Disable output file map diagnostic for non-incremental mode

[keith]

This re-implements this logic https://github.com/apple/swift/blob/3116eed2e465a2688f070b3b87adc106cbbaf09f/lib/Driver/Driver.cpp#L414-L417 to not warn when output file maps don't have a main entry when using WMO

[davidungar]

Thank you for doing this. It looks good, but before merging I'd like to see an XCTest added to check this. It might be easiest to add a test in IncrementalCompilationTests.swift, in which the test runs the driver both with- and without the -incremental flag and checks to see whether the diagnostic is emitted when appropriate.

Would you like to add such a test?

[brentleyjones]

FYI, this is still an issue in Xcode 13.0 beta 4.

[keith]

Updated with tests!

[artemcm]

@swift-ci please test

[artemcm]

@davidungar could you please take another look? It looks good to go to me.

[keith]

@davidungar mind taking another look here?

[keith]

@davidungar mind taking another look here?

[brentleyjones]

@artemcm @davidungar Could we please have another look at this? Thanks!

[davidungar]

Sorry this PR slipped under my radar. Thanks to @CodaFi for pinging me. In future, please feel free to ping me directly.
It would be great if you could add a comment somewhere (if it's not already there) explaining why one would want to exclude the main entry, or under what circumstances. Otherwise, LGTM and thank you for your patience!

[keith]

Done, thanks for following up. To be clear where do you mean when you say "ping you directly"?

[artemcm]

@swift-ci please test

[brentleyjones]

@artemcm Is this able to get CP'ed into 5.5?

[artemcm]

@artemcm Is this able to get CP'ed into 5.5?

Yeah, I think this change is pretty safe.
Please create a cherry-pick PR against release/5.5 and use something like swiftlang/swift#39140 as a template for the PR description.

[keith]

Thanks! Submitted #828 for the CP