[Installer] Allow disaling deterministic UUIDs

CHANGELOG.md

@@ -14,7 +14,8 @@ To install release candidates run `[sudo] gem install cocoapods --pre`
   [#2443](https://github.com/CocoaPods/CocoaPods/issues/2443)
 
 * `Pods.xcodeproj` will now be written with deterministic UUIDs, vastly reducing
-  project churn and merge conflicts.  
+  project churn and merge conflicts.  This behavior can be disabled via the new
+  `COCOAPODS_DISABLE_DETERMINISTIC_UUIDS` environment variable.
   [Samuel Giddins](https://github.com/segiddins)
 
 * [`cocoapods-stats`](https://github.com/CocoaPods/cocoapods-stats)

lib/cocoapods/config.rb

@@ -20,6 +20,7 @@ module Pod
       :clean               => true,
       :integrate_targets   => true,
       :deduplicate_targets => true,
+      :deterministic_uuids => ENV['COCOAPODS_DISABLE_DETERMINISTIC_UUIDS'].nil?,
       :lock_pod_source     => true,
       :new_version_message => ENV['COCOAPODS_SKIP_UPDATE_MESSAGE'].nil?,
 
@@ -95,6 +96,12 @@ module Pod
     attr_accessor :deduplicate_targets
     alias_method :deduplicate_targets?, :deduplicate_targets
 
+    # @return [Bool] Whether CocoaPods should give the pods project
+    #                deterministic UUIDs.
+    #
+    attr_accessor :deterministic_uuids
+    alias_method :deterministic_uuids?, :deterministic_uuids
+
     # @return [Bool] Whether the installer should skip the repos update.
     #
     attr_accessor :skip_repo_update

lib/cocoapods/installer.rb

@@ -644,7 +644,7 @@ module Pod
         pods_project.development_pods.remove_from_project if pods_project.development_pods.empty?
         pods_project.sort(:groups_position => :below)
         pods_project.recreate_user_schemes(false)
-        pods_project.predictabilize_uuids
+        pods_project.predictabilize_uuids if config.deterministic_uuids?
         pods_project.save
       end
     end