Fix memory leak

* string.c (str_replace_shared_without_enc): free previous buffer
  before replaced.

* parse.y (gettable): make sure in advance that the `__FILE__`
  object shares a fstring, to get rid of replacement with the
  fstring later.
  TODO: this hack may be needed in other places.

[Bug #15916]

Co-Authored-By: luke-gru (Luke Gruber) <luke.gru@gmail.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/string.c b/string.c
index b37b8542c7..186c71b40c 100644
--- a/string.c
+++ b/string.c
@@ -1162,6 +1162,13 @@ str_replace_shared_without_enc(VALUE str2, VALUE str)
     }
     else {
 	str = rb_str_new_frozen(str);
+        if (!STR_EMBED_P(str2) && !FL_TEST_RAW(str2, STR_SHARED|STR_NOFREE)) {
+            /* TODO: check if str2 is a shared root */
+            char *ptr2 = STR_HEAP_PTR(str2);
+            if (STR_HEAP_PTR(str) != ptr2) {
+                ruby_sized_xfree(ptr2, STR_HEAP_SIZE(str2));
+            }
+        }
 	FL_SET(str2, STR_NOEMBED);
 	RSTRING_GETMEM(str, ptr, len);
 	RSTRING(str2)->as.heap.len = len;