Check pre-requisites (XCode) upfront programatically

[radeksimko]

I appreciate that the Readme says I need XCode 11.0+ installed, but gon should probably fail early and gracefully to tell me this if for some reason I missed that instruction or I just switched to a freshly installed MacOS which just doesn't have XCode installed by default.

Currently it allows me to get through a few steps successfully and then fails with an error that may not be immediately understood and attributed to XCode by someone who doesn't know Apple Dev ecosystem.

   • signing artifacts
      • signing                   cmd=[gon .gon.hcl]
      • ==> ✏️  Signing files...
 cmd=gon
      •     Code signing successful
==> 📦  Creating Zip archive...
 cmd=gon
      •     Zip archive created with signed files
==> 📦  Creating dmg...
    This will open Finder windows momentarily.
 cmd=gon
      •     Dmg file created: ./dist/gon_macos.dmg
    Signing dmg...
 cmd=gon
      •     Dmg created and signed
==> 🍎  Notarizing...
    Files will be notarized concurrently to optimize queue wait
 cmd=gon
      •     Path: ./dist/gon_macos.zip
    Path: ./dist/gon_macos.dmg
 cmd=gon
      •     [gon_macos.dmg] Submitting file for notarization...
 cmd=gon
      •     [gon_macos.dmg] Error notarizing
 cmd=gon
      •     [gon_macos.zip] Submitting file for notarization...
 cmd=gon
      •     [gon_macos.zip] Error notarizing
 cmd=gon
      •
❗️ Error notarizing:

2 errors occurred:
	* error submitting for notarization:

xcrun: error: unable to find utility "altool", not a developer tool or in PATH

	* error submitting for notarization:

xcrun: error: unable to find utility "altool", not a developer tool or in PATH

Related: I was actually able to notarize a binary with XCode 10.3 on MacOS 10.14.6:

Xcode 10.3
Build version 10G8

I think what gon could check is roughly the following:

$ /usr/bin/xcodebuild -version
xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance
$ echo $?
1

and also check whether license was agreed to

$ xcodebuild --help


Agreeing to the Xcode/iOS license requires admin privileges, please run “sudo xcodebuild -license” and then retry this command.


$ echo $?
69

[pjebs]

Did you have to do anything special to make it work on Xcode 10.3? I only have XCode 10.1 which is the max I can have on my laptop.