Fix string delimiter with "@" confused for embedded variable (#1521)

Author: jemmaissroff

src/yarp.c

@@ -5801,7 +5801,7 @@ lex_interpolation(yp_parser_t *parser, const uint8_t *pound) {
             // If we didn't get an valid interpolation, then this is just regular
             // string content. This is like if we get "#@-". In this case the caller
             // should keep lexing.
-            parser->current.end = variable;
+            parser->current.end = pound + 1;
             return YP_TOKEN_NOT_PROVIDED;
         }
         case '$':

test/yarp/errors_test.rb

@@ -152,6 +152,13 @@ def test_unterminated_string
       ]
     end
 
+    def test_incomplete_instance_var_string
+      assert_errors expression('%@#@@#'), '%@#@@#', [
+        ["Incomplete instance variable", 4..5],
+        ["Expected a newline or semicolon after the statement", 4..4]
+      ]
+    end
+
     def test_unterminated_s_symbol
       assert_errors expression("%s[abc"), "%s[abc", [
         ["Expected a closing delimiter for the dynamic symbol", 3..3]

test/yarp/fixtures/strings.txt

@@ -99,3 +99,7 @@
 ?a "a"
 
 %Q{abc}
+
+%^#$^#
+
+%@#@#