reduce impact of 'unsafe C derivative' error to pointers and fix conditional expressions

Cython/Compiler/ExprNodes.py

@@ -9755,6 +9755,9 @@ class CondExprNode(ExprNode):
         else:
             self.constant_result = self.false_val.constant_result
 
+    def is_ephemeral(self):
+        return self.true_val.is_ephemeral() or self.false_val.is_ephemeral()
+
     def analyse_types(self, env):
         self.test = self.test.analyse_types(env).coerce_to_boolean(env)
         self.true_val = self.true_val.analyse_types(env)
@@ -9767,6 +9770,8 @@ class CondExprNode(ExprNode):
             self.true_val.type, self.false_val.type)
         if self.type.is_pyobject:
             self.result_ctype = py_object_type
+        elif self.true_val.is_ephemeral() or self.false_val.is_ephemeral():
+            error(self.pos, "Unsafe C derivative of temporary Python reference used in conditional expression")
         if self.true_val.type.is_pyobject or self.false_val.type.is_pyobject:
             self.true_val = self.true_val.coerce_to(self.type, env)
             self.false_val = self.false_val.coerce_to(self.type, env)
@@ -9798,7 +9803,7 @@ class CondExprNode(ExprNode):
         code.mark_pos(self.pos)
         self.allocate_temp_result(code)
         self.test.generate_evaluation_code(code)
-        code.putln("if (%s) {" % self.test.result() )
+        code.putln("if (%s) {" % self.test.result())
         self.eval_and_get(code, self.true_val)
         code.putln("} else {")
         self.eval_and_get(code, self.false_val)
@@ -9813,6 +9818,13 @@ class CondExprNode(ExprNode):
         expr.generate_post_assignment_code(code)
         expr.free_temps(code)
 
+    def generate_subexpr_disposal_code(self, code):
+        pass  # done explicitly above (cleanup must separately happen within the if/else blocks)
+
+    def free_subexpr_temps(self, code):
+        pass  # done explicitly above (cleanup must separately happen within the if/else blocks)
+
+
 richcmp_constants = {
     "<" : "Py_LT",
     "<=": "Py_LE",

Cython/Compiler/Nodes.py

@@ -4559,7 +4559,7 @@ class AssignmentNode(StatNode):
     def analyse_expressions(self, env):
         node = self.analyse_types(env)
         if isinstance(node, AssignmentNode):
-            if not node.rhs.type.is_pyobject and node.rhs.is_ephemeral():
+            if node.rhs.type.is_ptr and node.rhs.is_ephemeral():
                 error(self.pos, "Storing unsafe C derivative of temporary Python reference")
         return node
 

tests/errors/charptr_from_temp.pyx

@@ -44,6 +44,14 @@ cuptr = u
 cuptr = u + u"cba"
 
 
+# coercion in conditional expression => ok
+boolval = list(u)
+cptr = c_s if boolval else c_s
+
+# temp in conditional expression => error
+cptr = s + b'x' if boolval else s + b'y'
+
+
 _ERRORS = """
 16:8: Obtaining 'char *' from externally modifiable global Python value
 19:9: Storing unsafe C derivative of temporary Python reference
@@ -53,4 +61,6 @@ _ERRORS = """
 26:8: Storing unsafe C derivative of temporary Python reference
 41:9: Obtaining 'Py_UNICODE *' from externally modifiable global Python value
 44:10: Storing unsafe C derivative of temporary Python reference
+52:7: Storing unsafe C derivative of temporary Python reference
+52:7: Unsafe C derivative of temporary Python reference used in conditional expression
 """

tests/run/if_else_expr.pyx

@@ -40,5 +40,5 @@ def test_charptr_coercion(x):
     >>> print(test_charptr_coercion(False))
     def
     """
-    cdef char* s = 'abc' if x else 'def'
+    cdef char* s = b'abc' if x else b'def'
     return s.decode('ascii')