Fix formatting of trailing comments before equals

CHANGELOG.md

@@ -30,6 +30,7 @@
 - Rewatch: treat transitive workspace dependencies as local packages in monorepo roots. https://github.com/rescript-lang/rescript/pull/8411
 - Rewatch: use a single timestamp per compile pass. https://github.com/rescript-lang/rescript/pull/8428
 - Fix rewatch warning replay after early compile errors. https://github.com/rescript-lang/rescript/pull/8408
+- Fix formatting of trailing comments before `=` in let bindings. https://github.com/rescript-lang/rescript/pull/8444
 
 #### :memo: Documentation
 

compiler/syntax/src/res_printer.ml

@@ -70,6 +70,11 @@ let has_trailing_single_line_comment tbl loc =
   | Some (comment :: _) -> Comment.is_single_line_comment comment
   | _ -> false
 
+let has_any_trailing_line_comment tbl loc =
+  match Hashtbl.find_opt tbl.CommentTable.trailing loc with
+  | Some comments -> List.exists Comment.is_single_line_comment comments
+  | None -> false
+
 let has_comment_below tbl loc =
   match Hashtbl.find tbl.CommentTable.trailing loc with
   | comment :: _ ->
@@ -2441,7 +2446,15 @@ and print_value_binding ~state ~rec_flag (vb : Parsetree.value_binding) cmt_tbl
       | Braced braces -> print_braces doc expr braces
       | Nothing -> doc
     in
+    let pattern_has_trailing_line_comment =
+      has_any_trailing_line_comment cmt_tbl vb.pvb_pat.ppat_loc
+    in
     let pattern_doc = print_pattern ~state vb.pvb_pat cmt_tbl in
+    let equal_doc =
+      if pattern_has_trailing_line_comment then
+        Doc.indent (Doc.concat [Doc.hard_line; Doc.equal])
+      else Doc.text " ="
+    in
     (*
      * we want to optimize the layout of one pipe:
      *   let tbl = data->Js.Array2.reduce((map, curr) => {
@@ -2459,21 +2472,14 @@ and print_value_binding ~state ~rec_flag (vb : Parsetree.value_binding) cmt_tbl
         [
           Doc.group
             (Doc.concat
-               [
-                 attrs;
-                 header;
-                 pattern_doc;
-                 Doc.text " =";
-                 Doc.space;
-                 printed_expr;
-               ]);
+               [attrs; header; pattern_doc; equal_doc; Doc.space; printed_expr]);
           Doc.group
             (Doc.concat
                [
                  attrs;
                  header;
                  pattern_doc;
-                 Doc.text " =";
+                 equal_doc;
                  Doc.indent (Doc.concat [Doc.line; printed_expr]);
                ]);
         ]
@@ -2505,7 +2511,7 @@ and print_value_binding ~state ~rec_flag (vb : Parsetree.value_binding) cmt_tbl
              attrs;
              header;
              pattern_doc;
-             Doc.text " =";
+             equal_doc;
              (if should_indent then
                 Doc.indent (Doc.concat [Doc.line; printed_expr])
               else Doc.concat [Doc.space; printed_expr]);

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

@@ -10,6 +10,14 @@ let walkList: 'node. unit = comments => {
   let x /* comment */ = 0
 }
 
+let x // comment before equals
+  = 1
+
+let multilineString // comment before equals
+  = "
+multiline
+"
+
 let walkList: 'node. (
   ~prevLoc: Location.t=?,
   ~getLoc: 'node => Location.t,

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

@@ -10,6 +10,14 @@ let walkList: 'node. unit = comments => {
   let x /* comment */ = 0
 }
 
+let x // comment before equals
+= 1
+
+let multilineString // comment before equals
+= "
+multiline
+"
+
 let walkList: 'node. (
   ~prevLoc: Location.t=?,
   ~getLoc: 'node => Location.t,