New buffer for shared string

* string.c (rb_str_init): allocate new buffer if the string is
  shared.  [Bug #15937]

1 files changed, 9 insertions, 0 deletions

diff --git a/string.c b/string.c
index e402a5a7aa..3feeb8c705 100644
--- a/string.c
+++ b/string.c
@@ -1615,6 +1615,15 @@ rb_str_init(int argc, VALUE *argv, VALUE str)
                 char *new_ptr = ALLOC_N(char, (size_t)capa + termlen);
                 memcpy(new_ptr, RSTRING(str)->as.ary, RSTRING_EMBED_LEN_MAX + 1);
                 RSTRING(str)->as.heap.ptr = new_ptr;
+            }
+            else if (FL_TEST(str, STR_SHARED|STR_NOFREE)) {
+                const size_t size = (size_t)capa + termlen;
+                const char *const old_ptr = RSTRING_PTR(str);
+                const size_t osize = RSTRING(str)->as.heap.len + TERM_LEN(str);
+                char *new_ptr = ALLOC_N(char, (size_t)capa + termlen);
+                memcpy(new_ptr, old_ptr, osize < size ? osize : size);
+                FL_UNSET_RAW(str, STR_SHARED);
+                RSTRING(str)->as.heap.ptr = new_ptr;
 	    }
 	    else if (STR_HEAP_SIZE(str) != (size_t)capa + termlen) {
 		SIZED_REALLOC_N(RSTRING(str)->as.heap.ptr, char,