Emit W0102 (dangerous default value) when sets are used as default arguments for functions. Closes #92911

4 files changed, 26 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index b75206f81..68c6d0433 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,6 +3,9 @@ ChangeLog for PyLint
 
 	--
 
+    * Emit W0102 when sets are used as default arguments in functions
+      (patch by tmarek@google.com)
+
     * #77982 Do not emit E0602 for loop variables of comprehensions
       used as argument values inside a decorator (patch by tmarek@google.com)
 
diff --git a/checkers/base.py b/checkers/base.py
index c551a3576..5de570ff1 100644
--- a/checkers/base.py
+++ b/checkers/base.py
@@ -428,6 +428,12 @@ functions, methods
                 else:
                     msg = '%s (%s)' % (default.as_string(), value.as_string())
                 self.add_message('W0102', node=node, args=(msg,))
+            if value.qname() == '__builtin__.set':
+                if isinstance(default, astng.CallFunc):
+                    msg = default.as_string()
+                else:
+                    msg = '%s (%s)' % (default.as_string(), value.qname())
+                self.add_message('W0102', node=node, args=(msg,))
 
     @check_messages('W0101', 'W0150')
     def visit_return(self, node):
diff --git a/test/input/func_dangerous_default.py b/test/input/func_dangerous_default.py
index 0bf87278c..8a526e2eb 100644
--- a/test/input/func_dangerous_default.py
+++ b/test/input/func_dangerous_default.py
@@ -15,3 +15,18 @@ def function2(value = HEHE):
 def function3(value):
     """docstring"""
     print value
+
+def function4(value = set()):
+    """set is mutable and dangerous."""
+    print value
+
+def function5(value = frozenset()):
+    """frozenset is immutable and safe."""
+    print value
+
+GLOBAL_SET = set()
+
+def function6(value = GLOBAL_SET):
+    """set is mutable and dangerous."""
+    print value
+
diff --git a/test/messages/func_dangerous_default.txt b/test/messages/func_dangerous_default.txt
index 21d32e022..b8828443a 100644
--- a/test/messages/func_dangerous_default.txt
+++ b/test/messages/func_dangerous_default.txt
@@ -1,2 +1,4 @@
 W:  7:function1: Dangerous default value [] as argument
 W: 11:function2: Dangerous default value HEHE ({}) as argument
+W: 19:function4: Dangerous default value set() as argument
+W: 29:function6: Dangerous default value GLOBAL_SET (__builtin__.set) as argument