::method()
+}
+
+struct TypeA;
+impl Marker for TypeA {}
+struct TypeB;
+
+#[inline(never)]
+fn exit_if_not_eq(left: &str, right: &str) {
+    if left != right {
+        std::process::exit(1);
+    }
+}
+
+pub fn main() {
+    exit_if_not_eq("in specialized impl", const_bool::<TypeA>());
+    exit_if_not_eq("in default impl", const_bool::<TypeB>());
+    exit_if_not_eq("in specialized impl", const_str::<TypeA>());
+    exit_if_not_eq("in default impl", const_str::<TypeB>());
+    exit_if_not_eq("in specialized impl", run_method::<TypeA>());
+    exit_if_not_eq("in default impl", run_method::<TypeB>());
+}