Feature: Support Inlay Hint

analysis/src/Cli.ml

@@ -11,6 +11,7 @@ API examples:
   ./rescript-editor-analysis.exe references src/MyFile.res 10 2
   ./rescript-editor-analysis.exe rename src/MyFile.res 10 2 foo
   ./rescript-editor-analysis.exe diagnosticSyntax src/MyFile.res
+  /rescript-editor-analysis.exe inlayHint src/MyFile.res 25
 
 Dev-time examples:
   ./rescript-editor-analysis.exe dump src/MyFile.res src/MyFile2.res
@@ -65,6 +66,10 @@ Options:
 
     ./rescript-editor-analysis.exe diagnosticSyntax src/MyFile.res
 
+  inlayHint: get all inlay Hint with max length equal a 25 declared in MyFile.res
+
+    ./rescript-editor-analysis.exe inlayHint src/MyFile.res 25
+
   test: run tests specified by special comments in file src/MyFile.res
 
     ./rescript-editor-analysis.exe test src/src/MyFile.res
@@ -89,6 +94,8 @@ let main () =
     Commands.hover ~path
       ~pos:(int_of_string line, int_of_string col)
       ~currentFile ~debug:false
+  | [_; "inlayHint"; path; maxLength] ->
+    Commands.inlayhint ~path ~maxLength ~debug:false
   | [_; "codeAction"; path; line; col; currentFile] ->
     Commands.codeAction ~path
       ~pos:(int_of_string line, int_of_string col)

analysis/src/Commands.ml

@@ -28,6 +28,12 @@ let completion ~debug ~path ~pos ~currentFile =
     |> List.map Protocol.stringifyCompletionItem
     |> Protocol.array)
 
+let inlayhint ~path ~maxLength ~debug =
+  let result = match Hint.inlay ~path ~maxLength ~debug with
+  | [] -> Protocol.null
+  | hints -> hints |> Protocol.array in
+  print_endline result
+
 let hover ~path ~pos ~currentFile ~debug =
   let result =
     match Cmt.fullFromPath ~path with
@@ -382,6 +388,7 @@ let test ~path =
                                    (Protocol.stringifyRange range)
                                    indent indent newText)))
           | "dia" -> diagnosticSyntax ~path
+          | "hint" -> inlayhint ~path ~maxLength:"25" ~debug:true
           | _ -> ());
           print_newline ())
     in

analysis/src/Hint.ml

@@ -0,0 +1,121 @@
+open SharedTypes
+
+type inlayHintKind = Type | Parameter
+let inlayKindToNumber = function
+  | Type -> 1
+  | Parameter -> 2
+
+let locItemToTypeHint ~full:{file; package} locItem =
+  match locItem.locType with
+  | Constant t ->
+    Some
+      (match t with
+      | Const_int _ -> "int"
+      | Const_char _ -> "char"
+      | Const_string _ -> "string"
+      | Const_float _ -> "float"
+      | Const_int32 _ -> "int32"
+      | Const_int64 _ -> "int64"
+      | Const_nativeint _ -> "int")
+  | Typed (_, t, locKind) ->
+    let fromType typ =
+      typ |> Shared.typeToString
+      |> Str.global_replace (Str.regexp "[\r\n\t]") ""
+    in
+    Some
+      (match References.definedForLoc ~file ~package locKind with
+      | None -> fromType t
+      | Some (_, res) -> (
+        match res with
+        | `Declared -> fromType t
+        | `Constructor _ -> fromType t
+        | `Field -> fromType t))
+  | _ -> None
+
+let inlay ~path ~maxLength ~debug =
+  let maxlen = try Some(int_of_string maxLength) with Failure _ -> None in
+  let hints = ref [] in
+  let rec processFunction (exp : Parsetree.expression) =
+    match exp.pexp_desc with
+    | Pexp_fun (_, _, pat_exp, e) -> (
+      match pat_exp with
+      | {ppat_desc = Ppat_var _} ->
+        hints := (pat_exp.ppat_loc, Type) :: !hints;
+        processFunction e
+      | _ -> processFunction e)
+    | _ -> ()
+  in
+  let value_binding (iterator : Ast_iterator.iterator)
+      (vb : Parsetree.value_binding) =
+    (match vb with
+    | {
+     pvb_pat = {ppat_desc = Ppat_var _};
+     pvb_expr =
+       {
+         pexp_desc =
+           ( Pexp_constant _ | Pexp_tuple _ | Pexp_record _ | Pexp_variant _
+           | Pexp_apply _ | Pexp_match _ | Pexp_construct _ | Pexp_ifthenelse _
+           | Pexp_array _ | Pexp_ident _ | Pexp_try _ | Pexp_lazy _
+           | Pexp_send _ | Pexp_field _ | Pexp_open _ );
+       };
+    } ->
+      hints := (vb.pvb_pat.ppat_loc, Type) :: !hints
+    | {pvb_pat = {ppat_desc = Ppat_tuple tuples}} ->
+      List.iter
+        (fun (tuple : Parsetree.pattern) ->
+          hints := (tuple.ppat_loc, Type) :: !hints)
+        tuples
+    | {
+     pvb_pat = {ppat_desc = Ppat_var _};
+     pvb_expr = {pexp_desc = Pexp_fun (_, _, pat, e)};
+    } ->
+      (match pat with
+      | {ppat_desc = Ppat_var _} -> hints := (pat.ppat_loc, Type) :: !hints
+      | _ -> ());
+      processFunction e
+    | _ -> ());
+    Ast_iterator.default_iterator.value_binding iterator vb
+  in
+  let iterator = {Ast_iterator.default_iterator with value_binding} in
+  (if Filename.check_suffix path ".res" then
+   let parser =
+     Res_driver.parsingEngine.parseImplementation ~forPrinter:false
+   in
+   let {Res_driver.parsetree = structure} = parser ~filename:path in
+   iterator.structure iterator structure |> ignore
+  else
+    let parser = Res_driver.parsingEngine.parseInterface ~forPrinter:false in
+    let {Res_driver.parsetree = signature} = parser ~filename:path in
+    iterator.signature iterator signature |> ignore);
+  !hints
+  |> List.filter_map (fun (locOfName, hintKind) ->
+         let range = Utils.cmtLocToRange locOfName in
+         match Cmt.fullFromPath ~path with
+         | None -> None
+         | Some full -> (
+           match
+             References.getLocItem ~full
+               ~pos:(range.start.line, range.start.character + 1)
+               ~debug
+           with
+           | None -> None
+           | Some locItem -> (
+             let position : Protocol.position =
+               {line = range.start.line; character = range.end_.character}
+             in
+             match locItemToTypeHint locItem ~full with
+             | Some label -> (
+               let result =
+                 Protocol.stringifyHint
+                   {
+                     kind = inlayKindToNumber hintKind;
+                     position;
+                     paddingLeft = true;
+                     paddingRight = false;
+                     label = ": " ^ label;
+                   }
+               in
+               match maxlen with
+               | Some value -> if (String.length label) > value then None else Some(result)
+               | None -> Some(result))
+             | None -> None)))

analysis/src/Protocol.ml

@@ -1,6 +1,13 @@
 type position = {line: int; character: int}
 type range = {start: position; end_: position}
 type markupContent = {kind: string; value: string}
+type inlayHint = {
+  position: position;
+  label: string;
+  kind: int;
+  paddingLeft: bool;
+  paddingRight: bool;
+}
 
 type completionItem = {
   label: string;
@@ -128,6 +135,18 @@ let stringifyCodeAction ca =
     (codeActionKindToString ca.codeActionKind)
     (ca.edit |> stringifyCodeActionEdit)
 
+let stringifyHint hint =
+  Printf.sprintf
+    {|{
+    "position": %s,
+    "label": "%s",
+    "kind": %i,
+    "paddingLeft": %b,
+    "paddingRight": %b
+}|}
+    (stringifyPosition hint.position)
+    (Json.escape hint.label) hint.kind hint.paddingLeft hint.paddingRight
+
 (* https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#diagnostic *)
 let stringifyDiagnostic d =
   Printf.sprintf

analysis/tests/src/InlayHint.res

@@ -0,0 +1,20 @@
+let string = "ReScript"
+let number = 1
+let float = 1.1
+let char = 'c'
+
+let add = (x, y) => x + y
+
+let my_sum = 3->add(1)->add(1)->add(1)->add(8)
+
+let withAs = (~xx as yyy) => yyy + 1
+
+
+@react.component
+let make = (~name) => React.string(name)
+
+let tuple = ("ReScript", "lol")
+
+let (lang, _) = tuple
+
+//^hint

analysis/tests/src/expected/InlayHint.res.txt

@@ -0,0 +1,67 @@
+{                                      
+    "position": {"line": 17, "character": 9},
+    "label": ": string",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}, {
+    "position": {"line": 15, "character": 9},
+    "label": ": (string, string)",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}, {
+    "position": {"line": 13, "character": 17},
+    "label": ": string",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}, {
+    "position": {"line": 9, "character": 24},
+    "label": ": int",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}, {
+    "position": {"line": 7, "character": 10},
+    "label": ": int",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}, {
+    "position": {"line": 5, "character": 15},
+    "label": ": int",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}, {
+    "position": {"line": 5, "character": 12},
+    "label": ": int",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}, {
+    "position": {"line": 3, "character": 8},
+    "label": ": char",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}, {
+    "position": {"line": 2, "character": 9},
+    "label": ": float",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}, {
+    "position": {"line": 1, "character": 10},
+    "label": ": int",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}, {
+    "position": {"line": 0, "character": 10},
+    "label": ": string",
+    "kind": 1,
+    "paddingLeft": true,
+    "paddingRight": false
+}]

client/src/extension.ts

@@ -235,6 +235,17 @@ export function activate(context: ExtensionContext) {
   // Start the client. This will also launch the server
   client.start();
 
+  // Restart the language client automatically certain configuration changes.
+  // These are typically settings that affect the capabilities of the language
+  // client, and because of that requires a full restart.
+  context.subscriptions.push(
+    workspace.onDidChangeConfiguration(({ affectsConfiguration }) => {
+      if (affectsConfiguration("rescript.settings.inlayHints")) {
+        commands.executeCommand("rescript-vscode.restart_language_server");
+      }
+    })
+  );
+
   // Autostart code analysis if wanted
   if (
     workspace

package.json

@@ -132,6 +132,20 @@
 					"default": false,
 					"description": "Automatically start ReScript's code analysis."
 				},
+				"rescript.settings.inlayHints.enable": {
+					"type": "boolean",
+					"default": false,
+					"description": "Enable (experimental) inlay hints."
+				},
+				"rescript.settings.inlayHints.maxLength": {
+					"markdownDescription": "Maximum length for inlay hints. Set to null to have an unlimited length.",
+                    "default": 25,
+                    "type": [
+                        "null",
+                        "integer"
+                    ],
+                    "minimum": 0
+				},
 				"rescript.settings.binaryPath": {
 					"type": ["string", "null"],
 					"default": null,