Show unit parameters of a multi-parameter functor on hover

Codex review on #9083: a unit parameter showed as nothing, so hover on
`(P: Primitive, ()) => ...` read `(P: Primitive, ) => ...`. It shows as
`()` now, and a functor with only a unit parameter as `() => ...`, as the
formatter prints them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Kbf3gGkPma9LAZimuQjnrP
Claude-Session: https://claude.ai/code/session_01Kr4cjoUi2f5VpMvE6wT9bo
Signed-off-by: Christoph Knittel <ck@cca.io>

Author: cknitt

analysis/src/hover.ml

@@ -24,6 +24,7 @@ let show_module_top_level ?(functor_params = []) ~docstring ~is_type ~name
       ^ (if is_type then "type " ^ name ^ " = " else name ^ ": ")
       ^ (match functor_params with
         | [] -> ""
+        | ["()"] -> "() => "
         | params -> "(" ^ String.concat ", " params ^ ") => ")
       ^ "{" ^ "\n" ^ contents ^ "\n}")
   in

analysis/src/process_cmt.ml

@@ -50,10 +50,10 @@ let module_type_to_string (mty : Types.module_type) =
   | Mty_functor _ -> "{...}"
 
 (* A functor parameter as hover shows it, such as [O: Ord]; a generative
-   functor's [*] parameter shows as nothing, giving [() => ...]. *)
+   functor's [*] parameter shows as [()]. *)
 let functor_param ~name (mty : Types.module_type option) =
   match (name, mty) with
-  | "*", _ -> ""
+  | "*", _ -> "()"
   | _, None -> name
   | _, Some mty -> name ^ ": " ^ module_type_to_string mty
 

tests/analysis_tests/tests/src/HoverFunctor.res

@@ -38,3 +38,30 @@ module Counter = () => {
   //     ^hov
   let count = ref(0)
 }
+
+module type Primitive = {
+  type t
+}
+
+module Gen = (P: Primitive, ()) => {
+  //   ^hov
+  type t = P.t
+}
+
+module GenFirst = ((), P: Primitive) => {
+  //     ^hov
+  type t = P.t
+}
+
+module Curried = (A: Ord) => (B: Ord) => {
+  //     ^hov
+  type t = (A.t, B.t)
+}
+
+module GenCurried = () => (P: Primitive) => {
+  //     ^hov
+  type t = P.t
+}
+
+module GenApplied = Gen(IntOrd)
+//      ^hov

tests/analysis_tests/tests/src/expected/HoverFunctor.res.txt

@@ -46,3 +46,43 @@ Hover src/HoverFunctor.res 36:9
   }
 }
 
+Hover src/HoverFunctor.res 45:7
+{
+  "contents": {
+    "kind": "markdown",
+    "value": "```rescript\nmodule Gen: (P: Primitive, ()) => {\n  type t = P.t\n}\n```"
+  }
+}
+
+Hover src/HoverFunctor.res 50:9
+{
+  "contents": {
+    "kind": "markdown",
+    "value": "```rescript\nmodule GenFirst: ((), P: Primitive) => {\n  type t = P.t\n}\n```"
+  }
+}
+
+Hover src/HoverFunctor.res 55:9
+{
+  "contents": {
+    "kind": "markdown",
+    "value": "```rescript\nmodule Curried: (A: Ord, B: Ord) => {\n  type t = (A.t, B.t)\n}\n```"
+  }
+}
+
+Hover src/HoverFunctor.res 60:9
+{
+  "contents": {
+    "kind": "markdown",
+    "value": "```rescript\nmodule GenCurried: ((), P: Primitive) => {\n  type t = P.t\n}\n```"
+  }
+}
+
+Hover src/HoverFunctor.res 65:8
+{
+  "contents": {
+    "kind": "markdown",
+    "value": "```rescript\nmodule GenApplied: () => {\n  type t = IntOrd.t\n}\n```"
+  }
+}
+