Xcode 15 Duplicate Library Linker Warnings
Even though I’ve been seeing them all summer, and have been annoyed by them, I made the same mistake I often make: assuming that the problem was too obvious not to be fixed before Xcode 15 went public. Alas.
[…]
Something about the way Xcode infers library linkage dependencies has, for several years at least, led it to count dependencies from Swift packages separately from each package, and to subsequently pass the pertinent “-l” parameter to the linker redundantly for each such dependency. In other words, if you have three Swift packages that each require “-lc++”, Xcode generates a linker line that literally passes “-lc++ -lc++ -lc++” to the linker.
[…]
So why have the warnings only appeared now? One of the major changes in Xcode 15 was the introduction of a “completely rewritten linker”, which has been mostly transparent to me, but which was also to blame for an issue with Xcode 15 that prevented some apps from launching on older macOS (10.12) and iOS (14) systems. That bug has been addressed in the Xcode 15.1 beta 1 release, which was released this week.
The solution is to add the -no_warn_duplicate_libraries flag.
This simple declaration will address the problem on Xcode 15, but on Xcode 14 and earlier it will cause a link error because the old linker doesn’t recognize the argument. What we want to do if the project will continue to be built by both older and newer versions of Xcode, is to effectively derive a different value for
OTHER_LDFLAGSdepending on the version of Xcode itself.[…]
OTHER_LDFLAGSexpands toSUPPRESS_WARNING_FLAGS_YESon my Mac running Xcode 15.1, but on any version of Xcode 14 or earlier, it will expand toSUPPRESS_WARNING_FLAGS_NO, which expands to an empty value. No harm done.I hope you have enjoyed this somewhat elaborate journey through the powerful but difficult to grok world of nested build settings, and how they can be used to impose rudimentary logic to whichever settings require such finessing in your projects.
