Fix rb_interned_str_* functions to not assume static strings

Fixes [Feature #13381]

When passed a `fake_str`, `register_fstring` would create new strings
with `str_new_static`. That's not what was expected, and answer
almost no use cases.

1 files changed, 14 insertions, 0 deletions

diff --git a/ext/-test-/string/rb_interned_str.c b/ext/-test-/string/rb_interned_str.c
new file mode 100644
index 0000000..47643ec
--- /dev/null
+++ b/ext/-test-/string/rb_interned_str.c
@@ -0,0 +1,14 @@
+#include "ruby.h"
+
+static VALUE
+bug_rb_interned_str_dup(VALUE self, VALUE str)
+{
+    Check_Type(str, T_STRING);
+    return rb_interned_str(RSTRING_PTR(str), RSTRING_LEN(str));
+}
+
+void
+Init_string_rb_interned_str(VALUE klass)
+{
+    rb_define_singleton_method(klass, "rb_interned_str_dup", bug_rb_interned_str_dup, 1);
+}