add thir-print test

Author: ericmarkmartin

tests/ui/thir-print/thir-flat-const-variant.rs

@@ -0,0 +1,18 @@
+// compile-flags: -Z unpretty=thir-flat
+// check-pass
+
+// Previously, the constants with `Self::Bar(())` would be `Call`s instead of
+// `Adt`s in THIR.
+
+pub enum Foo {
+    Bar(()),
+}
+
+impl Foo {
+    const BAR1: Foo = Foo::Bar(());
+    const BAR2: Foo = Self::Bar(());
+    const BAR3: Self = Foo::Bar(());
+    const BAR4: Self = Self::Bar(());
+}
+
+fn main() {}