[ruby/yarp] fix: StatementsNode with out-of-order body nodes

The presence of the heredocs in this snippet with invalid syntax:

    for <<A + <<B
    A
    B

causes the MissingNode to have a location after other nodes in the
list, resulting in a StatementsNode with inverted start and end
locations:

      [ForNode(0...14)(
         MultiWriteNode(4...7)([InterpolatedStringNode(4...7)((4...7), [], (14...16))], nil, nil, nil, nil),
         MissingNode(16...16)(),
    >    StatementsNode(16...14)(
           [MissingNode(16...16)(), InterpolatedStringNode(10...13)((10...13), [], (16...18)), MissingNode(13...14)()]
         ),
         (0...3),
         (16...16),
         nil,
         (14...14)
       )]

which failed an assertion during serialization.

With this fix, the node's locations are:

      [ForNode(0...14)(
         MultiWriteNode(4...7)([InterpolatedStringNode(4...7)((4...7), [], (14...16))], nil, nil, nil, nil),
         MissingNode(16...16)(),
    >    StatementsNode(10...16)(
           [MissingNode(16...16)(), InterpolatedStringNode(10...13)((10...13), [], (16...18)), MissingNode(13...14)()]
         ),
         (0...3),
         (16...16),
         nil,
         (14...14)
       )]

Found by the fuzzer.

https://github.com/ruby/yarp/commit/09bcedc05e

2 files changed, 10 insertions, 2 deletions

diff --git a/test/yarp/fuzzer_test.rb b/test/yarp/fuzzer_test.rb
index 384f3ff0d2..d75d1422f0 100644
--- a/test/yarp/fuzzer_test.rb
+++ b/test/yarp/fuzzer_test.rb
@@ -22,5 +22,11 @@ module YARP
     snippet "incomplete escaped list", "%w[\\"
     snippet "incomplete escaped regex", "/a\\"
     snippet "unterminated heredoc with unterminated escape at end of file", "<<A\n\\"
+
+    snippet "statements node with multiple heredocs", <<~EOF
+      for <<A + <<B
+      A
+      B
+    EOF
   end
 end
diff --git a/yarp/yarp.c b/yarp/yarp.c
index 6fd16e16fc..40d8d3c972 100644
--- a/yarp/yarp.c
+++ b/yarp/yarp.c
@@ -3908,12 +3908,14 @@ yp_statements_node_location_set(yp_statements_node_t *node, const uint8_t *start
 // Append a new node to the given StatementsNode node's body.
 static void
 yp_statements_node_body_append(yp_statements_node_t *node, yp_node_t *statement) {
-    if (yp_statements_node_body_length(node) == 0) {
+    if (yp_statements_node_body_length(node) == 0 || statement->location.start < node->base.location.start) {
         node->base.location.start = statement->location.start;
     }
+    if (statement->location.end > node->base.location.end) {
+        node->base.location.end = statement->location.end;
+    }
 
     yp_node_list_append(&node->body, statement);
-    node->base.location.end = statement->location.end;
 
     // Every statement gets marked as a place where a newline can occur.
     statement->flags |= YP_NODE_FLAG_NEWLINE;