First step towards ast mapping

Author: nojaf

compiler/ml/ast_mapper_from0.ml

@@ -315,6 +315,9 @@ module E = struct
     let open Exp in
     let loc = sub.location sub loc in
     let attrs = sub.attributes sub attrs in
+    let has_jsx_attribute () =
+      attrs |> List.exists (fun ({txt}, _) -> txt = "JSX")
+    in
     match desc with
     | Pexp_ident x -> ident ~loc ~attrs (map_loc sub x)
     | Pexp_constant x -> constant ~loc ~attrs (map_constant x)
@@ -327,6 +330,10 @@ module E = struct
         (map_opt (sub.expr sub) def)
         (sub.pat sub p) (sub.expr sub e)
     | Pexp_function _ -> assert false
+    | Pexp_apply ({pexp_desc = Pexp_ident tag_name}, _args)
+      when has_jsx_attribute () ->
+      let attrs = attrs |> List.filter (fun ({txt}, _) -> txt <> "JSX") in
+      jsx_unary_element ~loc ~attrs tag_name []
     | Pexp_apply (e, l) ->
       let e =
         match (e.pexp_desc, l) with
@@ -376,7 +383,7 @@ module E = struct
     | Pexp_tuple el -> tuple ~loc ~attrs (List.map (sub.expr sub) el)
     (* <></> *)
     | Pexp_construct ({txt = Longident.Lident "[]" | Longident.Lident "::"}, _)
-      when attrs |> List.exists (fun ({txt}, _) -> txt = "JSX") ->
+      when has_jsx_attribute () ->
       let attrs = attrs |> List.filter (fun ({txt}, _) -> txt <> "JSX") in
       (* TODO: support spread *)
       jsx_fragment ~loc ~attrs loc.loc_start

compiler/ml/ast_mapper_to0.ml

@@ -281,6 +281,9 @@ module M = struct
 end
 
 module E = struct
+  let jsx_attr sub =
+    sub.attribute sub (Location.mknoloc "JSX", Parsetree.PStr [])
+
   (* Value expressions for the core language *)
 
   let map sub {pexp_loc = loc; pexp_desc = desc; pexp_attributes = attrs} =
@@ -420,11 +423,27 @@ module E = struct
       in
       let list_expr = Ast_helper.Exp.make_list_expression loc xs None in
       let mapped = sub.expr sub list_expr in
-      let jsx_attr =
-        sub.attribute sub (Location.mknoloc "JSX", Parsetree.PStr [])
+
+      {mapped with pexp_attributes = jsx_attr sub :: attrs}
+    | Pexp_jsx_unary_element
+        {
+          jsx_unary_element_tag_name = tag_name;
+          jsx_unary_element_props = _props;
+        } ->
+      let tag_ident = map_loc sub tag_name in
+      let children_expr =
+        Ast_helper0.Exp.construct ~loc {txt = Lident "()"; loc} None
+      in
+      let unit_expr =
+        Ast_helper0.Exp.construct ~loc:!Ast_helper0.default_loc
+          {txt = Lident "()"; loc = !Ast_helper0.default_loc}
+          None
       in
-      {mapped with pexp_attributes = jsx_attr :: attrs}
-    | Pexp_jsx_unary_element _ -> failwith "TODO: Pexp_jsx_unary_element 1"
+      apply ~loc ~attrs:(jsx_attr sub :: attrs) (ident tag_ident)
+        [
+          (Asttypes.Noloc.Labelled "children", children_expr);
+          (Asttypes.Noloc.Nolabel, unit_expr);
+        ]
     | Pexp_jsx_container_element _ ->
       failwith "TODO: Pexp_jsx_container_element 1"
 end