Fix comments attached to array element (#7672)

* Remove Example.res

* WIP

* Cleanup

* Refactor

* Add tests

* Update CHANGELOG

* Handle comment for array spread

Author: shulhi

CHANGELOG.md

@@ -51,6 +51,7 @@
 - Fix I/O error message when trying to extract extra info from non-existing file. https://github.com/rescript-lang/rescript/pull/7656
 - Fix fatal error when JSX expression used without configuring JSX in `rescript.json`. https://github.com/rescript-lang/rescript/pull/7656
 - Rewatch: Only allow access to `"bs-dev-dependencies"` from `"type": "dev"` source files. https://github.com/rescript-lang/rescript/pull/7650
+- Fix comment attached to array element. https://github.com/rescript-lang/rescript/pull/7672
 
 #### :nail_care: Polish
 

compiler/syntax/src/res_comments_table.ml

@@ -1028,6 +1028,38 @@ and walk_value_binding vb t comments =
 
 and walk_expression expr t comments =
   let open Location in
+  let walk_apply_expr call_expr arguments t comments =
+    let before, inside, after =
+      partition_by_loc comments call_expr.Parsetree.pexp_loc
+    in
+    let after =
+      if is_block_expr call_expr then (
+        let after_expr, rest =
+          partition_adjacent_trailing call_expr.Parsetree.pexp_loc after
+        in
+        walk_expression call_expr t (List.concat [before; inside; after_expr]);
+        rest)
+      else (
+        attach t.leading call_expr.Parsetree.pexp_loc before;
+        walk_expression call_expr t inside;
+        after)
+    in
+    let after_expr, rest =
+      partition_adjacent_trailing call_expr.Parsetree.pexp_loc after
+    in
+    attach t.trailing call_expr.Parsetree.pexp_loc after_expr;
+    walk_list
+      (arguments
+      |> List.map (fun (lbl, expr) ->
+             let loc =
+               match lbl with
+               | Asttypes.Labelled {loc} | Optional {loc} ->
+                 {loc with loc_end = expr.Parsetree.pexp_loc.loc_end}
+               | _ -> expr.pexp_loc
+             in
+             ExprArgument {expr; loc}))
+      t rest
+  in
   match expr.Parsetree.pexp_desc with
   | _ when comments = [] -> ()
   | Pexp_constant _ ->
@@ -1539,35 +1571,34 @@ and walk_expression expr t comments =
       }
     when Res_parsetree_viewer.is_tuple_array key_values ->
     walk_list [Expression key_values] t comments
-  | Pexp_apply {funct = call_expr; args = arguments} ->
-    let before, inside, after = partition_by_loc comments call_expr.pexp_loc in
-    let after =
-      if is_block_expr call_expr then (
-        let after_expr, rest =
-          partition_adjacent_trailing call_expr.pexp_loc after
+  | Pexp_apply {funct = call_expr; args = arguments} -> (
+    (* Special handling for Belt.Array.concatMany - treat like an array *)
+    match call_expr.pexp_desc with
+    | Pexp_ident
+        {
+          txt =
+            Longident.Ldot
+              (Longident.Ldot (Longident.Lident "Belt", "Array"), "concatMany");
+        }
+      when List.length arguments = 1 -> (
+      match arguments with
+      | [(_, {pexp_desc = Pexp_array sub_arrays})] ->
+        (* Collect all individual expressions from sub-arrays *)
+        let all_exprs =
+          List.fold_left
+            (fun acc sub_array ->
+              match sub_array.Parsetree.pexp_desc with
+              | Pexp_array exprs -> acc @ exprs
+              | _ -> acc @ [sub_array])
+            [] sub_arrays
         in
-        walk_expression call_expr t (List.concat [before; inside; after_expr]);
-        rest)
-      else (
-        attach t.leading call_expr.pexp_loc before;
-        walk_expression call_expr t inside;
-        after)
-    in
-    let after_expr, rest =
-      partition_adjacent_trailing call_expr.pexp_loc after
-    in
-    attach t.trailing call_expr.pexp_loc after_expr;
-    walk_list
-      (arguments
-      |> List.map (fun (lbl, expr) ->
-             let loc =
-               match lbl with
-               | Asttypes.Labelled {loc} | Optional {loc} ->
-                 {loc with loc_end = expr.Parsetree.pexp_loc.loc_end}
-               | _ -> expr.pexp_loc
-             in
-             ExprArgument {expr; loc}))
-      t rest
+        walk_list (all_exprs |> List.map (fun e -> Expression e)) t comments
+      | _ ->
+        (* Fallback to regular apply handling *)
+        walk_apply_expr call_expr arguments t comments)
+    | _ ->
+      (* Regular apply handling *)
+      walk_apply_expr call_expr arguments t comments)
   | Pexp_fun _ | Pexp_newtype _ -> (
     let _, parameters, return_expr = fun_expr expr in
     let comments =

compiler/syntax/src/res_printer.ml

@@ -4035,15 +4035,30 @@ and print_binary_expression ~state (expr : Parsetree.expression) cmt_tbl =
 and print_belt_array_concat_apply ~state sub_lists cmt_tbl =
   let make_spread_doc comma_before_spread = function
     | Some expr ->
+      (* Extract leading comments before dotdotdot *)
+      let leading_comments_doc =
+        print_leading_comments Doc.nil cmt_tbl.CommentTable.leading
+          expr.Parsetree.pexp_loc
+      in
+      (* Print expression without leading comments (they're already extracted) *)
+      let expr_doc =
+        let doc = print_expression ~state expr cmt_tbl in
+        match Parens.expr expr with
+        | Parens.Parenthesized -> add_parens doc
+        | Braced braces -> print_braces doc expr braces
+        | Nothing -> doc
+      in
+      (* Print trailing comments with the expression *)
+      let expr_with_trailing_comments =
+        print_trailing_comments expr_doc cmt_tbl.CommentTable.trailing
+          expr.Parsetree.pexp_loc
+      in
       Doc.concat
         [
           comma_before_spread;
+          leading_comments_doc;
           Doc.dotdotdot;
-          (let doc = print_expression_with_comments ~state expr cmt_tbl in
-           match Parens.expr expr with
-           | Parens.Parenthesized -> add_parens doc
-           | Braced braces -> print_braces doc expr braces
-           | Nothing -> doc);
+          expr_with_trailing_comments;
         ]
     | None -> Doc.nil
   in
@@ -4054,20 +4069,19 @@ and print_belt_array_concat_apply ~state sub_lists cmt_tbl =
       | _ -> Doc.concat [Doc.text ","; Doc.line]
     in
     let spread_doc = make_spread_doc comma_before_spread spread in
-    Doc.concat
-      [
-        Doc.join
-          ~sep:(Doc.concat [Doc.text ","; Doc.line])
-          (List.map
-             (fun expr ->
-               let doc = print_expression_with_comments ~state expr cmt_tbl in
-               match Parens.expr expr with
-               | Parens.Parenthesized -> add_parens doc
-               | Braced braces -> print_braces doc expr braces
-               | Nothing -> doc)
-             expressions);
-        spread_doc;
-      ]
+    let expressions_doc =
+      Doc.join
+        ~sep:(Doc.concat [Doc.text ","; Doc.line])
+        (List.map
+           (fun expr ->
+             let doc = print_expression_with_comments ~state expr cmt_tbl in
+             match Parens.expr expr with
+             | Parens.Parenthesized -> add_parens doc
+             | Braced braces -> print_braces doc expr braces
+             | Nothing -> doc)
+           expressions)
+    in
+    Doc.concat [expressions_doc; spread_doc]
   in
   Doc.group
     (Doc.concat

tests/syntax_tests/data/printer/comments/array.res

@@ -15,4 +15,40 @@ let _ = (
     ->Belt.SortArray.stableSortBy((a, b) =>
       compare(a.createdTime, b.createdTime)
     )
-  )[0]
+  )[0]
+
+let _ = [
+  // comment 1
+  a,
+  // comment 2
+  b,
+  // comment 3
+  c
+]
+
+let _ = [
+  // comment 1
+  a,
+  // comment 2
+  b, c
+]
+
+let _ = [
+  // comment 0
+  ...xs,
+  // comment 1
+  a,
+  // comment 2
+  b, c
+]
+
+let _ = [
+  // comment 0
+  ...xs,
+  // comment 1
+  a,
+  // comment 2
+  ...ys,
+  // comment 3
+  b, c
+]

tests/syntax_tests/data/printer/comments/expected/array.res.txt

@@ -10,3 +10,42 @@ let _ = a[0] // zz
   // This comment will vanish
   ->Belt.SortArray.stableSortBy((a, b) => compare(a.createdTime, b.createdTime))
 )[0]
+
+let _ = [
+  // comment 1
+  a,
+  // comment 2
+  b,
+  // comment 3
+  c,
+]
+
+let _ = [
+  // comment 1
+  a,
+  // comment 2
+  b,
+  c,
+]
+
+let _ = [
+  // comment 0
+  ...xs,
+  // comment 1
+  a,
+  // comment 2
+  b,
+  c,
+]
+
+let _ = [
+  // comment 0
+  ...xs,
+  // comment 1
+  a,
+  // comment 2
+  ...ys,
+  // comment 3
+  b,
+  c,
+]