Fix escapes in raw template payloads

CHANGELOG.md

@@ -36,6 +36,7 @@
 
 #### :bug: Bug fix
 
+- Fix escaped backticks and interpolation openers in backquoted `%raw`, `%ffi`, and `%re` payloads leaking into emitted JavaScript. https://github.com/rescript-lang/rescript/pull/8630
 - Fix the side-effect analysis treating bigint exponentiation and bounds-checked array and string reads as pure, which let dead-code elimination drop an unused one that throws: `let _ = 2n ** -1n` no longer raised. https://github.com/rescript-lang/rescript/pull/8617
 - Preserve record field `@as` annotations when formatting object types containing spreads. https://github.com/rescript-lang/rescript/pull/8619
 - Fix excessive parentheses and indentation in function assignments to refs, align record and array assignment formatting across refs and fields, and preserve function return-type parentheses and consistent JSX fragment layout in callbacks. https://github.com/rescript-lang/rescript/pull/8611

compiler/ml/ast_payload.ml

@@ -193,8 +193,8 @@ let raw_as_string_exp_exn ~(kind : Js_raw_info.raw_kind) ?is_function (x : t) :
                   _ );
           };
         ] ->
-      Some
-        (source.txt, Bs_flow_ast_utils.flow_deli_offset (Some "js"), expression)
+      let source = String_literal.decode_raw_template_source source.txt in
+      Some (source, Bs_flow_ast_utils.flow_deli_offset (Some "js"), expression)
     | PStr
         [
           {

compiler/ml/string_literal.ml

@@ -219,6 +219,39 @@ let decode_js_escapes =
 let decode_js_template_escapes =
   decode_js_escapes_with ~normalize_template_line_endings:true
 
+let decode_raw_template_source source =
+  let length = String.length source in
+  let buffer = Buffer.create length in
+  let rec loop index =
+    if index < length then
+      match String.unsafe_get source index with
+      | '\\' when index + 1 < length -> (
+        match String.unsafe_get source (index + 1) with
+        | ('\\' | '$' | '`') as escaped ->
+          Buffer.add_char buffer escaped;
+          loop (index + 2)
+        | '\n' -> loop (index + 2)
+        | '\r' ->
+          if index + 2 < length && String.unsafe_get source (index + 2) = '\n'
+          then loop (index + 3)
+          else loop (index + 2)
+        | '\226'
+          when index + 3 < length
+               && String.unsafe_get source (index + 2) = '\128'
+               && (String.unsafe_get source (index + 3) = '\168'
+                  || String.unsafe_get source (index + 3) = '\169') ->
+          loop (index + 4)
+        | escaped ->
+          Buffer.add_char buffer '\\';
+          Buffer.add_char buffer escaped;
+          loop (index + 2))
+      | character ->
+        Buffer.add_char buffer character;
+        loop (index + 1)
+  in
+  loop 0;
+  Buffer.contents buffer
+
 type encode_js_mode = String | Template
 
 let encode_js mode s =

compiler/ml/string_literal.mli

@@ -55,6 +55,12 @@ val decode_js_template_escapes : string -> string option
     as required by JavaScript template-literal semantics. Returns [None] for
     malformed escapes, malformed UTF-8, or an unescaped interpolation opener. *)
 
+val decode_raw_template_source : string -> string
+(** Remove the escapes that protect the surrounding ReScript template syntax
+    from JavaScript source embedded in a [raw], [ffi], or [re] extension.
+    Backslashes belonging to the embedded JavaScript, such as [\\n], are
+    preserved. *)
+
 val encode_js_string : string -> string
 (** Encode a semantic UTF-8 string as a canonical JavaScript string-literal
     body. *)

tests/ounit_tests/ounit_string_literal_tests.ml

@@ -407,6 +407,14 @@ let suites =
          ( "template segments reject interpolation openers" >:: fun _ ->
            assert_invalid_template "${value}";
            assert_template_decoded ~encoded:"\\${value}" ~expected:"${value}" );
+         ( "raw templates decode only their surrounding syntax escapes"
+         >:: fun _ ->
+           OUnit.assert_equal ~printer:(Printf.sprintf "%S")
+             {e|`${"hello"}` with \n and \t|e}
+             (String_literal.decode_raw_template_source
+                {e|\`\${"hello"}\` with \n and \t|e});
+           OUnit.assert_equal ~printer:(Printf.sprintf "%S") "continued"
+             (String_literal.decode_raw_template_source "con\\\r\ntinued") );
          ( "ordinary literals become semantic strings" >:: fun _ ->
            assert_parsed_string ~source:{|\x61\n\uD83D\uDE00|}
              ~expected_semantic:"a\n😀" );

tests/tests/src/gbk.mjs

@@ -9,6 +9,6 @@ console.log("你好");
 
 console.log("你好你好");
 
-console.log("\\u4f60\\u597d");
+console.log("\u4f60\u597d");
 
 /*  Not a pure module */

tests/tests/src/raw_output_test.mjs

@@ -9,6 +9,9 @@ function mk(fn) {
 
 console.log(1);
 
+var issue6236 = `${"hello"}`;
+;
+
 export {
   mk,
 }

tests/tests/src/raw_output_test.res

@@ -12,3 +12,9 @@ let mk = fn => fn()
 mk(%raw(`(_)=> console.log('should works')`))
 
 Console.log((() => 1)())
+
+// GitHub issue #6236: escapes needed for the surrounding ReScript template
+// must not survive in the emitted raw JavaScript.
+%%raw(`
+var issue6236 = \`\${"hello"}\`;
+`)

tests/tests/src/unsafe_ppx_test.mjs

@@ -5,7 +5,7 @@ import * as Pervasives from "@rescript/runtime/lib/es6/Pervasives.mjs";
 import * as Test_utils from "./test_utils.mjs";
 import * as Ffi_js_test from "./ffi_js_test.mjs";
 
-let x = "\\x01\\x02\\x03";
+let x = "\x01\x02\x03";
 
 let max = Math.max;