If no formula but multiple kegs, advise resolution

In this case the user will simply have to delete all but one keg in order to use the command that uses ARGV.kegs.

Refs #11050.

2 files changed, 11 insertions, 1 deletions

diff --git a/Library/Homebrew/cmd/unlink.rb b/Library/Homebrew/cmd/unlink.rb
index bf1f137e0..12b037781 100644
--- a/Library/Homebrew/cmd/unlink.rb
+++ b/Library/Homebrew/cmd/unlink.rb
@@ -1,6 +1,6 @@
 module Homebrew extend self
   def unlink
-    raise FormulaUnspecifiedError if ARGV.named.empty?
+    raise KegUnspecifiedError if ARGV.named.empty?
 
     ARGV.kegs.each do |keg|
       print "Unlinking #{keg}... "
diff --git a/Library/Homebrew/extend/ARGV.rb b/Library/Homebrew/extend/ARGV.rb
index 25d19e2e7..b994df658 100644
--- a/Library/Homebrew/extend/ARGV.rb
+++ b/Library/Homebrew/extend/ARGV.rb
@@ -16,6 +16,7 @@ module HomebrewArgvExtension
   end
 
   def kegs
+    rack = nil
     require 'keg'
     require 'formula'
     @kegs ||= downcased_unique_named.collect do |name|
@@ -47,6 +48,15 @@ module HomebrewArgvExtension
         Keg.new(linked_keg_ref.realpath)
       end
     end
+  rescue FormulaUnavailableError
+    if rack
+      raise <<-EOS.undent
+        Multiple kegs installed to #{rack}
+        Please remove all but one and then try again.
+      EOS
+    else
+      raise
+    end
   end
 
   # self documenting perhaps?