Implement compaction and embedded structs (#201)

GC compaction was introduced in Ruby 2.7.

Embedded Structs was introduced in Ruby 3.3. When enabled, the `struct
strscanner` is stored directly inside the object slot, meaning reading
the struct member doesn't require loading another memory region.

Author: byroot

ext/strscan/extconf.rb

@@ -5,6 +5,8 @@
   have_func("onig_region_memsize(NULL)")
   have_func("rb_reg_onig_match", "ruby/re.h")
   have_func("rb_deprecate_constant")
+  have_func("rb_gc_location", "ruby.h") # RUBY_VERSION >= 2.7
+  have_const("RUBY_TYPED_EMBEDDABLE", "ruby.h") # RUBY_VERSION >= 3.3
   create_makefile 'strscan'
 else
   File.write('Makefile', dummy_makefile("").join)

ext/strscan/strscan.c

@@ -182,37 +182,73 @@ extract_beg_len(struct strscanner *p, long beg_i, long len)
                                Constructor
    ======================================================================= */
 
+#ifdef RUBY_TYPED_EMBEDDABLE
+#  define HAVE_RUBY_TYPED_EMBEDDABLE 1
+#else
+# ifdef HAVE_CONST_RUBY_TYPED_EMBEDDABLE
+#  define RUBY_TYPED_EMBEDDABLE RUBY_TYPED_EMBEDDABLE
+#  define HAVE_RUBY_TYPED_EMBEDDABLE 1
+# else
+#  define RUBY_TYPED_EMBEDDABLE 0
+# endif
+#endif
+
+#ifdef HAVE_RB_GC_LOCATION
+static void
+strscan_compact(void *ptr)
+{
+    struct strscanner *p = ptr;
+    p->str = rb_gc_location(p->str);
+    p->regex = rb_gc_location(p->regex);
+}
+#else
+#define rb_gc_mark_movable rb_gc_mark
+#endif
+
 static void
 strscan_mark(void *ptr)
 {
     struct strscanner *p = ptr;
-    rb_gc_mark(p->str);
-    rb_gc_mark(p->regex);
+    rb_gc_mark_movable(p->str);
+    rb_gc_mark_movable(p->regex);
 }
 
 static void
 strscan_free(void *ptr)
 {
     struct strscanner *p = ptr;
     onig_region_free(&(p->regs), 0);
+#ifndef HAVE_RUBY_TYPED_EMBEDDABLE
     ruby_xfree(p);
+#endif
 }
 
 static size_t
 strscan_memsize(const void *ptr)
 {
-    const struct strscanner *p = ptr;
-    size_t size = sizeof(*p) - sizeof(p->regs);
+    size_t size = 0;
+#ifndef HAVE_RUBY_TYPED_EMBEDDABLE
+    size += sizeof(struct strscanner);
+#endif
+
 #ifdef HAVE_ONIG_REGION_MEMSIZE
-    size += onig_region_memsize(&p->regs);
+    const struct strscanner *p = ptr;
+    size += onig_region_memsize(&p->regs) - sizeof(p->regs);
 #endif
     return size;
 }
 
 static const rb_data_type_t strscanner_type = {
-    "StringScanner",
-    {strscan_mark, strscan_free, strscan_memsize},
-    0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED
+    .wrap_struct_name = "StringScanner",
+    .function = {
+        .dmark = strscan_mark,
+        .dfree = strscan_free,
+        .dsize = strscan_memsize,
+#ifdef HAVE_RB_GC_LOCATION
+        .dcompact = strscan_compact,
+#endif
+    },
+    .flags = RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED | RUBY_TYPED_EMBEDDABLE
 };
 
 static VALUE