Add "" and `` in string literals.

CHANGELOG.md

@@ -24,6 +24,7 @@ New features
 Enhancements
 ------------
 
+* Two double quotes (`""`) in a string literal now maps to `"`; two back-ticks (``` `` ```) in a literal string now maps to `` ` ``.
 * Added `Engine::register_type_with_name_raw` to register a custom type based on a fully-qualified type path.
 * Added `into_array` and `into_typed_array` for `Dynamic`.
 * Added `FnPtr::call` and `FnPtr::call_within_context` to simplify calling a function pointer.

src/tokenizer.rs

@@ -1175,6 +1175,15 @@ pub fn parse_string_literal(
                 result.push(next_char)
             }
 
+            // Double wrapper
+            _ if termination_char == next_char
+                && escape.is_empty()
+                && stream.peek_next().map_or(false, |c| c == termination_char) =>
+            {
+                eat_next(stream, pos);
+                result.push(termination_char)
+            }
+
             // Close wrapper
             _ if termination_char == next_char && escape.is_empty() => {
                 state.is_within_text_terminated_by = None;

tests/string.rs

@@ -8,6 +8,10 @@ fn test_string() -> Result<(), Box<EvalAltResult>> {
         engine.eval::<String>(r#""Test string: \u2764""#)?,
         "Test string: ❤"
     );
+    assert_eq!(
+        engine.eval::<String>(r#""Test string: ""\u2764""""#)?,
+        r#"Test string: "❤""#
+    );
     assert_eq!(
         engine.eval::<String>("\"Test\rstring: \\u2764\"")?,
         "Test\rstring: ❤"
@@ -24,6 +28,10 @@ fn test_string() -> Result<(), Box<EvalAltResult>> {
         engine.eval::<String>("     `Test string: \\u2764\nhello,\\nworld!`")?,
         "Test string: \\u2764\nhello,\\nworld!"
     );
+    assert_eq!(
+        engine.eval::<String>(r#"     `Test string: \\u2764\n``hello``,\\n"world"!`"#)?,
+        r#"Test string: \\u2764\n`hello`,\\n"world"!"#
+    );
     assert_eq!(
         engine.eval::<String>("     `\nTest string: \\u2764\nhello,\\nworld!`")?,
         "Test string: \\u2764\nhello,\\nworld!"