niti: fix CString::fast_cstring semantics

The old implementation of CString::fast_cstring used to create a new
CString instance instead of sharing the underlying buffer.

This in turn caused code relying on this semantic to fail as the memory
was not re-initialized properly.

This commit fixes this behaviour by introducing a new cstring
constructor specific for the VM and Interpreter.

Signed-off-by: Lucas Bajolet <lucas.bajolet@gmail.com>

diff --git a/src/interpreter/naive_interpreter.nit b/src/interpreter/naive_interpreter.nit
index ac7b970..45032fe 100644 (file)
--- a/src/interpreter/naive_interpreter.nit
+++ b/src/interpreter/naive_interpreter.nit
@@ -342,6 +342,18 @@ class NaiveInterpreter
                return instance
        end
 
+       # Return a new C string instance sharing the same data space as `txt`
+       fun c_string_instance_fast_cstr(txt: CString, from: Int): Instance
+       do
+               var ncstr = txt.fast_cstring(from)
+               var t = mainmodule.c_string_type
+
+               var instance = new PrimitiveInstance[CString](t, ncstr)
+               init_instance_primitive(instance)
+
+               return instance
+       end
+
        # Return a new C string initialized of `length`
        fun c_string_instance_len(length: Int): PrimitiveInstance[CString]
        do
@@ -1194,8 +1206,7 @@ redef class AMethPropdef
                        else if pname == "atoi" then
                                return v.int_instance(recvval.atoi)
                        else if pname == "fast_cstring" then
-                               var ns = recvval.fast_cstring(args[1].to_i)
-                               return v.c_string_instance(ns.to_s)
+                               return v.c_string_instance_fast_cstr(args[0].val.as(CString), args[1].to_i)
                        else if pname == "fetch_4_chars" then
                                return v.uint32_instance(args[0].val.as(CString).fetch_4_chars(args[1].to_i))
                        else if pname == "fetch_4_hchars" then