Prevent tapped symlinks showing up in git status

The symlinks taps write to Formula show up in git status, but this trick prevents this. brew-(un)tap maintain a .gitignore in Formula that contains all the symlinks brew-tap creates.

We add the .gitignore to the root .gitignore and TADA! Magic.

.gitignore

@@ -9,3 +9,4 @@
 .DS_Store
 /Library/LinkedKegs
 /Library/Taps
+/Library/Formula/.gitignore

Library/Homebrew/cmd/tap.rb

@@ -1,3 +1,5 @@
+require 'tempfile'
+
 HOMEBREW_LIBRARY = HOMEBREW_REPOSITORY/"Library"
 
 module Homebrew extend self
@@ -19,12 +21,23 @@ module Homebrew extend self
     raise "Already tapped!" if tapd.directory?
     abort unless system "git clone https://github.com/#{user}/homebrew-#{repo} #{tapd}"
 
+    gitignores = (HOMEBREW_LIBRARY/"Formula/.gitignore").read.split rescue []
+
     cd HOMEBREW_LIBRARY/"Formula"
     tapd.find_formula do |relative_pathname|
       # using the system ln is the only way to get relative symlinks
       system "ln -s ../Taps/#{user}-#{repo}/#{relative_pathname} 2>/dev/null"
-      opoo "#{relative_pathname.basename(".rb")} conflicts" unless $?.success?
+      if $?.success?
+        gitignores << relative_pathname.basename.to_s
+      else
+        opoo "#{relative_pathname.basename, ".rb"} conflicts"
+      end
     end
+
+    tf = Tempfile.new("brew-tap")
+    tf.write(gitignores.uniq.join("\n"))
+    tf.close
+    mv tf.path, "#{HOMEBREW_PREFIX}/Library/Formula/.gitignore"
   end
 
   private

Library/Homebrew/cmd/untap.rb

@@ -1,4 +1,5 @@
 require 'cmd/tap' # for Pathname.recursive_formula
+require 'tempfile'
 
 module Homebrew extend self
   def untap
@@ -7,11 +8,19 @@ module Homebrew extend self
 
     raise "No such tap!" unless tapd.directory?
 
-    tapd.find_formula do |pn|
-      pn = HOMEBREW_REPOSITORY/"Library/Formula"/pn.basename
-      pn.delete if pn.symlink? and pn.realpath.to_s =~ %r[^#{tapd.realpath}]
-    end
+    gitignores = (HOMEBREW_PREFIX/"Library/Formula/.gitignore").read.split rescue []
 
+    tapd.find_formula do |pn|
+      bn = pn.basename.to_s
+      pn = HOMEBREW_REPOSITORY/"Library/Formula"/bn
+      pn.delete if pn.symlink? and pn.realpath.to_s =~ %r[^#{tapd.realpath}]
+      gitignores.delete(bn)
+    end
     rm_rf tapd
+
+    tf = Tempfile.new("brew-untap")
+    tf.write(gitignores.join("\n"))
+    tf.close
+    mv tf.path, "#{HOMEBREW_PREFIX}/Library/Formula/.gitignore"
   end
 end