[ruby/yarp] handle missing HEREDOC endline at start of heredoc

https://github.com/ruby/yarp/commit/7b72493b6d

test/snapshots/heredoc_with_escaped_newline_at_start.txt

@@ -0,0 +1,45 @@
+ProgramNode(0...62)(
+  [],
+  StatementsNode(0...62)(
+    [CallNode(0...25)(
+       InterpolatedStringNode(0...9)((0...9), [], (27...34)),
+       (9...10),
+       (10...14),
+       nil,
+       ArgumentsNode(15...25)(
+         [RegularExpressionNode(15...21)(
+            (15...16),
+            (16...20),
+            (20...21),
+            "^ {",
+            0
+          ),
+          StringNode(23...25)((23...24), (24...24), (24...25), "")]
+       ),
+       nil,
+       nil,
+       0,
+       "gsub"
+     ),
+     CallNode(37...62)(
+       InterpolatedStringNode(37...46)((37...46), [], (65...73)),
+       (46...47),
+       (47...51),
+       nil,
+       ArgumentsNode(52...62)(
+         [RegularExpressionNode(52...58)(
+            (52...53),
+            (53...57),
+            (57...58),
+            "^ {",
+            0
+          ),
+          StringNode(60...62)((60...61), (61...61), (61...62), "")]
+       ),
+       nil,
+       nil,
+       0,
+       "gsub"
+     )]
+  )
+)

yarp/yarp.c

@@ -5653,13 +5653,23 @@ parser_lex(yp_parser_t *parser) {
                         break;
                     case '\\':
                         if (peek_at(parser, 1) == '\n') {
-                            yp_newline_list_append(&parser->newline_list, parser->current.end + 1);
-                            parser->current.end += 2;
-                            space_seen = true;
-                        } else if (parser->current.end + 2 < parser->end && peek_at(parser, 1) == '\r' && peek_at(parser, 2) == '\n') {
-                            yp_newline_list_append(&parser->newline_list, parser->current.end + 2);
-                            parser->current.end += 3;
-                            space_seen = true;
+                            if (parser->heredoc_end) {
+                                parser->current.end = parser->heredoc_end;
+                                parser->heredoc_end = NULL;
+                            } else {
+                                yp_newline_list_append(&parser->newline_list, parser->current.end + 1);
+                                parser->current.end += 2;
+                                space_seen = true;
+                            }
+                        } else if (peek_at(parser, 1) == '\r' && peek_at(parser, 2) == '\n') {
+                            if (parser->heredoc_end) {
+                                parser->current.end = parser->heredoc_end;
+                                parser->heredoc_end = NULL;
+                            } else {
+                                yp_newline_list_append(&parser->newline_list, parser->current.end + 2);
+                                parser->current.end += 3;
+                                space_seen = true;
+                            }
                         } else if (yp_char_is_inline_whitespace(*parser->current.end)) {
                             parser->current.end += 2;
                         } else {