John Snow <jsnow@redhat.com> writes:
On 12/16/20 4:22 AM, Markus Armbruster wrote:
2. On error with "no source info", don't crash.
I have my doubts on this one.
Such an error means the QAPI code generator screwed up, at least
in
theory. Crashing is only proper. It gets the screwup fixed.
QAPISemError and friends will also halt the generator and don't
produce output and will fail tests. They aren't less visible or more
ignorable somehow.
In practice, errors due to interactions between built-in stuff and
user-defined stuff could conceivably escape testing. I can't
remember such a case offhand.
Will the "no source info" error be more useful than a crash?
Possibly. Will it get the screwup fixed? Maybe not.
I don't understand this; if it's an error -- there's no QAPI, there's
no QEMU. It's definitely getting fixed.
If QAPISourceInfo is primarily used for printing error information, we
are already in a situation where the generator is hosed and has
wandered itself into a problem that can't be ignored.
There's no additional value in having python crash twice per every
crash because we have bad types in our error reporting functions.
Consider the following scenario. The average developer knows just
enough about QAPI to be dangerous. That's okay; if you had to be a QAPI
expert to modify the QAPI schema, we would have failed. Now meet Joe
Average. He's a good guy. Today his job happens to require extending
the QAPI schema. In a hurry, as usual. So Joe brings his well-honed
voodoo programming skills to bear, and writes something that looks
plausible to him. His build fails. He's not surprised; he's voodoo-
programming after all. However, the error message is less clear than
usual. Something about a '[builtin]' file. There is no '[builtin]'
file. What to do? Obvious! If a bit of voodoo doesn't get you over
the finish line, use more: twiddle the schema until it works.
If his build failed with a Python backtrace instead, Joe would
immediately know that he ran into a bug in our tooling he should report.
Again, I don't mean to criticize Joe. I've walked in his shoes myself.