Preserve the delimiter of strings in concatenation.

CHANGELOG.md

@@ -28,6 +28,7 @@
 
 #### :bug: Bug Fix
 
+- Fix issue where characters such as newlines would be escaped in a template string expression https://github.com/rescript-lang/rescript-compiler/issues/5638
 - Fix issue where pipe `->` processing eats up attributes https://github.com/rescript-lang/rescript-compiler/pull/5581
 - Fix issue where cancelling `rescript build` would leave the `.bsb.lock` file behind and block future builds
 

jscomp/core/js_exp_make.ml

@@ -511,15 +511,25 @@ let function_length ?comment (e : t) : t =
 *)
 
 let rec string_append ?comment (e : t) (el : t) : t =
+  let concat a b ~delim =
+    { e with expression_desc = Str { txt = a ^ b; delim } }
+  in
   match (e.expression_desc, el.expression_desc) with
-  | Str { txt = a }, String_append ({ expression_desc = Str { txt = b } }, c) ->
-      string_append ?comment (str (a ^ b)) c
-  | String_append (c, { expression_desc = Str { txt = b } }), Str { txt = a } ->
-      string_append ?comment c (str (b ^ a))
-  | ( String_append (a, { expression_desc = Str { txt = b } }),
-      String_append ({ expression_desc = Str { txt = c } }, d) ) ->
-      string_append ?comment (string_append a (str (b ^ c))) d
-  | Str { txt = a }, Str { txt = b } -> str ?comment (a ^ b)
+  | ( Str { txt = a; delim },
+      String_append ({ expression_desc = Str { txt = b; delim = delim_ } }, c) )
+    when delim = delim_ ->
+      string_append ?comment (concat a b ~delim) c
+  | ( String_append (c, { expression_desc = Str { txt = b; delim } }),
+      Str { txt = a; delim = delim_ } )
+    when delim = delim_ ->
+      string_append ?comment c (concat b a ~delim)
+  | ( String_append (a, { expression_desc = Str { txt = b; delim } }),
+      String_append ({ expression_desc = Str { txt = c; delim = delim_ } }, d) )
+    when delim = delim_ ->
+      string_append ?comment (string_append a (concat b c ~delim)) d
+  | Str { txt = a; delim }, Str { txt = b; delim = delim_ } when delim = delim_
+    ->
+      { (concat a b ~delim) with comment }
   | _, _ -> { comment; expression_desc = String_append (e, el) }
 
 let obj ?comment properties : t =

jscomp/test/template.js

@@ -0,0 +1,12 @@
+'use strict';
+
+
+var bla2 = "";
+
+function concat(param) {
+  return "\n    display:\r flex;\n   " + bla2 + "";
+}
+
+exports.bla2 = bla2;
+exports.concat = concat;
+/* No side effect */

jscomp/test/template.res

@@ -0,0 +1,9 @@
+let bla2 = ``
+
+let concat = () => {
+  let bla = `
+    display:\r flex;
+   `
+
+  `${bla}${bla2}`
+}

lib/4.06.1/unstable/js_compiler.ml

@@ -77523,15 +77523,25 @@ let function_length ?comment (e : t) : t =
 *)
 
 let rec string_append ?comment (e : t) (el : t) : t =
+  let concat a b ~delim =
+    { e with expression_desc = Str { txt = a ^ b; delim } }
+  in
   match (e.expression_desc, el.expression_desc) with
-  | Str { txt = a }, String_append ({ expression_desc = Str { txt = b } }, c) ->
-      string_append ?comment (str (a ^ b)) c
-  | String_append (c, { expression_desc = Str { txt = b } }), Str { txt = a } ->
-      string_append ?comment c (str (b ^ a))
-  | ( String_append (a, { expression_desc = Str { txt = b } }),
-      String_append ({ expression_desc = Str { txt = c } }, d) ) ->
-      string_append ?comment (string_append a (str (b ^ c))) d
-  | Str { txt = a }, Str { txt = b } -> str ?comment (a ^ b)
+  | ( Str { txt = a; delim },
+      String_append ({ expression_desc = Str { txt = b; delim = delim_ } }, c) )
+    when delim = delim_ ->
+      string_append ?comment (concat a b ~delim) c
+  | ( String_append (c, { expression_desc = Str { txt = b; delim } }),
+      Str { txt = a; delim = delim_ } )
+    when delim = delim_ ->
+      string_append ?comment c (concat b a ~delim)
+  | ( String_append (a, { expression_desc = Str { txt = b; delim } }),
+      String_append ({ expression_desc = Str { txt = c; delim = delim_ } }, d) )
+    when delim = delim_ ->
+      string_append ?comment (string_append a (concat b c ~delim)) d
+  | Str { txt = a; delim }, Str { txt = b; delim = delim_ } when delim = delim_
+    ->
+      { (concat a b ~delim) with comment }
   | _, _ -> { comment; expression_desc = String_append (e, el) }
 
 let obj ?comment properties : t =

lib/4.06.1/unstable/js_playground_compiler.ml

@@ -77523,15 +77523,25 @@ let function_length ?comment (e : t) : t =
 *)
 
 let rec string_append ?comment (e : t) (el : t) : t =
+  let concat a b ~delim =
+    { e with expression_desc = Str { txt = a ^ b; delim } }
+  in
   match (e.expression_desc, el.expression_desc) with
-  | Str { txt = a }, String_append ({ expression_desc = Str { txt = b } }, c) ->
-      string_append ?comment (str (a ^ b)) c
-  | String_append (c, { expression_desc = Str { txt = b } }), Str { txt = a } ->
-      string_append ?comment c (str (b ^ a))
-  | ( String_append (a, { expression_desc = Str { txt = b } }),
-      String_append ({ expression_desc = Str { txt = c } }, d) ) ->
-      string_append ?comment (string_append a (str (b ^ c))) d
-  | Str { txt = a }, Str { txt = b } -> str ?comment (a ^ b)
+  | ( Str { txt = a; delim },
+      String_append ({ expression_desc = Str { txt = b; delim = delim_ } }, c) )
+    when delim = delim_ ->
+      string_append ?comment (concat a b ~delim) c
+  | ( String_append (c, { expression_desc = Str { txt = b; delim } }),
+      Str { txt = a; delim = delim_ } )
+    when delim = delim_ ->
+      string_append ?comment c (concat b a ~delim)
+  | ( String_append (a, { expression_desc = Str { txt = b; delim } }),
+      String_append ({ expression_desc = Str { txt = c; delim = delim_ } }, d) )
+    when delim = delim_ ->
+      string_append ?comment (string_append a (concat b c ~delim)) d
+  | Str { txt = a; delim }, Str { txt = b; delim = delim_ } when delim = delim_
+    ->
+      { (concat a b ~delim) with comment }
   | _, _ -> { comment; expression_desc = String_append (e, el) }
 
 let obj ?comment properties : t =

lib/4.06.1/whole_compiler.ml

@@ -253491,15 +253491,25 @@ let function_length ?comment (e : t) : t =
 *)
 
 let rec string_append ?comment (e : t) (el : t) : t =
+  let concat a b ~delim =
+    { e with expression_desc = Str { txt = a ^ b; delim } }
+  in
   match (e.expression_desc, el.expression_desc) with
-  | Str { txt = a }, String_append ({ expression_desc = Str { txt = b } }, c) ->
-      string_append ?comment (str (a ^ b)) c
-  | String_append (c, { expression_desc = Str { txt = b } }), Str { txt = a } ->
-      string_append ?comment c (str (b ^ a))
-  | ( String_append (a, { expression_desc = Str { txt = b } }),
-      String_append ({ expression_desc = Str { txt = c } }, d) ) ->
-      string_append ?comment (string_append a (str (b ^ c))) d
-  | Str { txt = a }, Str { txt = b } -> str ?comment (a ^ b)
+  | ( Str { txt = a; delim },
+      String_append ({ expression_desc = Str { txt = b; delim = delim_ } }, c) )
+    when delim = delim_ ->
+      string_append ?comment (concat a b ~delim) c
+  | ( String_append (c, { expression_desc = Str { txt = b; delim } }),
+      Str { txt = a; delim = delim_ } )
+    when delim = delim_ ->
+      string_append ?comment c (concat b a ~delim)
+  | ( String_append (a, { expression_desc = Str { txt = b; delim } }),
+      String_append ({ expression_desc = Str { txt = c; delim = delim_ } }, d) )
+    when delim = delim_ ->
+      string_append ?comment (string_append a (concat b c ~delim)) d
+  | Str { txt = a; delim }, Str { txt = b; delim = delim_ } when delim = delim_
+    ->
+      { (concat a b ~delim) with comment }
   | _, _ -> { comment; expression_desc = String_append (e, el) }
 
 let obj ?comment properties : t =