[BUGFIX] Move unescape parsing to separate function (#1108)

Fixes #1107 
```
FunctionRuntimeException: Runtime error occurred when executing the function %from_json: Invalid control character
```

docs/source/config_reference/scripting/scripting_functions.rst

@@ -710,6 +710,24 @@ titlecase
 :description:
   Capitalize each word in the string.
 
+unescape
+~~~~~~~~
+:spec: ``unescape(string: String) -> String``
+
+:description:
+  Unescape symbols like newlines or tabs to their true form.
+
+:usage:
+
+.. code-block:: python
+
+   {
+     %unescape( "Hello\nWorld" )
+   }
+
+   # Hello
+   # World
+
 upper
 ~~~~~
 :spec: ``upper(string: String) -> String``

src/ytdl_sub/script/functions/string_functions.py

@@ -143,3 +143,22 @@ class StringFunctions:
             length=length,
             char=String("0"),
         )
+
+    @staticmethod
+    def unescape(string: String) -> String:
+        """
+        :description:
+          Unescape symbols like newlines or tabs to their true form.
+
+        :usage:
+
+        .. code-block:: python
+
+           {
+             %unescape( "Hello\\nWorld" )
+           }
+
+           # Hello
+           # World
+        """
+        return String(string.value.encode("utf-8").decode("unicode_escape"))

src/ytdl_sub/script/parser.py

@@ -301,16 +301,8 @@ class _Parser:
                 self._pos += len(str_open_token)
                 return String(value=string_value)
 
-            # Read literal "\n" as newlines
-            if self._read(increment_pos=False, length=2) == "\\n":
-                string_value += "\n"
-                self._pos += 2
-            elif self._read(increment_pos=False, length=2) == "\\t":
-                string_value += "\t"
-                self._pos += 2
-            else:
-                self._pos += 1
-                string_value += ch
+            self._pos += 1
+            string_value += ch
 
         raise STRINGS_NOT_CLOSED
 

tests/unit/script/functions/test_string_functions.py

@@ -129,18 +129,18 @@ class TestNumericFunctions:
     @pytest.mark.parametrize(
         "input_string, split, max_split, expected_output",
         [
-            ("no splits", " | ", None, ["no splits"]),
-            ("one | split", " | ", None, ["one", "split"]),
-            ("max | split | one", " | ", 1, ["max", "split | one"]),
-            ("multiline\ndescription", "\\n", None, ["multiline", "description"]),
+            ("no splits", "' | '", None, ["no splits"]),
+            ("one | split", "' | '", None, ["one", "split"]),
+            ("max | split | one", "' | '", 1, ["max", "split | one"]),
+            ("multiline\ndescription", "%unescape('\\n')", None, ["multiline", "description"]),
         ],
     )
     def test_split(
         self, input_string: str, split: str, max_split: Optional[int], expected_output: List[str]
     ):
         if max_split:
-            output = single_variable_output(f"{{%split('{input_string}', '{split}', {max_split})}}")
+            output = single_variable_output(f"{{%split('{input_string}', {split}, {max_split})}}")
         else:
-            output = single_variable_output(f"{{%split('{input_string}', '{split}')}}")
+            output = single_variable_output(f"{{%split('{input_string}', {split})}}")
 
         assert output == expected_output

tests/unit/script/types/test_string.py

@@ -46,14 +46,22 @@ class TestString:
             ("{%string('backslash \\\\')}", "backslash \\\\"),
             ("{%string('''triple quote with \" ' \\''')}", "triple quote with \" ' \\"),
             ('{%string("""triple quote with " \' \\""")}', "triple quote with \" ' \\"),
-            ("{%string('literal \\n newlines')}", "literal \n newlines"),
             ("{%string('supports \t tabs')}", "supports \t tabs"),
-            ("{%string('literal \\t tabs')}", "literal \t tabs"),
         ],
     )
     def test_string(self, string: str, expected_string: str):
         assert single_variable_output(string) == expected_string
 
+    @pytest.mark.parametrize(
+        "string, expected_string",
+        [
+            ("{%unescape('literal \\n newlines')}", "literal \n newlines"),
+            ("{%unescape('literal \\t tabs')}", "literal \t tabs"),
+        ],
+    )
+    def test_unescape(self, string: str, expected_string: str):
+        assert single_variable_output(string) == expected_string
+
     def test_null_is_empty_string(self):
         assert Script({"out": "{%string(null)}"}).resolve() == ScriptOutput({"out": String("")})