Adds JSON output to `outdated` command

After some musing on brunophilipe/Cakebrew#71, I thought it would
be useful to let Cakebrew and other tools grab the outdated formulae
version information using a method more elegant than regex.

Closes Homebrew/homebrew#30693.

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

3 files changed, 35 insertions, 10 deletions

diff --git a/Library/Contributions/brew_bash_completion.sh b/Library/Contributions/brew_bash_completion.sh
index 9068ac0c7..75ecf2b13 100644
--- a/Library/Contributions/brew_bash_completion.sh
+++ b/Library/Contributions/brew_bash_completion.sh
@@ -395,7 +395,7 @@ _brew_outdated ()
     local cur="${COMP_WORDS[COMP_CWORD]}"
     case "$cur" in
     --*)
-        __brewcomp "--quiet"
+        __brewcomp "--quiet --json=v1"
         return
         ;;
     esac
diff --git a/Library/Homebrew/cmd/outdated.rb b/Library/Homebrew/cmd/outdated.rb
index 6ae5254e5..10fa36953 100644
--- a/Library/Homebrew/cmd/outdated.rb
+++ b/Library/Homebrew/cmd/outdated.rb
@@ -3,14 +3,10 @@ require 'keg'
 
 module Homebrew
   def outdated
-    formulae = ARGV.resolved_formulae.any? ? ARGV.resolved_formulae : Formula.installed
-
-    outdated = outdated_brews(formulae) do |f, versions|
-      if ($stdout.tty? || ARGV.verbose?) && !ARGV.flag?("--quiet")
-        puts "#{f.full_name} (#{versions*', '} < #{f.pkg_version})"
-      else
-        puts f.full_name
-      end
+    if ARGV.json == "v1"
+      outdated = print_outdated_json
+    else
+      outdated = print_outdated
     end
     Homebrew.failed = ARGV.resolved_formulae.any? && outdated.any?
   end
@@ -37,4 +33,30 @@ module Homebrew
       end
     end.compact
   end
+
+  def formulae_to_check
+    ARGV.resolved_formulae.any? ? ARGV.resolved_formulae : Formula.installed
+  end
+
+  def print_outdated
+    outdated_brews(formulae_to_check) do |f, versions|
+      if ($stdout.tty? || ARGV.verbose?) && !ARGV.flag?("--quiet")
+        puts "#{f.full_name} (#{versions*', '} < #{f.pkg_version})"
+      else
+        puts f.full_name
+      end
+    end
+  end
+
+  def print_outdated_json
+    json = []
+    outdated = outdated_brews(formulae_to_check) do |f, versions|
+      json << {:name => f.name,
+               :installed_versions => versions.collect(&:to_s),
+               :current_version => f.pkg_version.to_s}
+    end
+    puts Utils::JSON.dump(json)
+
+    outdated
+  end
 end
diff --git a/Library/Homebrew/manpages/brew.1.md b/Library/Homebrew/manpages/brew.1.md
index 4b3ef93f5..8ba9c66e9 100644
--- a/Library/Homebrew/manpages/brew.1.md
+++ b/Library/Homebrew/manpages/brew.1.md
@@ -296,7 +296,7 @@ Note that these flags should only appear after a command.
 
     If `--installed` is passed, show options for all installed formulae.
 
-  * `outdated [--quiet|--verbose]`:
+  * `outdated [--quiet | --verbose | --json=v1 ]`:
     Show formulae that have an updated version available.
 
     By default, version information is displayed in interactive shells, and
@@ -307,6 +307,9 @@ Note that these flags should only appear after a command.
 
     If `--verbose` is passed, display detailed version information.
 
+    If `--json=<version>` is passed, the output will be in JSON format. The only
+    valid version is `v1`.
+
   * `pin` <formulae>:
     Pin the specified <formulae>, preventing them from being upgraded when
     issuing the `brew upgrade --all` command. See also `unpin`.