Adds support for swiftsourceinfo

[codeman9]

I took a stab at #496

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[codeman9]

@googlebot I signed it!

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[keith]

do we know what Xcode uses this for yet?

[codeman9]

do we know what Xcode uses this for yet?

No, I'm not sure what Xcode uses this for at the moment.

This is all the info I've found, I'm sure you've seen: https://forums.swift.org/t/proposal-emitting-source-information-file-during-compilation/28794 but I'm sure Xcode got/gets this information in other ways.

[keith]

yea it would just be nice to see what this fixes / breaks so we know it's producing valid ones

[codeman9]

yea it would just be nice to see what this fixes / breaks so we know it's producing valid ones

I will look into it a bit and see what I can find out.

[codeman9]

From a @kastiglione thread I found: "it's for swiftc to emit diagnostics across module boundaries" and "so as I understand, it's useful to the IDE only indirectly (the IDE displaying the compiler's diagnostics)"