Simplify error_already_set
`error_already_set` is more complicated than it needs to be, partly
because it manages reference counts itself rather than using
`py::object`, and partly because it tries to do more exception clearing
than is needed. This commit greatly simplifies it, and fixes #927.
Using `py::object` instead of `PyObject *` means we can rely on
implicit copy/move constructors.
The current logic did both a `PyErr_Clear` on deletion *and* a
`PyErr_Fetch` on creation. I can't see how the `PyErr_Clear` on
deletion is ever useful: the `Fetch` on creation itself clears the
error, so the only way doing a `PyErr_Clear` on deletion could do
anything if is some *other* exception was raised while the
`error_already_set` object was alive--but in that case, clearing some
other exception seems wrong. (Code that is worried about an exception
handler raising another exception would already catch a second
`error_already_set` from exception code).
The destructor itself called `clear()`, but `clear()` was a little bit
more paranoid that needed: it called `restore()` to restore the
currently captured error, but then immediately cleared it, using the
`PyErr_Restore` to release the references. That's unnecessary: it's
valid for us to release the references manually. This updates the code
to simply release the references on the three objects (preserving the
gil acquire).
`clear()`, however, also had the side effect of clearing the current
error, even if the current `error_already_set` didn't have a current
error (e.g. because of a previous `restore()` or `clear()` call). I
don't really see how clearing the error here can ever actually be
useful: the only way the current error could be set is if you called
`restore()` (in which case the current stored error-related members have
already been released), or if some *other* code raised the error, in
which case `clear()` on *this* object is clearing an error for which it
shouldn't be responsible.
Neither of those seem like intentional or desirable features, and
manually requesting deletion of the stored references similarly seems
pointless, so I've just made `clear()` an empty method and marked it
deprecated.
This also fixes a minor potential issue with the destruction: it is
technically possible for `value` to be null (though this seems likely to
be rare in practice); this updates the check to look at `type` which
will always be non-null for a `Fetch`ed exception.
This also adds error_already_set round-trip throw tests to the test
suite.
diff --git a/tests/test_exceptions.py b/tests/test_exceptions.py
index cc4baaa..06d442e 100644
--- a/tests/test_exceptions.py
+++ b/tests/test_exceptions.py
@@ -76,3 +76,47 @@
except m.MyException5_1:
raise RuntimeError("Exception error: caught child from parent")
assert msg(excinfo.value) == "this is a helper-defined translated exception"
+
+
+def test_nested_throws(capture):
+ """Tests nested (e.g. C++ -> Python -> C++) exception handling"""
+
+ def throw_myex():
+ raise m.MyException("nested error")
+
+ def throw_myex5():
+ raise m.MyException5("nested error 5")
+
+ # In the comments below, the exception is caught in the first step, thrown in the last step
+
+ # C++ -> Python
+ with capture:
+ m.try_catch(m.MyException5, throw_myex5)
+ assert str(capture).startswith("MyException5: nested error 5")
+
+ # Python -> C++ -> Python
+ with pytest.raises(m.MyException) as excinfo:
+ m.try_catch(m.MyException5, throw_myex)
+ assert str(excinfo.value) == "nested error"
+
+ def pycatch(exctype, f, *args):
+ try:
+ f(*args)
+ except m.MyException as e:
+ print(e)
+
+ # C++ -> Python -> C++ -> Python
+ with capture:
+ m.try_catch(
+ m.MyException5, pycatch, m.MyException, m.try_catch, m.MyException, throw_myex5)
+ assert str(capture).startswith("MyException5: nested error 5")
+
+ # C++ -> Python -> C++
+ with capture:
+ m.try_catch(m.MyException, pycatch, m.MyException5, m.throws4)
+ assert capture == "this error is rethrown"
+
+ # Python -> C++ -> Python -> C++
+ with pytest.raises(m.MyException5) as excinfo:
+ m.try_catch(m.MyException, pycatch, m.MyException, m.throws5)
+ assert str(excinfo.value) == "this is a helper-defined translated exception"