10 files changed, 381 insertions, 196 deletions

diff --git a/spec/ruby/optional/capi/encoding_spec.rb b/spec/ruby/optional/capi/encoding_spec.rb
index c14983c7ea..734b5f1253 100644
--- a/spec/ruby/optional/capi/encoding_spec.rb
+++ b/spec/ruby/optional/capi/encoding_spec.rb
@@ -745,4 +745,34 @@ describe "C-API Encoding function" do
       ruby_exe(code, args: "2>&1", exit_status: 1).should.include?('too many encoding (> 256) (EncodingError)')
     end
   end
+
+  describe "ONIGENC_IS_UNICODE" do
+    it "is true only for select UTF-related encodings" do
+      unicode = [
+        Encoding::UTF_8,
+        Encoding::UTF8_DOCOMO,
+        Encoding::UTF8_KDDI,
+        Encoding::UTF8_MAC,
+        Encoding::UTF8_SOFTBANK,
+        Encoding::CESU_8,
+        Encoding::UTF_16LE,
+        Encoding::UTF_16BE,
+        Encoding::UTF_32LE,
+        Encoding::UTF_32BE
+      ]
+      unicode.each do |enc|
+        @s.should.ONIGENC_IS_UNICODE(enc)
+      end
+
+      (Encoding.list - unicode).each { |enc|
+        @s.should_not.ONIGENC_IS_UNICODE(enc)
+      }
+    end
+
+    # Redundant with the above but more explicit
+    it "is false for the dummy UTF-16 and UTF-32 encodings" do
+      @s.should_not.ONIGENC_IS_UNICODE(Encoding::UTF_16)
+      @s.should_not.ONIGENC_IS_UNICODE(Encoding::UTF_32)
+    end
+  end
 end
diff --git a/spec/ruby/optional/capi/ext/encoding_spec.c b/spec/ruby/optional/capi/ext/encoding_spec.c
index aa8662cfbd..98d4e2e3b7 100644
--- a/spec/ruby/optional/capi/ext/encoding_spec.c
+++ b/spec/ruby/optional/capi/ext/encoding_spec.c
@@ -324,6 +324,10 @@ static VALUE encoding_spec_rb_define_dummy_encoding(VALUE self, VALUE name) {
   return INT2NUM(rb_define_dummy_encoding(RSTRING_PTR(name)));
 }
 
+static VALUE encoding_spec_ONIGENC_IS_UNICODE(VALUE self, VALUE encoding) {
+  return ONIGENC_IS_UNICODE(rb_to_encoding(encoding)) ? Qtrue : Qfalse;
+}
+
 void Init_encoding_spec(void) {
   VALUE cls;
   native_rb_encoding_pointer = (rb_encoding**) malloc(sizeof(rb_encoding*));
@@ -384,6 +388,7 @@ void Init_encoding_spec(void) {
   rb_define_method(cls, "ONIGENC_MBC_CASE_FOLD", encoding_spec_ONIGENC_MBC_CASE_FOLD, 1);
   rb_define_method(cls, "rb_enc_left_char_head", encoding_spec_rb_enc_left_char_head, 2);
   rb_define_method(cls, "rb_define_dummy_encoding", encoding_spec_rb_define_dummy_encoding, 1);
+  rb_define_method(cls, "ONIGENC_IS_UNICODE", encoding_spec_ONIGENC_IS_UNICODE, 1);
 }
 
 #ifdef __cplusplus
diff --git a/spec/ruby/optional/capi/ext/kernel_spec.c b/spec/ruby/optional/capi/ext/kernel_spec.c
index a8fed21b59..eee324052d 100644
--- a/spec/ruby/optional/capi/ext/kernel_spec.c
+++ b/spec/ruby/optional/capi/ext/kernel_spec.c
@@ -1,4 +1,5 @@
 #include "ruby.h"
+#include "ruby/vm.h"
 #include "rubyspec.h"
 
 #include <errno.h>
@@ -337,6 +338,15 @@ static VALUE kernel_spec_rb_set_end_proc(VALUE self, VALUE io) {
   return Qnil;
 }
 
+static void at_exit_hook(ruby_vm_t *vm) {
+  puts("ruby_vm_at_exit hook ran");
+}
+
+static VALUE kernel_spec_ruby_vm_at_exit(VALUE self) {
+  ruby_vm_at_exit(at_exit_hook);
+  return self;
+}
+
 static VALUE kernel_spec_rb_f_sprintf(VALUE self, VALUE ary) {
   return rb_f_sprintf((int)RARRAY_LEN(ary), RARRAY_PTR(ary));
 }
@@ -434,6 +444,7 @@ void Init_kernel_spec(void) {
   rb_define_method(cls, "rb_yield_splat", kernel_spec_rb_yield_splat, 1);
   rb_define_method(cls, "rb_exec_recursive", kernel_spec_rb_exec_recursive, 1);
   rb_define_method(cls, "rb_set_end_proc", kernel_spec_rb_set_end_proc, 1);
+  rb_define_method(cls, "ruby_vm_at_exit", kernel_spec_ruby_vm_at_exit, 0);
   rb_define_method(cls, "rb_f_sprintf", kernel_spec_rb_f_sprintf, 1);
   rb_define_method(cls, "rb_str_format", kernel_spec_rb_str_format, 3);
   rb_define_method(cls, "rb_make_backtrace", kernel_spec_rb_make_backtrace, 0);
diff --git a/spec/ruby/optional/capi/ext/string_spec.c b/spec/ruby/optional/capi/ext/string_spec.c
index 094013e049..74aa9e56e8 100644
--- a/spec/ruby/optional/capi/ext/string_spec.c
+++ b/spec/ruby/optional/capi/ext/string_spec.c
@@ -581,6 +581,14 @@ static VALUE string_spec_rb_str_to_interned_str(VALUE self, VALUE str) {
   return rb_str_to_interned_str(str);
 }
 
+static VALUE string_spec_rb_interned_str(VALUE self, VALUE str, VALUE len) {
+  return rb_interned_str(RSTRING_PTR(str), FIX2LONG(len));
+}
+
+static VALUE string_spec_rb_interned_str_cstr(VALUE self, VALUE str) {
+  return rb_interned_str_cstr(RSTRING_PTR(str));
+}
+
 void Init_string_spec(void) {
   VALUE cls = rb_define_class("CApiStringSpecs", rb_cObject);
   rb_define_method(cls, "rb_cstr2inum", string_spec_rb_cstr2inum, 2);
@@ -681,6 +689,8 @@ void Init_string_spec(void) {
   rb_define_method(cls, "rb_enc_interned_str_cstr", string_spec_rb_enc_interned_str_cstr, 2);
   rb_define_method(cls, "rb_enc_interned_str", string_spec_rb_enc_interned_str, 3);
   rb_define_method(cls, "rb_str_to_interned_str", string_spec_rb_str_to_interned_str, 1);
+  rb_define_method(cls, "rb_interned_str", string_spec_rb_interned_str, 2);
+  rb_define_method(cls, "rb_interned_str_cstr", string_spec_rb_interned_str_cstr, 1);
 }
 
 #ifdef __cplusplus
diff --git a/spec/ruby/optional/capi/io_spec.rb b/spec/ruby/optional/capi/io_spec.rb
index ab7a7fc8f6..dc4ac3e374 100644
--- a/spec/ruby/optional/capi/io_spec.rb
+++ b/spec/ruby/optional/capi/io_spec.rb
@@ -494,166 +494,164 @@ describe "C-API IO function" do
     end
   end
 
-  ruby_version_is "3.3" do
-    describe "rb_io_mode" do
-      it "returns the mode" do
-        (@o.rb_io_mode(@r_io) & 0b11).should == 0b01
-        (@o.rb_io_mode(@w_io) & 0b11).should == 0b10
-        (@o.rb_io_mode(@rw_io) & 0b11).should == 0b11
-      end
+  describe "rb_io_mode" do
+    it "returns the mode" do
+      (@o.rb_io_mode(@r_io) & 0b11).should == 0b01
+      (@o.rb_io_mode(@w_io) & 0b11).should == 0b10
+      (@o.rb_io_mode(@rw_io) & 0b11).should == 0b11
     end
+  end
 
-    describe "rb_io_path" do
-      it "returns the IO#path" do
-        @o.rb_io_path(@r_io).should == @r_io.path
-        @o.rb_io_path(@rw_io).should == @rw_io.path
-        @o.rb_io_path(@rw_io).should == @name
-      end
+  describe "rb_io_path" do
+    it "returns the IO#path" do
+      @o.rb_io_path(@r_io).should == @r_io.path
+      @o.rb_io_path(@rw_io).should == @rw_io.path
+      @o.rb_io_path(@rw_io).should == @name
     end
+  end
 
-    describe "rb_io_closed_p" do
-      it "returns false when io is not closed" do
-        @o.rb_io_closed_p(@r_io).should == false
-        @r_io.closed?.should == false
-      end
+  describe "rb_io_closed_p" do
+    it "returns false when io is not closed" do
+      @o.rb_io_closed_p(@r_io).should == false
+      @r_io.closed?.should == false
+    end
 
-      it "returns true when io is closed" do
-        @r_io.close
+    it "returns true when io is closed" do
+      @r_io.close
 
-        @o.rb_io_closed_p(@r_io).should == true
-        @r_io.closed?.should == true
-      end
+      @o.rb_io_closed_p(@r_io).should == true
+      @r_io.closed?.should == true
     end
+  end
 
-    quarantine! do # "Errno::EBADF: Bad file descriptor" at closing @r_io, @rw_io etc in the after :each hook
-      describe "rb_io_open_descriptor" do
-        it "creates a new IO instance" do
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.should.is_a?(IO)
-        end
-
-        it "return an instance of the specified class" do
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.class.should == File
+  quarantine! do # "Errno::EBADF: Bad file descriptor" at closing @r_io, @rw_io etc in the after :each hook
+    describe "rb_io_open_descriptor" do
+      it "creates a new IO instance" do
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.should.is_a?(IO)
+      end
 
-          io = @o.rb_io_open_descriptor(IO, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.class.should == IO
-        end
+      it "return an instance of the specified class" do
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.class.should == File
 
-        it "sets the specified file descriptor" do
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.fileno.should == @r_io.fileno
-        end
+        io = @o.rb_io_open_descriptor(IO, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.class.should == IO
+      end
 
-        it "sets the specified path" do
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.path.should == "a.txt"
-        end
+      it "sets the specified file descriptor" do
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.fileno.should == @r_io.fileno
+      end
 
-        it "sets the specified mode" do
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, CApiIOSpecs::FMODE_BINMODE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.should.binmode?
+      it "sets the specified path" do
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.path.should == "a.txt"
+      end
 
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, CApiIOSpecs::FMODE_TEXTMODE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.should_not.binmode?
-        end
+      it "sets the specified mode" do
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, CApiIOSpecs::FMODE_BINMODE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.should.binmode?
 
-        it "sets the specified timeout" do
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.timeout.should == 60
-        end
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, CApiIOSpecs::FMODE_TEXTMODE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.should_not.binmode?
+      end
 
-        it "sets the specified internal encoding" do
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.internal_encoding.should == Encoding::US_ASCII
-        end
+      it "sets the specified timeout" do
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.timeout.should == 60
+      end
 
-        it "sets the specified external encoding" do
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.external_encoding.should == Encoding::UTF_8
-        end
+      it "sets the specified internal encoding" do
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.internal_encoding.should == Encoding::US_ASCII
+      end
 
-        it "does not apply the specified encoding flags" do
-          name = tmp("rb_io_open_descriptor_specs")
-          File.write(name, "123\r\n456\n89")
-          file = File.open(name, "r")
+      it "sets the specified external encoding" do
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.external_encoding.should == Encoding::UTF_8
+      end
 
-          io = @o.rb_io_open_descriptor(File, file.fileno, CApiIOSpecs::FMODE_READABLE, "a.txt", 60, "US-ASCII", "UTF-8", CApiIOSpecs::ECONV_UNIVERSAL_NEWLINE_DECORATOR, {})
-          io.read_nonblock(20).should == "123\r\n456\n89"
-        ensure
-          file.close
-          rm_r name
-        end
+      it "does not apply the specified encoding flags" do
+        name = tmp("rb_io_open_descriptor_specs")
+        File.write(name, "123\r\n456\n89")
+        file = File.open(name, "r")
 
-        it "ignores the IO open options" do
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {external_encoding: "windows-1251"})
-          io.external_encoding.should == Encoding::UTF_8
+        io = @o.rb_io_open_descriptor(File, file.fileno, CApiIOSpecs::FMODE_READABLE, "a.txt", 60, "US-ASCII", "UTF-8", CApiIOSpecs::ECONV_UNIVERSAL_NEWLINE_DECORATOR, {})
+        io.read_nonblock(20).should == "123\r\n456\n89"
+      ensure
+        file.close
+        rm_r name
+      end
 
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {internal_encoding: "windows-1251"})
-          io.internal_encoding.should == Encoding::US_ASCII
+      it "ignores the IO open options" do
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {external_encoding: "windows-1251"})
+        io.external_encoding.should == Encoding::UTF_8
 
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {encoding: "windows-1251:binary"})
-          io.external_encoding.should == Encoding::UTF_8
-          io.internal_encoding.should == Encoding::US_ASCII
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {internal_encoding: "windows-1251"})
+        io.internal_encoding.should == Encoding::US_ASCII
 
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {textmode: false})
-          io.should_not.binmode?
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {encoding: "windows-1251:binary"})
+        io.external_encoding.should == Encoding::UTF_8
+        io.internal_encoding.should == Encoding::US_ASCII
 
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {binmode: true})
-          io.should_not.binmode?
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {textmode: false})
+        io.should_not.binmode?
 
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {autoclose: false})
-          io.should.autoclose?
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {binmode: true})
+        io.should_not.binmode?
 
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {path: "a.txt"})
-          io.path.should == "a.txt"
-        end
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {autoclose: false})
+        io.should.autoclose?
 
-        it "ignores the IO encoding options" do
-          io = @o.rb_io_open_descriptor(File, @w_io.fileno, CApiIOSpecs::FMODE_WRITABLE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {crlf_newline: true})
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, "a.txt", 60, "US-ASCII", "UTF-8", 0, {path: "a.txt"})
+        io.path.should == "a.txt"
+      end
 
-          io.write("123\r\n456\n89")
-          io.flush
+      it "ignores the IO encoding options" do
+        io = @o.rb_io_open_descriptor(File, @w_io.fileno, CApiIOSpecs::FMODE_WRITABLE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {crlf_newline: true})
 
-          @r_io.read_nonblock(20).should == "123\r\n456\n89"
-        end
+        io.write("123\r\n456\n89")
+        io.flush
 
-        it "allows wrong mode" do
-          io = @o.rb_io_open_descriptor(File, @w_io.fileno, CApiIOSpecs::FMODE_READABLE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
-          io.should.is_a?(File)
+        @r_io.read_nonblock(20).should == "123\r\n456\n89"
+      end
 
-          platform_is_not :windows do
-            -> { io.read_nonblock(1) }.should raise_error(Errno::EBADF)
-          end
+      it "allows wrong mode" do
+        io = @o.rb_io_open_descriptor(File, @w_io.fileno, CApiIOSpecs::FMODE_READABLE, "a.txt", 60, "US-ASCII", "UTF-8", 0, {})
+        io.should.is_a?(File)
 
-          platform_is :windows do
-            -> { io.read_nonblock(1) }.should raise_error(IO::EWOULDBLOCKWaitReadable)
-          end
+        platform_is_not :windows do
+          -> { io.read_nonblock(1) }.should raise_error(Errno::EBADF)
         end
 
-        it "tolerates NULL as rb_io_encoding *encoding parameter" do
-          io = @o.rb_io_open_descriptor_without_encoding(File, @r_io.fileno, 0, "a.txt", 60)
-          io.should.is_a?(File)
+        platform_is :windows do
+          -> { io.read_nonblock(1) }.should raise_error(IO::EWOULDBLOCKWaitReadable)
         end
+      end
 
-        it "deduplicates path String" do
-          path = "a.txt".dup
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
-          io.path.should_not equal(path)
+      it "tolerates NULL as rb_io_encoding *encoding parameter" do
+        io = @o.rb_io_open_descriptor_without_encoding(File, @r_io.fileno, 0, "a.txt", 60)
+        io.should.is_a?(File)
+      end
 
-          path = "a.txt".freeze
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
-          io.path.should_not equal(path)
-        end
+      it "deduplicates path String" do
+        path = "a.txt".dup
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
+        io.path.should_not equal(path)
+
+        path = "a.txt".freeze
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
+        io.path.should_not equal(path)
+      end
 
-        it "calls #to_str to convert a path to a String" do
-          path = Object.new
-          def path.to_str; "a.txt"; end
+      it "calls #to_str to convert a path to a String" do
+        path = Object.new
+        def path.to_str; "a.txt"; end
 
-          io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
+        io = @o.rb_io_open_descriptor(File, @r_io.fileno, 0, path, 60, "US-ASCII", "UTF-8", 0, {})
 
-          io.path.should == "a.txt"
-        end
+        io.path.should == "a.txt"
       end
     end
   end
diff --git a/spec/ruby/optional/capi/kernel_spec.rb b/spec/ruby/optional/capi/kernel_spec.rb
index 6633ee50c1..0a2362fb30 100644
--- a/spec/ruby/optional/capi/kernel_spec.rb
+++ b/spec/ruby/optional/capi/kernel_spec.rb
@@ -703,6 +703,12 @@ describe "C-API Kernel function" do
     end
   end
 
+  describe "ruby_vm_at_exit" do
+    it "runs a C function after the VM is terminated" do
+      ruby_exe("require #{kernel_path.inspect}; CApiKernelSpecs.new.ruby_vm_at_exit").should == "ruby_vm_at_exit hook ran\n"
+    end
+  end
+
   describe "rb_f_sprintf" do
     it "returns a string according to format and arguments" do
       @s.rb_f_sprintf(["%d %f %s", 10, 2.5, "test"]).should == "10 2.500000 test"
diff --git a/spec/ruby/optional/capi/object_spec.rb b/spec/ruby/optional/capi/object_spec.rb
index 8b4d8a9bba..6716fd9e33 100644
--- a/spec/ruby/optional/capi/object_spec.rb
+++ b/spec/ruby/optional/capi/object_spec.rb
@@ -1004,7 +1004,6 @@ describe "CApiObject" do
 
       it "calls the callback function for each cvar and ivar on a class" do
         exp = [:@@cvar, :foo, :@@cvar2, :bar, :@ivar, :baz]
-        exp.unshift(:__classpath__, 'CApiObjectSpecs::CVars') if RUBY_VERSION < "3.3"
 
         ary = @o.rb_ivar_foreach(CApiObjectSpecs::CVars)
         ary.should == exp
@@ -1012,7 +1011,6 @@ describe "CApiObject" do
 
       it "calls the callback function for each cvar and ivar on a module" do
         exp = [:@@mvar, :foo, :@@mvar2, :bar, :@ivar, :baz]
-        exp.unshift(:__classpath__, 'CApiObjectSpecs::MVars') if RUBY_VERSION < "3.3"
 
         ary = @o.rb_ivar_foreach(CApiObjectSpecs::MVars)
         ary.should == exp
diff --git a/spec/ruby/optional/capi/spec_helper.rb b/spec/ruby/optional/capi/spec_helper.rb
index e7abf46e6c..d937c967d0 100644
--- a/spec/ruby/optional/capi/spec_helper.rb
+++ b/spec/ruby/optional/capi/spec_helper.rb
@@ -59,7 +59,11 @@ def compile_extension(name)
   tmpdir = tmp("cext_#{name}")
   Dir.mkdir(tmpdir)
   begin
-    ["#{core_ext_dir}/rubyspec.h", "#{spec_ext_dir}/#{ext}.c"].each do |file|
+    files = ["#{core_ext_dir}/rubyspec.h", "#{spec_ext_dir}/#{ext}.c"]
+    if spec_ext_dir != core_ext_dir
+      files += Dir.glob("#{spec_ext_dir}/*.h")
+    end
+    files.each do |file|
       if cxx and file.end_with?('.c')
         cp file, "#{tmpdir}/#{File.basename(file, '.c')}.cpp"
       else
diff --git a/spec/ruby/optional/capi/string_spec.rb b/spec/ruby/optional/capi/string_spec.rb
index 72f20ee6a5..889f0a6cfe 100644
--- a/spec/ruby/optional/capi/string_spec.rb
+++ b/spec/ruby/optional/capi/string_spec.rb
@@ -1369,8 +1369,133 @@ describe "C-API String function" do
       result1.should_not.equal?(result2)
     end
 
+    it "preserves the encoding of the original string" do
+      result1 = @s.rb_str_to_interned_str("hello".dup.force_encoding(Encoding::US_ASCII))
+      result2 = @s.rb_str_to_interned_str("hello".dup.force_encoding(Encoding::UTF_8))
+      result1.encoding.should == Encoding::US_ASCII
+      result2.encoding.should == Encoding::UTF_8
+    end
+
     it "returns the same string as String#-@" do
       @s.rb_str_to_interned_str("hello").should.equal?(-"hello")
     end
   end
+
+  describe "rb_interned_str" do
+    it "returns a frozen string" do
+      str = "hello"
+      result = @s.rb_interned_str(str, str.bytesize)
+      result.should.is_a?(String)
+      result.should.frozen?
+      result.encoding.should == Encoding::US_ASCII
+    end
+
+    it "returns the same frozen string" do
+      str = "hello"
+      result1 = @s.rb_interned_str(str, str.bytesize)
+      result2 = @s.rb_interned_str(str, str.bytesize)
+      result1.should.equal?(result2)
+    end
+
+    it "supports strings with embedded null bytes" do
+      str = "foo\x00bar\x00baz".b
+      result = @s.rb_interned_str(str, str.bytesize)
+      result.should == str
+    end
+
+    it "return US_ASCII encoding for an empty string" do
+      result = @s.rb_interned_str("", 0)
+      result.should == ""
+      result.encoding.should == Encoding::US_ASCII
+    end
+
+    it "returns US_ASCII encoding for strings of only 7 bit ASCII" do
+      0x00.upto(0x7f).each do |char|
+        result = @s.rb_interned_str(char.chr, 1)
+        result.encoding.should == Encoding::US_ASCII
+      end
+    end
+
+    ruby_bug "21842", ""..."4.1" do
+      it "returns BINARY encoding for strings that use the 8th bit" do
+        0x80.upto(0xff) do |char|
+          result = @s.rb_interned_str(char.chr, 1)
+          result.encoding.should == Encoding::BINARY
+        end
+      end
+    end
+
+    it 'returns the same string when using non-ascii characters' do
+      str = 'こんにちは'
+      result1 = @s.rb_interned_str(str, str.bytesize)
+      result2 = @s.rb_interned_str(str, str.bytesize)
+      result1.should.equal?(result2)
+    end
+
+    ruby_bug "21842", ""..."4.1" do
+      it "returns the same string as String#-@" do
+        str = "hello".dup.force_encoding(Encoding::US_ASCII)
+        @s.rb_interned_str(str, str.bytesize).should.equal?(-str)
+      end
+    end
+  end
+
+  describe "rb_interned_str_cstr" do
+    it "returns a frozen string" do
+      str = "hello"
+      result = @s.rb_interned_str_cstr(str)
+      result.should.is_a?(String)
+      result.should.frozen?
+      result.encoding.should == Encoding::US_ASCII
+    end
+
+    it "returns the same frozen string" do
+      str = "hello"
+      result1 = @s.rb_interned_str_cstr(str)
+      result2 = @s.rb_interned_str_cstr(str)
+      result1.should.equal?(result2)
+    end
+
+    it "does not support strings with embedded null bytes" do
+      str = "foo\x00bar\x00baz".b
+      result = @s.rb_interned_str_cstr(str)
+      result.should == "foo"
+    end
+
+    it "return US_ASCII encoding for an empty string" do
+      result = @s.rb_interned_str_cstr("")
+      result.should == ""
+      result.encoding.should == Encoding::US_ASCII
+    end
+
+    it "returns US_ASCII encoding for strings of only 7 bit ASCII" do
+      0x01.upto(0x7f).each do |char|
+        result = @s.rb_interned_str_cstr(char.chr)
+        result.encoding.should == Encoding::US_ASCII
+      end
+    end
+
+    ruby_bug "21842", ""..."4.1" do
+      it "returns BINARY encoding for strings that use the 8th bit" do
+        0x80.upto(0xff) do |char|
+          result = @s.rb_interned_str_cstr(char.chr)
+          result.encoding.should == Encoding::BINARY
+        end
+      end
+    end
+
+    it 'returns the same string when using non-ascii characters' do
+      str = 'こんにちは'
+      result1 = @s.rb_interned_str_cstr(str)
+      result2 = @s.rb_interned_str_cstr(str)
+      result1.should.equal?(result2)
+    end
+
+    ruby_bug "21842", ""..."4.1" do
+      it "returns the same string as String#-@" do
+        str = "hello".dup.force_encoding(Encoding::US_ASCII)
+        @s.rb_interned_str_cstr(str).should.equal?(-str)
+      end
+    end
+  end
 end
diff --git a/spec/ruby/optional/capi/struct_spec.rb b/spec/ruby/optional/capi/struct_spec.rb
index cc8d7f932e..3f9eff52bc 100644
--- a/spec/ruby/optional/capi/struct_spec.rb
+++ b/spec/ruby/optional/capi/struct_spec.rb
@@ -239,78 +239,76 @@ describe "C-API Struct function" do
   end
 end
 
-ruby_version_is "3.3" do
-  describe "C-API Data function" do
-    before :all do
-      @s = CApiStructSpecs.new
-      @klass = @s.rb_data_define(nil, "a", "b", "c")
-    end
-
-    describe "rb_data_define" do
-      it "returns a subclass of Data class when passed nil as the first argument" do
-        @klass.should.is_a? Class
-        @klass.superclass.should == Data
-      end
-
-      it "returns a subclass of a class when passed as the first argument" do
-        superclass = Class.new(Data)
-        klass = @s.rb_data_define(superclass, "a", "b", "c")
-
-        klass.should.is_a? Class
-        klass.superclass.should == superclass
-      end
-
-      it "creates readers for the members" do
-        obj = @klass.new(1, 2, 3)
-
-        obj.a.should == 1
-        obj.b.should == 2
-        obj.c.should == 3
-      end
-
-      it "returns the member names as Symbols" do
-        obj = @klass.new(0, 0, 0)
-
-        obj.members.should == [:a, :b, :c]
-      end
-
-      it "raises an ArgumentError if arguments contain duplicate member name" do
-        -> { @s.rb_data_define(nil, "a", "b", "a") }.should raise_error(ArgumentError)
-      end
-
-      it "raises when first argument is not a class" do
-        -> { @s.rb_data_define([], "a", "b", "c") }.should raise_error(TypeError, "wrong argument type Array (expected Class)")
-      end
-    end
-
-    describe "rb_struct_initialize" do
-      it "sets all members for a Data instance" do
-        data = @klass.allocate
-        @s.rb_struct_initialize(data, [1, 2, 3]).should == nil
-        data.a.should == 1
-        data.b.should == 2
-        data.c.should == 3
-      end
-
-      it "freezes the Data instance" do
-        data = @klass.allocate
-        @s.rb_struct_initialize(data, [1, 2, 3]).should == nil
-        data.should.frozen?
-        -> { @s.rb_struct_initialize(data, [1, 2, 3]) }.should raise_error(FrozenError)
-      end
-
-      it "raises ArgumentError if too many values" do
-        data = @klass.allocate
-        -> { @s.rb_struct_initialize(data, [1, 2, 3, 4]) }.should raise_error(ArgumentError, "struct size differs")
-      end
-
-      it "treats missing values as nil" do
-        data = @klass.allocate
-        @s.rb_struct_initialize(data, [1, 2]).should == nil
-        data.a.should == 1
-        data.b.should == 2
-        data.c.should == nil
-      end
+describe "C-API Data function" do
+  before :all do
+    @s = CApiStructSpecs.new
+    @klass = @s.rb_data_define(nil, "a", "b", "c")
+  end
+
+  describe "rb_data_define" do
+    it "returns a subclass of Data class when passed nil as the first argument" do
+      @klass.should.is_a? Class
+      @klass.superclass.should == Data
+    end
+
+    it "returns a subclass of a class when passed as the first argument" do
+      superclass = Class.new(Data)
+      klass = @s.rb_data_define(superclass, "a", "b", "c")
+
+      klass.should.is_a? Class
+      klass.superclass.should == superclass
+    end
+
+    it "creates readers for the members" do
+      obj = @klass.new(1, 2, 3)
+
+      obj.a.should == 1
+      obj.b.should == 2
+      obj.c.should == 3
+    end
+
+    it "returns the member names as Symbols" do
+      obj = @klass.new(0, 0, 0)
+
+      obj.members.should == [:a, :b, :c]
+    end
+
+    it "raises an ArgumentError if arguments contain duplicate member name" do
+      -> { @s.rb_data_define(nil, "a", "b", "a") }.should raise_error(ArgumentError)
+    end
+
+    it "raises when first argument is not a class" do
+      -> { @s.rb_data_define([], "a", "b", "c") }.should raise_error(TypeError, "wrong argument type Array (expected Class)")
+    end
+  end
+
+  describe "rb_struct_initialize" do
+    it "sets all members for a Data instance" do
+      data = @klass.allocate
+      @s.rb_struct_initialize(data, [1, 2, 3]).should == nil
+      data.a.should == 1
+      data.b.should == 2
+      data.c.should == 3
+    end
+
+    it "freezes the Data instance" do
+      data = @klass.allocate
+      @s.rb_struct_initialize(data, [1, 2, 3]).should == nil
+      data.should.frozen?
+      -> { @s.rb_struct_initialize(data, [1, 2, 3]) }.should raise_error(FrozenError)
+    end
+
+    it "raises ArgumentError if too many values" do
+      data = @klass.allocate
+      -> { @s.rb_struct_initialize(data, [1, 2, 3, 4]) }.should raise_error(ArgumentError, "struct size differs")
+    end
+
+    it "treats missing values as nil" do
+      data = @klass.allocate
+      @s.rb_struct_initialize(data, [1, 2]).should == nil
+      data.a.should == 1
+      data.b.should == 2
+      data.c.should == nil
     end
   end
 end