implement String.new in Ruby

Co-authored-by: jhawthorn <john@hawthorn.email>

Author: tenderlove

common.mk

@@ -1201,6 +1201,7 @@ BUILTIN_RB_SRCS = \
 		$(srcdir)/ractor.rb \
 		$(srcdir)/string.rb \
 		$(srcdir)/symbol.rb \
+		$(srcdir)/string.rb \
 		$(srcdir)/timev.rb \
 		$(srcdir)/thread_sync.rb \
 		$(srcdir)/nilclass.rb \

inits.c

@@ -107,6 +107,7 @@ rb_call_builtin_inits(void)
     BUILTIN(hash);
     BUILTIN(string);
     BUILTIN(symbol);
+    BUILTIN(string);
     BUILTIN(timev);
     BUILTIN(thread_sync);
     BUILTIN(nilclass);

string.c

@@ -50,6 +50,7 @@
 #include "shape.h"
 #include "vm_sync.h"
 #include "ruby/internal/attr/nonstring.h"
+#include "builtin.h"
 
 #if defined HAVE_CRYPT_R
 # if defined HAVE_CRYPT_H
@@ -2142,29 +2143,26 @@ rb_str_init(int argc, VALUE *argv, VALUE str)
     return str;
 }
 
-/* :nodoc: */
+/* String.new fast path: no positional argument and no keywords.
+ * Returns the same empty, embedded, ASCII-8BIT string that String's alloc
+ * func produces (klass is always rb_cString here; the Ruby-side dispatch
+ * routes subclasses through Class#new). */
 static VALUE
-rb_str_s_new(int argc, VALUE *argv, VALUE klass)
+rb_str_s_new_empty(rb_execution_context_t *ec, VALUE klass)
 {
-    if (klass != rb_cString) {
-        return rb_class_new_instance_pass_kw(argc, argv, klass);
-    }
+    return empty_str_alloc(klass);
+}
 
-    static ID keyword_ids[2];
-    VALUE orig, opt, encoding = Qnil, capacity = Qnil;
-    VALUE kwargs[2];
+/* :nodoc: */
+static VALUE
+rb_str_s_new(struct rb_execution_context_struct *ec, VALUE klass, VALUE orig, VALUE no_str, VALUE encoding, VALUE no_encoding, VALUE capacity, VALUE no_capacity)
+{
     rb_encoding *enc = NULL;
+    int n = 0;
 
-    int n = rb_scan_args(argc, argv, "01:", &orig, &opt);
-    if (NIL_P(opt)) {
-        return rb_class_new_instance_pass_kw(argc, argv, klass);
-    }
-
-    keyword_ids[0] = rb_id_encoding();
-    CONST_ID(keyword_ids[1], "capacity");
-    rb_get_kwargs(opt, keyword_ids, 0, 2, kwargs);
-    encoding = kwargs[0];
-    capacity = kwargs[1];
+    if (RTEST(no_encoding)) encoding = Qundef;
+    if (RTEST(no_capacity)) capacity = Qundef;
+    if (!RTEST(no_str)) n = 1;
 
     if (n == 1) {
         orig = StringValue(orig);
@@ -12887,7 +12885,6 @@ Init_String(void)
 
     rb_include_module(rb_cString, rb_mComparable);
     rb_define_alloc_func(rb_cString, empty_str_alloc);
-    rb_define_singleton_method(rb_cString, "new", rb_str_s_new, -1);
     rb_define_singleton_method(rb_cString, "try_convert", rb_str_s_try_convert, 1);
     rb_define_method(rb_cString, "initialize", rb_str_init, -1);
     rb_define_method(rb_cString, "replace", rb_str_replace, 1);

string.rb

@@ -22,4 +22,35 @@ def ascii_only?
     Primitive.attr! :leaf
     Primitive.cexpr! 'rb_str_is_ascii_only_p(self)'
   end
+
+  # :nodoc:
+  def self._new(orig = (no_str = true; nil),
+                encoding: (no_encoding = true; nil),
+                capacity: (no_capacity = true; nil))
+
+    Primitive.rb_str_s_new(orig, no_str, encoding, no_encoding, capacity, no_capacity)
+  end
+  private_class_method :_new
+
+  #  call-seq:
+  #    String.new(string = ''.encode(Encoding::ASCII_8BIT), **options) -> new_string
+  #
+  #  :include: doc/string/new.rdoc
+  #
+  def self.new(...)
+    # If the receiver isn't a String, jbb
+    if Primitive.mandatory_only?
+      if String.equal?(self)
+        Primitive.rb_str_s_new_empty
+      else
+        super
+      end
+    else
+      if String.equal?(self)
+        _new(...)
+      else
+        super
+      end
+    end
+  end
 end