From af80c0248f26a8715d9f8647f9988ceded644061 Mon Sep 17 00:00:00 2001
From: Zac-HD <zac.hatfield.dodds@gmail.com>
Date: Tue, 7 Sep 2021 16:33:04 +1000
Subject: [PATCH 1/5] Strip trailing whitespace

---
 README.rst | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/README.rst b/README.rst
index e8934f3..322edc8 100644
--- a/README.rst
+++ b/README.rst
@@ -123,9 +123,9 @@ waste CPU instructions. Either prepend ``assert`` or remove it.
 **B016**: Cannot raise a literal. Did you intend to return it or raise
 an Exception?
 
-**B017**: ``self.assertRaises(Exception):`` should be considered evil. It can lead 
-to your test passing even if the code being tested is never executed due to a typo. 
-Either assert for a more specific exception (builtin or custom), use 
+**B017**: ``self.assertRaises(Exception):`` should be considered evil. It can lead
+to your test passing even if the code being tested is never executed due to a typo.
+Either assert for a more specific exception (builtin or custom), use
 ``assertRaisesRegex``, or use the context manager form of assertRaises
 (``with self.assertRaises(Exception) as ex:``) with an assertion against the
 data available in ``ex``.
@@ -220,7 +220,7 @@ Change Log
 21.4.3
 ~~~~~~
 
-* Verify the element in item_context.args is of type ast.Name for b017 
+* Verify the element in item_context.args is of type ast.Name for b017
 
 21.4.2
 ~~~~~~
@@ -231,7 +231,7 @@ Change Log
 ~~~~~~
 
 * Add B017: check for gotta-catch-em-all assertRaises(Exception)
-  
+
 21.3.2
 ~~~~~~
 

From 4fd2e86b5d0d39f029e52865ffce18ba5e3cbe35 Mon Sep 17 00:00:00 2001
From: Zac-HD <zac.hatfield.dodds@gmail.com>
Date: Tue, 7 Sep 2021 16:33:04 +1000
Subject: [PATCH 2/5] Add B018 - use exc chaining

---
 README.rst            | 10 ++++++++++
 bugbear.py            | 20 ++++++++++++++++++++
 tests/b018.py         | 18 ++++++++++++++++++
 tests/test_bugbear.py | 12 ++++++++++++
 4 files changed, 60 insertions(+)
 create mode 100644 tests/b018.py

diff --git a/README.rst b/README.rst
index 322edc8..de585e6 100644
--- a/README.rst
+++ b/README.rst
@@ -130,6 +130,11 @@ Either assert for a more specific exception (builtin or custom), use
 (``with self.assertRaises(Exception) as ex:``) with an assertion against the
 data available in ``ex``.
 
+**B018**: Within an ``except`` clause, raise exceptions with ``raise ... from err``
+or ``raise ... from None`` to distinguish them from errors in exception handling.
+See [the exception chaining tutorial](https://docs.python.org/3/tutorial/errors.html#exception-chaining)
+for details.
+
 
 Opinionated warnings
 ~~~~~~~~~~~~~~~~~~~~
@@ -217,6 +222,11 @@ MIT
 Change Log
 ----------
 
+Future
+~~~~~~
+
+* Add B018: check for ``raise`` without ``from`` in an ``except`` clause
+
 21.4.3
 ~~~~~~
 
diff --git a/bugbear.py b/bugbear.py
index 68b09db..0f26af7 100644
--- a/bugbear.py
+++ b/bugbear.py
@@ -292,6 +292,7 @@ def visit_Compare(self, node):
 
     def visit_Raise(self, node):
         self.check_for_b016(node)
+        self.check_for_b018(node)
         self.generic_visit(node)
 
     def visit_With(self, node):
@@ -426,6 +427,18 @@ def check_for_b017(self, node):
         ):
             self.errors.append(B017(node.lineno, node.col_offset))
 
+    def check_for_b018(self, node):
+        """Checks `raise` without `from` inside an `except` clause.
+
+        In these cases, you should use explicit exception chaining from the
+        earlier error, or suppress it with `raise ... from None`.  See
+        https://docs.python.org/3/tutorial/errors.html#exception-chaining
+        """
+        if node.cause is None and node.exc is not None and any(
+            isinstance(n, ast.ExceptHandler) for n in self.node_stack
+        ):
+            self.errors.append(B018(node.lineno, node.col_offset))
+
     def walk_function_body(self, node):
         def _loop(parent, node):
             if isinstance(node, (ast.AsyncFunctionDef, ast.FunctionDef)):
@@ -746,6 +759,13 @@ def visit(self, node):
         "context manager form of assertRaises."
     )
 )
+B018 = Error(
+    message=(
+        "B018 Within an `except` clause, raise exceptions with `raise ... from err` "
+        "or `raise ... from None` to distinguish them from errors in exception handling.  "
+        "See https://docs.python.org/3/tutorial/errors.html#exception-chaining for details."
+    )
+)
 
 # Warnings disabled by default.
 B901 = Error(
diff --git a/tests/b018.py b/tests/b018.py
new file mode 100644
index 0000000..e0d2098
--- /dev/null
+++ b/tests/b018.py
@@ -0,0 +1,18 @@
+"""
+Should emit:
+B018 - on lines 10, 11 and 16
+"""
+
+try:
+    raise ValueError
+except ValueError:
+    if "abc":
+        raise TypeError
+    raise UserWarning
+except AssertionError:
+    raise  # Bare `raise` should not be an error
+except Exception as err:
+    assert err
+    raise Exception("No cause here...")
+finally:
+    raise Exception("Nothing to chain from, so no warning here")
diff --git a/tests/test_bugbear.py b/tests/test_bugbear.py
index 0807f19..ee8c259 100644
--- a/tests/test_bugbear.py
+++ b/tests/test_bugbear.py
@@ -28,6 +28,7 @@
     B015,
     B016,
     B017,
+    B018,
     B901,
     B902,
     B903,
@@ -207,6 +208,17 @@ def test_b017(self):
         expected = self.errors(B017(22, 8))
         self.assertEqual(errors, expected)
 
+    def test_b018(self):
+        filename = Path(__file__).absolute().parent / "b018.py"
+        bbc = BugBearChecker(filename=str(filename))
+        errors = list(bbc.run())
+        expected = [
+            B018(10, 8),
+            B018(11, 4),
+            B018(16, 4),
+        ]
+        self.assertEqual(errors, self.errors(*expected))
+
     def test_b901(self):
         filename = Path(__file__).absolute().parent / "b901.py"
         bbc = BugBearChecker(filename=str(filename))

From 235ebae9418f1ee7511829347005acd1ffd288f9 Mon Sep 17 00:00:00 2001
From: Zac-HD <zac.hatfield.dodds@gmail.com>
Date: Tue, 7 Sep 2021 16:33:05 +1000
Subject: [PATCH 3/5] Format with black

---
 .flake8    | 2 +-
 bugbear.py | 6 ++++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/.flake8 b/.flake8
index dae0ba2..066df22 100644
--- a/.flake8
+++ b/.flake8
@@ -2,7 +2,7 @@
 # Keep in sync with setup.cfg which is used for source packages.
 
 [flake8]
-ignore = E203, E302, E501, E999
+ignore = E203, E302, E501, E999, W503
 max-line-length = 88
 max-complexity = 12
 select = B,C,E,F,W,B9
diff --git a/bugbear.py b/bugbear.py
index 0f26af7..9abc302 100644
--- a/bugbear.py
+++ b/bugbear.py
@@ -434,8 +434,10 @@ def check_for_b018(self, node):
         earlier error, or suppress it with `raise ... from None`.  See
         https://docs.python.org/3/tutorial/errors.html#exception-chaining
         """
-        if node.cause is None and node.exc is not None and any(
-            isinstance(n, ast.ExceptHandler) for n in self.node_stack
+        if (
+            node.cause is None
+            and node.exc is not None
+            and any(isinstance(n, ast.ExceptHandler) for n in self.node_stack)
         ):
             self.errors.append(B018(node.lineno, node.col_offset))
 

From 07a3c3dd91bf8d6ec1d40c75be7c9977716f4f64 Mon Sep 17 00:00:00 2001
From: Zac-HD <zac.hatfield.dodds@gmail.com>
Date: Tue, 7 Sep 2021 16:33:05 +1000
Subject: [PATCH 4/5] Allow explicit re-raise

This is useful when you want to explicitly modify the traceback, as done by Hypothesis and Trio
---
 bugbear.py    | 1 +
 tests/b018.py | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/bugbear.py b/bugbear.py
index 9abc302..5b2da3c 100644
--- a/bugbear.py
+++ b/bugbear.py
@@ -437,6 +437,7 @@ def check_for_b018(self, node):
         if (
             node.cause is None
             and node.exc is not None
+            and not (isinstance(node.exc, ast.Name) and node.exc.id.islower())
             and any(isinstance(n, ast.ExceptHandler) for n in self.node_stack)
         ):
             self.errors.append(B018(node.lineno, node.col_offset))
diff --git a/tests/b018.py b/tests/b018.py
index e0d2098..5d61237 100644
--- a/tests/b018.py
+++ b/tests/b018.py
@@ -14,5 +14,8 @@
 except Exception as err:
     assert err
     raise Exception("No cause here...")
+except BaseException as base_err:
+    # Might use this instead of bare raise with the `.with_traceback()` method
+    raise base_err
 finally:
     raise Exception("Nothing to chain from, so no warning here")

From 20a54139c8c5aef1d0243190fefa372256225afc Mon Sep 17 00:00:00 2001
From: Zac-HD <zac.hatfield.dodds@gmail.com>
Date: Wed, 8 Sep 2021 18:52:11 +1000
Subject: [PATCH 5/5] Disable raises check by default

---
 README.rst                 | 12 ++++++------
 bugbear.py                 | 23 ++++++++++++-----------
 tests/{b018.py => b904.py} |  2 +-
 tests/test_bugbear.py      | 24 ++++++++++++------------
 4 files changed, 31 insertions(+), 30 deletions(-)
 rename tests/{b018.py => b904.py} (94%)

diff --git a/README.rst b/README.rst
index de585e6..7f81cc5 100644
--- a/README.rst
+++ b/README.rst
@@ -130,11 +130,6 @@ Either assert for a more specific exception (builtin or custom), use
 (``with self.assertRaises(Exception) as ex:``) with an assertion against the
 data available in ``ex``.
 
-**B018**: Within an ``except`` clause, raise exceptions with ``raise ... from err``
-or ``raise ... from None`` to distinguish them from errors in exception handling.
-See [the exception chaining tutorial](https://docs.python.org/3/tutorial/errors.html#exception-chaining)
-for details.
-
 
 Opinionated warnings
 ~~~~~~~~~~~~~~~~~~~~
@@ -162,6 +157,11 @@ nothing else. If the attributes should be mutable, define the attributes
 in ``__slots__`` to save per-instance memory and to prevent accidentally
 creating additional attributes on instances.
 
+**B904**: Within an ``except`` clause, raise exceptions with ``raise ... from err``
+or ``raise ... from None`` to distinguish them from errors in exception handling.
+See [the exception chaining tutorial](https://docs.python.org/3/tutorial/errors.html#exception-chaining)
+for details.
+
 **B950**: Line too long. This is a pragmatic equivalent of
 ``pycodestyle``'s E501: it considers "max-line-length" but only triggers
 when the value has been exceeded by **more than 10%**. You will no
@@ -225,7 +225,7 @@ Change Log
 Future
 ~~~~~~
 
-* Add B018: check for ``raise`` without ``from`` in an ``except`` clause
+* Add B904: check for ``raise`` without ``from`` in an ``except`` clause
 
 21.4.3
 ~~~~~~
diff --git a/bugbear.py b/bugbear.py
index 5b2da3c..44cf9d4 100644
--- a/bugbear.py
+++ b/bugbear.py
@@ -292,7 +292,7 @@ def visit_Compare(self, node):
 
     def visit_Raise(self, node):
         self.check_for_b016(node)
-        self.check_for_b018(node)
+        self.check_for_b904(node)
         self.generic_visit(node)
 
     def visit_With(self, node):
@@ -427,7 +427,7 @@ def check_for_b017(self, node):
         ):
             self.errors.append(B017(node.lineno, node.col_offset))
 
-    def check_for_b018(self, node):
+    def check_for_b904(self, node):
         """Checks `raise` without `from` inside an `except` clause.
 
         In these cases, you should use explicit exception chaining from the
@@ -440,7 +440,7 @@ def check_for_b018(self, node):
             and not (isinstance(node.exc, ast.Name) and node.exc.id.islower())
             and any(isinstance(n, ast.ExceptHandler) for n in self.node_stack)
         ):
-            self.errors.append(B018(node.lineno, node.col_offset))
+            self.errors.append(B904(node.lineno, node.col_offset))
 
     def walk_function_body(self, node):
         def _loop(parent, node):
@@ -762,13 +762,6 @@ def visit(self, node):
         "context manager form of assertRaises."
     )
 )
-B018 = Error(
-    message=(
-        "B018 Within an `except` clause, raise exceptions with `raise ... from err` "
-        "or `raise ... from None` to distinguish them from errors in exception handling.  "
-        "See https://docs.python.org/3/tutorial/errors.html#exception-chaining for details."
-    )
-)
 
 # Warnings disabled by default.
 B901 = Error(
@@ -798,6 +791,14 @@ def visit(self, node):
     )
 )
 
+B904 = Error(
+    message=(
+        "B904 Within an `except` clause, raise exceptions with `raise ... from err` "
+        "or `raise ... from None` to distinguish them from errors in exception handling.  "
+        "See https://docs.python.org/3/tutorial/errors.html#exception-chaining for details."
+    )
+)
+
 B950 = Error(message="B950 line too long ({} > {} characters)")
 
-disabled_by_default = ["B901", "B902", "B903", "B950"]
+disabled_by_default = ["B901", "B902", "B903", "B904", "B950"]
diff --git a/tests/b018.py b/tests/b904.py
similarity index 94%
rename from tests/b018.py
rename to tests/b904.py
index 5d61237..104fda8 100644
--- a/tests/b018.py
+++ b/tests/b904.py
@@ -1,6 +1,6 @@
 """
 Should emit:
-B018 - on lines 10, 11 and 16
+B904 - on lines 10, 11 and 16
 """
 
 try:
diff --git a/tests/test_bugbear.py b/tests/test_bugbear.py
index ee8c259..3f91edc 100644
--- a/tests/test_bugbear.py
+++ b/tests/test_bugbear.py
@@ -28,7 +28,7 @@
     B015,
     B016,
     B017,
-    B018,
+    B904,
     B901,
     B902,
     B903,
@@ -208,17 +208,6 @@ def test_b017(self):
         expected = self.errors(B017(22, 8))
         self.assertEqual(errors, expected)
 
-    def test_b018(self):
-        filename = Path(__file__).absolute().parent / "b018.py"
-        bbc = BugBearChecker(filename=str(filename))
-        errors = list(bbc.run())
-        expected = [
-            B018(10, 8),
-            B018(11, 4),
-            B018(16, 4),
-        ]
-        self.assertEqual(errors, self.errors(*expected))
-
     def test_b901(self):
         filename = Path(__file__).absolute().parent / "b901.py"
         bbc = BugBearChecker(filename=str(filename))
@@ -272,6 +261,17 @@ def test_b903(self):
         errors = list(bbc.run())
         self.assertEqual(errors, self.errors(B903(32, 0), B903(38, 0)))
 
+    def test_b904(self):
+        filename = Path(__file__).absolute().parent / "b904.py"
+        bbc = BugBearChecker(filename=str(filename))
+        errors = list(bbc.run())
+        expected = [
+            B904(10, 8),
+            B904(11, 4),
+            B904(16, 4),
+        ]
+        self.assertEqual(errors, self.errors(*expected))
+
     def test_b950(self):
         filename = Path(__file__).absolute().parent / "b950.py"
         bbc = BugBearChecker(filename=str(filename))