Swift 5.7 docker image changes: missing cstddef include

Hi all,

We build a fairly complicated library using Docker. It contains C++ source code. It doesn't use the new, experimental C++ importer or anything — it just uses the same C++ support that SwiftPM has always had & exports its functionality through a C wrapper. It uses cxxLanguageStandard: .cxx11 in the Package.swift.

We had been using the swift:5.6 tag from dockerhub. When I upgrade us to the recently released swift:5.7, I get the following error in a C++ file:

/codebuild/output/[redacted file].cpp:17:10: fatal error: 'cstddef' file not found

#include <cstddef>


1 error generated.

error: fatalError

Is there anything that's changed in the 5.7 series of docker images which would cause cstddef to be unfindable, of all things? I always thought that wasn't even a real file on disk but something implemented by the compiler.

For future google searchers: I resolved this with an apt-get install build-essential. Just missing libstdc++ I think.