Eric Blake <ebl...@redhat.com> writes: > On 05/04/2017 03:06 AM, Markus Armbruster wrote: >> Eduardo Habkost <ehabk...@redhat.com> writes: >> >>> On Wed, May 03, 2017 at 06:07:43PM +0200, Markus Armbruster wrote: >>>> Eduardo Habkost <ehabk...@redhat.com> writes: >>>> >>>>> When parsing alternates from a string, there are some limitations in >>>>> what we can do, but it is a valid use case in some situations. We can >>>>> support booleans, integer types, and enums. >> >> By the way, the same restrictions apply to the "keyval" variant of the >> QObject input visitor. It's a known problem stated here: >> >> Message-ID: <8737exuz6u....@dusky.pond.sub.org> >> https://lists.gnu.org/archive/html/qemu-devel/2017-03/msg00046.html >> >> However, I failed to document it properly in the source. >> > >>>> Begs the question what happens when you violate these restrictions. >>> >>> Right now, we don't detect those cases and behavior is undefined. >>> I think it will be a good idea to give start_alternate() enough >>> information to detect those cases (by adding a 'const char *const >>> enum_table[]' parameter). >> >> Alternate types that won't work with the string input visitor can be >> detected at compile time (by qapi.py), but not their actual use. Pity. >> >> Do we actually use alternates that violate the restrictions? If not, we >> could simply restrict alternates so they work with *all* visitors. If >> we ever run into an actual need for alternates that don't, we'll be no >> worse off than now. >> >> Let's review existing alternates outside tests: >> >> * Qcow2OverlapChecks: struct + enum >> * BlockdevRef: struct + str >> * GuestFileWhence: int + enum (all enum members start with a letter) >> >> Restricting alternates looks practical to me. Eric, what do you think? > > As in: we forbid the combination of a scalar (whether 'int', 'number', > 'bool', and perhaps 'null') with a plain 'str' (since there's no way to > tell whether '1' should parse as an integer or the string "1"); and > combining a scalar with an 'enum' requires that all enum members be > distinct from what could otherwise be parsed as a scalar?
Exactly. > I can live > with such a restriction. Then let's do it. Eduardo, are you comfortable implementing this, or would you like me to do it?
