[SR-11293] swift-format crashes on ubuntu 19.04

[apple]

[SR-11293] swift-format crashes on ubuntu 19.04

[allevato]

I've also run into this on Linux, but admittedly it's not a platform that I'm regularly able to test on.

This appears to be an issue in swift-syntax; if I remember correctly, the call to dlsym here is returning nil instead of the pointer to the symbol that's statically linked into the executable:

https://github.com/apple/swift-syntax/blob/master/Sources/SwiftSyntax/AtomicCounter.swift#L42

I think the fact that SwiftSyntax uses dlsym to find that C function at runtime might mean that any Linux clients will be forced to pass something like --export-dynamic to the linker.

@akyrtzi, do you have any insight here?

[akyrtzi]

Whoa, I wasn't aware the `dlsym` trick is not working for linux. The point of this was to avoid needing to add a separate module, that would also have to be present for `import SwiftSyntax` to work, for just a single C function.

But instead of this trick, we could probably be able to use the `@_implementationOnly import` feature that was introduced in swift-5.1

[allevato]

swiftlang/swift-syntax#140 fixes the underlying issue in SwiftSyntax, but I'll wait to close this out until swift-format has been updated to depend on a version that includes that change.