Swift: teach autobuilder about SPM, CocoaPods, and Carthage

[AlexDenisov]

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[AlexDenisov]

Tests for SPM are not here, I'll add them in a later PR when I convert Xcode autobuilder into Swift autobuilder and make it also available on Linux.

[redsun82]

thanks!

[redsun82]

TIL about this ?: GNU extension that I knew nothing about 🙂

As a nit, this can be made more standard conforming using std::string_view, which contrary to std::string accepts a nullptr (and treats it equivalent to ""). Or move the getenv as a nested if, for example

if (!target.podfiles.empty()) {
  if (auto pod = getenv("CODEQL_SWIFT_POD_EXEC")) {
    pod_install(pod, podfile, dryRun);
  }
}

or as one single if with initialization:

if (auto pod = getenv("CODEQL_SWIFT_POD_EXEC"); pod && !target.podfiles.empty()) {
  pod_install(pod, podfile, dryRun);
}

[AlexDenisov]

The first snippet is not exactly correct as we may have podfiles on linux, but won't have pod executable there.
And I don't find the second necessarily better than what we have now

[redsun82]

as far as I understand, the first snippet is equivalent, as the pod installation will happen only if both the conditions are met. The conditions are just evaluated in swapped order (and the env variable won't be inspected if podfiles is empty).

What itches me here, is the use of a non-standard extension, that might also be surprising to some developers (it was a bit to me). On the other hand, we do enforce compilation with clang, so maybe the non-standardness is not such a big deal... It's just that I personally only use non-standard C++ stuff when there is no sensible alternative, which I think there is here.

But that's a nit, I'm also kinda ok with leaving this as is.

[AlexDenisov]

This is as non-standard as #pragma once 😄

[redsun82]

maybe as you are anyway creating this structure with fields for the different kinds of files, you can also split .xcodeproj and .xcworkspace in separate xcodeProjects and xcodeWorkspaces fields of this structure, and avoid testing the extension again later?

[AlexDenisov]

Yeah, I thought about this but decided not to as these two go hand in hand and it doesn't make much difference if we do it the other way.

[redsun82]

I think it'd be a tad cleaner, but I'll leave it to your judgement 🙂

[redsun82]

Only nits remaining, I'll be happy to reapprove if you do decide to change things around.