Import CRT to resolve free on Windows

[stevapple]

S:\sourcekit-lsp\Sources\SourceKitD\SKDResponse.swift:55:13: error: cannot find 'free' in scope
    defer { free(ptr) }
            ^~~~
S:\sourcekit-lsp\Sources\SourceKitD\SKDResponseArray.swift:65:13: error: cannot find 'free' in scope
    defer { free(ptr) }
            ^~~~
S:\sourcekit-lsp\Sources\SourceKitD\SKDRequestArray.swift:39:13: error: cannot find 'free' in scope
    defer { free(ptr) }
            ^~~~
S:\sourcekit-lsp\Sources\SourceKitD\SKDRequestDictionary.swift:64:13: error: cannot find 'free' in scope
    defer { free(ptr) }
            ^~~~
S:\sourcekit-lsp\Sources\SourceKitD\SKDResponseDictionary.swift:64:13: error: cannot find 'free' in scope
    defer { free(ptr) }

[compnerd]

Odd that we haven't hit this so far, but seems like a reasonable thing.

[compnerd]

@swift-ci please test

[compnerd]

@stevapple how come this is not needed on Darwin btw? I don't see an import Darwn here.

[stevapple]

@compnerd I didn’t figure out yet. It may share the same reason why we didn’t run into it before on Windows.

I guess this could be related with re-exported CStdlib symbols from some modules.

[compnerd]

Oh, it almost certainly is related to re-exporting. But, it would be good to understand what's the root cause for the change in that.

[stevapple]

But, it would be good to understand what's the root cause for the change in that.

May possibly be related to my fix on C header visibility… I opened this and swiftlang/swift-corelibs-foundation#3151 as preparation for the fix.

[ahoppen]

Windows noob question: Is CRT Window’s C standard library equivalent that defines free etc?

[stevapple]

Windows noob question: Is CRT Window’s C standard library equivalent that defines free etc?

It should be a superset of C standard library.

AFAIK the only drawback is that stdint.h is implicitly included in CRT.inttype. For explicit import you should use visualc.stdint instead.

[ahoppen]

The change sounds reasonable to me and I trust @compnerd’s judgment that it makes sense from a Windows perspective.