test: show bug compiling custom true / false constructors

test/blackbox-tests/custom-predef.t

@@ -0,0 +1,29 @@
+Demonstrate redefining the `true` / `false` constructors
+
+  $ . ./setup.sh
+  $ cat > x.ml <<EOF
+  > type t = A | true | false
+  > let z : t = A
+  > let x : t = true
+  > let y : t = false
+  > let t : bool = false
+  > EOF
+
+  $ melc -ppx melppx x.ml
+  // Generated by Melange
+  'use strict';
+  
+  
+  const z = /* A */0;
+  
+  const x = true;
+  
+  const y = true;
+  
+  const t = false;
+  
+  exports.z = z;
+  exports.x = x;
+  exports.y = y;
+  exports.t = t;
+  /* No side effect */