Support LSP function parameter auto-completion.

newtests/lsp/completion/params.js

@@ -0,0 +1,11 @@
+// @flow
+
+// Tests different auto complete items use the correct `kind`.
+// In VSCode, for example, this includes the autocomplete
+// icons used.
+
+let aFunction = (arg1: number, arg2: string) => null;
+
+function foo() {
+  const x = 15;
+}

newtests/lsp/completion/test.js

@@ -176,5 +176,70 @@ export default suite(
         [...lspIgnoreStatusAndCancellation],
       ),
     ]),
-  ],
+    test('textDocument/completion', [
+      addFile('params.js'),
+      ideStartAndConnect(),
+      ideRequestAndWaitUntilResponse('textDocument/completion', {
+        textDocument: {uri: '<PLACEHOLDER_PROJECT_URL_SLASH>params.js'},
+        position: {line: 9, character: 15},
+        context: { triggerKind: 1 }
+      }).verifyAllIDEMessagesInStep(
+        [
+          (() => {
+            const expectedResponse = {
+              isIncomplete: false,
+              items: [
+                {
+                  label: "x",
+                  kind: 6,
+                  detail: "number",
+                  inlineDetail: "number",
+                  insertTextFormat: 1
+                },
+                {
+                  label: "foo",
+                  kind: 3,
+                  detail: "() => void",
+                  inlineDetail: "()",
+                  itemType: "void",
+                  insertTextFormat: 1
+                },
+                {
+                  label: "exports",
+                  kind: 6,
+                  detail: "{||}",
+                  inlineDetail: "{||}",
+                  insertTextFormat: 1
+                },
+                {
+                  label: "aFunction",
+                  kind: 3,
+                  detail: "(arg1: number, arg2: string) => null",
+                  inlineDetail: "(arg1: number, arg2: string)",
+                  itemType: "null",
+                  insertTextFormat: 1
+                },
+                {
+                  label: "this",
+                  kind: 6,
+                  detail: "empty",
+                  inlineDetail: "empty",
+                  insertTextFormat: 1
+                },
+                {
+                  label: "super",
+                  kind: 6,
+                  detail: "typeof Object.prototype",
+                  inlineDetail: "typeof Object.prototype",
+                  insertTextFormat: 1
+                }
+              ]
+            };
+            return `textDocument/completion${JSON.stringify(expectedResponse)}`
+          })()
+        ],
+        [...lspIgnoreStatusAndCancellation],
+      ),
+    ]),
+  ]
 );

src/common/flow_lsp_conversions.ml

@@ -7,7 +7,24 @@
 
 module Ast = Flow_ast
 
+let flow_position_to_lsp (line: int) (char: int): Lsp.position =
+  let open Lsp in
+  {
+    line = line - 1;
+    character = char;
+  }
+
+let lsp_position_to_flow (position: Lsp.position): int * int =
+  let open Lsp in
+  let line = position.line + 1 in
+  let char = position.character
+  in
+  (line, char)
+
 let flow_completion_to_lsp
+    (line: int)
+    (character: int)
+    (is_snippet_supported: bool)
     (item: ServerProt.Response.complete_autocomplete_result)
   : Lsp.Completion.completionItem =
   let open Lsp.Completion in
@@ -18,17 +35,38 @@ let flow_completion_to_lsp
     let params = Core_list.map ~f:(fun p -> p.param_name ^ ": " ^ p.param_ty) params in
     "(" ^ (String.concat ", " params) ^ ")"
   in
-  let itemType, inlineDetail, detail = match item.func_details with
+  let flow_params_to_lsp_snippet name params =
+    let params = Core_list.mapi ~f:(fun i p -> "${" ^ string_of_int (i +1 ) ^ ":" ^ p.param_name ^ "}") params in
+    name ^ "(" ^ (String.concat ", " params) ^ ")"
+  in
+  let func_snippet item func_details =
+    let newText = flow_params_to_lsp_snippet item.res_name func_details.param_tys in
+    let open Lsp in
+    let start = (flow_position_to_lsp line (character - 1)) in
+    let end_ = (flow_position_to_lsp line (character + 1)) in
+    let textEdit: TextEdit.t = {
+      Lsp.TextEdit.range = {
+        start;
+        end_;
+      };
+      Lsp.TextEdit.newText = newText;
+    } in
+    [textEdit]
+  in
+  let itemType, inlineDetail, detail, insertTextFormat, textEdits = match item.func_details with
     | Some func_details ->
       let itemType = Some (trunc 30 func_details.return_ty) in
       let inlineDetail = Some (trunc 40 (flow_params_to_string func_details.param_tys)) in
       let detail = Some (trunc80 item.res_ty) in
-      itemType, inlineDetail, detail
+      let (insertTextFormat, textEdits) = match is_snippet_supported with
+        | true -> (Some SnippetFormat, (func_snippet item func_details))
+        | false -> (Some PlainText, [])  in
+      itemType, inlineDetail, detail, insertTextFormat, textEdits
     | None ->
       let itemType = None in
       let inlineDetail = Some (trunc80 item.res_ty) in
       let detail = Some (trunc80 item.res_ty) in
-      itemType, inlineDetail, detail
+      itemType, inlineDetail, detail, Some PlainText, []
   in
   {
     label = item.res_name;
@@ -39,9 +77,10 @@ let flow_completion_to_lsp
     documentation = None; (* This will be filled in by completionItem/resolve. *)
     sortText = None;
     filterText = None;
+    (* deprecated and should not be used *)
     insertText = None;
-    insertTextFormat = Some PlainText;
-    textEdits = [];
+    insertTextFormat;
+    textEdits;
     command = None;
     data = None;
   }
@@ -70,13 +109,6 @@ let loc_to_lsp_with_default (loc: Loc.t) ~(default_uri: string): Lsp.Location.t
   in
   { Lsp.Location.uri; range = loc_to_lsp_range loc; }
 
-let lsp_position_to_flow (position: Lsp.position): int * int =
-  let open Lsp in
-  let line = position.line + 1 in
-  let char = position.character
-  in
-  (line, char)
-
 let flow_edit_to_textedit (edit: Loc.t * string): Lsp.TextEdit.t =
   let loc, text = edit in
   { Lsp.TextEdit.range = loc_to_lsp_range loc; newText = text }

src/server/command_handler/commandHandler.ml

@@ -899,6 +899,7 @@ let handle_persistent_infer_type ~options ~id ~params ~loc ~metadata ~client ~pr
   end
 
 let handle_persistent_autocomplete_lsp ~options ~id ~params ~loc ~metadata ~client ~profiling ~env =
+  let is_snippet_supported = Persistent_connection.client_snippet_support client in
   let open Completion in
   let (file, line, char) = match loc with
   | Some loc -> loc
@@ -929,7 +930,7 @@ let handle_persistent_autocomplete_lsp ~options ~id ~params ~loc ~metadata ~clie
       let metadata = with_data ~extra_data metadata in
       begin match result with
         | Ok items ->
-          let items = Core_list.map ~f:Flow_lsp_conversions.flow_completion_to_lsp items in
+          let items = Core_list.map ~f: (Flow_lsp_conversions.flow_completion_to_lsp line char is_snippet_supported) items in
           let r = CompletionResult { Lsp.Completion.isIncomplete = false; items; } in
           let response = ResponseMessage (id, r) in
           Lwt.return (LspResponse (Ok ((), Some response, metadata)))

src/server/persistent_connection/persistent_connection.ml

@@ -232,3 +232,9 @@ let get_opened_files (clients: t) : SSet.t =
   List.fold_left per_client SSet.empty clients
 
 let get_id client = client.client_id
+
+let client_snippet_support (client: single_client) =
+  let open Lsp.Initialize in
+  match client.lsp_initialize_params with
+  | None -> false
+  | Some params -> params.client_capabilities.textDocument.completion.completionItem.snippetSupport

src/server/persistent_connection/persistent_connection.mli

@@ -77,3 +77,6 @@ val get_file: single_client -> string -> File_input.t
 
 val get_client: Prot.client_id -> single_client option
 val get_id: single_client -> Prot.client_id
+
+val client_snippet_support: single_client -> bool
+