Preserve coercion grouping in restricted expression contexts

Signed-off-by: Christoph Knittel <ck@cca.io>

Author: cknitt

compiler/syntax/src/res_printer.ml

@@ -2394,7 +2394,7 @@ and print_value_binding ~state ~rec_flag (vb : Parsetree.value_binding) cmt_tbl
                   print_typ_expr ~state pvc_type cmt_tbl;
                   Doc.text " =";
                   Doc.line;
-                  print_expression_with_comments ~state expr cmt_tbl;
+                  print_expression_with_comments_and_parens ~state expr cmt_tbl;
                 ]);
          ])
   | {
@@ -2438,7 +2438,8 @@ and print_value_binding ~state ~rec_flag (vb : Parsetree.value_binding) cmt_tbl
                     Doc.concat
                       [
                         Doc.line;
-                        print_expression_with_comments ~state expr cmt_tbl;
+                        print_expression_with_comments_and_parens ~state expr
+                          cmt_tbl;
                       ];
                   ]);
            ])
@@ -2465,7 +2466,8 @@ and print_value_binding ~state ~rec_flag (vb : Parsetree.value_binding) cmt_tbl
                     Doc.concat
                       [
                         Doc.line;
-                        print_expression_with_comments ~state expr cmt_tbl;
+                        print_expression_with_comments_and_parens ~state expr
+                          cmt_tbl;
                       ];
                   ]);
            ]))
@@ -3060,6 +3062,13 @@ and print_expression_with_comments ~state expr cmt_tbl : Doc.t =
   let doc = print_expression ~state expr cmt_tbl in
   print_comments doc cmt_tbl expr.Parsetree.pexp_loc
 
+and print_expression_with_comments_and_parens ~state expr cmt_tbl =
+  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
+
 and print_if_chain ~state pexp_attributes ifs else_expr cmt_tbl =
   let if_docs =
     Doc.join ~sep:Doc.space
@@ -5014,7 +5023,7 @@ and print_jsx_prop ~state prop cmt_tbl =
            [
              Doc.lbrace;
              Doc.dotdotdot;
-             print_expression_with_comments ~state value cmt_tbl;
+             print_expression_with_comments_and_parens ~state value cmt_tbl;
              Doc.rbrace;
            ])
   in
@@ -5418,7 +5427,7 @@ and print_case ~state (case : Parsetree.case) cmt_tbl =
            [
              Doc.line;
              Doc.text "if ";
-             print_expression_with_comments ~state expr cmt_tbl;
+             print_expression_with_comments_and_parens ~state expr cmt_tbl;
            ])
   in
   let should_inline_rhs =
@@ -5977,7 +5986,7 @@ and print_payload ~state (payload : Parsetree.payload) cmt_tbl =
           [
             Doc.line;
             Doc.text "if ";
-            print_expression_with_comments ~state expr cmt_tbl;
+            print_expression_with_comments_and_parens ~state expr cmt_tbl;
           ]
       | None -> Doc.nil
     in

tests/syntax_tests/data/printer/expr/coerce.res

@@ -88,3 +88,13 @@ let beforeJsx = () => {
   let value = (x :> string)
   <option value />
 }
+
+// These grammar positions don't parse a bare trailing coercion.
+let locallyAbstract: type a. a = (value :> a)
+let guarded = switch value {
+| _ if (flag :> bool) => value
+}
+let jsxSpread = <Component {...(props :> propsType)} />
+
+@attr(?value if (flag :> bool))
+let attributeGuard = value

tests/syntax_tests/data/printer/expr/expected/coerce.res.txt

@@ -98,3 +98,13 @@ let beforeJsx = () => {
   let value = (x :> string)
   <option value />
 }
+
+// These grammar positions don't parse a bare trailing coercion.
+let locallyAbstract: type a. a = (value :> a)
+let guarded = switch value {
+| _ if (flag :> bool) => value
+}
+let jsxSpread = <Component {...(props :> propsType)} />
+
+@attr(? value if (flag :> bool))
+let attributeGuard = value