Acquire GIL in nogil contexts to raise UnboundLocalError for unbound memoryview slices

Cython/Compiler/Code.py

@@ -1784,12 +1784,16 @@ class CCodeWriter(object):
 #        return self.putln("if (unlikely(%s < 0)) %s" % (value, self.error_goto(pos)))  # TODO this path is almost _never_ taken, yet this macro makes is slower!
         return self.putln("if (%s < 0) %s" % (value, self.error_goto(pos)))
 
-    def put_error_if_unbound(self, pos, entry):
+    def put_error_if_unbound(self, pos, entry, in_nogil_context=False):
         import ExprNodes
         if entry.from_closure:
             func = '__Pyx_RaiseClosureNameError'
             self.globalstate.use_utility_code(
                 ExprNodes.raise_closure_name_error_utility_code)
+        elif entry.type.is_memoryviewslice and in_nogil_context:
+            func = '__Pyx_RaiseUnboundMemoryviewSliceNogil'
+            self.globalstate.use_utility_code(
+                ExprNodes.raise_unbound_memoryview_utility_code_nogil)
         else:
             func = '__Pyx_RaiseUnboundLocalError'
             self.globalstate.use_utility_code(

Cython/Compiler/ExprNodes.py

@@ -1704,7 +1704,7 @@ class NameNode(AtomicExprNode):
             memslice_check = entry.type.is_memoryviewslice and self.initialized_check
 
             if null_code and raise_unbound and (entry.type.is_pyobject or memslice_check):
-                code.put_error_if_unbound(self.pos, entry)
+                code.put_error_if_unbound(self.pos, entry, self.in_nogil_context)
 
     def generate_assignment_code(self, rhs, code):
         #print "NameNode.generate_assignment_code:", self.name ###
@@ -9670,6 +9670,24 @@ static CYTHON_INLINE void __Pyx_RaiseClosureNameError(const char *varname) {
 }
 """)
 
+# Don't inline the function, it should really never be called in production
+raise_unbound_memoryview_utility_code_nogil = UtilityCode(
+proto = """
+static void __Pyx_RaiseUnboundMemoryviewSliceNogil(const char *varname);
+""",
+impl = """
+static void __Pyx_RaiseUnboundMemoryviewSliceNogil(const char *varname) {
+    #ifdef WITH_THREAD
+    PyGILState_STATE gilstate = PyGILState_Ensure();
+    #endif
+    __Pyx_RaiseUnboundLocalError(varname);
+    #ifdef WITH_THREAD")
+    PyGILState_Release(gilstate);
+    #endif
+}
+""",
+requires = [raise_unbound_local_error_utility_code])
+
 #------------------------------------------------------------------------------------
 
 getitem_dict_utility_code = UtilityCode(

tests/run/memoryview.pyx

@@ -197,6 +197,17 @@ def test_cdef_attribute():
 
     print ExtClass().mview
 
+@cython.boundscheck(False)
+def test_nogil_unbound_localerror():
+    """
+    >>> test_nogil_unbound_localerror()
+    Traceback (most recent call last):
+        ...
+    UnboundLocalError: local variable 'm' referenced before assignment
+    """
+    cdef int[:] m
+    with nogil:
+        m[0] = 10
 
 def basic_struct(MyStruct[:] mslice):
     """

tests/run/memslice.pyx

@@ -2043,3 +2043,4 @@ def test_dtype_object_scalar_assignment():
 
     (<object> m)[:] = SingleObject(3)
     assert m[0] == m[4] == m[-1] == 3
+