string.c: fix rb_external_str_new_with_enc

* string.c (rb_external_str_new_with_enc): do not search non-ascii
  by NULL pointer.  [ruby-core:84055] [Bug #14150]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60979 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/-test-/string/new.c

@@ -0,0 +1,21 @@
+#include "ruby.h"
+#include "ruby/encoding.h"
+
+VALUE
+bug_str_buf_new(VALUE self, VALUE len)
+{
+    return rb_str_buf_new(NUM2LONG(len));
+}
+
+VALUE
+bug_external_str_new(VALUE self, VALUE len, VALUE enc)
+{
+    return rb_external_str_new_with_enc(NULL, NUM2LONG(len), rb_to_encoding(enc));
+}
+
+void
+Init_new(VALUE klass)
+{
+    rb_define_singleton_method(klass, "buf_new", bug_str_buf_new, 1);
+    rb_define_singleton_method(klass, "external_new", bug_external_str_new, 2);
+}

string.c

@@ -1011,6 +1011,10 @@ rb_external_str_new_with_enc(const char *ptr, long len, rb_encoding *eenc)
     VALUE str;
     const int eidx = rb_enc_to_index(eenc);
 
+    if (!ptr) {
+	return rb_tainted_str_new_with_enc(ptr, len, eenc);
+    }
+
     /* ASCII-8BIT case, no conversion */
     if ((eidx == rb_ascii8bit_encindex()) ||
 	(eidx == rb_usascii_encindex() && search_nonascii(ptr, ptr + len))) {

test/-ext-/string/test_external_new.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: false
+require 'test/unit'
+require '-test-/string'
+
+class Test_StringExternalNew < Test::Unit::TestCase
+  def test_external_new_with_enc
+    Encoding.list.each do |enc|
+      assert_equal(enc, Bug::String.external_new(0, enc).encoding)
+    end
+  end
+end