On 4/15/21 3:00 AM, Markus Armbruster wrote:
John Snow <jsnow@redhat.com> writes:
On 3/30/21 1:18 PM, John Snow wrote:
Realizing now that this commit topic is wrong :)
A prior version modified the assertion, I decided it was less churn to
simply add one.
I think ideally we'd have no assertions here and we'd rely on the type
hints, but I don't think I can prove that this is safe until after part
6, so I did this for now instead.
Eventually, we'll be able to prove that 'info.line' must be an int and
is never None at static analysis time, and this assert can go
away. Until then, it's a type error to assume that self.info is not
None.
Signed-off-by: John Snow <jsnow@redhat.com>
---
scripts/qapi/error.py | 1 +
1 file changed, 1 insertion(+)
diff --git a/scripts/qapi/error.py b/scripts/qapi/error.py
index d179a3bd0c..d0bc7af6e7 100644
--- a/scripts/qapi/error.py
+++ b/scripts/qapi/error.py
@@ -25,6 +25,7 @@ def __init__(self, info, msg, col=None):
self.col = col
def __str__(self):
+ assert self.info is not None
loc = str(self.info)
if self.col is not None:
assert self.info.line is not None
Please show us the revised commit message. I'm asking because the
patch's purpose isn't quite clear to me. Peeking ahead at PATCH 7, I
see that info becomes Optional[QAPISourceInfo]. This means something
passes None for info (else you wouldn't make it optional). None info
Works (in the sense of "doesn't crash") as long as col is also None.
After the patch, it doesn't. I'm not saying that's bad, only that I
don't quite understand what you're trying to accomplish here.
Sure.
If you recall, I tried to enforce that QAPISourceInfo was *never* None
by creating a special value for QSI that represented "No Source
Info". Ultimately, that idea didn't go through and we solidified that
the 'info' parameter that gets passed around can sometimes be None.
Hence, this property is Optional[QAPISourceInfo].
Since I know you wanted to crash messily in the case that we allowed a
None-info to leak into a context like this, I added the new assertion
to make sure this remains the case.
(since str(None) evaluates to "None", it seemed like there was already
the implicit assumption that info would never be None. Plus, if 'col'
is set, mypy notices that we are performing an unsafe check on
self.info.line, which had to be remedied.)
Later in the series, after schema.py is typed, it may be possible to
remove these assertions as we may be able to rely on the strict typing
to prove that this situation can never occur. However, since schema.py
is not yet typed, we can't yet.
Alright. So given that, I think what you'd like to see for a commit
message is:
qapi/error: assert QAPISourceInfo is not None
We implicitly assume that self.info will never be None, as the error
reporting function will not produce meaningful output in this case,
and will crash if self.col was set. Assert that self.info is not None
in order to formalize this assumption.
We can not yet change the type of the initializer to prove that this
is provably true at static analysis time until the rest of this
library is fully typed.