John Snow <js...@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.
