nogil fix: disallow ExprStatNode to clean up Python expression results without holding the GIL

Cython/Compiler/Nodes.py

@@ -3346,6 +3346,12 @@ class ExprStatNode(StatNode):
     def analyse_expressions(self, env):
         self.expr.analyse_expressions(env)
 
+    def nogil_check(self, env):
+        if self.expr.type.is_pyobject:
+            self.gil_error()
+
+    gil_message = "Discarding owned Python object"
+
     def generate_execution_code(self, code):
         self.expr.generate_evaluation_code(code)
         if not self.expr.is_temp and self.expr.result():

tests/errors/nogil.pyx

@@ -89,13 +89,17 @@ _ERRORS = u"""
 1:5: Function with Python return type cannot be declared nogil
 4:5: Function declared nogil has Python locals or temporaries
 6:6: Assignment of Python object not allowed without gil
+9:5: Discarding owned Python object not allowed without gil
 11:5: Function with Python return type cannot be declared nogil
 15:5: Calling gil-requiring function not allowed without gil
 24:9: Calling gil-requiring function not allowed without gil
 26:12: Assignment of Python object not allowed without gil
+28:8: Discarding owned Python object not allowed without gil
 28:16: Constructing complex number not allowed without gil
 29:12: Accessing Python global or builtin not allowed without gil
+29:12: Discarding owned Python object not allowed without gil
 30:8: Backquote expression not allowed without gil
+30:8: Discarding owned Python object not allowed without gil
 30:9: Operation not allowed without gil
 31:15: Assignment of Python object not allowed without gil
 31:15: Operation not allowed without gil
@@ -105,20 +109,30 @@ _ERRORS = u"""
 32:25: Constructing Python list not allowed without gil
 32:25: Operation not allowed without gil
 33:17: Iterating over Python object not allowed without gil
+35:11: Discarding owned Python object not allowed without gil
 35:11: Indexing Python object not allowed without gil
+36:11: Discarding owned Python object not allowed without gil
 36:11: Slicing Python object not allowed without gil
 37:11: Constructing Python slice object not allowed without gil
+37:11: Discarding owned Python object not allowed without gil
 37:11: Indexing Python object not allowed without gil
 37:13: Converting to Python object not allowed without gil
 37:15: Converting to Python object not allowed without gil
 37:17: Converting to Python object not allowed without gil
 38:11: Accessing Python attribute not allowed without gil
-39: 9: Constructing Python tuple not allowed without gil
-40: 8: Constructing Python list not allowed without gil
-41: 8: Constructing Python dict not allowed without gil
+38:11: Discarding owned Python object not allowed without gil
+39:9: Constructing Python tuple not allowed without gil
+39:9: Discarding owned Python object not allowed without gil
+40:8: Constructing Python list not allowed without gil
+40:8: Discarding owned Python object not allowed without gil
+41:8: Constructing Python dict not allowed without gil
+41:8: Discarding owned Python object not allowed without gil
+42:12: Discarding owned Python object not allowed without gil
 42:12: Truth-testing Python object not allowed without gil
 43:13: Python type test not allowed without gil
+45:10: Discarding owned Python object not allowed without gil
 45:10: Operation not allowed without gil
+46:8: Discarding owned Python object not allowed without gil
 46:8: Operation not allowed without gil
 47:10: Assignment of Python object not allowed without gil
 47:14: Assignment of Python object not allowed without gil