uninitialized constant OS::Mac::CLT

Please fill out the issue checklist below and provide all the requested information.

ran a brew command and reproduced the problem with multiple formulae? If it's a problem with a single, official formula (not cask) please file this issue at Linuxbrew/homebrew-core: https://github.com/Linuxbrew/homebrew-core/issues/new/choose. If it's a brew cask problem please file this issue at https://github.com/Homebrew/homebrew-cask/issues/new/choose. If it's a tap (e.g. Homebrew/homebrew-php) problem please file this issue at the tap.
ran brew update and can still reproduce the problem?
ran brew doctor, fixed all issues and can still reproduce the problem?
ran brew config and brew doctor and included their output with your issue?

$ brew config
HOMEBREW_VERSION: 1.8.0
ORIGIN: https://github.com/Homebrew/brew
HEAD: fdd8e9b7cf1e53322492e1e90f685c19bdfde506
Last commit: 4 days ago
Core tap ORIGIN: https://github.com/Linuxbrew/homebrew-core
Core tap HEAD: 28a637313b565df784b2fb70ed7f372f8414ed72
Core tap last commit: 3 hours ago
HOMEBREW_PREFIX: /home/linuxbrew/.linuxbrew
HOMEBREW_CACHE: /home/linuxbrew/.cache/Homebrew
CPU: octa-core 64-bit ivybridge
Homebrew Ruby: 2.3.7 => /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/portable-ruby/2.3.7/bin/ruby
Clang: N/A
Git: 2.19.1 => /usr/bin/git
Curl: 7.47.0 => /usr/bin/curl
Kernel: Linux 4.4.0-135-generic x86_64 GNU/Linux
OS: Ubuntu 16.04.5 LTS (xenial)
Host glibc: 2.23
/usr/bin/gcc: 5.4.0
glibc: N/A
gcc: N/A
xorg: N/A

$ brew doctor
Your system is ready to brew.

To help us debug your issue please explain:

What you were trying to do (and why)

I was trying to install python@2 and python because they are dependencies of other formulae that I wanted to test (dartsim for example).

What happened (include command output)

They both failed with an error Error: uninitialized constant OS::Mac::CLT

$ brew install python
Error: uninitialized constant OS::Mac::CLT
Please report this bug:
  https://github.com/Linuxbrew/brew/wiki/troubleshooting
/home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/python.rb:23:in `block (2 levels) in <class:Python>'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:99:in `pour_bottle?'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:469:in `expand_dependencies'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:381:in `compute_dependencies'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:142:in `verify_deps_exist'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:135:in `prelude'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/install.rb:324:in `install_formula'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/install.rb:256:in `block in install'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/install.rb:254:in `each'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/install.rb:254:in `install'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/brew.rb:89:in `<main>'

$ brew install python@2
Error: uninitialized constant OS::Mac::CLT
Please report this bug:
  https://github.com/Linuxbrew/brew/wiki/troubleshooting
/home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/python@2.rb:25:in `block (2 levels) in <class:PythonAT2>'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:99:in `pour_bottle?'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:469:in `expand_dependencies'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:381:in `compute_dependencies'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:142:in `verify_deps_exist'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:135:in `prelude'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/install.rb:324:in `install_formula'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/install.rb:256:in `block in install'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/install.rb:254:in `each'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/install.rb:254:in `install'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/brew.rb:89:in `<main>'

What you expected to happen

I expected macOS settings to be ignored on linux.

Step-by-step reproduction instructions (by running brew commands)

$ docker run -it linuxbrew/brew bash
linuxbrew@31c9b78e5eb0:~$ brew install python
...
linuxbrew@31c9b78e5eb0:~$ brew install python@2
...

On Linuxbrew/brew MacOS::CLT.installed? is set to true.

brew/Library/Homebrew/os/linux.rb

Lines 22 to 28 in 8f5de98

    
           module CLT 
        
             module_function 
        
             def installed? 
        
               true 
        
             end 
        
           end

That's a hack though, and not one that I'd like to commit to Homebrew/brew.
44 formulae in Linuxbrew/core use if MacOS::CLT.installed?. I'd rather patch these formulae to instead use if !OS.mac? || MacOS::CLT.installed?.

Here's a PR to fix this issue: https://github.com/Linuxbrew/homebrew-core/pull/10012

I merged PR #10012, which should fix this issue!