Support null encoding for rb_enc_interned_str_cstr

CHANGELOG.md

@@ -9,6 +9,8 @@ Bug fixes:
 
 Compatibility:
 
+* Allow null encoding pointer in `rb_enc_interned_str_cstr` (@thomasmarshall).
+
 Performance:
 
 Changes:

lib/cext/ABI_check.txt

@@ -1 +1 @@
-13
+14

spec/ruby/optional/capi/ext/string_spec.c

@@ -573,7 +573,7 @@ static VALUE string_spec_rb_str_unlocktmp(VALUE self, VALUE str) {
 }
 
 static VALUE string_spec_rb_enc_interned_str_cstr(VALUE self, VALUE str, VALUE enc) {
-  rb_encoding *e = rb_to_encoding(enc);
+  rb_encoding *e = NIL_P(enc) ? 0 : rb_to_encoding(enc);
   return rb_enc_interned_str_cstr(RSTRING_PTR(str), e);
 }
 

spec/ruby/optional/capi/string_spec.rb

@@ -1236,6 +1236,14 @@ def inspect
     it "returns the same string as String#-@" do
       @s.rb_enc_interned_str_cstr("hello", Encoding::UTF_8).should.equal?(-"hello")
     end
+
+    ruby_bug "#20322", ""..."3.4" do
+      it "uses the default encoding if encoding is null" do
+        str = "hello"
+        val = @s.rb_enc_interned_str_cstr(str, nil)
+        val.encoding.should == Encoding::ASCII_8BIT
+      end
+    end
   end
 
   describe "rb_str_to_interned_str" do

src/main/c/cext/string.c

@@ -439,7 +439,7 @@ long rb_str_coderange_scan_restartable(const char *s, const char *e, rb_encoding
 }
 
 VALUE rb_enc_interned_str_cstr(const char *ptr, rb_encoding *enc) {
-  VALUE str = rb_enc_str_new_cstr(ptr, enc);
+  VALUE str = rb_enc_str_new_cstr(ptr, enc ? enc : rb_ascii8bit_encoding());
   return rb_str_to_interned_str(str);
 }