“brew install -s” does not compile from source

I want to install vim via homebrew, from the compile, but even when I ran the command with -s flag, the compile does not occur.

brew install -s vim --with-luajit

Or

brew reinstall -s vim --with-luajit

==> Reinstalling vim

==> Downloading https://homebrew.bintray.com/bottles/vim-8.1.0202

Already downloaded: /Users/me/Library/Caches/Homebrew/vim-8.1.0202.high_sierra.bottle.tar.gz

==> Pouring vim-8.1.0202.high_sierra.bottle.tar.gz

? /usr/local/Cellar/vim/8.1.0202: 1,434 files, 23.4MB

As far as I know, the -s flag or --build-from-source compiles it, not pour, but this always pours for some reasons.

How can I compile vim from scratch?

I use macOS 10.14 Beta and homebrew 1.7.1.

UPDATE

With -v flag, it first rmed several files under /usr/local/. Then reinstalling, downloading, verifying, and pouring showed up in the order. The pouring process showed the following:

tar xf /Users/me/Library/Caches/Homebrew/vim-8.1.0202.high_sierra.bottle.tar.gz -C /var/folders/vk/cbdc97r515b0lv_p1dq_852r0000gn/T/d20180806-64534-6ra3ai

Then it showed "finishing up" process, and then ran several ln -s commands. After that, it showed the following:

/usr/bin/sandbox-exec -f /private/tmp/homebrew20180806-64695-e9syu8.sb nice /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -W0 -I /Library/Ruby/Gems/2.3.0/gems/did_you_mean-1.0.0/lib:/Library/Ruby/Site/2.3.0:/Library/Ruby/Site/2.3.0/x86_64-darwin18:/Library/Ruby/Site/2.3.0/universal-darwin18:/Library/Ruby/Site:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/vendor_ruby/2.3.0:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/vendor_ruby/2.3.0/x86_64-darwin18:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/vendor_ruby/2.3.0/universal-darwin18:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/vendor_ruby:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/x86_64-darwin18:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/universal-darwin18:/usr/local/Homebrew/Library/Homebrew/cask/lib:/usr/local/Homebrew/Library/Homebrew — /usr/local/Homebrew/Library/Homebrew/postinstall.rb /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/vim.rb -v -s –with-luajit –force

brew doctor showed the following (I omitted unrelevant parts such as Python or miniconda):

Warning: You are using macOS 10.14.
We do not provide support for this pre-release version.
You will encounter build failures and other breakages.
Please create pull-requests instead of asking for help on Homebrew's
GitHub, Discourse, Twitter or IRC. As you are running this pre-release version,
you are responsible for resolving any issues you experience.

Warning: The Command Line Tools header package must be installed on Mojave.
The installer is located at:
/Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg