Simplify string literal abstraction

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

Author: cknitt

compiler/ml/ast_mapper_from0.ml

@@ -88,11 +88,6 @@ let has_template_attr attrs =
 let remove_template_attr attrs =
   List.filter (fun ({Location.txt}, _) -> txt <> "res.template") attrs
 
-let decode_js_string ~loc s =
-  match String_literal.decode_js_escapes s with
-  | Some s -> s
-  | None -> Location.raise_errorf ~loc "Invalid string escape sequence"
-
 let normalize_ppx_semantic_string semantic =
   let length = String.length semantic in
   let buffer = Buffer.create length in

compiler/ml/string_literal.ml

@@ -240,14 +240,6 @@ let template_from_source source : template_segment option =
 let template_from_semantic semantic : template_segment =
   Valid {source = encode_js_template semantic; semantic}
 
-let string_as_template (literal : string_literal) : template_segment =
-  match literal with
-  | Valid {source; semantic} -> (
-    match decode_js_template_escapes source with
-    | Some decoded when decoded = semantic -> Valid {source; semantic}
-    | _ -> template_from_semantic semantic)
-  | Invalid_source _ -> template_from_semantic ""
-
 let concat_template segments =
   let source = String.concat "" (List.map source segments) in
   let semantic = String.concat "" (List.map semantic segments) in

compiler/ml/string_literal.mli

@@ -3,7 +3,9 @@ type template_kind
 type 'kind payload
 
 type string_literal = string_kind payload
-(** A validated ordinary JavaScript string body and its semantic value. *)
+(** An ordinary JavaScript string body and its semantic value. Parser error
+    recovery may retain an invalid source spelling with an empty placeholder
+    semantic value. *)
 
 type template_segment = template_kind payload
 (** A validated JavaScript template segment and its semantic value. *)
@@ -52,10 +54,6 @@ val template_from_source : string -> template_segment option
 val template_from_semantic : string -> template_segment
 (** Construct a template segment with canonical source spelling. *)
 
-val string_as_template : string_literal -> template_segment
-(** Convert an ordinary string payload to a template segment, preserving its
-    source spelling when that spelling has the same template semantics. *)
-
 val concat_template : template_segment list -> template_segment
 (** Concatenate template segments, preserving their combined source spelling
     when it still decodes to the combined semantic value and otherwise using a

tests/ounit_tests/ounit_string_literal_tests.ml

@@ -407,19 +407,6 @@ let suites =
          ( "template segments reject interpolation openers" >:: fun _ ->
            assert_invalid_template "${value}";
            assert_template_decoded ~encoded:"\\${value}" ~expected:"${value}" );
-         ( "ordinary strings convert safely to template segments" >:: fun _ ->
-           let preserved =
-             String_literal.string_from_source {|\x61|}
-             |> Option.get |> String_literal.string_as_template
-           in
-           OUnit.assert_equal ~printer:(Printf.sprintf "%S") {|\x61|}
-             (String_literal.source preserved);
-           let escaped_interpolation =
-             String_literal.string_from_source "${value}"
-             |> Option.get |> String_literal.string_as_template
-           in
-           OUnit.assert_equal ~printer:(Printf.sprintf "%S") "\\${value}"
-             (String_literal.source escaped_interpolation) );
          ( "ordinary literals become semantic strings" >:: fun _ ->
            assert_parsed_string ~source:{|\x61\n\uD83D\uDE00|}
              ~expected_semantic:"a\n😀" );