macOS: Advise how to "uninstall any existing Swift installation(s)"

[BrianHenryIE]

When I run swiftly-install.sh it helpfully says:

Warning: existing installation of Swift detected at /usr/bin/swift To ensure swiftly-installed toolchains can be found by the shell, uninstall any existing Swift installation(s).

My existing setup:

% cat ~/.zshrc 

...

# Use /Library/Developer/Toolchains/ rather than /usr/bin/swift
#export TOOLCHAINS=swift
export TOOLCHAINS=$(plutil -extract CFBundleIdentifier raw /Library/Developer/Toolchains/swift-latest.xctoolchain/Info.plist)

% which swift

/usr/bin/swift

% swift --version

Apple Swift version 6.0-dev (LLVM 0ad8ad0245d47b4, Swift 5916325b39fe7a5)
Target: arm64-apple-macosx14.0

% ls -l /Library/Developer/Toolchains/

total 0
drwxr-xr-x  7 root  wheel  224 Jul 15 17:17 swift-5.10.1-RELEASE.xctoolchain
drwxr-xr-x  7 root  wheel  224 Jul 13 13:54 swift-DEVELOPMENT-SNAPSHOT-2024-07-11-a.xctoolchain
lrwxr-xr-x  1 root  wheel   81 Jul 16 21:43 swift-latest.xctoolchain -> /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2024-07-11-a.xctoolchain

To use the swiftly installed Swift version, I just had to remove the export TOOLCHAINS= line from my .zshrc.

It would be nice to scan the file for that line to advise clearly what needs to be changed.

After:

% which swift

/Users/brianhenry/Library/Application Support/swiftly/bin/swift

% swift --version
 
Apple Swift version 5.7.3 (swift-5.7.3-RELEASE)
Target: arm64-apple-macosx14.0

% swiftly list

Installed release toolchains
----------------------------
Swift 5.7.3 (in use)

Installed snapshot toolchains
-----------------------------

% ls -l ~/Library/Developer/Toolchains
                                
total 0
drwxr-xr-x  7 brianhenry  staff  224 Jul 16 21:31 swift-5.7.3-RELEASE.xctoolchain
lrwxr-xr-x  1 brianhenry  staff   78 Jul 16 21:31 swift-latest.xctoolchain -> /Users/brianhenry/Library/Developer/Toolchains/swift-5.7.3-RELEASE.xctoolchain

The check is basically:

if [ -n "`$SHELL -c 'echo $ZSH_VERSION'`" ]; then
    if [[ $(cat "$HOME/.zshrc" | grep -e "^\s*export TOOLCHAINS=") ]]; then
        echo "TOOLCHAINS is set in ~/.zshrc"
    else
        echo "TOOLCHAINS is NOT set in ~/.zshrc"
    fi
fi

[cmcgee1024]

Would PR #317 be sufficient to support switching between the Xcode selected toolchain and one of the swiftly installed ones?