Implement Write Barrier

StringScanner holds the string being scanned, and a regex for methods
like `match?`. Triggering the write barrier for those allows us to mark
this as WB protected.

Author: composerinteralia

ext/strscan/strscan.c

@@ -209,7 +209,7 @@ strscan_memsize(const void *ptr)
 static const rb_data_type_t strscanner_type = {
     "StringScanner",
     {strscan_mark, strscan_free, strscan_memsize},
-    0, 0, RUBY_TYPED_FREE_IMMEDIATELY
+    0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED
 };
 
 static VALUE
@@ -273,7 +273,7 @@ strscan_initialize(int argc, VALUE *argv, VALUE self)
         p->fixed_anchor_p = false;
     }
     StringValue(str);
-    p->str = str;
+    RB_OBJ_WRITE(self, &p->str, str);
 
     return self;
 }
@@ -303,7 +303,7 @@ strscan_init_copy(VALUE vself, VALUE vorig)
     orig = check_strscan(vorig);
     if (self != orig) {
 	self->flags = orig->flags;
-	self->str = orig->str;
+	RB_OBJ_WRITE(vself, &self->str, orig->str);
 	self->prev = orig->prev;
 	self->curr = orig->curr;
 	if (rb_reg_region_copy(&self->regs, &orig->regs))
@@ -467,7 +467,7 @@ strscan_set_string(VALUE self, VALUE str)
     struct strscanner *p = check_strscan(self);
 
     StringValue(str);
-    p->str = str;
+    RB_OBJ_WRITE(self, &p->str, str);
     p->curr = 0;
     CLEAR_MATCH_STATUS(p);
     return str;
@@ -712,7 +712,7 @@ strscan_do_scan(VALUE self, VALUE pattern, int succptr, int getstr, int headonly
 
     if (RB_TYPE_P(pattern, T_REGEXP)) {
         OnigPosition ret;
-        p->regex = pattern;
+        RB_OBJ_WRITE(self, &p->regex, pattern);
         ret = rb_reg_onig_match(p->regex,
                                 p->str,
                                 headonly ? strscan_match : strscan_search,