Install specific Rubocop version.

Closes Homebrew/homebrew#39620.

2 files changed, 7 insertions, 4 deletions

diff --git a/Library/Homebrew/cmd/style.rb b/Library/Homebrew/cmd/style.rb
index 3f78a85dc..7ca50e803 100644
--- a/Library/Homebrew/cmd/style.rb
+++ b/Library/Homebrew/cmd/style.rb
@@ -6,7 +6,7 @@ module Homebrew
       ARGV.formulae.map(&:path)
     end
 
-    Homebrew.install_gem_setup_path! "rubocop"
+    Homebrew.install_gem_setup_path! "rubocop", "0.31.0"
 
     args = [
       "--format", "simple", "--config",
diff --git a/Library/Homebrew/utils.rb b/Library/Homebrew/utils.rb
index fb9759584..bb90f6cbf 100644
--- a/Library/Homebrew/utils.rb
+++ b/Library/Homebrew/utils.rb
@@ -121,13 +121,16 @@ module Homebrew
     HOMEBREW_REPOSITORY.cd { `git show -s --format="%cr" HEAD 2>/dev/null`.chuzzle }
   end
 
-  def self.install_gem_setup_path! gem, executable=gem
+  def self.install_gem_setup_path! gem, version=nil, executable=gem
     require "rubygems"
     ENV["PATH"] = "#{Gem.user_dir}/bin:#{ENV["PATH"]}"
 
-    unless quiet_system "gem", "list", "--installed", gem
+    args = [gem]
+    args << "-v" << version if version
+
+    unless quiet_system "gem", "list", "--installed", *args
       safe_system "gem", "install", "--no-ri", "--no-rdoc",
-                                    "--user-install", gem
+                                    "--user-install", *args
     end
 
     unless which executable