From cdcc3a50fe825516e7c6f08e073d030a61f37fd1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=89tienne=20Barri=C3=A9?= <etienne.barrie@gmail.com>
Date: Thu, 27 Nov 2025 16:12:17 +0100
Subject: [PATCH 1/2] Test and restore behavior around to_json changing depth

When serializing an Array, and one of the elements of the Array requires
calling `to_json`, if the depth is changed, it will be used for the next
entries, which wasn't the case before
5abd43490714460e1ec1fa382f82a09485eed563, and is not the case with
TruffleRuby and JRuby.

Additionally, with TruffleRuby and JRuby the state's depth after the
`to_json` call is used to close the Array, which isn't the case with
CRuby.
---
 ext/json/ext/generator/generator.c |  2 ++
 test/json/json_generator_test.rb   | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/ext/json/ext/generator/generator.c b/ext/json/ext/generator/generator.c
index 6ece9f05..58d22ea7 100644
--- a/ext/json/ext/generator/generator.c
+++ b/ext/json/ext/generator/generator.c
@@ -1295,6 +1295,8 @@ static void generate_json_fallback(FBuffer *buffer, struct generate_json_data *d
     VALUE tmp;
     if (rb_respond_to(obj, i_to_json)) {
         tmp = rb_funcall(obj, i_to_json, 1, vstate_get(data));
+        GET_STATE(data->vstate);
+        data->depth = state->depth;
         Check_Type(tmp, T_STRING);
         fbuffer_append_str(buffer, tmp);
     } else {
diff --git a/test/json/json_generator_test.rb b/test/json/json_generator_test.rb
index c01ed678..fa102f06 100755
--- a/test/json/json_generator_test.rb
+++ b/test/json/json_generator_test.rb
@@ -321,6 +321,30 @@ def test_allow_nan
     end
   end
 
+  def test_depth_bad_to_json
+    obj = Object.new
+    def obj.to_json(state)
+      state.depth += 1
+      "{#{state.object_nl}"\
+        "#{state.indent * state.depth}\"foo\":#{state.space}1#{state.object_nl}"\
+        "#{state.indent * (state.depth - 1)}}"
+    end
+    indent = "  " * 2 if RUBY_ENGINE != "ruby"
+    assert_equal <<~JSON.chomp, JSON.pretty_generate([obj] * 2)
+      [
+        {
+          "foo": 1
+        },
+        {
+            "foo": 1
+          }
+      #{indent}]
+    JSON
+    state = JSON::State.new(object_nl: "\n", array_nl: "\n", space: " ", indent: "  ")
+    state.generate(obj)
+    assert_equal 1, state.depth
+  end
+
   def test_depth
     pretty = { object_nl: "\n", array_nl: "\n", space: " ", indent: "  " }
     state = JSON.state.new(**pretty)

From 6195c2ab03bb98b27d1a255b0a8b9a94251d19e1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=89tienne=20Barri=C3=A9?= <etienne.barrie@gmail.com>
Date: Fri, 28 Nov 2025 15:53:58 +0100
Subject: [PATCH 2/2] Reproduce C ext behavior of ignoring mutated depth in
 arrays

---
 java/src/json/ext/Generator.java      | 4 ++--
 java/src/json/ext/GeneratorState.java | 2 +-
 lib/json/truffle_ruby/generator.rb    | 2 +-
 test/json/json_generator_test.rb      | 8 +++++---
 4 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/java/src/json/ext/Generator.java b/java/src/json/ext/Generator.java
index 78281dbd..0caa6948 100644
--- a/java/src/json/ext/Generator.java
+++ b/java/src/json/ext/Generator.java
@@ -462,10 +462,10 @@ static void generateArray(ThreadContext context, Session session, RubyArray<IRub
             generateFor(context, session, element, buffer);
         }
 
-        int oldDepth = state.decreaseDepth();
+        state.depth = --depth;
         if (!arrayNLEmpty) {
             buffer.write(arrayNLBytes, arrayNLBegin, arrayNLSize);
-            Utils.repeatWrite(buffer, indentUnit, oldDepth);
+            Utils.repeatWrite(buffer, indentUnit, depth);
         }
 
         buffer.write((byte) ']');
diff --git a/java/src/json/ext/GeneratorState.java b/java/src/json/ext/GeneratorState.java
index b12ca2c3..327405a8 100644
--- a/java/src/json/ext/GeneratorState.java
+++ b/java/src/json/ext/GeneratorState.java
@@ -107,7 +107,7 @@ public class GeneratorState extends RubyObject {
     /**
      * The current depth (inside a #to_json call)
      */
-    private int depth = 0;
+    protected int depth = 0;
 
     static final ObjectAllocator ALLOCATOR = GeneratorState::new;
 
diff --git a/lib/json/truffle_ruby/generator.rb b/lib/json/truffle_ruby/generator.rb
index 9ac46cc8..006576cc 100644
--- a/lib/json/truffle_ruby/generator.rb
+++ b/lib/json/truffle_ruby/generator.rb
@@ -626,7 +626,7 @@ def json_transform(state)
               end
               first = false
             }
-            depth = state.depth -= 1
+            state.depth = depth -= 1
             result << state.array_nl
             result << state.indent * depth if indent
             result << ']'
diff --git a/test/json/json_generator_test.rb b/test/json/json_generator_test.rb
index fa102f06..510a946f 100755
--- a/test/json/json_generator_test.rb
+++ b/test/json/json_generator_test.rb
@@ -329,7 +329,6 @@ def obj.to_json(state)
         "#{state.indent * state.depth}\"foo\":#{state.space}1#{state.object_nl}"\
         "#{state.indent * (state.depth - 1)}}"
     end
-    indent = "  " * 2 if RUBY_ENGINE != "ruby"
     assert_equal <<~JSON.chomp, JSON.pretty_generate([obj] * 2)
       [
         {
@@ -338,11 +337,14 @@ def obj.to_json(state)
         {
             "foo": 1
           }
-      #{indent}]
+      ]
     JSON
     state = JSON::State.new(object_nl: "\n", array_nl: "\n", space: " ", indent: "  ")
     state.generate(obj)
-    assert_equal 1, state.depth
+    assert_equal 1, state.depth # FIXME
+    state.depth = 0
+    state.generate([obj])
+    assert_equal 0, state.depth
   end
 
   def test_depth