Integrate with Ruby 4.1 ruby_sized_xfree

Ensure that buffer sizes have been properly tracked when running
in debug mode, and appease the GC slightly when running in release
mode.

Ref: https://bugs.ruby-lang.org/issues/21861

Author: byroot

CHANGES.md

@@ -2,6 +2,8 @@
 
 ### Unreleased
 
+* Integrate with Ruby 4.1 `ruby_sized_xfree`.
+
 ### 2026-06-03 (2.19.8)
 
 * Fix 1-byte buffer overread on EOS errors.

ext/json/ext/fbuffer/fbuffer.h

@@ -64,7 +64,7 @@ static inline void fbuffer_consumed(FBuffer *fb, size_t consumed)
 static void fbuffer_free(FBuffer *fb)
 {
     if (fb->ptr && fb->type == FBUFFER_HEAP_ALLOCATED) {
-        ruby_xfree(fb->ptr);
+        JSON_SIZED_FREE_N(fb->ptr, fb->capa);
     }
 }
 
@@ -88,7 +88,7 @@ static void fbuffer_realloc(FBuffer *fb, size_t required)
             fb->type = FBUFFER_HEAP_ALLOCATED;
             MEMCPY(fb->ptr, old_buffer, char, fb->len);
         } else {
-            REALLOC_N(fb->ptr, char, required);
+            JSON_SIZED_REALLOC_N(fb->ptr, char, required, fb->capa);
         }
         fb->capa = required;
     }

ext/json/ext/generator/extconf.rb

@@ -6,6 +6,7 @@
 else
   append_cflags("-std=c99")
   have_const("RUBY_TYPED_EMBEDDABLE", "ruby.h") # RUBY_VERSION >= 3.3
+  have_func("ruby_xfree_sized", "ruby.h") # RUBY_VERSION >= 4.1
 
   $defs << "-DJSON_GENERATOR"
   $defs << "-DJSON_DEBUG" if ENV.fetch("JSON_DEBUG", "0") != "0"

ext/json/ext/json.h

@@ -49,6 +49,24 @@ typedef unsigned char _Bool;
 #endif
 #endif
 
+#ifndef HAVE_RUBY_XFREE_SIZED
+static inline void ruby_xfree_sized(void *ptr, size_t oldsize)
+{
+    ruby_xfree(ptr);
+}
+
+static inline void *ruby_xrealloc2_sized(void *ptr, size_t new_elems, size_t elem_size, size_t old_elems)
+{
+    return ruby_xrealloc2(ptr, new_elems, elem_size);
+}
+#endif
+
+# define JSON_SIZED_REALLOC_N(v, T, m, n) \
+    ((v) = (T *)ruby_xrealloc2_sized((void *)(v), (m), sizeof(T), (n)))
+
+# define JSON_SIZED_FREE(v) ruby_xfree_sized((void *)(v), sizeof(*(v)))
+# define JSON_SIZED_FREE_N(v, n) ruby_xfree_sized((void *)(v), sizeof(*(v)) * (n))
+
 #ifndef HAVE_RB_EXT_RACTOR_SAFE
 #   undef RUBY_TYPED_FROZEN_SHAREABLE
 #   define RUBY_TYPED_FROZEN_SHAREABLE 0

ext/json/ext/parser/extconf.rb

@@ -6,6 +6,7 @@
 have_func("rb_str_to_interned_str", "ruby.h") # RUBY_VERSION >= 3.0
 have_func("rb_hash_new_capa", "ruby.h") # RUBY_VERSION >= 3.2
 have_func("rb_hash_bulk_insert", "ruby.h") # Missing on TruffleRuby
+have_func("ruby_xfree_sized", "ruby.h") # RUBY_VERSION >= 4.1
 
 if RUBY_ENGINE == "ruby"
   have_const("RUBY_TYPED_EMBEDDABLE", "ruby.h") # RUBY_VERSION >= 3.3

ext/json/ext/parser/parser.c

@@ -211,7 +211,7 @@ static rvalue_stack *rvalue_stack_grow(rvalue_stack *stack, VALUE *handle, rvalu
     if (stack->type == RVALUE_STACK_STACK_ALLOCATED) {
         stack = rvalue_stack_spill(stack, handle, stack_ref);
     } else {
-        REALLOC_N(stack->ptr, VALUE, required);
+        JSON_SIZED_REALLOC_N(stack->ptr, VALUE, required, stack->capa);
         stack->capa = required;
     }
     return stack;
@@ -250,7 +250,7 @@ static void rvalue_stack_mark(void *ptr)
 
 static void rvalue_stack_free_buffer(rvalue_stack *stack)
 {
-    ruby_xfree(stack->ptr);
+    JSON_SIZED_FREE_N(stack->ptr, stack->capa);
     stack->ptr = NULL;
 }
 
@@ -260,7 +260,7 @@ static void rvalue_stack_free(void *ptr)
     if (stack) {
         rvalue_stack_free_buffer(stack);
 #ifndef HAVE_RUBY_TYPED_EMBEDDABLE
-        ruby_xfree(stack);
+        JSON_SIZED_FREE(stack, sizeof(*stack));
 #endif
     }
 }