Implement JSON::ResumableParser

Only available on MRI for now.

Author: byroot

CHANGES.md

@@ -2,6 +2,9 @@
 
 ### Unreleased
 
+* Changed the C parser to no longer be recursive, so parsing very deep documents with `max_nesting: false` will no longer
+  result in `SystemStackError stack level too deep` errors.
+* Added `JSON::ResumableParser` to parse streams of JSON documents. Not yet available on JRuby.
 * Deprecate default support of JavaScript comments in the parser and add `allow_comments: true` parsing option.
 * Integrate with Ruby 4.1 `ruby_sized_xfree`.
 

ext/json/ext/json.h

@@ -28,8 +28,13 @@
 #else
 # define JSON_UNREACHABLE_RETURN UNREACHABLE_RETURN
 #endif
+
 /* shims */
 
+#ifndef UNDEF_P
+#define UNDEF_P(val) (val == Qundef)
+#endif
+
 #if SIZEOF_UINT64_T == SIZEOF_LONG_LONG
 # define INT64T2NUM(x) LL2NUM(x)
 # define UINT64T2NUM(x) ULL2NUM(x)