Fix merlin-lib 4.18 compatibility

- Restore local Typed_hole module with can_be_hole and is_a_hole functions
  (merlin-lib 4.18 doesn't have Merlin_analysis.Typed_hole)
- Remove hint_function_params from Inlay_hints (not available in 4.18)
- Use 5-argument form of Query_protocol.Inlay_hints

Author: davesnx

ocaml-lsp-server/src/code_actions/action_construct.ml

@@ -14,7 +14,7 @@ let code_action pipeline doc (params : CodeActionParams.t) =
       let src = Document.source doc in
       Compl.prefix_of_position ~short_path:false src pos
     in
-    if not (Merlin_analysis.Typed_hole.can_be_hole prefix)
+    if not (Typed_hole.can_be_hole prefix)
     then None
     else (
       let structures =
@@ -25,7 +25,7 @@ let code_action pipeline doc (params : CodeActionParams.t) =
         let pos = Mpipeline.get_lexing_pos pipeline pos in
         Mbrowse.enclosing pos [ Mbrowse.of_typedtree typedtree ]
       in
-      if not (Merlin_analysis.Typed_hole.is_a_hole structures)
+      if not (Typed_hole.is_a_hole structures)
       then None
       else (
         (* ocaml-lsp can provide [Construct] values as completion entries, so

ocaml-lsp-server/src/compl.ml

@@ -315,7 +315,7 @@ let complete
                 let* item = completion_item_capability in
                 item.deprecatedSupport)
            in
-           if not (Merlin_analysis.Typed_hole.can_be_hole prefix)
+           if not (Typed_hole.can_be_hole prefix)
            then Complete_by_prefix.complete merlin prefix pos ~resolve ~deprecated
            else (
              let reindex_sortText completion_items =

ocaml-lsp-server/src/inlay_hints.ml

@@ -29,22 +29,12 @@ let compute (state : State.t) { InlayHintParams.range; textDocument = { uri }; _
           c.hint_pattern_variables)
         |> Option.value ~default:false
       in
-      let hint_function_params =
-        Option.map state.configuration.data.inlay_hints ~f:(fun c ->
-          c.hint_function_params)
-        |> Option.value ~default:false
-      in
       Document.Merlin.with_pipeline_exn ~name:"inlay-hints" doc (fun pipeline ->
         let start = range.start |> Position.logical
         and stop = range.end_ |> Position.logical in
         let command =
           Query_protocol.Inlay_hints
-            ( start
-            , stop
-            , hint_let_bindings
-            , hint_pattern_variables
-            , hint_function_params
-            , not inside_test )
+            (start, stop, hint_let_bindings, hint_pattern_variables, not inside_test)
         in
         let hints = Query_commands.dispatch pipeline command in
         List.filter_map

ocaml-lsp-server/src/typed_hole.ml

@@ -1,5 +1,23 @@
 open Import
 
+let syntax_repr = "_"
+let can_be_hole s = String.equal syntax_repr s
+
+(* the pattern matching below is taken and modified (minimally, to adapt the
+   return type) from [Query_commands.dispatch]'s [Construct] branch;
+
+   If we directly dispatched [Construct] command to merlin, we'd be doing
+   useless computations: we need info whether the expression at the cursor is a
+   hole, we don't need constructed expressions yet.
+
+   Ideally, merlin should return a callback [option], which is [Some] when the
+   context is applicable. *)
+let is_a_hole = function
+  | (_, Browse_raw.Module_expr { mod_desc = Tmod_hole; _ }) :: (_, _) :: _
+  | (_, Browse_raw.Expression { exp_desc = Texp_hole; _ }) :: _ -> true
+  | [] | (_, _) :: _ -> false
+;;
+
 let in_range range holes =
   match range with
   | None -> holes

ocaml-lsp-server/src/typed_hole.mli

@@ -1,3 +1,19 @@
+(** This module should be used to work with typed holes. The main goal is to
+    hide syntactic representation of a typed hole, which may change in future *)
+
+(** checks whether the current string matches the syntax representation of a
+    typed hole *)
+val can_be_hole : string -> bool
+
+(** [is_a_hole nodes] checks whether the leaf node [1] is a typed hole
+
+    Note: this function is extracted from merlin sources handling [Construct]
+    command in [merlin/src/frontend/query_commands.ml]
+
+    [1] leaf node is the head of the list, as
+    [Mbrowse.t = (Env.t * Browse_raw.node) list]*)
+val is_a_hole : (Ocaml_typing.Env.t * Merlin_specific.Browse_raw.node) list -> bool
+
 val find
   :  range:Range.t option
   -> position:Position.t