Add reproduction case for #1980

CHANGES.md

@@ -13,6 +13,7 @@ Sat Dec 20 11:15:42 CET 2025
   + 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 to ensure the behavior showed in issue #1980
     - Add a test case illustrating how a snippet produces two unrelated errors in issue #2000. (#2003)
     - Add a test reproducing issue #1983 where `document` command which sometime concatenates consecutive variants and labels (#2005)
     - Signature-help should trigger on unfinished `let ... in` bindings (#2009)

tests/test-dirs/issue1980.t

@@ -0,0 +1,32 @@
+  $ cat > test.ml <<EOF
+  > module rec M : sig
+  >   val f : unit -> unit
+  > end = struct
+  >   let f () = ()
+  > end
+  > and N : sig
+  >   val foo : unit -> unit
+  > end = struct
+  >   let foo () = M.f ()
+  > end
+  > let foo () = M.f ()
+  > EOF
+
+  $ ocamlmerlin single locate -position 11:16 -look-for implementation -filename test.ml < test.ml | jq .value
+  {
+    "file": "$TESTCASE_ROOT/test.ml",
+    "pos": {
+      "line": 4,
+      "col": 6
+    }
+  }
+
+-- FIXME : Merlin should return the definition position instead of the declaration one
+  $ ocamlmerlin single locate -position 9:18 -look-for implementation -filename test.ml < test.ml | jq .value
+  {
+    "file": "$TESTCASE_ROOT/test.ml",
+    "pos": {
+      "line": 2,
+      "col": 6
+    }
+  }