From f4bd4361d477afb0775cb5b5e04eaf4def42b66f Mon Sep 17 00:00:00 2001
From: Jean Boussier <jean.boussier@gmail.com>
Date: Mon, 15 Jun 2026 16:05:03 +0200
Subject: [PATCH] ResumableParser#partial_value avoid mutating the stacks

Fix: https://github.com/ruby/json/issues/1005

`parser.state.frames` and `parser.state.value_stack` need to
be updated to point to the copy.
---
 ext/json/ext/parser/parser.c       |  3 +++
 test/json/resumable_parser_test.rb | 14 ++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/ext/json/ext/parser/parser.c b/ext/json/ext/parser/parser.c
index 15e79b24..e722a1a7 100644
--- a/ext/json/ext/parser/parser.c
+++ b/ext/json/ext/parser/parser.c
@@ -2496,6 +2496,9 @@ static VALUE cResumableParser_partial_value(VALUE self)
     JSON_ResumableParser *original_parser = ResumableParser_acquire(self, false);
     JSON_ResumableParser parser = *original_parser;
 
+    parser.state.frames = &parser.frames;
+    parser.state.value_stack = &parser.value_stack;
+
     if (parser.value_stack.head == 0) {
         return Qnil;
     }
diff --git a/test/json/resumable_parser_test.rb b/test/json/resumable_parser_test.rb
index bab92c8d..600cd33e 100644
--- a/test/json/resumable_parser_test.rb
+++ b/test/json/resumable_parser_test.rb
@@ -156,6 +156,20 @@ def test_partial_value
     assert_partial_value([1, { "a" => 1, "b" => { "c" => nil } }], '[1, { "a": 1, "b": { "c"')
   end
 
+  def test_partial_value_issue_1005
+    data = <<~JSON
+      [
+      []
+      ]
+    JSON
+    data.each_line do |line|
+      @parser << line
+      @parser.parse
+      @parser.partial_value # This unexpected parse error doesn't happen if we comment this out
+    end
+    assert_equal [[]], @parser.value
+  end
+
   def test_partial_value_missing
     assert_nil @parser.partial_value
   end