prune: handle broken app symlinks

Remove broken symlinks from `/Applications` and `~/Applications` that
were previously created by `brew linkapps`, but are no longer valid
because formulae were uninstalled or the provided apps have changed.

Library/Homebrew/cmd/prune.rb

@@ -1,5 +1,6 @@
 require "keg"
 require "cmd/tap"
+require "cmd/unlinkapps"
 
 module Homebrew
   def prune
@@ -45,5 +46,7 @@ module Homebrew
       print "and #{d} directories " if d > 0
       puts "from #{HOMEBREW_PREFIX}"
     end unless ARGV.dry_run?
+
+    unlinkapps_prune(:dry_run => ARGV.dry_run?, :quiet => true)
   end
 end

Library/Homebrew/cmd/unlinkapps.rb

@@ -9,22 +9,30 @@ module Homebrew
 
   private
 
+  def unlinkapps_prune(opts = {})
+    opts = opts.merge(:prune => true)
+    unlinkapps_from_dir(linkapps_target(:local => false), opts)
+    unlinkapps_from_dir(linkapps_target(:local => true), opts)
+  end
+
   def unlinkapps_from_dir(target_dir, opts = {})
     return unless target_dir.directory?
     dry_run = opts.fetch(:dry_run, false)
+    quiet = opts.fetch(:quiet, false)
 
     apps = Pathname.glob("#{target_dir}/*.app").select do |app|
-      unlinkapps_unlink?(app)
+      unlinkapps_unlink?(app, opts)
     end
 
     ObserverPathnameExtension.reset_counts!
 
+    app_kind = opts.fetch(:prune, false) ? " (broken link)" : ""
     apps.each do |app|
       app.extend(ObserverPathnameExtension)
       if dry_run
-        puts "Would unlink: #{app}"
+        puts "Would unlink#{app_kind}: #{app}"
       else
-        puts "Unlinking: #{app}"
+        puts "Unlinking#{app_kind}: #{app}" unless quiet
         app.unlink
       end
     end
@@ -44,12 +52,14 @@ module Homebrew
     #{HOMEBREW_PREFIX}/opt/
   ].freeze
 
-  def unlinkapps_unlink?(target_app)
+  def unlinkapps_unlink?(target_app, opts = {})
     # Skip non-symlinks and symlinks that don't point into the Homebrew prefix.
     app = "#{target_app.readlink}" if target_app.symlink?
     return false unless app && app.start_with?(*UNLINKAPPS_PREFIXES)
 
-    if ARGV.named.empty?
+    if opts.fetch(:prune, false)
+      !File.exist?(app) # Remove only broken symlinks in prune mode.
+    elsif ARGV.named.empty?
       true
     else
       ARGV.kegs.any? { |keg| app.start_with?("#{keg}/", "#{keg.opt_record}/") }

Library/Homebrew/manpages/brew.1.md

@@ -340,7 +340,9 @@ With `--verbose` or `-v`, many commands print extra debugging information. Note
 
   * `prune` [`--dry-run`]:
     Remove dead symlinks from the Homebrew prefix. This is generally not
-    needed, but can be useful when doing DIY installations.
+    needed, but can be useful when doing DIY installations. Also remove broken
+    app symlinks from `/Applications` and `~/Applications` that were previously
+    created by `brew linkapps`.
 
     If `--dry-run` or `-n` is passed, show what would be removed, but do not
     actually remove anything.

share/doc/homebrew/brew.1.html

@@ -267,7 +267,9 @@ valid version is <code>v1</code>.</p></dd>
 <dt><code>pin</code> <var>formulae</var></dt><dd><p>Pin the specified <var>formulae</var>, preventing them from being upgraded when
 issuing the <code>brew upgrade</code> command. See also <code>unpin</code>.</p></dd>
 <dt><code>prune</code> [<code>--dry-run</code>]</dt><dd><p>Remove dead symlinks from the Homebrew prefix. This is generally not
-needed, but can be useful when doing DIY installations.</p>
+needed, but can be useful when doing DIY installations. Also remove broken
+app symlinks from <code>/Applications</code> and <code>~/Applications</code> that were previously
+created by <code>brew linkapps</code>.</p>
 
 <p>If <code>--dry-run</code> or <code>-n</code> is passed, show what would be removed, but do not
 actually remove anything.</p></dd>

share/man/man1/brew.1

@@ -365,7 +365,7 @@ Pin the specified \fIformulae\fR, preventing them from being upgraded when issui
 .
 .TP
 \fBprune\fR [\fB\-\-dry\-run\fR]
-Remove dead symlinks from the Homebrew prefix\. This is generally not needed, but can be useful when doing DIY installations\.
+Remove dead symlinks from the Homebrew prefix\. This is generally not needed, but can be useful when doing DIY installations\. Also remove broken app symlinks from \fB/Applications\fR and \fB~/Applications\fR that were previously created by \fBbrew linkapps\fR\.
 .
 .IP
 If \fB\-\-dry\-run\fR or \fB\-n\fR is passed, show what would be removed, but do not actually remove anything\.