Every time DarwinSDKInfo reads a new key out of SDKSettings, a boatload
of test SDKSettings files need to be updated across several repositories
and forks and branches. It’s tedious to be careful to update those with
real values so that the tests are properly regression testing older
SDKs. It’s important to be careful so that the tests are accurate, e.g.
to prevent the scenario where DarwinSDKInfo starts reading a new key out
of SDKSettings and assumes that it’s always available everywhere, when
in reality it was only added a few releases ago and will break with
older SDKs. If the test SDKSettings files continue to be updated ad hoc,
it’s going to be really easy to copy/paste a default value everywhere,
and then clients will see incorrect behaviors with the real SDKs, or
even compiler crashes if the key is unconditionally read. Preemptively
add all of the maybe-possibly-compiler relevant keys to the test
SDKSettings files from the real SDKs so that the test files are an
accurate representation and shouldn't need to be touched in the future.
Where the test SDKSettings have intentionally doctored data, add a
Comments key explaining what is changed from the real SDK, and alter the
SDK name with a tag indicating the change.
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