install: add --only-dependencies option

The traditional approach to installing the dependencies of a formula is
the following:

  brew install `brew deps formula`

This approach ignores any options that are specified in the parent
formula. This pull request adds a --only-dependencies option to brew
install that installs the dependencies of a formula with optional flags,
but returns before installing the parent formula.

Closes Homebrew/homebrew#25272.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

2 files changed, 13 insertions, 1 deletions

diff --git a/Library/Homebrew/extend/ARGV.rb b/Library/Homebrew/extend/ARGV.rb
index 5aa90dbb9..c2e1a9c2e 100644
--- a/Library/Homebrew/extend/ARGV.rb
+++ b/Library/Homebrew/extend/ARGV.rb
@@ -102,6 +102,10 @@ module HomebrewArgvExtension
     include? '--ignore-dependencies'
   end
 
+  def only_deps?
+    include? '--only-dependencies'
+  end
+
   def json
     value 'json'
   end
diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index a78fd0d13..8990b3afc 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -15,13 +15,14 @@ class FormulaInstaller
   include FormulaCellarChecks
 
   attr_reader :f
-  attr_accessor :tab, :options, :ignore_deps
+  attr_accessor :tab, :options, :ignore_deps, :only_deps
   attr_accessor :show_summary_heading, :show_header
 
   def initialize ff
     @f = ff
     @show_header = false
     @ignore_deps = ARGV.ignore_deps? || ARGV.interactive?
+    @only_deps = ARGV.only_deps?
     @options = Options.new
     @tab = Tab.dummy_tab(ff)
 
@@ -105,6 +106,8 @@ class FormulaInstaller
 
     compute_and_install_dependencies unless ignore_deps
 
+    return if only_deps
+
     if ARGV.build_bottle? && (arch = ARGV.bottle_arch) && !Hardware::CPU.optimization_flags.include?(arch)
       raise "Unrecognized architecture for --bottle-arch: #{arch}"
     end
@@ -270,6 +273,7 @@ class FormulaInstaller
     fi.tab = dep_tab
     fi.options = dep_options
     fi.ignore_deps = true
+    fi.only_deps = false
     fi.show_header = false
     oh1 "Installing #{f} dependency: #{Tty.green}#{dep}#{Tty.reset}"
     outdated_keg.unlink if outdated_keg
@@ -282,6 +286,8 @@ class FormulaInstaller
   end
 
   def caveats
+    return if only_deps
+
     if ARGV.homebrew_developer? and not f.keg_only?
       audit_bin
       audit_sbin
@@ -299,6 +305,8 @@ class FormulaInstaller
   end
 
   def finish
+    return if only_deps
+
     ohai 'Finishing up' if ARGV.verbose?
 
     install_plist