From 2d2e0d2f236e21bd0b6722823d95bf0aeaf24316 Mon Sep 17 00:00:00 2001
From: Hynek Schlawack <hs@ox.cx>
Date: Wed, 4 Nov 2020 10:04:20 +0100
Subject: [PATCH 1/4] Fix exception chaining on PyPy

Fixes #703
---
 changelog.d/703.change.rst |  1 +
 src/attr/_make.py          | 29 ++++++++++++++++++++++++-----
 tests/test_next_gen.py     | 31 +++++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+), 5 deletions(-)
 create mode 100644 changelog.d/703.change.rst

diff --git a/changelog.d/703.change.rst b/changelog.d/703.change.rst
new file mode 100644
index 000000000..c0fde46f6
--- /dev/null
+++ b/changelog.d/703.change.rst
@@ -0,0 +1 @@
+``raise from`` now works on frozen classes on PyPy.
diff --git a/src/attr/_make.py b/src/attr/_make.py
index 84b63d55c..49484f935 100644
--- a/src/attr/_make.py
+++ b/src/attr/_make.py
@@ -12,6 +12,7 @@
 from . import _config, setters
 from ._compat import (
     PY2,
+    PYPY,
     isclass,
     iteritems,
     metadata_proxy,
@@ -527,11 +528,29 @@ def _transform_attrs(
     return _Attributes((attrs, base_attrs, base_attr_map))
 
 
-def _frozen_setattrs(self, name, value):
-    """
-    Attached to frozen classes as __setattr__.
-    """
-    raise FrozenInstanceError()
+if PYPY:
+
+    def _frozen_setattrs(self, name, value):
+        """
+        Attached to frozen classes as __setattr__.
+        """
+        if isinstance(self, BaseException) and name in (
+            "__cause__",
+            "__context__",
+        ):
+            BaseException.__setattr__(self, name, value)
+            return
+
+        raise FrozenInstanceError()
+
+
+else:
+
+    def _frozen_setattrs(self, name, value):
+        """
+        Attached to frozen classes as __setattr__.
+        """
+        raise FrozenInstanceError()
 
 
 def _frozen_delattrs(self, name):
diff --git a/tests/test_next_gen.py b/tests/test_next_gen.py
index 941ec0a57..0ebad8d2f 100644
--- a/tests/test_next_gen.py
+++ b/tests/test_next_gen.py
@@ -4,6 +4,8 @@
 
 import re
 
+from functools import partial
+
 import pytest
 
 import attr
@@ -238,3 +240,32 @@ class B:
             @attr.define(on_setattr=attr.setters.validate)
             class C(A):
                 pass
+
+    @pytest.mark.parametrize(
+        "decorator",
+        [
+            partial(attr.s, frozen=True, slots=True, auto_exc=True),
+            attr.frozen,
+            attr.define,
+            attr.mutable,
+        ],
+    )
+    def test_discard_context(self, decorator):
+        """
+        raise from None works.
+
+        Regression test for #703.
+        """
+
+        @decorator
+        class MyException(Exception):
+            x: str = attr.ib()
+
+        with pytest.raises(MyException) as ei:
+            try:
+                raise ValueError()
+            except ValueError:
+                raise MyException("foo") from None
+
+        assert "foo" == ei.value.x
+        assert ei.value.__cause__ is None

From e419166305d9e1f0225b58bb37b53a31f94b31cc Mon Sep 17 00:00:00 2001
From: Hynek Schlawack <hs@ox.cx>
Date: Wed, 4 Nov 2020 10:06:11 +0100
Subject: [PATCH 2/4] Add newsfragment

---
 changelog.d/712.change.rst | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/712.change.rst

diff --git a/changelog.d/712.change.rst b/changelog.d/712.change.rst
new file mode 100644
index 000000000..c0fde46f6
--- /dev/null
+++ b/changelog.d/712.change.rst
@@ -0,0 +1 @@
+``raise from`` now works on frozen classes on PyPy.

From 4df8a987beb608af4d3d787abc0ca9010d0e24a5 Mon Sep 17 00:00:00 2001
From: Hynek Schlawack <hs@ox.cx>
Date: Wed, 4 Nov 2020 10:13:25 +0100
Subject: [PATCH 3/4] Blankly exclude PyPy from coverage reporting

---
 pyproject.toml      | 4 ++++
 src/attr/_compat.py | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index f711b8c06..c41357b30 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -13,6 +13,10 @@ source = ["src", ".tox/*/site-packages"]
 
 [tool.coverage.report]
 show_missing = true
+exclude_lines = [
+    # PyPy is unacceptably slow under coverage.
+    "if PYPY:",
+]
 
 
 [tool.black]
diff --git a/src/attr/_compat.py b/src/attr/_compat.py
index bed5b1357..f55a8265d 100644
--- a/src/attr/_compat.py
+++ b/src/attr/_compat.py
@@ -132,7 +132,7 @@ def make_set_closure_cell():
     """
     # pypy makes this easy. (It also supports the logic below, but
     # why not do the easy/fast thing?)
-    if PYPY:  # pragma: no cover
+    if PYPY:
 
         def set_closure_cell(cell, value):
             cell.__setstate__((value,))

From d9370b0e4ad5e7e5f1ee41026d43a5c8ab3ed953 Mon Sep 17 00:00:00 2001
From: Hynek Schlawack <hs@ox.cx>
Date: Wed, 4 Nov 2020 10:31:13 +0100
Subject: [PATCH 4/4] Manually add default no cover marker

---
 pyproject.toml      | 1 +
 src/attr/_compat.py | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index c41357b30..14f65a366 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -14,6 +14,7 @@ source = ["src", ".tox/*/site-packages"]
 [tool.coverage.report]
 show_missing = true
 exclude_lines = [
+    "pragma: no cover",
     # PyPy is unacceptably slow under coverage.
     "if PYPY:",
 ]
diff --git a/src/attr/_compat.py b/src/attr/_compat.py
index f55a8265d..b0ead6e1c 100644
--- a/src/attr/_compat.py
+++ b/src/attr/_compat.py
@@ -91,7 +91,7 @@ def metadata_proxy(d):
         res.data.update(d)  # We blocked update, so we have to do it like this.
         return res
 
-    def just_warn(*args, **kw):  # pragma: nocover
+    def just_warn(*args, **kw):  # pragma: no cover
         """
         We only warn on Python 3 because we are not aware of any concrete
         consequences of not setting the cell on Python 2.