Better fix for #1836: set frame flags to make CPython create a new dict for...

Better fix for #1836: set frame flags to make CPython create a new dict for "frame.f_locals" at need.

Cython/Compiler/ExprNodes.py

@@ -9249,7 +9249,9 @@ class CodeObjectNode(ExprNode):
         file_path = StringEncoding.bytes_literal(func.pos[0].get_filenametable_entry().encode('utf8'), 'utf8')
         file_path_const = code.get_py_string_const(file_path, identifier=False, is_str=True)
 
-        flags = []
+        # This combination makes CPython create a new dict for "frame.f_locals" (see GH #1836).
+        flags = ['CO_OPTIMIZED', 'CO_NEWLOCALS']
+
         if self.def_node.star_arg:
             flags.append('CO_VARARGS')
         if self.def_node.starstar_arg:

Cython/Utility/Profile.c

@@ -252,7 +252,7 @@ static int __Pyx_TraceSetupAndCall(PyCodeObject** code,
             tstate,                          /*PyThreadState *tstate*/
             *code,                           /*PyCodeObject *code*/
             $moddict_cname,                  /*PyObject *globals*/
-            PyDict_New()                     /*PyObject *locals*/
+            0                                /*PyObject *locals*/
         );
         if (*frame == NULL) return 0;
         if (CYTHON_TRACE && (*frame)->f_trace == NULL) {
@@ -311,7 +311,8 @@ static PyCodeObject *__Pyx_createFrameCodeObject(const char *funcname, const cha
         #endif
         0,                /*int nlocals,*/
         0,                /*int stacksize,*/
-        0,                /*int flags,*/
+        // make CPython use a fresh dict for "f_locals" at need (see GH #1836)
+        CO_OPTIMIZED | CO_NEWLOCALS,  /*int flags,*/
         $empty_bytes,     /*PyObject *code,*/
         $empty_tuple,     /*PyObject *consts,*/
         $empty_tuple,     /*PyObject *names,*/

tests/run/line_trace.pyx

@@ -58,9 +58,23 @@ cdef int trace_trampoline(PyObject* _traceobj, PyFrameObject* _frame, int what,
 
 
 def _create_trace_func(trace):
+    local_names = {}
+
     def _trace_func(frame, event, arg):
-        trace.append((map_trace_types(event), frame.f_lineno -
-                                      frame.f_code.co_firstlineno))
+        trace.append((map_trace_types(event), frame.f_lineno - frame.f_code.co_firstlineno))
+
+        lnames = frame.f_code.co_varnames
+        if frame.f_code.co_name in local_names:
+            assert lnames == local_names[frame.f_code.co_name]
+        else:
+            local_names[frame.f_code.co_name] = lnames
+
+        # Currently, the locals dict is empty for Cython code, but not for Python code.
+        if frame.f_code.co_name.startswith('py_'):
+            # Change this when we start providing proper access to locals.
+            assert frame.f_locals
+        else:
+            assert not frame.f_locals
 
         return _trace_func
     return _trace_func
@@ -232,3 +246,14 @@ def disable_trace(func, *args):
     finally:
         PyEval_SetTrace(NULL, None)
     return trace
+
+
+def global_name(global_name):
+    """
+    >>> global_name(123)
+    444
+    >>> global_name(111)
+    432
+    """
+    # See GH #1836: accessing "frame.f_locals" deletes locals from globals dict.
+    return global_name + 321