json-stream reporter should always print at least {} on error

[bhamiltoncx]

I upgraded Xcode to 7.2 today without installing the simulators.

When I used xctool -reporter json-stream from Buck, Buck's JSON parser failed because xctool printed nothing to stdout (not even an empty JSON object {}). It did print an error message to stderr:

% /path/to/xctool -reporter json-stream -sdk iphonesimulator run-tests -logicTest /path/to/test.xctest
ERROR: SDK 'iphonesimulator' doesn't exist. Possible SDKs include:

It'd be nice if xctool could make sure to print a valid JSON object to stdout even on failure.

[bhamiltoncx]

(This is arguably not really that big of a deal, so feel free to close if you don't agree. I just filed it in case you wanted to consider including error reporting inside json-stream or another reporter.)

[ExtremeMan]

Thanks for filing. I will have a look if it is something easy to fix. We have many asserts in the code though. So if we even fix such error messages and log them appropriately to reporters we will hit the same issue if any of asserts fires.

[bhamiltoncx]

Right. I think asserts are probably not the best check for a lot of these (especially ones which can fire due to user-provided data).

It's probably time to introduce real error-reporting infrastructure to xctool and stop relying on asserts :)