Fix comments removed in JSX (#7424)

* WIP

* Add test

* Update CHANGELOG

Author: shulhi

CHANGELOG.md

@@ -29,6 +29,7 @@
 
 - Fix broken `bstracing` CLI location. https://github.com/rescript-lang/rescript/pull/7398
 - Fix field flattening optimization to avoid creating unnecessary copies of allocating constants. https://github.com/rescript-lang/rescript-compiler/pull/7421
+- Fix leading comments removed when braces inside JSX contains `let` assignment. https://github.com/rescript-lang/rescript/pull/7424
 
 #### :house: Internal
 

compiler/syntax/src/res_printer.ml

@@ -4584,6 +4584,18 @@ and get_line_sep_for_jsx_children (children : Parsetree.jsx_children) =
 
 and print_jsx_children ~state (children : Parsetree.jsx_children) cmt_tbl =
   let open Parsetree in
+  let get_loc (expr : Parsetree.expression) =
+    let braces =
+      expr.pexp_attributes
+      |> List.find_map (fun (attr, _) ->
+             match attr with
+             | {Location.txt = "res.braces"; loc} -> Some loc
+             | _ -> None)
+    in
+    match braces with
+    | None -> expr.pexp_loc
+    | Some loc -> loc
+  in
   let sep = get_line_sep_for_jsx_children children in
   let print_expr (expr : Parsetree.expression) =
     let leading_line_comment_present =
@@ -4599,7 +4611,7 @@ and print_jsx_children ~state (children : Parsetree.jsx_children) cmt_tbl =
       else Doc.concat [Doc.lbrace; inner_doc; Doc.rbrace]
     in
     match Parens.jsx_child_expr expr with
-    | Nothing -> expr_doc
+    | Nothing -> print_comments expr_doc cmt_tbl (get_loc expr)
     | Parenthesized -> add_parens_or_braces expr_doc
     | Braced braces_loc ->
       print_comments (add_parens_or_braces expr_doc) cmt_tbl braces_loc
@@ -4608,19 +4620,6 @@ and print_jsx_children ~state (children : Parsetree.jsx_children) cmt_tbl =
   | JSXChildrenItems [] -> Doc.nil
   | JSXChildrenSpreading child -> Doc.concat [Doc.dotdotdot; print_expr child]
   | JSXChildrenItems children ->
-    let get_loc (expr : Parsetree.expression) =
-      let braces =
-        expr.pexp_attributes
-        |> List.find_map (fun (attr, _) ->
-               match attr with
-               | {Location.txt = "res.braces"; loc} -> Some loc
-               | _ -> None)
-      in
-      match braces with
-      | None -> expr.pexp_loc
-      | Some loc -> loc
-    in
-
     let rec visit acc children =
       match children with
       | [] -> acc

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

@@ -65,6 +65,15 @@ module Cite = {
   React.string("Hello, World!")}
 </div>
 
+<div>
+  // Outside comment
+  {
+    // But this one is inside
+    let x = 1
+    let y = 2
+  }
+</div>
+
 let x =
   <>
     // before a

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

@@ -67,6 +67,14 @@ value=""
     React.string("Hello, World!")}
 </div>
 
+<div>
+  // Outside comment
+  {// But this one is inside
+    let x = 1
+    let y = 2
+  }
+</div>
+
 let x = <>
   // before a
   {a} // after a