net: macOS link of Go c-archive now requires -lresolv in 1.20 #58159
Description
Go 1.20rc3.
I tried to convert our application (@tailscale) over to Go 1.20 but hit macOS compilation errors in Xcode for our target (a network extension) that links in Go code:
/Applications/Xcode-13.4.1.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -target arm64-apple-macos10.13 -isysroot /Applications/Xcode-13.4.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.3.sdk -L/Users/github-ci/Library/Developer/Xcode/DerivedData/IPN-dcmqhkiofztpxzcjkertpymoivvw/Build/Intermediates.noindex/ArchiveIntermediates/IPN-macOS/BuildProductsPath/Release -F/Users/github-ci/Library/Developer/Xcode/DerivedData/IPN-dcmqhkiofztpxzcjkertpymoivvw/Build/Intermediates.noindex/ArchiveIntermediates/IPN-macOS/BuildProductsPath/Release -filelist /Users/github-ci/Library/Developer/Xcode/DerivedData/IPN-dcmqhkiofztpxzcjkertpymoivvw/Build/Intermediates.noindex/ArchiveIntermediates/IPN-macOS/IntermediateBuildFilesPath/IPN.build/Release/IPNExtension-macOS.build/Objects-normal/arm64/IPNExtension.LinkFileList -exported_symbols_list IPNExtension/exported-symbols.exp -Xlinker -rpath -Xlinker /usr/lib/swift -Xlinker -rpath -Xlinker @executable_path/../Frameworks -Xlinker -rpath -Xlinker @executable_path/../../../../Frameworks -dead_strip -Xlinker -object_path_lto -Xlinker /Users/github-ci/Library/Developer/Xcode/DerivedData/IPN-dcmqhkiofztpxzcjkertpymoivvw/Build/Intermediates.noindex/ArchiveIntermediates/IPN-macOS/IntermediateBuildFilesPath/IPN.build/Release/IPNExtension-macOS.build/Objects-normal/arm64/IPNExtension_lto.o -fapplication-extension -fobjc-link-runtime -L/Applications/Xcode-13.4.1.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx -L/usr/lib/swift -Xlinker -add_ast_path -Xlinker /Users/github-ci/Library/Developer/Xcode/DerivedData/IPN-dcmqhkiofztpxzcjkertpymoivvw/Build/Intermediates.noindex/ArchiveIntermediates/IPN-macOS/IntermediateBuildFilesPath/IPN.build/Release/IPNExtension-macOS.build/Objects-normal/arm64/IPNExtension.swiftmodule -e _NSExtensionMain -lipn-go-arm64\ x86_64 -framework NetworkExtension -Xlinker -dependency_info -Xlinker /Users/github-ci/Library/Developer/Xcode/DerivedData/IPN-dcmqhkiofztpxzcjkertpymoivvw/Build/Intermediates.noindex/ArchiveIntermediates/IPN-macOS/IntermediateBuildFilesPath/IPN.build/Release/IPNExtension-macOS.build/Objects-normal/arm64/IPNExtension_dependency_info.dat -o /Users/github-ci/Library/Developer/Xcode/DerivedData/IPN-dcmqhkiofztpxzcjkertpymoivvw/Build/Intermediates.noindex/ArchiveIntermediates/IPN-macOS/IntermediateBuildFilesPath/IPN.build/Release/IPNExtension-macOS.build/Objects-normal/arm64/Binary/IPNExtension
Undefined symbols for architecture arm64:
"_res_9_nsearch", referenced from:
_internal/syscall/unix.libresolv_res_9_nsearch_trampoline.abi0 in libipn-go-arm64 x86_64.a(go.o)
"_res_9_nclose", referenced from:
_internal/syscall/unix.libresolv_res_9_nclose_trampoline.abi0 in libipn-go-arm64 x86_64.a(go.o)
"_res_9_ninit", referenced from:
_internal/syscall/unix.libresolv_res_9_ninit_trampoline.abi0 in libipn-go-arm64 x86_64.a(go.o)
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
...
The following build commands failed:
Ld /Users/github-ci/Library/Developer/Xcode/DerivedData/IPN-dcmqhkiofztpxzcjkertpymoivvw/Build/Intermediates.noindex/ArchiveIntermediates/IPN-macOS/IntermediateBuildFilesPath/IPN.build/Release/IPNExtension-macOS.build/Objects-normal/arm64/Binary/IPNExtension normal arm64 (in target 'IPNExtension-macOS' from project 'IPN')
I assume this is fallout from https://tip.golang.org/doc/go1.20#cgo ...
On macOS, the net and os/user packages have been rewritten not to use cgo: the same code is now used for cgo and non-cgo builds as well as cross-compiled builds.
Unfortunately I don't have a small easy repro. (Nothing is small or easy with Xcode)
/cc @rsc @ianlancetaylor