Objective-C Runtime Differs in Pch File and Swiftshims Errors in Macos Catalina 10.15.6, Xcode 11.6, MAC Catalyst App

Objective-C runtime differs in PCH file and SwiftShims errors in macOS Catalina 10.15.6, Xcode 11.6, Mac Catalyst app

This occurs when your iOS target is 13.5, adjusting it upwards or downwards in your app target's General > Deployment Info setting will resolve the issue.

Change from this (which generates error):

To this (i.e. a number higher or lower) than iOS 13.5:

I don't know why this happens but it reliably solves the issue and when changed back to iOS 13.5 the crash happens again.

error: target Objective-C runtime differs in PCH file vs. current file

After capturing Xcode's full command-line, I noticed that it had -x objective-c flag while my CMake had not!

After searching (about how CMake support's Obj-C),
found actual mistake!

1. Basically, CMake needed me to do something like:

project(MyProject C CXX OBJC OBJCXX)

Instead of:

project(MyProject)

2. Also, should add Obj-C flags into CMAKE_OBJC_FLAGS instead of CMAKE_C_LINK_FLAGS variable.

3. Now CMake automaticaly adds missing -x objective-c flag, and I just need to add my custom flags.

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Full Xcode command-line:

-x objective-c -target x86_64-apple-ios13.6-macabi -fmessage-length=0 -fdiagnostics-show-note-include-stack -fmacro-backtrace-limit=0 -fobjc-arc -fmodules -gmodules -fmodules-cache-path=/Users/admin/Library/Developer/Xcode/DerivedData/ModuleCache.noindex -fmodules-prune-interval=86400 -fmodules-prune-after=345600 -fbuild-session-file=/Users/admin/Library/Developer/Xcode/DerivedData/ModuleCache.noindex/Session.modulevalidation -fmodules-validate-once-per-build-session -fmodule-name=MyProject -fapplication-extension -fpascal-strings -O0 -fno-common -DDEBUG=1 -DOBJC_OLD_DISPATCH_PROTOTYPES=0 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -fasm-blocks -fstrict-aliasing -g -fprofile-instr-generate -fcoverage-mapping -index-store-path /MyBuildDir/Index/DataStore -iquote /MyBuildDir-cofig/MyProject-generated-files.hmap -I/MyBuildDir-cofig/MyProject-own-target-headers.hmap -I/MyBuildDir-cofig/MyProject-all-non-framework-target-headers.hmap -ivfsoverlay /MyBuildDir-cofig/all-product-headers.yaml -iquote /MyBuildDir-cofig/MyProject-project-headers.hmap -I/MyProductDir/include -isystem /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/iOSSupport/usr/include -I/MyBuildDir-cofig/DerivedSources-normal/x86_64 -I/MyBuildDir-cofig/DerivedSources/x86_64 -I/MyBuildDir-cofig/DerivedSources -F/MyProductDir -iframework /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/iOSSupport/System/Library/Frameworks -MMD -MT dependencies -MF /MyBuildDir-cofig/Objects-normal/x86_64/my-source.d --serialize-diagnostics /MyBuildDir-cofig/Objects-normal/x86_64/my-source.dia -c /Users/admin/my-project/my-source.m -o /MyBuildDir-cofig/Objects-normal/x86_64/my-source.o

Note that I replaced paths to shorten above, like:

MyBuildDir        => /Users/admin/Library/Developer/Xcode/DerivedData/MyProject-gczfeuobxydqjrfbdhwzpqjsseyr

MyBuildDir-config => /Users/admin/Library/Developer/Xcode/DerivedData/MyProject-gczfeuobxydqjrfbdhwzpqjsseyr/Build/Intermediates.noindex/MyProject.build/Debug-maccatalyst/MyProject.build/

MyProductDir      => /Users/admin/Library/Developer/Xcode/DerivedData/MyProject-gczfeuobxydqjrfbdhwzpqjsseyr/Build/Products/Debug-maccatalyst

file has been modified since the precompiled header was built

Deleting ~/Library/Developer/Xcode and restarting Xcode fixed this for me (Xcode 6 B7). Suspect an aggressive caching bug. Warning! This deletes archives from all your projects.

No amount of cleaning / build folder cleaning / derived data deleting helped before that.

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