From 4058e12fc3c95f6cda16fa8c969c20aed99dbf71 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Wed, 8 Jul 2026 02:12:02 +0000
Subject: [PATCH] Make RBS::Location write-barrier protected

Mark the Location TypedData object with RUBY_TYPED_WB_PROTECTED and route
every write to the embedded `buffer` VALUE through RB_OBJ_WRITE. Once an
object is write-barrier protected, the GC can skip it during minor
collections instead of marking it every time, which speeds up GC.

All buffer assignments (initialize, initialize_copy, and the three
rbs_new_location* constructors) now go through the write barrier so the
old-to-young reference from a promoted Location to its Buffer is tracked
correctly.
---
 ext/rbs_extension/legacy_location.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/ext/rbs_extension/legacy_location.c b/ext/rbs_extension/legacy_location.c
index 36006878e..ef263fb48 100644
--- a/ext/rbs_extension/legacy_location.c
+++ b/ext/rbs_extension/legacy_location.c
@@ -91,7 +91,7 @@ static rb_data_type_t location_type = {
     { rbs_loc_mark, (RUBY_DATA_FUNC) rbs_loc_free, rbs_loc_memsize },
     0,
     0,
-    RUBY_TYPED_FREE_IMMEDIATELY
+    RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED
 };
 
 static VALUE location_s_allocate(VALUE klass) {
@@ -114,10 +114,11 @@ static VALUE location_initialize(VALUE self, VALUE buffer, VALUE start_pos, VALU
     int end = FIX2INT(end_pos);
 
     *loc = (rbs_loc) {
-        .buffer = buffer,
+        .buffer = Qnil,
         .rg = (rbs_loc_range) { start, end },
         .children = NULL,
     };
+    RB_OBJ_WRITE(self, &loc->buffer, buffer);
 
     return Qnil;
 }
@@ -127,10 +128,11 @@ static VALUE location_initialize_copy(VALUE self, VALUE other) {
     rbs_loc *other_loc = rbs_check_location(other);
 
     *self_loc = (rbs_loc) {
-        .buffer = other_loc->buffer,
+        .buffer = Qnil,
         .rg = other_loc->rg,
         .children = NULL,
     };
+    RB_OBJ_WRITE(self, &self_loc->buffer, other_loc->buffer);
 
     if (other_loc->children != NULL) {
         rbs_loc_legacy_alloc_children(self_loc, other_loc->children->cap);
@@ -193,7 +195,8 @@ VALUE rbs_new_location(VALUE buffer, rbs_range_t rg) {
     rbs_loc *loc;
     VALUE obj = TypedData_Make_Struct(RBS_Location, rbs_loc, &location_type, loc);
 
-    rbs_loc_init(loc, buffer, (rbs_loc_range) { rg.start.char_pos, rg.end.char_pos });
+    rbs_loc_init(loc, Qnil, (rbs_loc_range) { rg.start.char_pos, rg.end.char_pos });
+    RB_OBJ_WRITE(obj, &loc->buffer, buffer);
 
     return obj;
 }
@@ -202,7 +205,8 @@ VALUE rbs_new_location2(VALUE buffer, int start_char, int end_char) {
     rbs_loc *loc;
     VALUE obj = TypedData_Make_Struct(RBS_Location, rbs_loc, &location_type, loc);
 
-    rbs_loc_init(loc, buffer, (rbs_loc_range) { .start = start_char, .end = end_char });
+    rbs_loc_init(loc, Qnil, (rbs_loc_range) { .start = start_char, .end = end_char });
+    RB_OBJ_WRITE(obj, &loc->buffer, buffer);
 
     return obj;
 }
@@ -211,7 +215,8 @@ static VALUE rbs_new_location_from_loc_range(VALUE buffer, rbs_loc_range rg) {
     rbs_loc *loc;
     VALUE obj = TypedData_Make_Struct(RBS_Location, rbs_loc, &location_type, loc);
 
-    rbs_loc_init(loc, buffer, rg);
+    rbs_loc_init(loc, Qnil, rg);
+    RB_OBJ_WRITE(obj, &loc->buffer, buffer);
 
     return obj;
 }