Reset Xcode. Clean, clear module cache, Derived Data and Xcode Caches. You can thank me later.

resetXcode.sh

#!/bin/bash
killall Xcode
xcrun -k
xcodebuild -alltargets clean
rm -rf "$(getconf DARWIN_USER_CACHE_DIR)/org.llvm.clang/ModuleCache"
rm -rf "$(getconf DARWIN_USER_CACHE_DIR)/org.llvm.clang.$(whoami)/ModuleCache"
rm -rf ~/Library/Developer/Xcode/DerivedData/*
rm -rf ~/Library/Caches/com.apple.dt.Xcode/*
open /Applications/Xcode.app

later: thanks!

you da bomb

Didn't work, still showing me old logs when I relaunch Xcode.

Boom! Found this via Google. Great job

Worked for me. I'm using Swift4.1 (Xcode9.3)

worked for me XCode9.4. I had XCode10 beta installed, but it did not work. Then I installed XCode 9.4 which was working, then I removed Xcode10beta, after that the Xcode 9.4 did not work until I ran resetXcode.sh

If you're removing DerivedData and the ModuleCache xcodebuild -alltargets clean is probably redundant.

Optionally consider adding pkill -int com.apple.CoreSimulator.CoreSimulatorService, which we do between Xcode upgrades to minimize the potential for simulator flakiness.

Worked for me with Xcode 9.4.1.
Also, I replaced the last line in script with

TARGET=(*.xcworkspace)
if [ $TARGET == "*.xcworkspace" ]; then
    TARGET=(*.xcodeproj)
    if [ $TARGET == "*.xcodeproj" ]; then
        TARGET=""
    fi
fi
if [ $TARGET != "" ]; then
    open -a "/Applications/Xcode.app" "$TARGET"
else
    echo *** Xcode workspace or project not found
fi

Very nice, fixed an issue I and others had after a react-native-firebase release
invertase/react-native-firebase#2269
thank you!

you are a GENIUS !! dammmmm

I created a shell script (tested on bash or zsh) to do this inside any Xcode workspace or project folder.
Check its gist's here.

Life saver!

Great gist!