[ruby/prism] Fix %Q with newline delimiter and heredoc interpolation

The lexer did not jump to the `heredoc_end`, causing the heredoc end delimiter
to be parsed twice.

Normally the heredocs get flushed when a newline is encountered. But because
the newline is part of the string delimiter, that codepath is not taken.

Fixes [Bug #21758]

ruby/prism@7440eb4b11

Author: Earlopain

prism/prism.c

@@ -11612,6 +11612,13 @@ parser_lex(pm_parser_t *parser) {
                         LEX(PM_TOKEN_LABEL_END);
                     }
 
+                    // When the delimiter itself is a newline, we won't
+                    // get a chance to flush heredocs in the usual places since
+                    // the newline is already consumed.
+                    if (term == '\n' && parser->heredoc_end) {
+                        parser_flush_heredoc_end(parser);
+                    }
+
                     lex_state_set(parser, PM_LEX_STATE_END);
                     lex_mode_pop(parser);
                     LEX(PM_TOKEN_STRING_END);

test/prism/errors/heredoc_percent_q_newline_delimiter.txt

@@ -0,0 +1,11 @@
+%q
+#{<<B}
+B
+^ unexpected constant, expecting end-of-input
+
+<<A; %q
+A
+#{<<B}
+B
+^ unexpected constant, expecting end-of-input
+

test/prism/fixtures/heredoc_percent_q_newline_delimiter.txt

@@ -0,0 +1,22 @@
+%Q
+#{<<B}
+B
+
+%
+#{<<B}
+B
+
+<<A; %Q
+A
+#{<<B}
+B
+
+<<A; %
+A
+#{<<B}
+B
+
+# \r\n
+%Q
+#{<<B}
+B

test/prism/ruby/parser_test.rb

@@ -62,6 +62,9 @@ class ParserTest < TestCase
       "alias.txt",
       "seattlerb/bug_215.txt",
 
+      # %Q with newline delimiter and heredoc interpolation
+      "heredoc_percent_q_newline_delimiter.txt",
+
       # 1.. && 2
       "ranges.txt",
 

test/prism/ruby/ruby_parser_test.rb

@@ -37,6 +37,7 @@ class RubyParserTest < TestCase
       "alias.txt",
       "dsym_str.txt",
       "dos_endings.txt",
+      "heredoc_percent_q_newline_delimiter.txt",
       "heredocs_with_fake_newlines.txt",
       "heredocs_with_ignored_newlines.txt",
       "method_calls.txt",