Merge pull request #256 from masamitsu-murase/modify_string_slice

"slice" of shared string returns invalid result

src/string.c

@@ -1199,14 +1199,14 @@ mrb_str_eql(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_str_subseq(mrb_state *mrb, mrb_value str, int beg, int len)
 {
-  struct RString *s;
+  struct RString *orig, *s;
   struct mrb_shared_string *shared;
 
-  s = mrb_str_ptr(str);
-  str_make_shared(mrb, s);
-  shared = s->aux.shared;
+  orig = mrb_str_ptr(str);
+  str_make_shared(mrb, orig);
+  shared = orig->aux.shared;
   s = mrb_obj_alloc_string(mrb);
-  s->ptr = shared->ptr + beg;
+  s->ptr = orig->ptr + beg;
   s->len = len;
   s->aux.shared = shared;
   s->flags |= MRB_STR_SHARED;

test/t/string.rb

@@ -256,6 +256,9 @@ assert('String#slice', '15.2.10.5.34') do
   d1 = 'abc'.slice(0, 0)
   e1 = 'abc'.slice(1, 2)
 
+  # slice of shared string
+  e11 = e1.slice(0)
+
   # args is RegExp
   # TODO SEGFAULT ATM
 
@@ -265,7 +268,7 @@ assert('String#slice', '15.2.10.5.34') do
 
   a == 'a' and b == 'c' and c == nil and d == nil and
     a1 == nil and b1 == nil and c1 == nil and d1 == '' and
-    e1 == 'bc' and
+    e1 == 'bc' and e11 == 'b' and
     a3 == 'bc' and b3 == nil
 end