Add a reproduction for issue #2000.

CHANGES.md

@@ -8,6 +8,7 @@ unreleased
   + test suite
     - Add a test to ensure the behavior showed in issue #1517 is no longer relevant (#1995)
     - Add a test to ensure the code fragment exhibited in issue #1118 no longer makes Merlin crash (#1996)
+    - Add a test case illustrating how a snippet produces two unrelated errors in issue #2000. (#2003)
 
 merlin 5.6
 ==========

tests/test-dirs/issue2000.t

@@ -0,0 +1,41 @@
+  $ cat >main.ml <<EOF
+  > let a : type b. 'a as b list = []
+  > EOF
+
+FIXME: This syntactically perfectly valid OCaml produce two unrelated cryptic error message.
+See https://github.com/ocaml/merlin/issues/2000.
+  $ $MERLIN single errors -filename main.ml <main.ml
+  {
+    "class": "return",
+    "value": [
+      {
+        "start": {
+          "line": 1,
+          "col": 4
+        },
+        "end": {
+          "line": 1,
+          "col": 33
+        },
+        "type": "typer",
+        "sub": [],
+        "valid": true,
+        "message": "This definition has type bool which is less general than 'a. 'a"
+      },
+      {
+        "start": {
+          "line": 1,
+          "col": 21
+        },
+        "end": {
+          "line": 1,
+          "col": 23
+        },
+        "type": "parser",
+        "sub": [],
+        "valid": true,
+        "message": "In this scoped type, variable 'b is reserved for the local type b."
+      }
+    ],
+    "notifications": []
+  }