3 files changed, 101 insertions, 9 deletions

diff --git a/spec/ruby/core/module/set_temporary_name_spec.rb b/spec/ruby/core/module/set_temporary_name_spec.rb
index 12541374ae..12c1c214dd 100644
--- a/spec/ruby/core/module/set_temporary_name_spec.rb
+++ b/spec/ruby/core/module/set_temporary_name_spec.rb
@@ -108,13 +108,18 @@ ruby_version_is "3.3" do
       m.name.should == "fake_name_2"
     end
 
-    it "does not affect a name of a module nested into an anonymous module with a temporary name" do
-      m = Module.new
-      m::N = Module.new
-      m::N.name.should =~ /\A#<Module:0x\h+>::N\z/
-
-      m.set_temporary_name("foo")
-      m::N.name.should =~ /\A#<Module:0x\h+>::N\z/
+    ruby_bug "#21094", ""..."3.5" do
+      it "also updates a name of a nested module" do
+        m = Module.new
+        m::N = Module.new
+        m::N.name.should =~ /\A#<Module:0x\h+>::N\z/
+
+        m.set_temporary_name "m"
+        m::N.name.should == "m::N"
+
+        m.set_temporary_name nil
+        m::N.name.should == nil
+      end
     end
 
     it "keeps temporary name when assigned in an anonymous module" do
diff --git a/test/ruby/test_module.rb b/test/ruby/test_module.rb
index 5d254452c6..9a21113fe0 100644
--- a/test/ruby/test_module.rb
+++ b/test/ruby/test_module.rb
@@ -3378,13 +3378,22 @@ class TestModule < Test::Unit::TestCase
     m::N.set_temporary_name(nil)
     assert_nil(m::N.name)
 
+    m::N.const_set(:O, Module.new)
+    m.const_set(:Recursive, m)
+    m::N.const_set(:Recursive, m)
+    m.const_set(:A, 42)
+
     m.set_temporary_name(name = "fake_name")
     name.upcase!
     assert_equal("fake_name", m.name)
     assert_raise(FrozenError) {m.name.upcase!}
+    assert_equal("fake_name::N", m::N.name)
+    assert_equal("fake_name::N::O", m::N::O.name)
 
     m.set_temporary_name(nil)
     assert_nil m.name
+    assert_nil m::N.name
+    assert_nil m::N::O.name
 
     assert_raise_with_message(ArgumentError, "empty class/module name") do
       m.set_temporary_name("")
diff --git a/variable.c b/variable.c
index 2d022d59b1..23602687e2 100644
--- a/variable.c
+++ b/variable.c
@@ -166,6 +166,80 @@ is_constant_path(VALUE name)
     return true;
 }
 
+struct sub_temporary_name_args {
+    VALUE names;
+    ID last;
+};
+
+static VALUE build_const_path(VALUE head, ID tail);
+static void set_sub_temporary_name_foreach(VALUE mod, struct sub_temporary_name_args *args, VALUE name);
+
+static VALUE
+set_sub_temporary_name_recursive(VALUE mod, VALUE data, int recursive)
+{
+    if (recursive) return Qfalse;
+
+    struct sub_temporary_name_args *args = (void *)data;
+    VALUE name = 0;
+    if (args->names) {
+        name = build_const_path(rb_ary_last(0, 0, args->names), args->last);
+    }
+    set_sub_temporary_name_foreach(mod, args, name);
+    return Qtrue;
+}
+
+static VALUE
+set_sub_temporary_name_topmost(VALUE mod, VALUE data, int recursive)
+{
+    if (recursive) return Qfalse;
+
+    struct sub_temporary_name_args *args = (void *)data;
+    VALUE name = args->names;
+    if (name) {
+        args->names = rb_ary_hidden_new(0);
+    }
+    set_sub_temporary_name_foreach(mod, args, name);
+    return Qtrue;
+}
+
+static enum rb_id_table_iterator_result
+set_sub_temporary_name_i(ID id, VALUE val, void *data)
+{
+    val = ((rb_const_entry_t *)val)->value;
+    if (rb_namespace_p(val) && !RCLASS_EXT(val)->permanent_classpath) {
+        VALUE arg = (VALUE)data;
+        struct sub_temporary_name_args *args = data;
+        args->last = id;
+        rb_exec_recursive_paired(set_sub_temporary_name_recursive, val, arg, arg);
+    }
+    return ID_TABLE_CONTINUE;
+}
+
+static void
+set_sub_temporary_name_foreach(VALUE mod, struct sub_temporary_name_args *args, VALUE name)
+{
+    RCLASS_SET_CLASSPATH(mod, name, FALSE);
+    struct rb_id_table *tbl = RCLASS_CONST_TBL(mod);
+    if (!tbl) return;
+    if (!name) {
+        rb_id_table_foreach(tbl, set_sub_temporary_name_i, args);
+    }
+    else {
+        long names_len = RARRAY_LEN(args->names); // paranoiac check?
+        rb_ary_push(args->names, name);
+        rb_id_table_foreach(tbl, set_sub_temporary_name_i, args);
+        rb_ary_set_len(args->names, names_len);
+    }
+}
+
+static void
+set_sub_temporary_name(VALUE mod, VALUE name)
+{
+    struct sub_temporary_name_args args = {name};
+    VALUE arg = (VALUE)&args;
+    rb_exec_recursive_paired(set_sub_temporary_name_topmost, mod, arg, arg);
+}
+
 /*
  *  call-seq:
  *     mod.set_temporary_name(string) -> self
@@ -224,7 +298,9 @@ rb_mod_set_temporary_name(VALUE mod, VALUE name)
 
     if (NIL_P(name)) {
         // Set the temporary classpath to NULL (anonymous):
-        RCLASS_SET_CLASSPATH(mod, 0, FALSE);
+        RB_VM_LOCK_ENTER();
+        set_sub_temporary_name(mod, 0);
+        RB_VM_LOCK_LEAVE();
     }
     else {
         // Ensure the name is a string:
@@ -241,7 +317,9 @@ rb_mod_set_temporary_name(VALUE mod, VALUE name)
         name = rb_str_new_frozen(name);
 
         // Set the temporary classpath to the given name:
-        RCLASS_SET_CLASSPATH(mod, name, FALSE);
+        RB_VM_LOCK_ENTER();
+        set_sub_temporary_name(mod, name);
+        RB_VM_LOCK_LEAVE();
     }
 
     return mod;