B022: No arguments passed to contextlib.suppress (#231)

* B022: No arguments passed to contextlib.suppress
  * Update README.rst
  * Disclaimer note on rule scope

Author: jpy-git

README.rst

@@ -141,6 +141,12 @@ garbage collection.
 **B021**: f-string used as docstring. This will be interpreted by python
 as a joined string rather than a docstring.
 
+**B022**: No arguments passed to `contextlib.suppress`.
+No exceptions will be suppressed and therefore this context manager is redundant.
+N.B. this rule currently does not flag `suppress` calls to avoid potential false
+positives due to similarly named user-defined functions.
+
+
 Opinionated warnings
 ~~~~~~~~~~~~~~~~~~~~
 

bugbear.py

@@ -387,6 +387,7 @@ def visit_Raise(self, node):
 
     def visit_With(self, node):
         self.check_for_b017(node)
+        self.check_for_b022(node)
         self.generic_visit(node)
 
     def compose_call_path(self, node):
@@ -739,6 +740,20 @@ def check_for_b021(self, node):
                 B021(node.body[0].value.lineno, node.body[0].value.col_offset)
             )
 
+    def check_for_b022(self, node):
+        item = node.items[0]
+        item_context = item.context_expr
+        if (
+            hasattr(item_context, "func")
+            and hasattr(item_context.func, "value")
+            and hasattr(item_context.func.value, "id")
+            and item_context.func.value.id == "contextlib"
+            and hasattr(item_context.func, "attr")
+            and item_context.func.attr == "suppress"
+            and len(item_context.args) == 0
+        ):
+            self.errors.append(B022(node.lineno, node.col_offset))
+
 
 @attr.s
 class NameFinder(ast.NodeVisitor):
@@ -965,6 +980,13 @@ def visit(self, node):
         "This will be interpreted by python as a joined string rather than a docstring."
     )
 )
+B022 = Error(
+    message=(
+        "B022 No arguments passed to `contextlib.suppress`."
+        "No exceptions will be suppressed and therefore this"
+        "context manager is redundant."
+    )
+)
 
 # Warnings disabled by default.
 B901 = Error(

tests/b022.py

@@ -0,0 +1,19 @@
+"""
+Should emit:
+B022 - on lines 8
+"""
+
+import contextlib
+
+with contextlib.suppress():
+    raise ValueError
+
+with contextlib.suppress(ValueError):
+    raise ValueError
+
+exceptions_to_suppress = []
+if True:
+    exceptions_to_suppress.append(ValueError)
+
+with contextlib.suppress(*exceptions_to_suppress):
+    raise ValueError

tests/test_bugbear.py

@@ -32,6 +32,7 @@
     B019,
     B020,
     B021,
+    B022,
     B901,
     B902,
     B903,
@@ -303,6 +304,12 @@ def test_b021_classes(self):
         )
         self.assertEqual(errors, expected)
 
+    def test_b022(self):
+        filename = Path(__file__).absolute().parent / "b022.py"
+        bbc = BugBearChecker(filename=str(filename))
+        errors = list(bbc.run())
+        self.assertEqual(errors, self.errors(B022(8, 0)))
+
     def test_b901(self):
         filename = Path(__file__).absolute().parent / "b901.py"
         bbc = BugBearChecker(filename=str(filename))